Machining

Machining

A while back, I removed a particular caster assembly from the ScopeRoller product list because it was just too much work to make. It was a complex part, with two protrusions that replaced an even more complex foot on the Vixen HAL-110 tripod leg.

Another customer needs it, and because he was confused about what Vixen tripod he had, I feel somewhat compelled to build the right part to replace what I have already made. I've been planning to work on the HAL-110 tripod leg problem anyway, so it's not that big a pain.

What made the part in question complicated was:

1. I needed to make cuts in three different dimensions, and the workpiece would have been very difficult to position in one direction because it was 2.69" wide--and the mill vise that I have is only 2" wide. Yes, there are ways to get around that, but they involve cutting vertically over a very great distance--and when the height of a workpiece exceeds the height of the vise jaws by too large a margin, you have to make very small cuts (.010" or .020" at a time), or risk having the workpiece pull out of the jaws.

2. I had too large of a base that set on the caster, relative to the protrusions that go into the Vixen tripod leg. This meant that I had to either do a lot of cutting with relatively coarse tools (like a bandsaw), and then mill for precise dimensions. There isn't much (at least in my garage) in between the .05" - .1" precision of a bandsaw, and the .001" - .003" precision of a vertical mill.

So I have shrunk down the dimensions of the base a bit. Now the amounts to be removed from a solid block of Delrin are much less. Two .210" sections have to be cut off; a .130" section; a .060" section. And a 0.500" section in the middle, that I will do with a .4375" drill, and two bandsaw cuts.

By experimentation, I have concluded that when the monstrous, 0.75" diameter, 1.75" long end mill is in play, I can remove .020" of Delrin at a time with the edge of the end mill. (This means that I move the end mill up alongside the plastic, and cut a 1.5" high, .020" depth section of Delrin at a time.) Using the frace of the end mill, I can remove .050" of Delrin at a time. This means that it only takes a few passes back and forth to remove what is in the way.

I can also see why CNC vertical mills make so much sense. Much of what is happening here is repeating certain steps. If I had the CNC control unit, I would spend a bit of time programming the motions once. Then I would position the workpiece in the mill vise, start it up, and walk away. Ten minutes later, that operation would be complete, and I could move the workpiece to a new position and have it resume.