Pete.
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- Kent, UK
So armed with the sensitive dial gauge I got off Jezguz I have started on my version of a repeat-o-meter. This tool is what you use for detecting local wear in a surface plate, for instance if someone had been using the same spot on the plate for a long time or perhaps (god forbid) used their granite plate for lapping. The most popular instrument of this type is the Rahn repeat-o-meter but at 12" long that one is a little too cumbersome (and a lot too expensive) for my use.
The principle is that you have a (relatively) heavy body sitting on three pads so it never rocks, and a separate shoe piece on the front that can hinge through a very small angle with one pad on the end. When you move the body about a plate the forward foot will follow the contour of the surface and a dial indicator fitted directly above the front pad directly records any up/down movement.
I wanted a device of about 8" long and very narrow so that I can use it to detect twist in a straight edge. I had some cast iron pieces about 7/8" thick so I chopped 8" off one of those and that gave me the material to make the body and the shoe. Here's the basic tool part-finished. I didn't take any progress shots as my phone was in the house on charge (and I don't like it anywhere near when I'm surface grinding cast iron anyway) but the pieces are so simple it's hardly worth explaining. I milled a 10mm slot in the bar and cut it off with a thin disc then cleaned it all up on the mill.
Here's the hinge. I used a 30 thou slitting saw to make two slits each side about .300" deep.
Then I drilled and tapped four holes for M5 grub screws. Had to put a ball bearing in the bottom of the hole because I couldn't quite tap the threads deep enough and I didn't have any dog point screws.
The hinge is made from a stanley blade just ground to shape. I set the gap with a couple of 5 thou shims and it allows 65 thou total deflection on the end of the shoe.
.
Once it was assembled I drilled four holes in the base and set some round HSS bar into the holes with loctite. Cut them off with a mini grinder then ground them flat on my surface grinder.
So far it has come out perfect. The original repeat-o-meter has two metal bars on the side to control the movement of the shoe so the hinge doesn't break. Mine doesn't need them because the 5 thou gap keeps deflection to a minimum, and anyway if the hinge cracks it's 5 minutes work to make a replacement.
I'm looking forward to getting this finished, mounting the dial gauge and seeing how well it works.
The principle is that you have a (relatively) heavy body sitting on three pads so it never rocks, and a separate shoe piece on the front that can hinge through a very small angle with one pad on the end. When you move the body about a plate the forward foot will follow the contour of the surface and a dial indicator fitted directly above the front pad directly records any up/down movement.
I wanted a device of about 8" long and very narrow so that I can use it to detect twist in a straight edge. I had some cast iron pieces about 7/8" thick so I chopped 8" off one of those and that gave me the material to make the body and the shoe. Here's the basic tool part-finished. I didn't take any progress shots as my phone was in the house on charge (and I don't like it anywhere near when I'm surface grinding cast iron anyway) but the pieces are so simple it's hardly worth explaining. I milled a 10mm slot in the bar and cut it off with a thin disc then cleaned it all up on the mill.
Here's the hinge. I used a 30 thou slitting saw to make two slits each side about .300" deep.
Then I drilled and tapped four holes for M5 grub screws. Had to put a ball bearing in the bottom of the hole because I couldn't quite tap the threads deep enough and I didn't have any dog point screws.
The hinge is made from a stanley blade just ground to shape. I set the gap with a couple of 5 thou shims and it allows 65 thou total deflection on the end of the shoe.
.
Once it was assembled I drilled four holes in the base and set some round HSS bar into the holes with loctite. Cut them off with a mini grinder then ground them flat on my surface grinder.
So far it has come out perfect. The original repeat-o-meter has two metal bars on the side to control the movement of the shoe so the hinge doesn't break. Mine doesn't need them because the 5 thou gap keeps deflection to a minimum, and anyway if the hinge cracks it's 5 minutes work to make a replacement.
I'm looking forward to getting this finished, mounting the dial gauge and seeing how well it works.