Yesterday I thought I had made some improvement in the accuracy department with my ShapeOko.
This evening I ran a job that demonstrated that I was all wet.
As you may or may not know, I make 1911 pistol grips. Each grip has two holes in it, spaced 3.074″ inches apart.
I have a couple of jigs and such for drilling the holes and shaping the grips. I thought I had written up a blog post about my process, but apparently not. I’ll add that to the to-do list.
In any case, one of the things I want to do is use the ShapeOko to mill out the grips.
Tonight I started making a fixture to hold the blanks. The first step was to bore two holes in the fixture that were 3.074″ apart. Simple enough. Or so I thought.
I used my Perl script to generate the G Code and ran it. It looked great. Then I grabbed one of my grip templates with the holes drilled in it and compared the holes. Oh hell.
I thought the template might be off a little bit, but this was really bad. So I measured the hole spacing.
3.114″ center to center. Off by .040″. Whisky-Tango-Foxtrot?
Apparently the correction factor I came up with was not quite right. Perhaps measuring the error over only .900″ is not enough. Maybe the cogs on the belts are not as evenly spaced as they should be.
In any case, I re-figured the correction factor using the 3″ dimension, entered it into the GRBL shield and did the holes again. They came out within .002″. Which is pretty damned close.
I did the same on the Y axis over a 2.25 inch span and got it to come within .006″.
So, I guess I need to clamp down a piece of MDF and bore some holes in it, measure them and figure out what’s really happening.
And here I had thought I was being so smart yesterday.
Well, I’m closer now than yesterday, so that’s something I guess.