I discovered that the beautiful parts that I made a couple of days ago are just a bit short for the tripod in question. (Fortunately, I discovered this before shipping.) I discovered that what had been the franchisee for Metal Supermarkets in Boise has moved to Garden City, and become Gem State Metals, and I went there to get some 2" OD, .125" wall aluminum tubing. Instead of boring from 1.47" to 1.73", I just bought tubing that was already 1.74", and made one quick pass with the emery cloth on the inside to make it pretty.
But I also suddenly found that the easy time I had three nights ago squaring the 1/4" wall aluminum tubing didn't work with .125" wall tubing. Why? Same alloy: 6061 T6. It turns out that:
1. Getting very precisely centered in the lathe is far more important with aluminum than acetal--probably because the aluminum isn't self-lubricating.
2. Boring the inside of the tube requires a relatively low speed, but a heavier cut, to avoid "chattering," which often leads to the part being pulled from the chuck. But squaring the tubing requires a medium to medium-high speed, and at least until you get an even end, very light cuts, typically .005"-.010". I wasted a solid hour figuring this out.
Experience, unfortunately, is among the most expensive things to get. I just hope that this experience turns into something economically useful, unlike most everything else with which I have developed an expertise.
Showing posts with label machining. Show all posts
Showing posts with label machining. Show all posts
Wednesday, July 21, 2010
Sunday, July 18, 2010
Manufacturing in Aluminum
I am beginning to switch over from manufacturing my casters assemblies entirely in acetal to primarily aluminum, for a variety of reasons that I have discussed previously. I was a little unsure if I was going to get a pretty finish on the aluminum or not--but here's the first article for one of the round sleeve models.
It is gorgeous--and all I had to do was to hold some 150 emery cloth to it while it was turning it on the lathe!
The first happy customer for the aluminum version for the new Losmandy Lightweight tripod sent me these pictures.
This picture emphasizes how well the Deluxe wheels work in high grass.
It is gorgeous--and all I had to do was to hold some 150 emery cloth to it while it was turning it on the lathe!
The first happy customer for the aluminum version for the new Losmandy Lightweight tripod sent me these pictures.
This picture emphasizes how well the Deluxe wheels work in high grass.
Wednesday, July 7, 2010
Fun With Machining
I spent a bit of time resisting the urge to use inappropriate language while working on a caster set for the Stellarvue Walnut Tripod used on a number of their mounts. I have a customer in Peru who runs a telescope store there, and he has apparently sold quite a number of mounts with this tripod--and wants a rolling solution.
Anyway, after a lot of experimentation, I produced a fascinating and infuriating prototype out of acetal that some lucky customer will get at a bargain price:
I have since come up with something that does the same thing, but that is dramatically simpler to make, and uses mostly off-the-shelf parts:
That piece of wood is a just a chunk of pine that I have planed to the dimensions of the Stellarvue tripod leg, plus or minus a few thousandths of an inch. The hole in the underside is threaded for a 3/8"-16 thumbscrew. It turns out that the tripod leg will be held in just by friction for the vast majority of customers, but a thumbscrew provides a way to secure it. I put the hole in the underside so that any marring that the thumbscrew makes on the leg won't be particularly visible--and using a 3/8" diameter bolt means that the pressure will be applied over a large area, allowing the same force to be applied to be applied at a lower pressure, causing less damage to the tripod leg. Using a thumbscrew also discourages the customer from using a wrench, which would certainly mark the tripod leg.
This is considerably simpler and faster to make than the prototype, and without any temptation to curse! I think it also looks better, and unlike the acetal that I have previously used, any shavings or leftover parts from this are aluminum scrap that can be recycled, to protect Mother Earth, and ScopeRoller's botttom line, which is the more important definition of being Green. There are several new tripods that I now have to support, such as the new Losmandy GM-8 tripod--and this is definitely the direction of the future for ScopeRoller.
Anyway, after a lot of experimentation, I produced a fascinating and infuriating prototype out of acetal that some lucky customer will get at a bargain price:
I have since come up with something that does the same thing, but that is dramatically simpler to make, and uses mostly off-the-shelf parts:
That piece of wood is a just a chunk of pine that I have planed to the dimensions of the Stellarvue tripod leg, plus or minus a few thousandths of an inch. The hole in the underside is threaded for a 3/8"-16 thumbscrew. It turns out that the tripod leg will be held in just by friction for the vast majority of customers, but a thumbscrew provides a way to secure it. I put the hole in the underside so that any marring that the thumbscrew makes on the leg won't be particularly visible--and using a 3/8" diameter bolt means that the pressure will be applied over a large area, allowing the same force to be applied to be applied at a lower pressure, causing less damage to the tripod leg. Using a thumbscrew also discourages the customer from using a wrench, which would certainly mark the tripod leg.
This is considerably simpler and faster to make than the prototype, and without any temptation to curse! I think it also looks better, and unlike the acetal that I have previously used, any shavings or leftover parts from this are aluminum scrap that can be recycled, to protect Mother Earth, and ScopeRoller's botttom line, which is the more important definition of being Green. There are several new tripods that I now have to support, such as the new Losmandy GM-8 tripod--and this is definitely the direction of the future for ScopeRoller.
Thursday, July 1, 2010
Never Mill What You Can Buy
The more time I spent trying to mill what I needed (a square hole with a 30 degree angle at the bottom), the more I realized that I needed to find something off the shelf. And sure enough: I found some square and rectangular aluminum tubing the dimensions required for this project. I can plug the bottom of the tubing with a piece of acetal tapped to accept casters, and use machine screws to lock the plug into the tubing.
A few rules for machining stuff:
1. Machine the last .050" inches; use coarser tools to get closer. A chop saw gets you to 1/16" of an inch. I have a planer that lets me get down to .1", easily.
2. Never try to machine something from scratch if there is a part available off the shelf that is close to what you need. The time that you spend trying to machine a block into any shape except a square, rectangle, or a circle, is going to be significant. If you can find that shape off the shelf, whatever you spend on the part will be worth it in time savings and frustration reduction.
3. Always look for a way to machine the part while it is still simple enough to easily clamp to the table (usually because it still has a flat surface). This often means doing something out of the logical sequence.
