First rule of lapping plates - don’t talk about lapping plates?

[TaperPin]

The el cheapo diamond lapping disks seem to be popping up on more benches in various industries in place of iron lapping plates or sandpaper covered granite, but rarely does anyone admit to using them. By no means are these things super flat, but usually they are flatter than 99% of what comes off a milling machine.

Anyone have a favorite brand and size? Have you used them and given up, or are they the best thing since sliced bread?

I ordered a few different brands of 6” in various grit for a slow speed carbide grinder, but I’ve been using them more and more flat on the bench top for chisel sharpening, general steel flattening and truing up worn abrasive stones. A larger size without a center hole would be nice.

The other issue is how to hold onto these things on the bench? I want to use adhesive spray and stick it to a flat piece of steel, but it’s also nice to use different grit at times so that’s not a great option. I’ve used multiple magnetic bases to coral it on the metal bench top, but that’s not a very elegant solution. An 1/8” rubber pad holds onto them ok, until metal dust or wd40 gets under there - also not a great solution.

I lucked into what might be a 50 year supply of fine diamond powder and have a flat steel plate, and right next to that is a dedicated sand paper covered piece of granite, but I keep finding the diamond disk is faster and easier for little lapping jobs that don’t have to be super flat.

 

[Jonnyofalltrades]

Very interesting. I have never seen one of these before. I had to check out THK's website, and thoroughly enjoyed the chinglish.
These products are mostly geared towards working with rocks/gems, but if they work well, I will be first in line.

 

[TaperPin]

These products are mostly geared towards working with rocks/gems, but if they work well, I will be first in line.

I first heard of them from the groups who do a lot of machinery scraping of bearing surfaces - the little slow speed (300 rpm) grinders use these disks to sharpen carbide scraping blades, which get touched up quite often. The grinder is also good for lathe tooling - an easy to build and cheaper alternative to a dedicated carbide grinder for low volume users.

The construction is very much like a diamond sharpening stone, just in disk form, and the backing is a little too flexible. I may buy a cast iron flywheel to sit on the bench and epoxy a 12” 1000 grit to it, and get a ground aluminum disk and epoxy the 3000 onto it and just lay it on top of the other when using it.

 

[Jonnyofalltrades]

I'm fairly deep into the machine scraping rabbit hole, and I have yet to hear of these low speed grinders. Any further info, TaperPin?

 

[TaperPin]

I'm fairly deep into the machine scraping rabbit hole, and I have yet to hear of these low speed grinders. Any further info, TaperPin?

Sure - Stefan makes good project videos and has good judgement - his accent is pretty heavy, but you’ll like his stuff. He also has some good scraping videos.

Steve Summers s a good job on his:

 

[TaperPin]

As with everything Amazon sells, the pay-for-play discs are much more expensive than the ones they don’t make as much profit on - $60 12” discs come up first, then $50, and after searching 10 different ways this $35 disc showed up. It will get epoxied to a fairly flat ground 12” steel disk.

10” is probably the ideal size for something like this - but I’ll know for sure after using it a bit.

 

[TaperPin]

I'm fairly deep into the machine scraping rabbit hole, and I have yet to hear of these low speed grinders. Any further info, TaperPin?

Are you rebuilding an old lathe?

 

[Jonnyofalltrades]

Not yet!
Bought a 3'x4' Mitutoyo granite surface plate. Spent an entire winter's worth of bedtime reading on old scraping textbooks.
Haven't started on the lathe. I use it constantly, so it doesn't work for me to take it out of commission for a year. Probably not the best candidate for a rebuild, either. It is an older Taiwanese 14x40. Good lathe, but if I'm going to rebuild I should probably start with a Colchester or Yamazaki or something heavier to begin with.

 

[TaperPin]

Not yet!
Bought a 3'x4' Mitutoyo granite surface plate. Spent an entire winter's worth of bedtime reading on old scraping textbooks.
Haven't started on the lathe. I use it constantly, so it doesn't work for me to take it out of commission for a year. Probably not the best candidate for a rebuild, either. It is an older Taiwanese 14x40. Good lathe, but if I'm going to rebuild I should probably start with a Colchester or Yamazaki or something heavier to begin with.

That’s a nice size plate - they seem to come up locally for almost nothing when I’m wrapped up with something else, and are nowhere to be seen otherwise.

I made the mistake you’re wisely trying to avoid. I picked up a light weight 15” for scrap price and now wish I had invested the time in a heavier model with bigger through bore.

 

[jdh47]

Tom Lipton (OxToolCo) on YouTube has some videos about lapping and making your own lapping plates. He has some good videos about grinding and making V-blocks, angle plates and other fixturing.

 

[Jonnyofalltrades]

Tom Lipton (OxToolCo) on YouTube has some videos about lapping and making your own lapping plates. He has some good videos about grinding and making V-blocks, angle plates and other fixturing.

Yes, I like his videos a lot.
I bought my granite plate off of my employer brand new. It was an extra, just taking up space. Got it for $200!
I have so many visitors to my shop ask what I need a big rock like that for.

 

[jdh47]

The granite plates I have are surface plates and somehow I ended up with a lot of them. I use them all for measuring things. You can lap pretty well with different grit wet or dry sand paper glued to a glass plate. Tom uses cast iron or copper embedded plates for lapping. If you make a copper penny plate you need three. The sand paper is cheap and works well. After it's used up just scrape it off and glue on another.

 

[TaperPin]

One thing I may never get used to is how well diamond dust imbeds in cast iron, especially when rolled into the surface with a hardened roller. Plates almost have to be permanently labeled with the size of diamond dust used.

I was really impressed with the fellow that trued up his surface plate with a cast iron surface plate.

 

[TaperPin]

The 12” 3000 grit disk showed up and I’m very happy with it, There is a .030” curve to the plate, but it flattens out nicely. Not all granite countertops tops are flat, but I have a scrap of black that’s very good and will be the backer for this plate to just sit on the bench. If it were a 10” I’d be tempted to get a cheap small granite surface plate to rubber cement it to.

The surface is more consistent than expected, although it does have tiny little bumps about every inch that need to be worn down before anything requiring a good cosmetic finish is flattened on it - it’s no better or worse than a flat diamond stone, just much larger. As is, it’s perfect for sharpening wood chisels, hand sharpening carbide scraper blades, or touching up a carbide insert. I had an extra Remington recoil lug laying around that was out of flat by .0005” and it was very fast to take the majority of that down, although it’s really not good for that purpose because of the cosmetic streaks caused by the bumps.

I have the feeling this will be useful to quickly remove roughness and the cast iron lapping plate with diamond dust slurry will finish it off.

I think I’ll be ordering a 400 grit and 1000 grit of the same size.