Machining

I've received a lot more emails about than I expected--and it appears that many of my readers have misunderstood my complaints. It is, of course, simply impossible that I have not articulated my irritation properly. :-)

Why am I not running out and buying a lathe right now? It is not because my time is too valuable. I actually have a bit of spare time at the moment. I am not interested in investing upwards of $700 for a quality piece of machinery, only to discover that what I think is a medium sized market for the telescope mount accessory that I am building is really a very, very tiny market. If the market turns out to be as big as I think, I'll run out and buy a lathe.

It is not because learning to use such a tool is beneath me. I am actually fascinated by machine tools. If I were fabuluously rich, I would have a lathe and a vertical mill in my garage. I like working with tools. But I also know that there is a learning curve associated with any skill, and I have seen just enough of machining to recognize that it is a substantial skill--it involves both significant book learning, and significant hands on experience.

My frustration is that I have now had two different machinists agree to build parts at prices that were either very reasonable, or tolerable. One just disappeared on me, and another essentially decided that he was too busy.

I understand that setting up tooling for some types of machining is substantially time consuming. I've built some tooling for manufacturing one set of parts from Delrin--fortunately, parts that I can make with a miter saw and a drill press. In this case, there isn't really any tooling. The steps required to make these parts are:

1. Turn a 2.375" plastic rod down to 2.355". Depending on the accuracy of the lathe, and the length of the rod, this can be a problem, but you can also start by cutting the rod into 4" lengths, and turn each 4" length. Because the two ends are going to be cut off in step 2, you can hold the stock in place with a Forstner bit or a screw.

2. Make two 30 degree angle cuts with a saw. A miter saw works for this--the only hard part is getting the rod to not rotate while cutting. (This is not a machining operation; no precision requirements.)

3. Make a 3/8"-16 x 1" deep tapped hole in the face of one end. There is no requirement for even hundredths of inch accuracy on centering the hole. Because you have cut both ends in step 2, you can put this in a drill press clamp, drill the hole, and then use an electric drill with a 3/8"-16 tap in it.

The only part of this operation that is beyond my ability is step 1. If I could buy 3.355" and 3.460" diameter rod, I wouldn't be looking for a machinist. Unfortunately, almost all extruded rods are made only to nominal diameters. If you buy plastic rod that is listed as 3.375", it may be as much as 0.1" oversize. You pay for precision--and in some sizes, you can't even pay fo precision--you just can't get that size.

Fortunately, I have a co-worker who has a lathe and a mill. He is taking the fairly sweet layoff incentive package that our employer is offering, and he figures that he can put his equipment to work doing something interesting, and perhaps it will turn into a steady income for both of us.

UPDATE: It occurs to me that 2.355" is also 59.814 mm. It is possible that some precisely 60mm plastic rod could be sanded down to fit. But I am not having much luck finding 60mm Delrin, UHMW, or similar plastics. The other size that I need--2.460"--is not any even size in metric.