Why is this lapping taking sooo long???

I am trying to get my coticule lapped with 220 grit 3m wet/dry sand paper. Most of the stone is flat but the corners on both ends still seem to slope downward.

http://straightrazorpalace.com/membe...n-coticule.jpg

I have followed the tutorials on lapping marking the surface with a grid and moving the stone in a circular motion. At first, I used 320 grit because it was the closest I could find then I found some 220 at an auto parts store. I have made progress as the corners that were left with pencil marks have gotten smaller. But they are still there!

I have worked on this thing for over three hours total...does this sound right? The corners didn't seem to slope that much to the naked eye (it actually looked nice and flat to my optimistic imagination :o).

So my question is, "do I just keep going or is something wrong with my method or my stone?"

If I have some areas which are just not going down I try to apply more pressure on those areas.

If the corners are sloping downward more needs to come off from the center out. When I have run into that I have looked at my pencil grid and gotten what I needed of the actual area used for honing flat. I let the corners slope if they are not in the area making blade contact. Eventually over years,with continued honing and lapping it will get there. I only take off what I have to in a situation like that.

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Originally Posted by sproosemoose

If I have some areas which are just not going down I try to apply more pressure on those areas.

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But doesn't that defeat the purpose of overall perfect flatness? I mean, if I apply pressure to an area that is already sloping downward just to erase the pencil marks, wouldn't that increase the slope rather than decrease it?

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Originally Posted by JimmyHAD

If the corners are sloping downward more needs to come off from the center out. When I have run into that I have looked at my pencil grid and gotten what I needed of the actual area used for honing flat. I let the corners slope if they are not in the area making blade contact. Eventually over years,with continued honing and lapping it will get there. I only take off what I have to in a situation like that.

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Thank you, I had actually wondered if this was the case. I notice that the start position for my razor during honing would actually be beyond the corner that is sloping.

keep your pressure light and in the center of the stone let the sandpaper do the work too much pressure will only clog the paper. tape that sand paper down flat, if the rounded off corners are not too large your razor wont touch them anyway.

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Originally Posted by pstrjp

But doesn't that defeat the purpose of overall perfect flatness? I mean, if I apply pressure to an area that is already sloping downward just to erase the pencil marks, wouldn't that increase the slope rather than decrease it?

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Well yes but I am not saying that. If your pencil grid shows that most of the stone is flat but the corners are sloped out towards the end of the stone it may not be necessary to continue until all is on the same plane.

We are just trying to get a flat honing surface. If I've got plenty of stone to hone on that is flat I won't bother seeking perfection in going beyond what I've already removed for the sake of absolute flatness. Here is a pic of 4 Eschers. The stone at the top and the stone at the bottom are sloping in the corners but I don't hone there so I'm not worried about it. If I needed to use that part of the stone I would keep on until it was flat.

if i were you i wouldn't worry about it. it is small stone you most likely end up using x strokes and you will never touch corners.
your stone shouldn't be perfect flat anyway.
hope this helps.

What is the substrate the paper is on?

Where did you learn to make circular motions. Sometimes circles are ok but imho most prone to inaccuracy.

I would agree that the corners are not all that important.

The closer you get to lapping the stone flat the longer it takes to lap the higher areas down. This is because you have a flat area that gets larger as you remove material. It can take forever to reduce the whole surface enough to eliminate a rounded corner (as you know). I wouldn't worry about the corners. After you radius the long edges of the stone you will have a honing surface that is very slightly curved inward at the ends where you don't use it anyway.

On natural stones I'm alot mor forgiving on full area flatness. As jimmy pointed ou about checking the honing path to see if the area in question is a problem. Naturals are a limited item and once used up cannot be replaced, so I take a minimal amount of material off and learn to use what I can on that one stone. Synthetics I have no problem grinding away as someone will just make more...

Keep the pressure light.

when lapping a rock it is too easy to rock the hone
and make it rounder and rounder.

Try strokes in only one direction till you get a flat region.

Try figure eight strokes once you get a
flat surface and can detect zero rocking.

In normal honing the rock will have a cup in it
and the edges will lap first. This seems
inside out.

If the majority of the top is flat -- use it with a
light touch and apply your rubbing stone to the
high spots.

Others mentioned using X strokes....
A variety of strokes can match a hone to a razor
or a razor to the hone....

No rush in washing the hone down the drain....

Perhaps that coticule is possessed -- send it my way and I will send the evil spirits packing. Be advised that it might take some time.

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Originally Posted by kevint

What is the substrate the paper is on?

Where did you learn to make circular motions. Sometimes circles are ok but imho most prone to inaccuracy.

I would agree that the corners are not all that important.

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I put the paper on a piece of finished marble slab (about 10" X 5") and I learned to use circular motions from SRP wiki "lapping 101". It said you could use circles or figure 8's according to your preference.

I really appreciate everybody's input, especially the very relieving advice/confirmation that the corners could be left alone for now.

And BTW stimpy, thanks for putting the idea in my head that my stone may be possessed as I go into my first attempt at honing!:eek:

the best motion is front and back alternating left and right to form a sorta X; turning the stone end to end (often)to keep pressure application issues equalized helps as well.

Forget about the corners, they are of no importance when honing.

I agree with that Randy. But I question why, because typical use results in high corners and ends -dished in the middle.

3 hours on a coticule should do it I'd think.

Which is the reason for my pointing out making circles is not the best approach and just perhaps the cause of low corners which in the extremes of accuracy would require some deft hand work to have equalized pressure as you come round and round

Whatta ya think?

Kevint...... I have the same question about his lapping and the results so far.
I will try to explain what I do if the OP wants me to.
Maybe he has it sorted out by now.

I picked the Xs technique that Kevin mentioned from the Shapton USA site's old FAQ. Also turn the stone every so often and I'm under running water getting rid of the swarf as I go. I imagine if swarf was allowed to build it could lead to inaccuracies.

That sounds like what I do. Works well for me. Thanks Jimmy.
Are any graphics available on that?

Here is is Randy complete with text and a video.

Thanks Jimmy. His method is almost what I do. He actually turns the stone, angles, towards the right corner of the lapping plate, performs a few laps, then turns the stone towards the left corner and performs a few laps. I do not turn the stone at an angle. Instead I keep the stone at a North-South orientation at all times and push the entire stone towards the upper right corner for a few laps and then the upper left corner for a few laps. Then turn the stone end for end and repeat. etc...
After the left and right motions then I perform a few North-South, then return to the angled motion again etc
It creates a cross hatched scratched pattern that removes material much faster.

I do the same thing Randy. Great minds think alike. :)