Friday, May 13, 2016

I'm Just A Boring Guy

I had another piece that needed boring for G0704 CNC conversion project.  This one is the biggest piece that's going to get bored, a ballnut mount for the Z axis.  That's a bigger ballscrew/nut combination than the X or Y axes because of the bigger load it has to move.  Due to the part's geometry, I didn't see how to get it onto the lathe.  This time it was over to the G0704 to cut it.  Again, boring is a fundamental operation, and when I bought the mill, I bought a boring head as part of the tooling.  It's a clone of the Criterion style head (like that link, but not exactly).
That hunk o' aluminum is 1 1/4" thick, 2.9" long and 2.25" wide.  The big hole is 1.42 diameter and the boring head was spinning when I took this picture.  The piece will get a pattern of 1/4-20 holes in the large hexagonal area and some 5/16-18 holes into the base (on the left).  I'll do all the precision drilling on the little Sherline.  I'm all but sure this is the biggest hunk of metal to work in the job.  

To me, it's worth noting that this is the first time I ever had that boring head in the mill.  I've never run a boring head on any milling machine.  The diameter was supposed to be 1.420, and came out 1.423. 


  1. Very nice work. You got within 3 thou of the spec on your very first use of the boring head. Again, very, very well done, and the surface finish looks good.

    How did you center for the hole? Wiggler into a layout prick mark? Edge finder and then math? Dial indicator?

    I wonder if going a little undersize, and then honing up to the final dimension with a brake cylinder hone would have worked.

    1. The plan was to sneak up on the final size, but I think my boring head moves a little while spinning. It's an LMS 3662, which looks just like the one on Amazon I linked to. One thing LMS does over many other sellers is more QC. You can't inspect quality into a product, but you can weed out the bad ones.

      When I got the mill, I got a drill chuck from them that they claimed met .004" TIR. I measured it and got closer to .010". Told them about it and they said, "Nope, nope, nope. The replacement is on the way". Sure enough, the new chuck was under .004, though not by much.

      I centered it by coloring the aluminum with a black sharpie, then scratching it with my calipers. Put a spotting drill bit in the chuck and centered it on the lines under a 10x magnifier. Once that was centered, I locked down the table and drilled out some holes making it bigger (1/4 then 1/2), finally cutting it with a 3/4" end mill.

    2. And you did it all "old school." Well maybe old school would have you using a vernier caliper, but even with magnifiers, I struggle to read the vernier scale.
      Did you mention that you had either an electronic or laser edge finder a while back, or am I not remembering correctly.

    3. Right - I have a laser edge finder. And two (three?) of the mechanical types. I didn't use it because of the way this hole is located on the prints. Its center is referenced to the right edge (in the pic) and the other edges of the big hexagonal piece. It was definitely old school, using the caliper jaws to scratch the Sharpie. "Sharpie - it's the new Dykem!".

      I always work under 4x Optivisors. For this one, I wanted the 10x magnifier, like this one.

  2. I took a look at the laser edge finders at LMS. Maybe one will pop up on sale, I get their sale mails, so fingers crossed.
    We drilled a lot of holes in the shipyard that were laid out with Dykem (the old Sharpie!), prick and center punched marked, then a couple of witness circles to check for drift, then the hole was drilled with a series of drill bits.
    Later the use of carbide tipped hole saws made it all a lot easier.