3M 30 micron diamond lapping film?

The guy I bought my Biax from swears by 3M diamond lapping film. He says he uses it between machine components e.g. inside a dovetail (with the gib removed) to lap one part against the other.

This is something that never came up during the scraping class I attended. Can anyone comment on this product and how it can be used?

metalmagpie

About 45 years ago I worked at an HIFI electronics repair shop (remember when folks got stuff fixed?). We got hold of 3M "Imperial lapping film" and developed a way to re-lap tape recorder heads if they were not too worn.

The heads would get grooves worn, and if the tape travel was not perfect, they would have dropout of highs when the tape rode up on the side of the groove. We used the film, in a series of steps, to grind down the head to smooth condition by hand, with the least possible removal of material at the gap. Since new heads were a couple hundred bucks, and we (mostly "I") could resurface a head and align the machine in under an hour and a half, we did a fair number pf them (no guarantee, but you save money if it works out).

The finest ones gave a good finish, and we had an 80% or better success rate. Just an odd use, but that lapping film really worked very well.

I have no idea just what it would be good for in scraping. That method you describe sounds rather uncontrolled, hard to understand how it is really a reasonable approach. "Accelerated wear", more likely.

Makes me think of the hobby groups with folks happily pouring 400 grit and oil on the ways and "lapping the machine back to accuracy".

I second JST: the main goal of scraping is re-establishing alignment. If you apply some abrasive film to something that has been worn out of alignment by moving over the very same mating surface, how would you expect to re-establish the proper geonetry and alignment?

Paolo

I have never heard of it before and can see it being used after one side is finished and your going to match fit the other side of a cast iron dovetail or a gib. I am going to buy some and give it a try before saying it won't work. Years ago I heard that Fadal used double face carpet tape and sand paper put on square ways and sanded Tucite. I never tried it as I can scrape it fast. Also I don't like putting sand paper on a plate to sand something as the edge's get low as it rocks as you push it back and forth. I am not to old to learn some new tricks.

If one side is finished, then I can see it, kind-of. The point about it rocking and creating a "bow" is a good one, you might have to put in a "jury gib" to hold it straight. Seems like a bunch of trouble for not a lot of gain.

BTW, the lapping film is nothing like sandpaper, it is very thin, and of course has extremely fine abrasive, which is also very well bonded to the backing..

We used to use this for putting a polish on the ends of fiber optic connectors, once the fiber was glued in place.
Fixture to hold it all square and all.

The diamond lapping film is on very thin plastic, mylar I suspect, and comes in various grades.

The same lapping films are available with Alox and Sic abrasives as well. From my experience lapping things flat on sandpaper I think it is a bad idea. The periphery of the lapped part will be low compared to the rest.

how well does the film mitigate that problem? i have some 3m diamond stuff, but i never chekced this.