Tuesday, March 21, 2006

This Isn't Really About Machining, In Spite of the Pictures

It is about how the things you learn as a child stick with you. When I was a child, my father was a tinkerer. He fixed cars, appliances--you name it. When my sister's TR6 needed a transmission rebuild to make it saleable--no problem. It was a major project, but he dropped the transmission, took it apart, and replaced the damaged gears.

It was memorable. One gear was missing 40% of its teeth--it became a candlestick holder in our house for many years. The experience of replacing these parts was a learning experience about British automobiles. At one point, he found out that the concept of "interchangeable parts" had apparently not taken hold very well in the British automobile industry. When he took back a transmission part that didn't fit, the auto parts store explained that he had received the right part--but even in the same year, there was considerable variation in parts, and they gladly exchanged it for another supposedly identical part--and this one fit.

I never liked being involved in these projects. My father would have me help him, but I always resented it, because I wanted to be reading. Getting your hands dirty making stuff just didn't do anything for me, except bore me silly.

Somehow or another, I ended up learning a lot from watching him, especially when he was doing something that mattered to me. For example, by junior high, I needed a bookshelf--a big bookshelf. We built one--and he taught me that you use screws, not nails, for anything you might ever have to repair. You can remove and replace screws without damaging the wood--unlike nails. I still have that bookshelf today--very solid, and in no danger of getting creaky.

When I wanted a big telescope, my father knew exactly where to go to find parts intended for that purpose--and parts not intended for that purpose! We built a serviceable mount from plumbing parts and a rolling tripod that we found in a junkyard.

Finder scopes too expensive for our limited budget? He found a right angle telescope originally intended for some military application. There were no cross lines on the reticle--only horizontal lines. So we disassembled it, used a glass cutter to scribe a vertical line, and then put it back together again. No illuminated reticle? He drilled a small hole in the side of the tube, and by holding up a very small red light bulb, we achieved the desired result. It looked very retro, but it worked well.

I learned a lot from my father about tools and making things (usually against my will), and in recent years, I have been using some of that knowledge. For example, the ScopeRoller manufacturing operation requires me to turn cylinders of plastic to a particular diameter. You can't just put the cylinder in a three-jaw chuck, and then move the cutting tool down the entire length of the cylinder. Where the cylinder sits in the chuck, the jaws get in the way of the cutting tool. You can't turn the cylinder most of its length, and then turn it around, and complete the process--the cylinder doesn't end up in quite the same position, and you get a discontinuity where the turning operation ends.

So here's the solution that I made, starting with a round rod of aluminum.

Click to enlarge

Click to enlarge

The female end is 3/4"-16 threaded to screw onto the headstock of the lathe. The male end is 3/8"-16 threaded. I face the two ends of the plastic cylinder, and then drill a small hole in the exact center of each end. then I drill and tap a 3/8"-16 hole in one end of the cylinder. This threads onto the 3/8"-16 male end of the adapter. Then I use a live center in the tailstock to suspend the cylinder, and now I can turn the entire length of the cylinder to a precise diameter in one smooth operation.

The art of making this adapter was relatively simple.

1. Face the two ends of a piece of aluminum rod so that they are exactly square.

2. Drill a hole in one end with a 1/2" drill bit.

3. Use a boring bit to enlarge the hole to .673" diameter (the size that the 3/4"-16 tap requires).

4. Use a 3/4"-16 tap to thread the hole.

5. Mount this on the headstock, so that it can now be turned exactly on axis.

6. Because tapping a hole often ends up slightly off exactly perpendicular (and this needs to be a very precise part), I then refaced the end of the aluminum, put the part back in the 3-jaw chuck, and refaced the end with the 3/4"-16 hole.

7. Remount the workpiece on the headstock's 3/4"-16 threads.

8. Cut away the unmounted end of the cylinder until you have a .39" diameter by .5" long stem.

9. Use a 3/8"-16 die to thread the stem.

10. Drill three holes perpendicular to the sides of the workpiece, so that if it gets stuck on the headstock threads (which it did, at one point), I can stick metal rods into them to get more leverage for loosening it.

11. Polish everything up nicely.

Whenever you start to wonder if the things that you are teaching your children--and not just useful skills, like use of tools, but the important things, like right and wrong, compassion, and justice, think back to the things you learned from your parents--and see how often you are putting those ideas to work today.

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