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

Originally Posted by SharpMan

Wait a minute, you used a dmt plate to flatten a certified
granite lapping plate? If that is whay you ''did'', then I am
sorry, but your granite lapping plate isn't flat anymore.

The certified lapping plate when new is very flat, flatter
than any diamond stone. A floatglass plate isn't as flat
as a certified plate, but it is flat enough for our purposes.

If I understood you correctly, I am sorry to say that you have
ruined your granite surface plate.

Sharpman

This is an old thread,

Anyway, it was a certified DMT to 0.0001". The granite plate was supposedly certified to the same range although it was visibly out. The certification that was provided was worth about as much as the paper it was stamped on. Luckily my DMT certification was a little more reliable.

A certification is only as good as the person who certified it, so i have learned. But i'm guessing you are aware of this as you know that my certified DMT isn't completely flat either, but my DMT was flatter then the granite at the time.

P.S. Its far from ruined and lapps perfectly now. I have tested several rulers and my certified DMT on the granite plate and they all show the granite being flat from all directions, also, as mentioned the granite plate isn't that much bigger then my DMT (10" x 3") and i used a glass plate that was much larger.

I take it you tried lapping something similar to know it doesn't work?

Brighty, Carba-Tec is having a sale 1-3 Dec.
That's where Pauly got his BMF lapping plate designed for use with powders.
FWIW

Originally Posted by Brighty83

This is an old thread,

Anyway, it was a certified DMT to 0.0001". The granite plate was supposedly certified to the same range although it was visibly out. The certification that was provided was worth about as much as the paper it was stamped on. Luckily my DMT certification was a little more reliable.

A certification is only as good as the person who certified it, so i have learned. But i'm guessing you are aware of this as you know that my certified DMT isn't completely flat either, but my DMT was flatter then the granite at the time.

P.S. Its far from ruined and lapps perfectly now. I have tested several rulers and my certified DMT on the granite plate and they all show the granite being flat from all directions, also, as mentioned the granite plate isn't that much bigger then my DMT (10" x 3") and i used a glass plate that was much larger.

I take it you tried lapping something similar to know it doesn't work?

From the DMT site:

With a consistent, aggressive diamond surface and precision ground, hand certified flat to +/- 0.0005”, the Dia-Flat™ Lapping Plate assures precise results when flattening stones. It's extra-large surface area makes it easy to use.

The diaflat is certified flat to 0.0005, not 0.0001. I am not sure, but I am guessing
that the steel plate on which the diamond are put has that flatness.

Did you use a certified straight edge to check for flatness? A standard ruler is not flat
enough to check these things.

You are correct in mentioning that certification by itself doesn't mean much. I would
advise you to use a certified straight edge to check the flatness of the plate if you
haven't already.

Of course I am hoping that you were succesful in making your granite
plate flatter, but I think the opposite unfortunately has happened.

Sharpman

Originally Posted by Havachat45

Brighty, Carba-Tec is having a sale 1-3 Dec.
That's where Pauly got his BMF lapping plate designed for use with powders.
FWIW

Thanks Geoff - i will have to see if my local one is too! Also, do you have a new bike?

Originally Posted by SharpMan

From the DMT site:

The diaflat is certified flat to 0.0005, not 0.0001. I am not sure, but I am guessing
that the steel plate on which the diamond are put has that flatness.

Did you use a certified straight edge to check for flatness? A standard ruler is not flat
enough to check these things.

You are correct in mentioning that certification by itself doesn't mean much. I would
advise you to use a certified straight edge to check the flatness of the plate if you
haven't already.

Of course I am hoping that you were succesful in making your granite
plate flatter, but I think the opposite unfortunately has happened.

Sharpman

Your are correct, mine states "Hand certified flat to: less then +\- 0.0005"



But i am generally happy when i can place two stones on top of each other with a small a mount of water, lift them just off the table by the top stone and have them stick together. If no air get in between to make them fall apart i know they are close enough, or closer then what is required. if they come apart after a few seconds i know there is a concave or a convex. So far, no stone i have ever received out the box has ever passed this test but they always pass after they are lapped.

As mentioned previously in this thread, they don't need to be 100% flat but if you get get them close to 100% its not a bad thing. Flattening the granite with the glass alone should achieve this.

You just destroyed your granite lapping plate.
And as was already said: you really don't require micrometer flat surfaces for razor honing.
Sandpaper on glass or even just a ceramic tile is flat enough for all intents and purposes regarding razor honing.

Originally Posted by Bruno

You just destroyed your granite lapping plate.

How can that assumption be made without seeing the plate youself before and after?

Because of what was done with it.
Lapping stones like those granite stones are meant to be used and lapped a certain way.

If you rub a small DMT over a large granite surface, different parts of the granite surface get worn differently, because the DMT will not touch every part of the big stone the same amount of time with the same amount of pressure.

The DMT may be flat to very tight margins, but used like that, it is pretty much impossible to achieve the same level of flatness on the big surface. The level of wear will be different. So if the granite plate started out with the same tolerances as the DMT, the tolerances will be much worse after the lapping operation.

You can lap a small surface with a bigger surface.
You cannot lap a big surface with a smaller surface and get a consistent overall flatness.

After reading this I am wondering about what I do. I use a large 3/4 piece of tempered glass and place wet/dry sandpaper on it to lap my hones. Did I need to check the flatness of the glass?

No. For the purpose of flattening a hone for use, you really don't need micrometer flatness.
The error in the sandpaper (which is soft as well -> variable flatness) alone is much worse than the variations in the glass.

I had a D8C that I sent back to dia-sharp because it wasn't flat. Matter of fact I sent back a 1200 at the same time. IT wasn't flat either. They agreed on the 325 and sent a new one back. They didn't agree on the 1200 and returned it with the new 325. I checked it with a Starrett straight edge. Flip your plate over and check it with a straight edge. It will tell you if it is flat within dia-sharp's tolerances. As for the granite, I agree with Bruno that it is probably no longer flat.

It is worth noting however, I talked to a machinist about granite plates and they change over time. Not only from a certain amount of wear due to use but just from atmospheric conditions IIRC. They have to be re-certified every now and again. Anyway, also like Bruno says, this business of honing razors doesn't require as much precision in flatness as some of us OCD practitioners desire.