A few rules for machining stuff:
1. Machine the last .050" inches; use coarser tools to get closer. A chop saw gets you to 1/16" of an inch. I have a planer that lets me get down to .1", easily.
2. Never try to machine something from scratch if there is a part available off the shelf that is close to what you need. The time that you spend trying to machine a block into any shape except a square, rectangle, or a circle, is going to be significant. If you can find that shape off the shelf, whatever you spend on the part will be worth it in time savings and frustration reduction.
3. Always look for a way to machine the part while it is still simple enough to easily clamp to the table (usually because it still has a flat surface). This often means doing something out of the logical sequence.
Thursday, June 24, 2010
Square Hole Drill
Yes, there is such a thing--it's not a prank you play on apprentice machinists. "Mike, could you go retrieve the square hole drill?" It turns out that a combination of a triangular cutter turning on an offset will actually cut a square. There's a demonstration here of how this works--apparently a practical application of pure math. This company sells a variant that produces a variety of polygonal shapes using this approach.
I have a request for a new ScopeRoller variant that requires me to cut a rectangular blind hole in acetal--and the more direct approach (using a small diameter end mill to square a round hole) doesn't produce a particularly attractive finish. I'm still mulling over some other way to accomplish the same ends.
I have a request for a new ScopeRoller variant that requires me to cut a rectangular blind hole in acetal--and the more direct approach (using a small diameter end mill to square a round hole) doesn't produce a particularly attractive finish. I'm still mulling over some other way to accomplish the same ends.
Saturday, June 12, 2010
I'm Glad That I Made These Expensive
Generally, the caster assemblies that I make for telescopes are in one of three categories: round ones that go inside the tripod leg, round ones that lock onto the outside of the tripod leg, and square ones that go inside the tripod leg. One of the weird exceptions are the casters for the Vixen HAL-110 and HAL-130 tripods.
These tripods have such oddly shaped legs that none of those strategies seemed to make sense, so I decided to make a replacement for the "foot" that would replace it. The "feet" on these tripods are held in by four M4 screws, so I machine an insert that replaces the foot and its insert--and the standard screws go into holes that I tap in the insert. It looks a bit odd once installed, but it works well.
The most annoying part of making this rather complex part has been my continuing learning experience with the vertical mill. Previous postings have discussed the problem of not using the right type of end mill, and trying to work around insufficient capacity in the standard mill vise that comes with the Sherline vertical mill.
Today was one of those days where I put quite a few hours into getting a set made up for a customer--and I'm glad that I charge a bit of a premium for these, because of it. Past difficulties have made me very wary of trying to use the Sherline mill vise for this--but today I managed to make everything work. Today's lessons learned:
1. There is a socket head 10-32 screw that does the clamping on the Sherline mill vise. As the socket head wears out, it gets harder and harder to really lock down the workpiece. Fortunately, I keep a spare or two lying around. It's time to replenish my spare collection.
2. I now use the roughing end mill for all operations on this part. Yes, this one is only 3/8" diameter, so it takes two passes to cut the 0.50" slot through the insert that I make. But it does not catch the workpiece and throw it, as happens with some of the two and four flute end mills.
3. I noticed that some people make what are called vise stops for the Sherline mill vise. A vise stop is something that attaches to the mill vise and provides a place for a workpiece to stop (as you might guess from the name). The advantage of this is that if you are making a number of pieces that are identical, you can get away with using an edge finder only on the first piece, which is located against the vise stop. Then, your handwheels are correctly zeroed for all subsequent workpieces that go up against the vise stop.
I haven't made a vise stop--but because all of these workpieces start out as a rectangular solid, and I machine them within a few thousandths of inch of each other, I can use the edge of the mill vise as a rudimentary mill stop. I can rub my finger along the transition between the workpiece and the mill vise and feel a discrepancy of .005" pretty effectively. For these parts, that's quite sufficient accuracy.
4. One of the slowest parts of machining is cutting away excess material. These workpieces needed to be machined down to blocks that are 3.42" x 2.62" x 0.75". I asked Interstate Plastics to cut me a piece that was 2 5/8" wide by 3/4" by 11". The 2 5/8" actually came out about 2.68", so there was only about .060" to remove--and just squaring that dimension was .020" of the cutting. The sheet they cut this from was actually 0.752", and was close enough that it was a waste of time trying to improve on that.
The first piece that I cut from the 11" long stock was 3.50"--and while .080" doesn't sound like much, trust me, my fly cutter really doesn't like taking off more than .010" at a time--maybe .020" if I move the fly cutter slowly across the end. The closer to you get to the desired length, the better. After I had trimmed that first one down to 3.42", I used it on the chop saw to set the length for the next two workpieces. Both came out at about 3.45". The act of squaring the ends took off most of the .030" that needed to go away. In machining, time is money, and material that you throw away in the trash can is time and money wasted.
5. I have been making the 0.5" slot through the middle of this piece by using the bandsaw to make two 1 1/2" long cuts, then using a .4375" drill bill on the drill press to knock out holes between the cuts. This means that I am only having to clean up the slot--not cut it from scratch, which is very slow. The bandsaw, unfortunately, doesn't really cut acetal all that well, because it is so much harder than wood. As a result, unless I go very slowly, the blade starts to bend to the side. I have concluded that it is simpler and faster to just skip the bandsaw part of the operation. I can use the .4375" drill bit to make several holes in a row, and the results are just about the same.
These tripods have such oddly shaped legs that none of those strategies seemed to make sense, so I decided to make a replacement for the "foot" that would replace it. The "feet" on these tripods are held in by four M4 screws, so I machine an insert that replaces the foot and its insert--and the standard screws go into holes that I tap in the insert. It looks a bit odd once installed, but it works well.
The most annoying part of making this rather complex part has been my continuing learning experience with the vertical mill. Previous postings have discussed the problem of not using the right type of end mill, and trying to work around insufficient capacity in the standard mill vise that comes with the Sherline vertical mill.
