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| Lapping - I just can't do it :( https://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=55282 |
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| Author: | jfmckenna [ Sun Sep 25, 2022 9:27 am ] |
| Post subject: | Lapping - I just can't do it :( |
I have been at this for an hour and a half and I just give up. My wrists is hurting and my fingers can barely move. Is there some sort of technique y'all have for doing this accurately and quickly? I have made sure my stones are dead flat. I've tried using a block of wood to hold the blade down as I push it back and forth. I can barely type right now. 
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| Author: | Aaron O [ Sun Sep 25, 2022 10:12 am ] |
| Post subject: | Re: Lapping - I just can't do it :( |
What are you trying to do? The cutting edge is only at the tip. Try the ruler trick. |
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| Author: | DennisK [ Sun Sep 25, 2022 10:18 am ] |
| Post subject: | Re: Lapping - I just can't do it :( |
It sounds like you're doing it right, with flat stones and wood block hold-down, so I'm not sure what's causing the problem. One thing that can help is to place the wood block pretty far from the edge on the coarsest grit, and move slightly closer to the edge with each successive grit. If you ever move farther from the edge on a finer grit, it will concentrate pressure on the hump between the polished area and the rough remainder of the blade, resulting in the pattern you have. One easy solution is to use the "ruler trick" where you use a thin shim (traditionally a ruler, but I would use a strip of masking tape) to tilt the blade up and create a very shallow bevel. As long as the sharp edge of the chipbreaker makes contact with the surface of the blade, it will function just fine. The chipbreaker should be ground slightly concave to concentrate pressure on the edge, but if your microbevel angle is steeper than the angle that the chipbreaker underside approaches the blade, you will get a small gap just before the chipbreaker edge, which will catch wood chips and cause more trouble than if you didn't have a chipbreaker at all. Here's a drawing, with angles exaggerated to hopefully show what I mean. |
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| Author: | TerrenceMitchell [ Sun Sep 25, 2022 11:02 am ] |
| Post subject: | Re: Lapping - I just can't do it :( |
Agree with the previous. Looks like you are working on a blade for a traditional frog, with a chip-breaker. When this is the case, almost nothing (depending on the stiffness of your chip-breaker) comes in contact with that back side of the blade you are working so hard to flatten. When you have a bevel up plane, like a block plane, the back flatness does matter, but not in this case. I've used the ruler trick for more years than I can count, and it's the best approach I've found for blades with chip-breakers. And it is true, only that last bit of steel matters in a situation like this. The rest of the blade is to help hold it in place, and provide mass to help avoid chatter. All that said, if you do, in fact, come across a blade that will bed against the plane with the bevel up, you will want it flat. lapping the entire back of a modern blade is a ton of work, and something you shouldn't have to do unless it's defective, or neglected. In order to do this, you really need to have some more course grits to start with if you ever want to finish. Looks like you are on about 1,000-2,000 in the photo. Do some adhesive sand paper on a small granite plate or piece of float glass, starting at 100-200 and work your way up. When I have a lot of work to do like this, I'll put a couple pieces of tape on the front and back 1/3, folding the tape on itself and making an upside down "T" and stick those on the blade to form little "handles". Hard to describe without a picture. That will allow you to do a lot of light/medium work without destroying your hands. Using traditional sharpening stones for a job like this is going to be tough if you aren't very experienced, and have a range of stone grits. Keeping the stone flat for more than a minute or two is very challenging, particularly on the rougher grits, and once it starts to dish out, you will need to start over. Good luck, and don't start peaking at high-quality replacements blades. They will take all the fun out of your weekends spent lapping 
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| Author: | jfmckenna [ Sun Sep 25, 2022 12:00 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
I never heard of this trick but it sounds perfect. This is indeed a bevel up block plane blade. I have flattened the stones several times as I work. It is really amazing how much stone gets used up in a short period of time. |
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| Author: | Ken Nagy [ Sun Sep 25, 2022 12:08 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
