My only real accomplishment since the last update, showing the completed X and Y axis ballnut mounts, was to complete Z-axis.
The Z mount was the biggest piece I've done yet, and I had to learn a few new things to get it completed. As I mentioned, to bore the large (1.110") hole in the Y axis mount, I put it in the four jaw chuck on the lathe, turned a plug to fit the hole I had drilled in it, centered it, and bored it on the lathe. The Z- axis piece has an even larger hole, 1.420", and the size/shape of the part wouldn't fit in my four jaw (well, maybe there's a way, but I didn't see it). Instead, I put it on the G0704 itself and used my boring head.
You'll note the large chamfers on this part. I cut these on the G0704 as well, clamping the piece down after using a combination square to position the part so that straight cuts took off the excess material (those chamfers are 0.375 on a side from the square corners).
Then came drilling and tapping the 1/4-20 holes. For the first time, I barfed this up. The holes were far enough off that I could get only one screw in the ballnut.
Now what? I've never relocated holes before, but it really is a fundamental skill we should all have. I know in commercial shops they may drill it out larger and put in a PEM nut, or use a welder to fill it, but I don't have a TIG welder and wouldn't know how to use it if I had one. So acting on the advice of a friend, I got a half inch aluminum rod, turned it down to thread and made 1/4-20 aluminum screws to plug the holes with. Used red LockTite to hold them in place, sawed them off with a slitting saw on my Sherline, then milled them just a little proud of the surface (like .002) with the G0704. This is on the Sherline, before I milled them.
I think my error was in setting my zero on the Sherline before I drilled, because after flipping the part, finding zeroes again, and putting a small peck at each hole with a center drill, the marks all appeared to be in the right place.
The same friend suggested that since I have the master location (the ballnut that has to mount), why not make a tool to fit in the hole that will better center a drill and mark it that way? So I turned down some more of that 1/2" aluminum bar to fit the holes in the ballnut, then center drilled them on the lathe for a 1/16" drill bit. I made four and put them in the four corner screw holes in the ballnut, and clamped the ballnut to the mount with C clamps. Drilled holes with a 1/16 bit. Broke the first bit and while muttering obscenities and looking for the next size up to continue, found that "someone" had bought and stashed three 1/16 bits. No more excitement because I remembered to use just a tiny dab of tapping fluid. Once the four were drilled, I moved two tools to the center holes, re-clamped, and drilled them.
Moved it to the Griz and mounted my drill chuck. Carefully centered the bit three times, using a 7/64 bit, then three more times using the bit that came in my old Craftsman drill and tap set for 1/4-20. While doing the larger holes, I could feel that some times it felt way too easy. Turned out two of the aluminum threaded screws had backed out. So I put them back with more Locktite. The result: perfect fit.
The little tools are in the lower right.
So that's where I am now. I'm down to four parts to make: the X and Y motor mounts, the Y axis spacer and the X-axis end cap. The end cap has a lot of machining that needs to be done, and I think I'll do that last. I spent three weeks on this part, though, so I hope I pick up some speed.
Every part is a puzzle!
Bob