Today was one of those days where I put quite a few hours into getting a set made up for a customer--and I'm glad that I charge a bit of a premium for these, because of it. Past difficulties have made me very wary of trying to use the Sherline mill vise for this--but today I managed to make everything work. Today's lessons learned:
1. There is a socket head 10-32 screw that does the clamping on the Sherline mill vise. As the socket head wears out, it gets harder and harder to really lock down the workpiece. Fortunately, I keep a spare or two lying around. It's time to replenish my spare collection.
2. I now use the roughing end mill for all operations on this part. Yes, this one is only 3/8" diameter, so it takes two passes to cut the 0.50" slot through the insert that I make. But it does not catch the workpiece and throw it, as happens with some of the two and four flute end mills.
3. I noticed that some people make what are called vise stops for the Sherline mill vise. A vise stop is something that attaches to the mill vise and provides a place for a workpiece to stop (as you might guess from the name). The advantage of this is that if you are making a number of pieces that are identical, you can get away with using an edge finder only on the first piece, which is located against the vise stop. Then, your handwheels are correctly zeroed for all subsequent workpieces that go up against the vise stop.
I haven't made a vise stop--but because all of these workpieces start out as a rectangular solid, and I machine them within a few thousandths of inch of each other, I can use the edge of the mill vise as a rudimentary mill stop. I can rub my finger along the transition between the workpiece and the mill vise and feel a discrepancy of .005" pretty effectively. For these parts, that's quite sufficient accuracy.
4. One of the slowest parts of machining is cutting away excess material. These workpieces needed to be machined down to blocks that are 3.42" x 2.62" x 0.75". I asked Interstate Plastics to cut me a piece that was 2 5/8" wide by 3/4" by 11". The 2 5/8" actually came out about 2.68", so there was only about .060" to remove--and just squaring that dimension was .020" of the cutting. The sheet they cut this from was actually 0.752", and was close enough that it was a waste of time trying to improve on that.
The first piece that I cut from the 11" long stock was 3.50"--and while .080" doesn't sound like much, trust me, my fly cutter really doesn't like taking off more than .010" at a time--maybe .020" if I move the fly cutter slowly across the end. The closer to you get to the desired length, the better. After I had trimmed that first one down to 3.42", I used it on the chop saw to set the length for the next two workpieces. Both came out at about 3.45". The act of squaring the ends took off most of the .030" that needed to go away. In machining, time is money, and material that you throw away in the trash can is time and money wasted.
5. I have been making the 0.5" slot through the middle of this piece by using the bandsaw to make two 1 1/2" long cuts, then using a .4375" drill bill on the drill press to knock out holes between the cuts. This means that I am only having to clean up the slot--not cut it from scratch, which is very slow. The bandsaw, unfortunately, doesn't really cut acetal all that well, because it is so much harder than wood. As a result, unless I go very slowly, the blade starts to bend to the side. I have concluded that it is simpler and faster to just skip the bandsaw part of the operation. I can use the .4375" drill bit to make several holes in a row, and the results are just about the same.
Tuesday, June 8, 2010
ScopeRoller: I Can Fantasize About Doing This Full-Time
I received three orders today, and a query about what to order from Australia. Fortunately, two of the orders that arrived today were for the same model, so I am doing a mass production run (well, as mass production as ScopeRoller gets).
I fantasize sometimes about getting to the point where I get a dozen orders a day, at which point I would buy a CNC mill and lathe, set up the workpiece every few minutes, and let the computer do all the thinking.
I fantasize sometimes about getting to the point where I get a dozen orders a day, at which point I would buy a CNC mill and lathe, set up the workpiece every few minutes, and let the computer do all the thinking.
Sunday, May 30, 2010
Why Everyone Needs A Tap & Die Set
If you don't know what a tap & die set is (and there are many who do not): A tap is a hardened steel tool that cuts threads in a drilled hole. (A chart like this will tell you what size the hole should be into which you turn the tap to make various sizes of threads.) A die is a hardened steel tool that cuts threads onto an existing stem. The hexagonal things in this picture are dies. While you can use a die to thread a part that has never had threads, most consumers use a die to rethread a part whose threads have been damaged. (Usually a threaded part attached to something really, really hard to replace!)
Some years ago, my best friend gave me a Black & Decker ratcheting screwdriver set. It was a little orange case that had a ratcheting handle into which you could insert zillions of different bits: all the different sizes of Philips bits; standard screw head bits; hexagonal bits; some that I have never seen before.
If you didn't know that there are different sizes of screwdriver bits--well, I didn't really fully understand this, and why it mattered, until a few years ago. You already know that some screwdriver blades are too thick to go into the screw head. If you insist on using the wrong size bit, sometimes you accomplishing nothing; sometimes you chew up the head of the screw--and then you have drill out the screw, or use a Vise-Grip to grab hold and unscrew it. (Brutal, ugly, and sometimes the head breaks off the screw.)
Anyway, a very nice set. When you put the various bits into the handle, there was a spring loaded ball bearing that held the bit in place with friction. One day several years ago, I noticed that the bits were no longer staying in the handle--just falling right out. The ball bearing was missing--and for the life of me, I can't figure out how it could have stayed there.
I tried to buy a replacement handle--but that didn't seem to be available, and the bits were not the same dimensions as other, similar handles. Even worse: most off them didn't have the neat ratcheting capability. I could buy an entire replacement set (handle and bits)--but these were a bit spendy, and I would have a bunch of bits that were duplicates.
I was looking at this earlier this evening, and I noticed that the little hole in which the ball bearing had resided was .099" diameter. This was just a bit smaller than the hole size you use with a 6-32 tap. (The number 6-32 means a #6 sized screw, with 32 threads per inch.) I grabbed my 6-32 tap, and tapped this hole. Then I turned a 6-32 screw into the hole. Friction between the screw and the bits holds the bits in place just fine, and you don't have to loosen the screw to remove the bit. The only improvement I might make is to replace this conventional 6-32 screw with a 6-32 set screw so that there is nothing sticking out from the side.
Some years ago, my best friend gave me a Black & Decker ratcheting screwdriver set. It was a little orange case that had a ratcheting handle into which you could insert zillions of different bits: all the different sizes of Philips bits; standard screw head bits; hexagonal bits; some that I have never seen before.
