Thread: Lapping Plates - Glass or Granite or somthing else?

I have both a glass lapping plate and a granite lapping plate but what is better?

I would have thought glass would wear less but in the wood working shop around Perth they only sell granite plate with a certified accuracy.

I would also like to to say, the granite plate that i have with its certified accuracy of 0.0001" is not that accurate! lol i chucked my certified DMT plate on it and a ruler and it had sections where light was visible. The glass plate is also slightly out (I'm using a 6mm thick glass chopping board) but not my too much

I have now lapped the granite plate with my certified DMT, not as hard of a process as i was expecting but i guess it was only slightly out.

I then chucked a stone and lapped it on the granite plate with a 600 grit powder and it turned out extremely smooth and flat and very quickly! My glass plate would have left scratching in the stone still i think...

So will granite be as hard wearing as glass or is glass longer lasting, is the granite more accurate or would glass be just as good or more accurate. Which would be better for lapping in general?

Thanks!

as long as the plate is flat enough, it does not matter what the material is. Micron accuracy is not needed as long as it is reasonable accuracy.

but if i can lap the granite flat with a DMT is this going to cause problems with wearing when lapping? Basically, what i want to know is, should i be using the glass for most stuff and finish on the granite or with the granite be fine for anything and everything?

Who on here uses granite and who uses glass and what are your thoughts on the subject?

Now that i have started using lapping plates i don't think i could go back to sandpaper lapping, the powders on the plate are so much faster at lapping! I just dont want to lap a few hard stone with my 90 grit powder and end up with a granite bowel and need to flatten the plate after X amount of laps

Wait i think I finally understand what you are saying. You do not lap with the granite, you put sand paper on it and lap on the sand paper.

How did you come to the idea to lap with the granite or glass plates in the first place?

A few of the guys on here lap with the granite or glass using the lapping powders.

The granite plate I purchase is sold specifically for lapping powders. If you haven't tried it, look into it as its a great alternative to sandpaper.

This is the plate I got. Granite Surface Plate : CARBA-TEC

Why use the lapping plate if you have a DMT?

The powders are much faster then the dmt plates. I have the XXC lapping plate (not the sharpening plate) and the 90 grit powered remove twice as much in half the time.

I also have 425 (worn 325) dmt and the 600 grit powders smooths the scratches from both those plates with ease

And then you have the options of moving to another grit on the same plate. The cost of the powders is probably slightly cheaper then sandpaper and more accurate too. I find when I lapwith sandpaper after a while the sheets begin to curle and that causes slight imperfections on the stones.

If you go much higher the in the dmt's there are threads of guys stuffing them very quickly through lapping.

The only reason I got into the powders for lapping is due to a few stones that gave me hell lol after talking to members they sugested this method

Originally Posted by Brighty83

The only reason I got into the powders for lapping is due to a few stones that gave me hell lol after talking to members they sugested this method

I know what you mean. I lapped my 4/8 combo flat with sandpaper on a granite tile and it took me all afternoon (and a whole pack of sandpaper). Later I picked up some 90 grit powder for an unrelated experiment and used it to grind down the 8k some more to get rid of some grittyness. WAY faster.

Lee Valley sells mylar sheets that you're supposed to stick to their glass plate, it cushions the grit and cuts better. I'm not sure if it's supposed to protect the plate from wear, but I imagine it does at least partially. I had a bunch of transparent printer sheets lying around and tried sticking one to my granite. It did seem to protect the surface but grit tends to get under the edges and make even more of a mess.

Bryghty,
I never heard of this use of the plate, but if it works it is fine.

My question is exactly how are you going to lap a 300x230mm plate flat with an 8x3 DMT?
Second all people that I know that own such plate, use it with sand paper for lapping stones and it works perfectly well, why make a mess with powders, and more importantly how is that plate lapped after that?

I lapped it as much as i could with the DMT and finished it on the glass plate. I wasn't sure it was going to work but it worked very well! I tested it after with a torch and a metal ruler and no light shined threw after in any direction.

Also keeping in mind i probably only removed 1mm off the top in total, maybe less.

Just sliding the DMT back and foward accross the stone


And then finishing with a few powders on the glass

Originally Posted by mainaman

why make a mess with powders, and more importantly how is that plate lapped after that?

Im actually finding it makes less mess too then sandpaper as you dont have 20 sheets of sandpaper left over that need to be disposed off, just give it a wipe and its all clean!