JF. If you want that flat, you need a very coarse stone. It is not lapping when it isn't flat to begin with. You know the result. I like large cutoff wheels used to cut hard steel. We used them at work. Rubber wheels. Mostly some kind of rubbery compound with diamond dust impregnated through it. We threw them out when they got too small. You can probably ask any shop around if they will save them for you. Or buy one. I'm pretty sure they are relatively cheap. I use them for rough sharpening on anything that is flat, and even things that aren't. I go side to side, so the edge is very smooth. Some guy put his on a spindle horizontally, and turned it slow. By hand on a table works fine. Hone and lap after. I tried to find them online, and all I see are reinforced discs. These are just compound and diamond dust. Yes. they can break if you abuse them! The reinforced ones won't work. You are using the entire SIDE of the wheel. It is only 1/8 thick or so. Ours were about 24" diameter, in a box of ten, We threw them out at 12-13" or when they blew up! They were Dia-Tool. We cut hardened dies up to make shorter ones, for emergency tools. If you can't find them, you still need a coarse stone. Or the side of a bench grinder. |
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| Author: | DennisK [ Sun Sep 25, 2022 2:47 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
TerrenceMitchell wrote: Agree with the previous. Looks like you are working on a blade for a traditional frog, with a chip-breaker. When this is the case, almost nothing (depending on the stiffness of your chip-breaker) comes in contact with that back side of the blade you are working so hard to flatten. When you have a bevel up plane, like a block plane, the back flatness does matter, but not in this case. Huh, i thought the opposite was true... that it only matters on a bevel-down plane, due to the potential chipbreaker gap shown in my previous post. On a bevel-up block plane, having a slight bevel on the back side only changes the effective cutting angle by a fraction of a degree, and poses no threat to functionality as far as I can imagine. jfmckenna wrote: I have flattened the stones several times as I work. It is really amazing how much stone gets used up in a short period of time. That's probably the problem then. If you can afford it, buy 3 DMT Dia-sharp stones: extra-extra-coarse, fine, and extra-extra-fine. That will go from a new rough ground blade or torn up old blade to a good edge in a short time. I only polish further on a waterstone when I need fluffy thin shavings like for plate jointing. Mine are 8x3" size with continuous grit, not the kind with holes. And don't buy double sided, those are slightly curved and therefore useless. The XXC is good for many things besides sharpening too. Like a piece of everlasting waterproof sandpaper glued to a perfectly flat block 
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| Author: | TerrenceMitchell [ Sun Sep 25, 2022 4:03 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
DennisK wrote: TerrenceMitchell wrote: Agree with the previous. Looks like you are working on a blade for a traditional frog, with a chip-breaker. When this is the case, almost nothing (depending on the stiffness of your chip-breaker) comes in contact with that back side of the blade you are working so hard to flatten. When you have a bevel up plane, like a block plane, the back flatness does matter, but not in this case. Huh, i thought the opposite was true... that it only matters on a bevel-down plane, due to the potential chipbreaker gap shown in my previous post. On a bevel-up block plane, having a slight bevel on the back side only changes the effective cutting angle by a fraction of a degree, and poses no threat to functionality as far as I can imagine. I agree the last bit of the blade needs to have a gap-free connection with the chip-breaker, or chips will get caught in there. But the rest of the surface doesn't really matter. On a bevel up (block plane) most of that surface rests on the plane bed, and you need a great match to avoid rocking and chatter. Also, the ruler trick changes the cutting angle ever so slightly on a bevel-down blade with a chip-breaker... but on a block plane, the ruler trick has no effect on the cutting angle. If you do a microlevel on a block plane blade, that will change the cutting angle, and is one of the ways people with low-angle, bevel-up planes change their plane's performance based on the species and figure they are working on. It's easy to swap out the blade on those, where as a bevel down (traditional style) plane requires replacement of the frog, which is a hassle. Hand planes are quite the rabbit hole of woodworking. And they are dangerous for those, like me, who enjoy buying hand tools. I confess, there are too many in my tool cabinet
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| Author: | TerrenceMitchell [ Sun Sep 25, 2022 4:03 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
Deleted duplicate post. |
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| Author: | DennisK [ Sun Sep 25, 2022 5:19 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