If you didn't know that there are different sizes of screwdriver bits--well, I didn't really fully understand this, and why it mattered, until a few years ago. You already know that some screwdriver blades are too thick to go into the screw head. If you insist on using the wrong size bit, sometimes you accomplishing nothing; sometimes you chew up the head of the screw--and then you have drill out the screw, or use a Vise-Grip to grab hold and unscrew it. (Brutal, ugly, and sometimes the head breaks off the screw.)
Anyway, a very nice set. When you put the various bits into the handle, there was a spring loaded ball bearing that held the bit in place with friction. One day several years ago, I noticed that the bits were no longer staying in the handle--just falling right out. The ball bearing was missing--and for the life of me, I can't figure out how it could have stayed there.
I tried to buy a replacement handle--but that didn't seem to be available, and the bits were not the same dimensions as other, similar handles. Even worse: most off them didn't have the neat ratcheting capability. I could buy an entire replacement set (handle and bits)--but these were a bit spendy, and I would have a bunch of bits that were duplicates.
I was looking at this earlier this evening, and I noticed that the little hole in which the ball bearing had resided was .099" diameter. This was just a bit smaller than the hole size you use with a 6-32 tap. (The number 6-32 means a #6 sized screw, with 32 threads per inch.) I grabbed my 6-32 tap, and tapped this hole. Then I turned a 6-32 screw into the hole. Friction between the screw and the bits holds the bits in place just fine, and you don't have to loosen the screw to remove the bit. The only improvement I might make is to replace this conventional 6-32 screw with a 6-32 set screw so that there is nothing sticking out from the side.
Saturday, May 29, 2010
Precision Machining
I am increasingly pleased with my ability to make stuff very accurately. I received an order for some ScopeRollers for the Celestron CI-700 tripod a few days ago. Much of the work on machining a part is the setup: putting the cutting tool in place; installing the drill chuck in the tailstock; positioning the tailstock; zeroing the handwheels. Therefore, if you are going to make three parts, making nine identical parts isn't even twice the work. I wasn't putting any extraordinary effort into this, but because I have become fairly adept at this, I turned out nine perfectly squared cylinders that ranged from 3.599" to 3.602" in length; that's a .08% variance in length.
Sunday, March 28, 2010
Upgrading My Vertical Mill
Upgrading My Vertical Mill
I bought a used Sherline Model 5000 vertical mill several years ago. I've mentioned in the past the problems that I have had with the limited capacity of the standard mill vise that comes with this vertical mill, and my mildly clever solution to the problem. However, the problem remained that the Model 5000 only has about 3" of travel in the Y-axis--and except for the very smallest workpieces, that just isn't enough. You can reorient a part to do the movement in the X-axis--but that only goes so far.
Anyway, I was thinking a few weeks ago about replacing the base (on which the Y-axis moves) and the lead screw as a way of expanding the Y-axis travel--but then I searched to see if anyone offered such an upgrade. Sherline will sell you what seems to be the Model 5400 base, which gets you a couple more inches of travel--but it's expensive, especially compared to the A2Z Corporation's extended travel base and lead screw, which cost me $255 plus shipping.
There were no instructions with it, and it took a couple of emails back and forth to figure out how to install the lead screw correctly with the existing wheels. But it does work, and works well. As you can see from the attached picture, I now about 9" of Y-axis travel--enough that I would need to add more height extenders between the mill column and motor/quill assembly to take advantage of all that travel.
Pretty obviously, as you add more extenders, you are likely compromising vertical accuracy. I probably will never use all the travel that this base gives me--but if I needed more travel in exchange for less Z-axis accuracy, it's available. The longer base also weighs a lot more, and makes the whole assembly more stable. (You can bolt the base down to a table, but then you lose the flexibility of being able to pick it up and move it to another work location.)
I bought a used Sherline Model 5000 vertical mill several years ago. I've mentioned in the past the problems that I have had with the limited capacity of the standard mill vise that comes with this vertical mill, and my mildly clever solution to the problem. However, the problem remained that the Model 5000 only has about 3" of travel in the Y-axis--and except for the very smallest workpieces, that just isn't enough. You can reorient a part to do the movement in the X-axis--but that only goes so far.
Anyway, I was thinking a few weeks ago about replacing the base (on which the Y-axis moves) and the lead screw as a way of expanding the Y-axis travel--but then I searched to see if anyone offered such an upgrade. Sherline will sell you what seems to be the Model 5400 base, which gets you a couple more inches of travel--but it's expensive, especially compared to the A2Z Corporation's extended travel base and lead screw, which cost me $255 plus shipping.
There were no instructions with it, and it took a couple of emails back and forth to figure out how to install the lead screw correctly with the existing wheels. But it does work, and works well. As you can see from the attached picture, I now about 9" of Y-axis travel--enough that I would need to add more height extenders between the mill column and motor/quill assembly to take advantage of all that travel.
Pretty obviously, as you add more extenders, you are likely compromising vertical accuracy. I probably will never use all the travel that this base gives me--but if I needed more travel in exchange for less Z-axis accuracy, it's available. The longer base also weighs a lot more, and makes the whole assembly more stable. (You can bolt the base down to a table, but then you lose the flexibility of being able to pick it up and move it to another work location.)
Sunday, August 23, 2009
Ecologically Correct Corvettes
Ecologically Correct Corvettes
A lot of people love making working, scale models of various machines:
A lot of people love making working, scale models of various machines:
My current project is a 1/6th scale Chevrolet 327 cu in V8. Based on a 1964 365 hp Corvette motor, measurements have been taken from an actual engine as to be most accurate. The head and block began as billet aluminum that have been painstakingly machined on a Bridgeport-style mill. The 5-main crank has real babbit bearings, while the cam is a scale 30-30 Duntov.Dies were developed for stamping out the front cover, oil pan and rockers. The pistons and water pump housing are cast aluminum, and the valve covers are going to be investment cast.
Since this engine is a runner, there is spark ignition, a pressurized oil system and a cooling system just like its big brother.
