Thread: How does Lapping actually work?

Reading this topic I started to think about a Glass DE razor hone that I received by surprise when I bought the DE razor off eBay. The glass hone is Dished! While I haven't tried it. The idea is to move the blade up and down the dish to hone it! Based on everything that's been said about Flat, how would this glass hone work?? Then if it works, then Why wouldn't the dished hone,above, not work if you 'back' honed the razor?

Johnus, there are threads on the internet on sharpening double edge razors on the inside of a glass. And I recall seeing concave glass or porcelain Double edge blade hones. I suspect the goal was to hone both ends of the blade at the same angle and an easy, safe way to hold the blade. The hone does not have to be flat, just at a consistent angle and an even grit cutting height.

I believe the scratches don’t matter because if the surface of the hone or tops of the grit is even, the razor edge will bridge the scratch. If you were to keep the razor exactly in the same track with the scratch it could cause a land/protrusion in the edge, but doing so on a random scratch would be impossible, one of the benefits of the x stroke pattern.

To answer the original question (or attempt to):

Yes, 250/400 grit sandpaper will leave scratches on your hone. Don't panic though, the finish off of 400 grit paper is fine. I used 400 grit paper to finish my hones for a while.

So you get the flat part, that's good. But what else does lapping do? For one it cleans the hone. IME, plenty of swarf builds up, esp on the finer hones.

IMO lapping controls the texture of the surface, and thus its level of aggression. Heres what I think:

After lapping, the hone's surface is covered with ridges and valleys left by the grit of your lapping plate. The razor edge contacts only the peaks on a freshly lapped hone, and exerts more pressure on each contact point than if it were making contact all over the edge. The ridges wear quickly and make fast cutting slurry. New cutting material is constantly exposed. Swarf collects in the valleys. After a while the peaks and valleys left by your lapping plate, will wear down. The hone smooths and begins to act finer and slower. The razor is exposing less material and swarf begins to clog the stone. Re lapping the surface, preps your hone with new peaks and valleys and the hone gets more aggressive again.

When I lap with the Norton plate I see the above in action. My stones are definately more "ready to work" right after lapping. After a while they do slow down, and polish finer. On the 8k, I even see a yellow slurry form after the first, no pressure strokes and the stone seems very quick cutting. I don't think the stone works as well after lot's of use without lapping.

With luck, some of this made sense.

Michael

Originally Posted by Euclid440

there are threads on the internet on sharpening double edge razors on the inside of a glass.

____________________________________

My grandfather extended the life of his razor blades with a drinking glass back in the early 1900's. My father did also.

Jerry

Originally Posted by Johnus

Reading this topic I started to think about a Glass DE razor hone that I received by surprise when I bought the DE razor off eBay. The glass hone is Dished! While I haven't tried it. The idea is to move the blade up and down the dish to hone it! Based on everything that's been said about Flat, how would this glass hone work?? Then if it works, then Why wouldn't the dished hone,above, not work if you 'back' honed the razor?

When you press down on the DE blade inside the glass it flexes flat so the edge is not actually meeting a curved surface as you might think.

Originally Posted by LameBMX

......chomp....
Let alone learning and starting a coti progression on a dished stone, sounds like heck to troubleshoot when I dont have the stone experience, or means to check how the bevel is going for a razor level edge. Means I could only confirm it works, not that it dont work. Only way I could confirm it dont work is over a course of years. And I havent even touched on the battle to consistently lap out a dish. :/ too much for me.

Of interest I honed with a coti for years and never lapped it flat.
No slurry... just used it like a barber hone wet with tap water.

The hone and my three razors abraded together and shaved just fine.

Then one fine day I discovered this place. I lapped my coti flat
and to my distress learned that the razor and hone no longer
shared a common profile.

It took months and a Norton 4k/8k combo lapping on a tile etc...
to get things back to normal shave ready.

Thus began HAD, RAD, SAD and serious latherin.

Originally Posted by onimaru55

When you press down on the DE blade inside the glass it flexes flat so the edge is not actually meeting a curved surface as you might think.

You can always not push it all the way down. if you have a clear glass, experiment to find the pressure where the bevel contacts the glass.

Some of those curved glass DE hones also had a flat side for straight razors IIRC.

Originally Posted by onimaru55

Some of those curved glass DE hones also had a flat side for straight razors IIRC.

I have often thought that the dished out hones from the late19th & early 20th century and the designed curved glass hones were used for the troublesome old wedges. Like if you have a lovely old dished hone and the wedge blade just rides on the spine and the edge and therefore taking out all the grinding on the sides of the wedge blade. Alx

Originally Posted by alx

I have often thought that the dished out hones from the late19th & early 20th century and the designed curved glass hones were used for the troublesome old wedges. Like if you have a lovely old dished hone and the wedge blade just rides on the spine and the edge and therefore taking out all the grinding on the sides of the wedge blade. Alx

This is a very well thought out observation.