Thread: DMT 8C Lapper not so flat - Any Thoughts?

Here are a couple of photos of my new DMT8C I use to lap my Naniwa stones with. It turns out that the DMT is not very flat...

OK, I'm not a master lapper yet, but do you guys think this is normal, or should I look into it? Look at the right side of the photo, I checked it on 3 different glass panels with the same result, the middle of the DMT is slightly higher than the sides. I push down slightly on the left side, then the right side lifts up, and vice versa.




And here is what this DMT did to my Naniwas. You can see the light coming through the centre when the Naniwa stones are face to face. They are all now slightly dished by the DMT8C.

My Naniwa 8K & 12K


My Naniwa 1K & 5K

Just to be sure, if you have not put the plate against a straight edge, try that first to make sure it is the plate.

Send it back to DMT. It would not hurt to give them a call. I have many DMT products and they will stand behind their products.

If this is not normal, I will consider sending it back, but I do not live in the USA, so it is a nightmare sending stuff back and forth.

If you guys think this DMT is normal, I will continue using it.

Maybe DMT's tolerances are just so far off perfect that this is deemed "normal"? Any ideas?

I don't have a straight edge measurer, so the best I can use would be perfectly flat glass, this is why I checked it on 3 different glass panels, on 3 different surfaces as well, just to be sure. All the same result...

Originally Posted by leadingedge

If you guys think this DMT is normal, I will continue using it.

No way! This is not normal, IMHO.
I use the DMT 8C to lap the Naniwa's too and they're so flat that they "suck" when rubbing against each other. I can lift the upper naniwa and have the lower naniwa rise by itself just because of the lack of air between them.

This makes me wondering: How do you LAP a LAPPING stone? With a even more coarser stone? What guarantees that the lapping stones are perfectly flat?

These diamond plates can not be lapped - they are diamonds bonded to a metal plate. It is the plate that is dished if it is untrue - lapping it would damage it

How new is the plate ? Did you take a plane blade or something and rub it out ? I don't have planes so I used the shank of a heavy 12" screw driver for mine. What I'm getting at is there may be high spots on the diamond coating. Probably not as high as what you've got there but it might help.

Flip the plate to the smooth side and check it with a straight edge. It will be no less flat on the smooth side than it is on the diamond side, and it is easier to see if the plate itself is flat, and if not how far out it is.

I've returned two diamond plates to Dia-Sharp here. A 325 D8C and a 1200 D8EF. They agreed with me that the D8C was not flat within their specifications but said that the D8F was within their tolerances. It took a month or so but I eventually received a new D8C and they returned my same D8EF to me.

So number one, you have to return it to Dia-Sharp for a replacement. They will replace it if, once they test it, the plate is not within the tolerance they mfg them at. If it is within their tolerances they will return it as is. You should get with them via email.

Thanks guys, will try and find some way of measuring the DMT again, but I am pretty sure that it is not flat. The result is shown in my Naniwa stones pictures.

I lap extremely lightly with only the weight of the stone lying on the DMT, so it takes forever to do, and I keep running water on the lapping, and swivel the Naniwa around 180 degrees every few minutes, just to be sure that all areas are covered by slight unevenness in the DMT, but this still does not work.

This is dissapointing and unfortunate, and I will try and find a way to sort this mess out; I don't live in the USA, so sending stuff back and forth with numerous phone calls will probably be more expensive than I can imagine.

I guess the way to go here would be just to bite the bullet and go for the Shapton DGLP.... That is if nobody has had any problems with them...?

Anyone?

It is also possible that while lapping you are spending more time on the middle of your hones than the edges. As already mentioned, checking the DMT for flatness would be a good idea.

A non-flat DMT is definitely unusual. I don't think I've ever heard of one up till now, and it seems lots of people use them. Maybe you got unlucky. You could try a DGLP, but I highly doubt a second DMT would be non-flat, and it's a much less expensive "experiment."

I do move the stones around to avoid lapping the centre too much, so I don't think that is the case. Every minute or so while making small circles, I lap towards the sides, and back to the centre. I also make sure that there is not too much slurry to affect the centre of the stones, so I doubt if this is the case...

It seems that I am certainly not the only one finding a DMT that is not flat. Got some info from a PM converation with another highly respected member that he has had more that his share of DMT's that is not flat...

Originally Posted by holli4pirating

It is also possible that while lapping you are spending more time on the middle of your hones than the edges. As already mentioned, checking the DMT for flatness would be a good idea.

A non-flat DMT is definitely unusual. I don't think I've ever heard of one up till now, and it seems lots of people use them. Maybe you got unlucky. You could try a DGLP, but I highly doubt a second DMT would be non-flat, and it's a much less expensive "experiment."

Well, here is the verdict. The DMT8C I have is definitely NOT straight. I checked the top of the plate, and the bottom of the plate, and just to be sure, I used 2 different Stainless steel edges. Can this be used for lapping guys? Check out the photos below:

Bottom of the DMT8C Plate:


Top of it, edge #1 (Edge rocks from side to side, as the centre is higher)


Top of it, edge #2


Bugger.