There's video of the engine running. Because it is 1/6th scale (in linear dimensions), that means that the displacement of the engine is 1/6th x 1/6th x 1/6th, or 1/216th of the original engine, so the power output is going to be...tiny. But I suppose if you were making a 1964 Corvette for the original, incredibly bad 1960s TV series Land of the Giants, this would be the correct motive force for our little heroes to get around in...until one of the dogs decides it would make a fine plaything.
Wednesday, July 22, 2009
Clever Way to Center A Part In a 3-Jaw Chuck
Clever Way to Center A Part In a 3-Jaw Chuck
Without using a dial indicator (although this guy does it show how well it works).
I'm not sure that it is much faster than what I am doing now with the dial indicator, but if you were stranded on a desert island with a lathe and no dial indicator....
Without using a dial indicator (although this guy does it show how well it works).
I'm not sure that it is much faster than what I am doing now with the dial indicator, but if you were stranded on a desert island with a lathe and no dial indicator....
Saturday, July 18, 2009
Dial Calipers & Self-Centering Chucks
Dial Calipers & Self-Centering Chucks
I mentioned a few days ago that because I had bought a 4 jaw chuck (which doesn't self-center workpieces), I had been forced to put together something to hold a dial indicator in position, so that I could more precisely center the workpiece.
I also mentioned some months back that squaring the ends of a cylinder on the lathe is a bit of challenge if you aren't pretty close to a right angle when the workpiece comes out of the chop saw. But even with the greatest care in setting the angle on the chop saw, it is still a bit of a struggle. You can get a cylinder square by trimming one end, then the other, each time getting a bit closer to truly square. But this is slow, and you end up wasting a lot of material that way, since it may take several times through to get acceptably square.
So I put my dial indicator assembly to work with the self-centering 3 jaw chuck that I normally use for squaring workpieces for ScopeRoller. This made it possible to center the workpiece within about .010" very quickly (with gentle little taps on the end until I reached that goal). After trimming both ends, I had .002" accuracy on squaring, and it greatly simplified centering holes.
I mentioned a few days ago that because I had bought a 4 jaw chuck (which doesn't self-center workpieces), I had been forced to put together something to hold a dial indicator in position, so that I could more precisely center the workpiece.
I also mentioned some months back that squaring the ends of a cylinder on the lathe is a bit of challenge if you aren't pretty close to a right angle when the workpiece comes out of the chop saw. But even with the greatest care in setting the angle on the chop saw, it is still a bit of a struggle. You can get a cylinder square by trimming one end, then the other, each time getting a bit closer to truly square. But this is slow, and you end up wasting a lot of material that way, since it may take several times through to get acceptably square.
So I put my dial indicator assembly to work with the self-centering 3 jaw chuck that I normally use for squaring workpieces for ScopeRoller. This made it possible to center the workpiece within about .010" very quickly (with gentle little taps on the end until I reached that goal). After trimming both ends, I had .002" accuracy on squaring, and it greatly simplified centering holes.
Saturday, July 11, 2009
4-Jaw Chuck
4-Jaw Chuck
It rather sounds like a nickname you might give a person who can't keep his trap shut, doesn't it? Actually, a "chuck" is a device used to hold either a drill bit in place, or a workpiece on a lathe. Typically, 3-jaw chucks are self-centering; if you put something round or hexagonal in the jaws, and tighten the chuck, the workpiece gets centered. Not perfectly--but good enough for most lathe work.
A 4-jaw chuck is useful for holding rectangular, square, or irregular shaped objects. The 4-jaw chuck comes in both self-centering and non-self-centering forms. Self-centering is great for square workpieces, but not so useful for other shapes.
I have a 3.5" 3-jaw chuck for the Sherline lathe, and it works very well--but there are times that I need to turn bigger pieces--for example, when I wanted to very, very slightly enlarge the interior of a 6" diameter aluminum tube. And the 3.5" chuck just won't handle that. Strictly speaking, a Sherline isn't powerful enough to turn 5" diameter pieces of steel or aluminum; it's a bit insane to try it. But this will be an occasional use, and one where I will be turning pieces very slowly, taking very small strips at a time.
So, before I became utterly disenchanted with Sears, I saw that they were having a sale on 6" 3-jaw chucks. But it wasn't a thread that matches the Sherline (3/4"-16), and I wasn't sure that I wanted to spend a lot of time trying to find an adapter that let it fit. They did have a 6" 4-jaw, non-self-centering chuck at the discounted price of $53--which is an incredible bargain.
Okay, it's intended for their wood lathe--but I figured that for the relatively low precision stuff that I would use it for, it would probably work.
And it does. Of course, to get enough clearance between the chuck and the lathe bed on the Sherline, I had to put another spacer block under the headstock. Okay, got one of those that I use on the vertical mill.
Then I have to raise the tool holder up another 1.25". Okay, so I machined a spacer to fit between the cross-slide and tool holder. But I couldn't find a 10-32 3.5" long socket head screw--so I machined a stainless steel adapter 1.25" long that is 10-32 female on one end, and 10-32 male on the other--and now the cutting tool is in position.
Next issue: how do you center a workpiece? I found some instructions scattered about the web, but in essence, what you do is use a dial indicator on top of the workpiece, and slowly rotate the workpiece, watching how much motion there is. When you get to the lowest point, you loosen the jaw that is on top, rotate it 180 degrees, and tighten that jaw (and get progressively less vigorous each time). Repeat until you get the variation down low enough to make you happy.
So I used some scrap Delrin to make a holder that slides into the T-slot on the cross-slide and holds the dial indicator in position. (That means lots and lots of holes in the holder so that the dial indicator can be put at many different heights, depending on the diameter of the workpiece--or even if I use it with the standard chuck, and without the extra spacers.)
Click to enlarge
With one piece, I was able to adjust it to the point where there was only about .001" variation as I turned the workpiece. With another piece, I could never get it closer than about .004"--which probably means that the workpiece isn't perfectly round. (No surprise--they make these things oversize so that you can turn them to diameter.)
All in all, a pretty impressive purchase for $53 plus tax and shipping.
Don't tell Sherline. The owner would probably grin at my creativity in using a Sherline to turn stuff that is big but not very tough; their lawyers would probably file an injunction to get me to stop doing something that could cause the end of the world!
