Im building a CNC mill, and I think Ill need a chunkier square when I eventually get to the aligning stage.

I came across a webpage sometime ago (can't find it now of course) that showed how to make one from a chunk of cast iron. Not having a lump of iron the right sort of shape I poke about and found some thick walled steel box section. Hurrah, that'll do to try the process at least, and might even work for the intended job

To start the long edges are made parallel. Fortunately I have a reasonable surface grinder, so I slapped the box onto the mag chuck and started making sparks:

The weld seam was something like 0,004 lower that the edges. Not too bad.

I planned to rough grind and then finish, so once both sides had cleaned up I checked it on the surface plate.

 Basically zero movement on a 0.0001" DTI.

I was well chuffed

Now the long edges parallel It was time to rough in the ends. I hacksawed them roughly square, whacked it in a known OK grinding vice and made some more sparks:

Then with parallel ends that should be close to square it was back to the surface plate to measure up:

DTI on a surface gage rocked left and right for the high reading. Turned out to be leaning by about 0.007". For the first round of squaring up it was back to the grinder with some feeler gages:

0.003" under one side and clean up one end, then flip and make parallel (without the feelers).

At this point I left it to sit for a couple of days, partially to let it move if it was going to, and partially cos I have other things to do…

It did move, and the long sides were slightly out, something like 4 tenths IIRC. So I did a light set of finish passes on them. This is the start of one ( the beautiful dark corner):

Ended up back to basically as good as I can measure

Then another round of measure the squareness. I couldn't easily get the round part of the surface gage to touch and have the DTI at the height I wanted due to the way the angles worked out. Fortunately the surface gage has a V in the front, so one bearing later I have a round bumper again and I could measure over pretty much the full height.:

This time I needed an offset with precision in the tenths region, so I made a pair of gage block stacks with the required offset ( IIRC it was 0.2 on one side and 0.2014 on the other). The square was supported on these on the grinder, mag'd and clamped so I didn't get any ideas about flying away and then a fresh dress and a light grind and I cleaned up the ends.

The finished square has come out OK:

Its roughly 90 degrees – I calculated it to 89.996 / 90.004 based on the measurements. Ill check it again in a few weeks to see if it moves, but even if it does it'll likely be close enough for what I need.

Dave

Edited By Dave S on 11/05/2022 21:36:28

Surely the point is to make things?

I don’t think a cylindrical square will work for what I think I’ll need – as with the parallel faces I can square vertically and with another square horizontally at the same time.
Still if it turns out I need one I do know I can turn to under a tenth over 20” or so because not that long ago I had to…

Dave