Lapping Questions

Okay. So one thing I have established is the finer the lapping surface, the better the finish on the stone? But does it make any difference? If I lap with a DMT-XX, will it be a faster cutter? will it leave a coarser cut on my blade? How about a DMT-C? And should I take it all the way to F? To E? If this is the case, and I bought a combo DMT stone, would an XX/C be more practical or a C/F, or even as low as F/E?
The other question is (lol I can't believe I'm gonna say this) does size matter? I find it hard to conceive that an 8x3 stone is flat if you say, used a 6x2 lap stone, or is there some special technique to this? As a follow up, if a smaller stone doesn't work well, should the lap stone be bigger, or will as-big suffice?
I ask these questions sort of preemptively, as within the week I will probably have order a couple of stones, potentially varying in size from 4.5x1 to 10x3. There will definitely be at least one 8x3.
Thanks!

It's definitely preferrable to have a nice smooth surface to hone on than a rough one, as it feels much better. How that actually affects the scratch pattern and honing properties is unknown to me. You should be careful about using the finer DMTs to lap, as I've read some stories about some actually losing diamonds. I use a DMT D8C (325 grit) for my lapping, but just use wet/dry sandpaper placed on the DMT surface to do any finer lapping/polishing of the stone's surface. If I want to get really crazy with polishing the surface (translation, this is what I do....) after the DMT I go to 600 grit wet/dry, then 1000, then 1500, then 2000. Depending on the stone, going to 2000 grit is excessive as it won't be any improvement (eg. on a coticule).

That's what I do at least, take it for what it's worth. :)

For many hones, in particular the harder ones, the surface off of a DMTXX 120 grit is just fine. Now if you tried to lap a soft hone, like a Naniwa with it, you would have a mess. Maybe about a year ago, DMT was declaring that only the DMTXX was appropriate for waterstones. Now their FAQ says that you can go up to a DMTC with waterstones. Do not use a finer grit than the 320 grit DMTC or you are in peril of the grit of the hone undercutting the grit of the DMT plate.

The DMTXX is a faster cutter. If you have a few grooves in a hone, I don't think that's going to impact the blade. If you have many many grooves in the hone, I'm still not certain. In theory, if you have a rougher surface on a flat hone, you are increasing the pressure exerted at any given point between the hone and the blade because the force is not uniformly distributed.

Size does matter. Ideally, the lapping plate should be of comparable size to the hone if you want the best chance of keeping everything, both the hone and plate, flat. I think you can get away with a smaller plate on an 8x3 hone, but you need to be very careful about keeping the two plates parallel and spend equal time on all areas of the hone. It would probably be better to use even less pressure when using a smaller lapping plate.

I used the wrong terminology earlier, its the X, not XX. I didn't realise the difference.
Okay. So I have a 3-line Swaty, and will get a synth hone set approximately 200-8k (I will most likely only need 1k-8k, but boht sets I'm looking at are combos, so the 1k is paried with something in the 200s), and a German finisher.... Escher, Thuringen, etc. Maybe a coticule. The Swaty I'm assuming I'll need the X for, but I've heard barber hones kill DMTs, so maybe it would be the perfect way to break in a C to use on the other ones? Also, would I be able to lap a 200 grit stone with an X (220 grit)? Or would the 200 grit stone chomp on the X?

Right now I am looking at either of these two stones:
10" DuoSharp® Bench Stone Coarse/Extra-Coarse - W250CXNB - The Consumer Link - 10x4 incher, can be had for about $95 at other places.
8" DuoSharp® Bench Stone Coarse/Extra-Coarse - W8CXNB - The Consumer Link- 8x2.625 incher, probably cheaper elsewhere too

I was looking mostly at the top one because it could easily flatten the whole stone at once, making it guaranteed level easily. However, the 8 incher is cheaper, but because it would be narrower than the synth hones, would this make it difficult to lap?
Also, I was looking at swarf holed ones because my thinking was this will make it easier to lap- what would be "slurry" instead of clogging will go into the holes. Are the holy ones okay or should I go with the continuous surface ones? (all of these are narrower than the 3inch wide Nortons and similar)

Because the surface of waterstones dissolves during use to release a slurry, the lapping grit doesn't matter much with them. With a ceramic or oilstone however, the finer the polish the finer they will cut. Spyderco claims that the reason their UF hone cuts finer than their F hone is because the UF hone is flattened with a surface grinder which (among other things) leaves a smoother finish on the hone.

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Originally Posted by khaos

Right now I am looking at either of these two stones:
10" DuoSharp® Bench Stone Coarse/Extra-Coarse - W250CXNB - The Consumer Link - 10x4 incher, can be had for about $95 at other places.
8" DuoSharp® Bench Stone Coarse/Extra-Coarse - W8CXNB - The Consumer Link- 8x2.625 incher, probably cheaper elsewhere too

I was looking mostly at the top one because it could easily flatten the whole stone at once, making it guaranteed level easily. However, the 8 incher is cheaper, but because it would be narrower than the synth hones, would this make it difficult to lap?
Also, I was looking at swarf holed ones because my thinking was this will make it easier to lap- what would be "slurry" instead of clogging will go into the holes. Are the holy ones okay or should I go with the continuous surface ones? (all of these are narrower than the 3inch wide Nortons and similar)

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I don't think you need the larger one. The movements made by lapping don't need to involve long sweeping strokes so you really don't need that extra room. Regarding the duosharps, because the diamond surface is not continuous, it would SEEM that it would be a better choice as it would allow swarf to flow away easier. For some reason, and I might be imagining it, I thought that DMT did not recommend the Duosharps for lapping. I suggest you contact the company directly to check on this.

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Originally Posted by mparker762

Because the surface of waterstones dissolves during use to release a slurry, the lapping grit doesn't matter much with them.

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Sorry I don't agree with this.

First, if waterstones dissolved, then mine would be gone because in the past I have stored Norton hones submerged in water for months at a time. They don't dissolve.

Second, the grit of the lapping plate certainly does matter. The reason that DMT recommends a DMTXX for lapping waterstones, and specifically declares that nothing finer than the DMTC should be used for lapping, is because the finer plates end up losing their diamonds. The substrate of the finer plates gets undercut by the grit of the hones and this causes the release of the diamonds.

DMT's R&D lapping plate is a XX 10" duosharp. XX on both sides. Wish it was XX/C, but cest la vie, I didn't pay for it; can't complain. I can only send my recommendation on.

I've used the DuoSharp and the DiaSharp 325s for lapping. No big difference that I could see.

DMT says the polka-dot models are a bit more aggressive.

Does anyone know if lapping a 200 grit thing with a 220 grit DMT will damage the diamonds? My gut tells me that its the material strength that counts less than the grit- ie. diamonds are a **** ton harder than anything else so it should be fine, just really slow. Is that true or should I worry?

Should work ok as long as the 200 grit target isn't diamond. Go slow and check often just in case. Use lots of water.