It rather sounds like a nickname you might give a person who can't keep his trap shut, doesn't it? Actually, a "chuck" is a device used to hold either a drill bit in place, or a workpiece on a lathe. Typically, 3-jaw chucks are self-centering; if you put something round or hexagonal in the jaws, and tighten the chuck, the workpiece gets centered. Not perfectly--but good enough for most lathe work.
A 4-jaw chuck is useful for holding rectangular, square, or irregular shaped objects. The 4-jaw chuck comes in both self-centering and non-self-centering forms. Self-centering is great for square workpieces, but not so useful for other shapes.
I have a 3.5" 3-jaw chuck for the Sherline lathe, and it works very well--but there are times that I need to turn bigger pieces--for example, when I wanted to very, very slightly enlarge the interior of a 6" diameter aluminum tube. And the 3.5" chuck just won't handle that. Strictly speaking, a Sherline isn't powerful enough to turn 5" diameter pieces of steel or aluminum; it's a bit insane to try it. But this will be an occasional use, and one where I will be turning pieces very slowly, taking very small strips at a time.
So, before I became utterly disenchanted with Sears, I saw that they were having a sale on 6" 3-jaw chucks. But it wasn't a thread that matches the Sherline (3/4"-16), and I wasn't sure that I wanted to spend a lot of time trying to find an adapter that let it fit. They did have a 6" 4-jaw, non-self-centering chuck at the discounted price of $53--which is an incredible bargain.
Okay, it's intended for their wood lathe--but I figured that for the relatively low precision stuff that I would use it for, it would probably work.
And it does. Of course, to get enough clearance between the chuck and the lathe bed on the Sherline, I had to put another spacer block under the headstock. Okay, got one of those that I use on the vertical mill.
Then I have to raise the tool holder up another 1.25". Okay, so I machined a spacer to fit between the cross-slide and tool holder. But I couldn't find a 10-32 3.5" long socket head screw--so I machined a stainless steel adapter 1.25" long that is 10-32 female on one end, and 10-32 male on the other--and now the cutting tool is in position.
Next issue: how do you center a workpiece? I found some instructions scattered about the web, but in essence, what you do is use a dial indicator on top of the workpiece, and slowly rotate the workpiece, watching how much motion there is. When you get to the lowest point, you loosen the jaw that is on top, rotate it 180 degrees, and tighten that jaw (and get progressively less vigorous each time). Repeat until you get the variation down low enough to make you happy.
So I used some scrap Delrin to make a holder that slides into the T-slot on the cross-slide and holds the dial indicator in position. (That means lots and lots of holes in the holder so that the dial indicator can be put at many different heights, depending on the diameter of the workpiece--or even if I use it with the standard chuck, and without the extra spacers.)
Click to enlarge
With one piece, I was able to adjust it to the point where there was only about .001" variation as I turned the workpiece. With another piece, I could never get it closer than about .004"--which probably means that the workpiece isn't perfectly round. (No surprise--they make these things oversize so that you can turn them to diameter.)
All in all, a pretty impressive purchase for $53 plus tax and shipping.
Don't tell Sherline. The owner would probably grin at my creativity in using a Sherline to turn stuff that is big but not very tough; their lawyers would probably file an injunction to get me to stop doing something that could cause the end of the world!
Saturday, June 13, 2009
New ScopeRoller Casters
New ScopeRoller Casters
I've just added several new tripods to the supported line of products:
ScopeRollerTM LXD55 for the Meade LXD55 tripod.
ScopeRollerTM VHAL110 for the Vixen HAL-110 tripod.
ScopeRollerTM VHAL130 for the Vixen HAL-130 tripod.
ScopeRollerTM OptMini for the iOptron Minitower tripod.
The sets for the Vixen HAL-110 and HAL-130 are actually more like a relaunch. I had grown too frustrated trying to machine these slightly complex parts before figuring out how to better grip the workpieces and how to select the right endmill for the job.
I've just added several new tripods to the supported line of products:
ScopeRollerTM LXD55 for the Meade LXD55 tripod.
ScopeRollerTM VHAL110 for the Vixen HAL-110 tripod.
ScopeRollerTM VHAL130 for the Vixen HAL-130 tripod.
ScopeRollerTM OptMini for the iOptron Minitower tripod.
The sets for the Vixen HAL-110 and HAL-130 are actually more like a relaunch. I had grown too frustrated trying to machine these slightly complex parts before figuring out how to better grip the workpieces and how to select the right endmill for the job.
Saturday, May 30, 2009
It's All In The Choice of Endmill
It's All In The Choice of End Mill
I mentioned a few days ago the inability to take big cuts when milling, even with this new, rather powerful drill press vise that I was using. I had an inspiration, while driving back from Bend.
Until now, I was using a 3/4" diameter, 1 1/2" long two flute roughing mill to do the coarse excavation. Partly this was because a two flute mill is considered the better choice for aluminum and plastic, and partly because the diameter let me do a 1.5" wide section in just over two passes. The more I tried to visualize the method by which a two flute mill cuts, the more I began to wonder if a mill with more cutting surfaces might do to job better--like fine teeth on a saw blade work better on a hard surface than coarse teeth.
Sure enough, I pulled out a 3/8" diameter, four flute end mill called a "rougher"--and discovered that I could mill a .192" deep section in Delrin without any fighting at all. I can't take out as wide of a section at once, but being able to cut this deeply means one vertical movement, and then several passes to cut the 1.5" x .210" section. I suspect also that a larger diameter four flute end mill might also work just as well, and with less passes.
I mentioned a few days ago the inability to take big cuts when milling, even with this new, rather powerful drill press vise that I was using. I had an inspiration, while driving back from Bend.
Until now, I was using a 3/4" diameter, 1 1/2" long two flute roughing mill to do the coarse excavation. Partly this was because a two flute mill is considered the better choice for aluminum and plastic, and partly because the diameter let me do a 1.5" wide section in just over two passes. The more I tried to visualize the method by which a two flute mill cuts, the more I began to wonder if a mill with more cutting surfaces might do to job better--like fine teeth on a saw blade work better on a hard surface than coarse teeth.
