How hard is gauge plate?

I just happened to have this same job in the workshop today, which reminded me of questions raised in this thread, while making a cotter clamp for my upgraded carriage stop. (Which is another story, more of which anon.)

1/4" BSW taps.

Tapping a 1/4" BSW thread into the brass cotter clamp

Screwing in a 1/4" UNC screw by hand. No binding. No slop. No dramas. It always works for me.

Sorry about the sideways pics. They were right way up at my end before uploading and there seems to be no facility this end to rotate them. Perhaps some kindly mod will stop by and rectify?

Mod edit: rotated photos.

Edited By SillyOldDuffer on 09/03/2022 10:36:04

The gauge plate arrived. I, naively perhaps, expected 3/4" to be 3/4".

it is in fact oversize and as a woodworker I have no way of machining it.

So I am slowly grinding one side down with a piece of 100 micron lapping film stuck to a piece of plate glass.

That sounds like slow work. How much too big is it? What is it that you are making out of it?

Rectangular gauge plate is ground to tolerance on the wider sides (usually a thou or two) but left as sawn on the narrow sides. What size did you order?

Andrew

It's 3/4" x 1/4" bar 18 inches long. It slides in a slot 3/4 wide in a tablesaw cast iron top. It needs to be a tight fit with minimal sideways movement.

The narrow sides are rough sawn and it's about 250 microns too wide.

sorry for the mix of measurements but I never did get used to using an imperial vernier.

Don't worry, I do the same after growing up with Imperial in Australia, then we converted to Metric, then I went to live in America and had to convert my brain back again to Imperial, and now I am back in Metric Australia I still have to look up what 250 microns is in "thou" before I can think about it.

You might make quicker progress if you file the edge of the gauge plate down using something like a 10-inch (250mm!) flat file applied carefully. For what you are doing, a piece of 3/4 x 1/4 Bright Drawn Mild Steel flat bar might have been closer to size in all directions. Usually within a thou or two of the nominal size. (Or a 0.025mm or two!)

I wanted something a bit harder with some resistance to rust and I wasn't sure how accurate mild steel would be.

The cost of the steel was low compared to the cost of sending it to Italy.

No problem with the measurements, I'm bilingual.

The gauge plate will be ground on the wide surfaces as standard, so the 1/4" dimension will be accurate but the 3/4" dimension will not be. The only exception is that square section gauge plate is ground on all four sides.

Personally I'd draw file one edge to fit rather than lapping. I use micrometers for accurate measurement, not verniers.

Andrew

I have always wanted a micrometre but can't really justify the cost. My Mitutoyo vernier is good enough for what I do.