Gotcha. I was thinking of the fine polished surface. Bevel-up does indeed need a larger portion of the back side flattened. But in either case only the last little bit needs to be fully polished. |
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| Author: | TerrenceMitchell [ Sun Sep 25, 2022 6:47 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
DennisK wrote: Gotcha. I was thinking of the fine polished surface. Bevel-up does indeed need a larger portion of the back side flattened. But in either case only the last little bit needs to be fully polished. Totally agree. Polishing anything other than the actual cutting surface of a blade is just cosmetic. Though I've seen lots of people do it, you won't find mine that way! I do get close to a polish on the backs of my chisels, but that's a whole other can of worms... |
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| Author: | dofthesea [ Sun Sep 25, 2022 7:47 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
What grits are you utilizing? |
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| Author: | James Orr [ Mon Sep 26, 2022 1:11 am ] |
| Post subject: | Re: Lapping - I just can't do it :( |
My first thought was the ruler trick as well. Keep in mind that for reasons I don't think anyone actually recognize materializing, the ruler trick isn't recommended for chisels. To lap the backs of chisels I use sand paper on a small granite surface plate from Woodcraft. Skip to 5:45 for a demo. |
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| Author: | TerrenceMitchell [ Mon Sep 26, 2022 7:42 am ] |
| Post subject: | Re: Lapping - I just can't do it :( |
James Orr wrote: My first thought was the ruler trick as well. Keep in mind that for reasons I don't think anyone actually recognize materializing, the ruler trick isn't recommended for chisels. To lap the backs of chisels I use sand paper on a small granite surface plate from Woodcraft. Skip to 5:45 for a demo. +1 Chisels need completely flat backs for accurate paring operations. |
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| Author: | gregorio [ Mon Sep 26, 2022 8:44 am ] |
| Post subject: | Re: Lapping - I just can't do it :( |
I cant help but think, the David Attenborough of Woodworking. “Such beautiful movement is rarely seen. Dance in the woodworking world is little understood.” : ) |
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| Author: | Aaron O [ Mon Sep 26, 2022 2:32 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
A friend recommended Shapton Ceramic stones when I wanted to switch to Water Stones. They don’t need to be kept soaked. Started with 1k and 8k, and continued using lower grit diamonds, which was really good for a while. Currently have 320, 1k, 8k, and 12k (which is next level polishing - scary sharp who?). Only change I would make is 5k instead of 8k (if I knew I was going to 12k, I would’ve saved $$$.) Got rid of all my oil and Diamond stones. https://www.sharpeningsupplies.com/Shap ... P1548.aspx Stumpynubs posted a vid where he ruler tricked chisels. Rob Cosman’s response is https://youtu.be/uB_sveNY08A Note: I think this is a good vid that briefly goes over the ruler trick on planes as well. Personally, I ruler tricked my chisels years ago. Logically, I never use my chisels for any visually flat joint like Rob’s, and validated with Stumpy’s perspective. I do, however, polish the backs for mitered purfling and binding, particularly my Japanese chisels which is ONLY used for that purpose (ok, this one is not ruler tricked). |
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| Author: | Tom G [ Mon Sep 26, 2022 4:31 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
I once lapped an old no.8 iron with light pitting using a dia sharp extra fine plate, as it was all i had at the time, foolishly thinking the polish would get continuous after another wee session I'd not advise it, and won't admit how much time it actually took, but took longer than hours  Somehow with all that lapping the iron did actually manage to stay flat enough, as it had a belly like that, although I did do plenty of skewing to counter this, (which likely thinned the allready thin iron, plus wiping the diamonds off the perimeter of the hone, just something to be aware of whilst your at it. I think David W on utube might have a block design worth making in this case https://www.youtube.com/watch?v=OOMjSwcEnsU |
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| Author: | jfmckenna [ Mon Sep 26, 2022 6:09 pm ] |
| Post subject: | Re: Lapping - I just can't do it :( |
A piece of masking tape on the edge of the stone worked perfectly! Thanks so much for that tip. I also saw a video where they used the scary sharp method of glass and sand paper and the technique he used to lap that was all pull strokes. I think that worked well too. IDK what grit my coarse stone is as the number wore off but it's a Norton stone and IIRC it was 400/1000. Then I follow that up with 4000/8000 and then leather. Shaves forearm hairs right off! |
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