Sure enough, I pulled out a 3/8" diameter, four flute end mill called a "rougher"--and discovered that I could mill a .192" deep section in Delrin without any fighting at all. I can't take out as wide of a section at once, but being able to cut this deeply means one vertical movement, and then several passes to cut the 1.5" x .210" section. I suspect also that a larger diameter four flute end mill might also work just as well, and with less passes.
Saturday, May 23, 2009
Techniques For Coarse Vertical Milling?
Techniques For Coarse Vertical Milling?
I've got a question that some of my clever readers might be able to answer: is there a coarse and powerful equivalent of a vertical mill? Here's the problem: the Sherline vertical mill, even with a stronger vise, still doesn't like taking more than about .050" of Delrin at a cut. I'm making cuts of about .210" deep. If I could find some way to take off .150"-.175" with a powerful but perhaps not terribly accurate tool, then I could use the vertical mill to do the rest.
I've tried to use a bandsaw for this and I'm not impressed with results, partly because a bandsaw intended for wood tends to flex when you ask it to cut something as strong as Delrin. I need a way to rapidly remove rectangles of Delrin.
The temptation is strong to use a drill press, and move the material through an end mill held in the drill press. This doesn't really work because drill presses aren't designed to handle the sideways load, and the spindle detaches after a couple of minutes. (And it's probably not good for it, anyway.)
Is there some other common tool that can be used for this operation? I've experimented with a router, but if you use it for anything but a pretty big piece of wood, it throws the workpiece to the far side of the garage with great enthusiasm! (Be glad that you weren't at the far side of the garage.)
I suspect that a dado blade on a table saw might be way to do this, although I've never used a dado blade before. I suspect that if I used a 1/4" wide dado blade, and lowered it far enough that only about .1875" of it was exposed, I could use a fence on the table saw to make repeated passes through it. For the 1.5" x 2.62" x .1875" section that I need to remove, this would be six passes, each of them only a few seconds long. Then I could complete the process quickly and precisely on the vertical mill.
I've got a question that some of my clever readers might be able to answer: is there a coarse and powerful equivalent of a vertical mill? Here's the problem: the Sherline vertical mill, even with a stronger vise, still doesn't like taking more than about .050" of Delrin at a cut. I'm making cuts of about .210" deep. If I could find some way to take off .150"-.175" with a powerful but perhaps not terribly accurate tool, then I could use the vertical mill to do the rest.
I've tried to use a bandsaw for this and I'm not impressed with results, partly because a bandsaw intended for wood tends to flex when you ask it to cut something as strong as Delrin. I need a way to rapidly remove rectangles of Delrin.
The temptation is strong to use a drill press, and move the material through an end mill held in the drill press. This doesn't really work because drill presses aren't designed to handle the sideways load, and the spindle detaches after a couple of minutes. (And it's probably not good for it, anyway.)
Is there some other common tool that can be used for this operation? I've experimented with a router, but if you use it for anything but a pretty big piece of wood, it throws the workpiece to the far side of the garage with great enthusiasm! (Be glad that you weren't at the far side of the garage.)
I suspect that a dado blade on a table saw might be way to do this, although I've never used a dado blade before. I suspect that if I used a 1/4" wide dado blade, and lowered it far enough that only about .1875" of it was exposed, I could use a fence on the table saw to make repeated passes through it. For the 1.5" x 2.62" x .1875" section that I need to remove, this would be six passes, each of them only a few seconds long. Then I could complete the process quickly and precisely on the vertical mill.
Sunday, May 17, 2009
More On The Modified Drill Press Vise
More On The Modified Drill Press Vise
I used to make a ScopeRoller set for the Vixen HAL-110 tripod. Or more accurately, I made one, because it was a challenge--and since then, I have turned away a second order for it, and for the very similar HAL-130. Why? Because I couldn't hold the workpiece solidly enough in the Sherline mill vise to machine the part.
The modified drill press vise seems to be doing the job adequately. I can take much deeper cuts, because it holds the workpiece much more solidly, and because it is big enough for me to lay the workpiece (which is 2.62" wide) down flat for milling. In addition, the drill press vise is big enough that I will be able (I think) be able to put three workpieces in at once, and use a fly cutter to do some of the operations all at once. (I might have to bolt all three of them together, however, to make sure that they don't slip on the Delrin to Delrin surfaces. Not a problem. I drill a hole anyway to speed up milling a slot, so I can use that hole for the bolt.)
I also had a chance to do some more accuracy checks. In the Y-direction, accuracy is excellent. I squared my workpiece, and it was square within the limits of my measuring device (<.001"). In the Z-direction, it isn't quite as good; within .015". Part of the problem may be that the movable vise jaw has some play in it (of course), and so if the workpiece is off-center between the jaws, it tends to pivot the workpiece slightly.
I put a piece of Delrin of almost the same width in the vise at the same time, to reduce the pivot; it seems to have knocked it down to perhaps .008". That's good enough for the rough cuts for which I am using it. It is probably good enough to ship to customers; but if I decide to be more careful, I can rough cut to 1.40", and then remove the last .010" with the workpiece sitting vertically.
I used to make a ScopeRoller set for the Vixen HAL-110 tripod. Or more accurately, I made one, because it was a challenge--and since then, I have turned away a second order for it, and for the very similar HAL-130. Why? Because I couldn't hold the workpiece solidly enough in the Sherline mill vise to machine the part.
The modified drill press vise seems to be doing the job adequately. I can take much deeper cuts, because it holds the workpiece much more solidly, and because it is big enough for me to lay the workpiece (which is 2.62" wide) down flat for milling. In addition, the drill press vise is big enough that I will be able (I think) be able to put three workpieces in at once, and use a fly cutter to do some of the operations all at once. (I might have to bolt all three of them together, however, to make sure that they don't slip on the Delrin to Delrin surfaces. Not a problem. I drill a hole anyway to speed up milling a slot, so I can use that hole for the bolt.)
