Weekend Shop Update on the 1 by 1 - part 4

"When we last left the story"  I had shown the derivation of some extra tool paths that the CAM program wouldn't create and showed the cut out of Side 2. 

The other side plate shouldn't be hard, especially with the lessons learned already, right?  Yeah, I had to cut the last few passes around the outline due to the cutter slipping upward in its holder, but that was one time versus the three times on the other piece.  Here's the way it turned out, and I'll show you this before I explain things.

That uncut area on the top around the two bolts is supposed to be 0.124" above the rest of the top surface. That's 4 passes at .031" per pass; the rest of that surface is the right depth.  In the red highlight box where you see the ledge and across the right side, it's .093 - three passes. I ran the file again, just to watch through the first four layers and the cutter just never went there. I was concerned it might have been from my editing the file, but that was just to keep the cutter out of the uncut area. It went into that area on the right to cut it down to -.093, it just didn't go back to cut the last pass. I've been using Deskproto for about 10 years and I can't think of another time it did something like this.

It wasn't hard to use my Logitech Rumblepad controller to cut the rest of that away, but it was odd and therefore unsettling.  After all, the reason we use CAM programs instead of coding everything by hand is they're supposed to make complex shapes easier without making mistakes like this. 

Now it was time to take both pieces off the mill, de-burr them, then bolt them together, smooth them and remount to get ready to drill the holes for the two tooling pins that go into both sides to hold them in the right positions.  That makes it easier to take them apart and put them back together precisely, which I'm going to have to do.  Other than breaking the one fine sanding belt I own before I was fully done with sanding, there were no issues.

This is where I made a silly screw-up and spent a day trying to find it.  The issue centers on the dimensions in red in this drawing. 

The problem showed up when I went to position the centering drill over the hole for one of the tooling pins circled in red.  It looked too close to the top edge, and instead of measuring what's in the red oval, I got more like .150 to .160 instead of .220.  That led to studying it for hours, looking at other measurements and just being confused.  The overall length and width of the plates were right.  The dimensions going left to right looked fine.  The dimensions from the edges of the raised area to the part's edges were also offset.  IIRC, the top one, 0.696 was too small and the 0.625 on the bottom was too big. 

What this would mean was that the CAM program had shifted the centerline X-axis upward in this view.  I couldn't figure out how it could do that and not mess up the whole part. 

Late one night last week, after puzzling over this for hours, I took yet another look at the work and realized my mistake.  I had put the two pieces on mill backwards.  Notice the ~45 degree angle in the drawing is at lower left.  Here you can see it's on upper left.  The top of this stack is side 2.  You can tell it from side 1 by the machining marks

Since the next operation was just positioning the mill and drilling a total of 11 holes of different sizes, it didn't take as much time to finish this phase of the machining as it did to figure out what I did wrong setting up to do it. 

There are five large holes with a counterbore; those had to be done in three steps; the two tooling pin holes had to be prepared in three steps also and tooling pins cut to length.  So it wasn't simply drilling 11 holes, but it wasn't hard just a lot of motions.

These are complex pieces.  The vertical side facing you, the right and the far vertical sides all get drilled and tapped holes.  Two per side on both side plates.  The far side gets a 1.1" diameter hole bored into it, centered on the plane where the two side plates touch.  And lots more.  I'll be working on these for a while, but I think the way most of that should get done is with the machining vise on the mill's table.