Thread: using a coarse stone to lap a finer one works because ...?

I note that it is recommended to use, say, a DMT 325 to lap a finer grit hone so as to eliminate any non-flatness. But why doesn't this then ruin the finer stone's finish? Is it that there are now coarse grooves worn into the finer stone but they don't matter because the blade rides above them, only contacting the fine grit surface, the void space that now exists in the fine hone simply existing and not doing any good but also not doing any harm? And over multiple passes the entire blade surface gets to contact the finer stone material?

That's the only thing that seems to make sense to me but perhaps I'm missing something.

I beleive a coarser grit stone is used to establish flatness. Reason being is that it will be much faster than a finer grit stone. After that, there are two things that can happen.

1) You can use it as is. The random patterning of the DMT should prevent any grooving in your finer hone stone and as long as you did not have any larger particles get in while lapping you should still be at the same grit as you were before.

2) You can them procede to lapp your now flat stone with finer grit items (wet/dry sandpaper, higher grade DMTs, or whatever) to establish a extremely falt and smooth surface.


That being said, I haven't lapped a honing stone to date, and this is based on my limited knowledge from reading. Hopefully someone with a bit more know how will chime in.

Matt

Originally Posted by MattCB

I beleive a coarser grit stone is used to establish flatness. Reason being is that it will be much faster than a finer grit stone. After that, there are two things that can happen.

1) You can use it as is. The random patterning of the DMT should prevent any grooving in your finer hone stone and as long as you did not have any larger particles get in while lapping you should still be at the same grit as you were before.

2) You can them procede to lapp your now flat stone with finer grit items (wet/dry sandpaper, higher grade DMTs, or whatever) to establish a extremely falt and smooth surface.


That being said, I haven't lapped a honing stone to day and this is based on my limited knowledge from reading. Hopefully someone with a bit more know how will chime in.

Matt

Zackly my thoughts as well. When I finish wood or metal I, of course, progress up through the grit levels. But in that case I'm altering the finish for it's visual appeal. Since I've seen nothing written in the SR forum about moving up through the grit levels when lapping hones I got curious if it was because the visual of a finer grit hone isn't relevant and the action of using it with some coarser grooves is the same, albeit a little slower due to the reduced surface area of "good" grit.

Here is a link to a video by gssixgun explaining lapping Norton hones that may answer your questions;
gssixgun norton 4k 8k lapping

Originally Posted by DoughBoy68

Here is a link to a video by gssixgun explaining lapping Norton hones that may answer your questions;
gssixgun norton 4k 8k lapping

Thanks for the link.

For purposes of this explanation lets pretend that there are only two category of hones; Hard: ie. Arkansas and barber hones, Soft: synthetic water hones.

For the soft category the binder is so soft/friable that the peaks don't matter as they are quickly broken down.

For the hard category the binder is so similar to the grit that the peaks do matter. Hard hones need lapped to flatness but also need smoothed to prevent deep gouges in the items being honed. See Translucent Prep for a good procedure.

Jonathan

it's simple. A coarse stone will quickly flatten a softer stone. If you want you can then use a fine stone to put a polish on the stone. In my case I use a shapton flattening plate and I use carbide on it to quickly flatten and then use alumina to polish it off.

Originally Posted by thebigspendur

it's simple. A coarse stone will quickly flatten a softer stone. If you want you can then use a fine stone to put a polish on the stone. In my case I use a shapton flattening plate and I use carbide on it to quickly flatten and then use alumina to polish it off.

Thanks. You're using two concepts, I believe. coarse/fine and hard/soft. So when you say a coarse stone will quickly flatten a softer stone I'm presuming you mean a coarse and hard stone will quickly flatten a softer one?

I can be more specific. If I'm using a DMT 325 and Naniwa 5000, 8000, 12000 (with wet sandpaper thrown in along with a flat surface) how would you recommend lapping them before blade sharpening?

TIA

Crowden

Use the DMT 325 flatten/clean and then start honing...


Assuming the DMT is not brandy spanking new, as it would have to have the high points knocked off

Hone Lapping 101. Once the hones are initially lapped occasionally clean the hones up just prior to honing with the DMT.

Wet & Dry is not necessary but could be used. Do be cautious of grit contamination any time but especially with w&d paper.

Jonathan