I also had a chance to do some more accuracy checks. In the Y-direction, accuracy is excellent. I squared my workpiece, and it was square within the limits of my measuring device (<.001"). In the Z-direction, it isn't quite as good; within .015". Part of the problem may be that the movable vise jaw has some play in it (of course), and so if the workpiece is off-center between the jaws, it tends to pivot the workpiece slightly.
I put a piece of Delrin of almost the same width in the vise at the same time, to reduce the pivot; it seems to have knocked it down to perhaps .008". That's good enough for the rough cuts for which I am using it. It is probably good enough to ship to customers; but if I decide to be more careful, I can rough cut to 1.40", and then remove the last .010" with the workpiece sitting vertically.
Saturday, May 16, 2009
Truing The Mill Vise
Truing The Mill Vise
I've mentioned my efforts to turn a cheap Chinese drill press vise into a mill vise for my Sherline. More of the saga.
One of the reasons that mill vises have a crisp edge at the bottom is so that you can align it with the mill table. The jaws of the mill vise, and the base of the mill vise, are very precisely parallel, so that when you move the mill table side to side, the workpiece only moves side to side, in the X-axis, not the Z-axis. And yes, I can (and I'm sure that you can) feel a discrepancy of .002" or .003" between two edges, so if the mill vise base and the table feel parallel, there is less (sometimes much less) than .003" difference.
So the first step was to figure out how to get this drill press vise's jaws and base parallel. I spent a lot of time trying to figure out how to clamp the drill press vise in a position that would allow me to mill an even line on the base. Eventually, this was my strategy:
The piece of bar aluminum in the mill vise is 1.007" thick (+- .001"--I measured it, and I was impressed at the accuracy). The drill press vise is clamped onto the bar aluminum. (It wouldn't clamp in the mill vise and still have the drill press vise base exposed to the end mill.) There's obviously a problem here of accumulating tolerances, but even assuming .002" at the mill vise base, .001" from the mill vise jaw, .001" from the aluminum bar, and perhaps .005" from the drill press vise itself, that's less than .010" total--and the next step makes even this discrepancy go away.
So now I made a series of passes with the end mill (a four flute roughing mill intended for steel) until I had a consistent edge on the drill press vise base. It looks terrible, but when I clamped it to the mill table, I had a repeatable line.
Now I used the end mill on the fixed jaw of the drill press vise to make it parallel to the base. It took a couple of passes for the original manufacturing marks to go away--and now, because I was moving the fixed jaw parallel to the base, because the base is parallel to the table, the fixed jaw is as parallel to the base as the intrinsic accuracy of the vertical mill.
I'm sure that this is still not as accurate as a proper mill vise--but for larger workpieces, it is sufficient--and it holds workpieces--even that slippery Delrin--far more solidly than the mill vise that I already had.
I've mentioned my efforts to turn a cheap Chinese drill press vise into a mill vise for my Sherline. More of the saga.
One of the reasons that mill vises have a crisp edge at the bottom is so that you can align it with the mill table. The jaws of the mill vise, and the base of the mill vise, are very precisely parallel, so that when you move the mill table side to side, the workpiece only moves side to side, in the X-axis, not the Z-axis. And yes, I can (and I'm sure that you can) feel a discrepancy of .002" or .003" between two edges, so if the mill vise base and the table feel parallel, there is less (sometimes much less) than .003" difference.
So the first step was to figure out how to get this drill press vise's jaws and base parallel. I spent a lot of time trying to figure out how to clamp the drill press vise in a position that would allow me to mill an even line on the base. Eventually, this was my strategy:
The piece of bar aluminum in the mill vise is 1.007" thick (+- .001"--I measured it, and I was impressed at the accuracy). The drill press vise is clamped onto the bar aluminum. (It wouldn't clamp in the mill vise and still have the drill press vise base exposed to the end mill.) There's obviously a problem here of accumulating tolerances, but even assuming .002" at the mill vise base, .001" from the mill vise jaw, .001" from the aluminum bar, and perhaps .005" from the drill press vise itself, that's less than .010" total--and the next step makes even this discrepancy go away.
So now I made a series of passes with the end mill (a four flute roughing mill intended for steel) until I had a consistent edge on the drill press vise base. It looks terrible, but when I clamped it to the mill table, I had a repeatable line.
Now I used the end mill on the fixed jaw of the drill press vise to make it parallel to the base. It took a couple of passes for the original manufacturing marks to go away--and now, because I was moving the fixed jaw parallel to the base, because the base is parallel to the table, the fixed jaw is as parallel to the base as the intrinsic accuracy of the vertical mill.
I'm sure that this is still not as accurate as a proper mill vise--but for larger workpieces, it is sufficient--and it holds workpieces--even that slippery Delrin--far more solidly than the mill vise that I already had.
Thursday, May 14, 2009
The Difference The Right Vise Makes
The Difference The Right Vise Makes
I mentioned a few days back that I was machining a cheap drill press vise to make it more precise for use on the Sherline vertical mill--and what a difference it makes! I filled a ScopeRoller order last night where I could have left these three rectangles the size that they came out of the chopsaw--but there was enough variation that it would have looked bad, and besides, when you mill the edges, it looks so much nicer!
Anyway, this drill press vise has a lot more clamping force, and I was able to lock all three 1/2" thick pieces of Delrin in position at once. Because it clamped them so solidly, I found that the fly cutter was happy even doing .025" deep cuts across all three chunks, even turning the lead screw as fast as I could. What a difference! My vertical mill is now a source of joy, not frustration. Even machining big pieces of aluminum works well now.
I mentioned a few days back that I was machining a cheap drill press vise to make it more precise for use on the Sherline vertical mill--and what a difference it makes! I filled a ScopeRoller order last night where I could have left these three rectangles the size that they came out of the chopsaw--but there was enough variation that it would have looked bad, and besides, when you mill the edges, it looks so much nicer!
Anyway, this drill press vise has a lot more clamping force, and I was able to lock all three 1/2" thick pieces of Delrin in position at once. Because it clamped them so solidly, I found that the fly cutter was happy even doing .025" deep cuts across all three chunks, even turning the lead screw as fast as I could. What a difference! My vertical mill is now a source of joy, not frustration. Even machining big pieces of aluminum works well now.
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