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Help with lapping a chisel

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Forum topic by pierce85 posted 07-23-2011 04:09 AM 2616 views 0 times favorited 15 replies Add to Favorites Watch
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pierce85

508 posts in 2022 days


07-23-2011 04:09 AM

Topic tags/keywords: question chisel sharpening

I’m lapping the back of a Stanley chisel for practice and can’t seem to get it flat. I’m using a tool-grade granite slab with 60 grit sandpaper. I’m moving the chisel crosswise across the surface with even pressure on the blade, not touching the handle. The pattern I’m getting on the back is a rougher surface toward the handle, a more polished surface along the center, and a rougher surface toward the bevel – around an 1/8 of an inch from the tip – which does not seem to be progressing as much as the rest of the blade.

I’ve been at this for the past couple of hours. I started with 100 grit, moved to 80 grit, and am now at 60 grit. I would have thought that with 60 grit a lot of material would be removed and fairly quickly. There’s a tiny amount of pitting toward the bevel, which I’m using as a guide to judge my progress. It’s being reduced but very slowly.

Am I doing anything wrong or will this just take more time? The more polished area in the center makes me think my technique is flawed.


15 replies so far

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Chris Camp

14 posts in 2335 days


#1 posted 07-23-2011 06:22 PM

60 grit is awfully coarse. I’d recommend using 400 grit wet/dry sandpaper lubricated with mineral spirits.

-- I'm always thinking one step ahead, like a carpenter building stairs...

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bigike

4048 posts in 2748 days


#2 posted 07-23-2011 06:55 PM

for a chisel all you need is the part just behind the tip to be flat about 1/16 or so behind it. I know you said it’s for practice but JFYI. One of those grits should have worked by now it sounds like your doing the right thing as far as I know. Flat surface, coarse grit, and pressure while keeping the chisel itself flat. Try a belt sander with WD-40 as a lubricant.

I forgot to mention try a marker to judge your progress.

-- Ike, Big Daddies Woodshop, http://www.icombadaniels@yahoo.com

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Arch_E

47 posts in 1981 days


#3 posted 07-23-2011 07:05 PM

Sometimes the blade backs can be really out of flat. Your marks may just be exposing where the low (shiney) spots are. And, yep, it’s those dips that have to lapped down to; however, only the 1/16” at the cutting edge matters for the moment. It just means possibly that chisel is not too flat.

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pierce85

508 posts in 2022 days


#4 posted 07-23-2011 09:18 PM

Thanks for the replies! I switched to 120 and that seems be working better than the coarser grits. I took a marker to the surface as suggested and all but 1/8 of an inch from the tip came completely off after a couple of passes. So I have more work to do.

I want to get the entire surface lapped and to a polish for practice sake. I have a new set of Narex chisels that should not need anywhere near this amount of work, but I want to develop my technique on something a little more challenging first.

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Dan

3630 posts in 2340 days


#5 posted 07-24-2011 08:27 AM

Try changing grits often. If you spend to much time on 120 grit then the scratch patterns become harder to remove. I usually start with 120 for a few min then go to 180 then 220 then back to 120 so on and so forth. Once it looks like I have the majority flat then I move up to the finer grits.

-- Dan - "Collector of Hand Planes"

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ramone

18 posts in 933 days


#6 posted 11-22-2015 08:44 AM

... following up on this thread since i’m new to sharpening …

... i’m getting ready to lap some chisels and plane blades and was planning to start with my diamond stone … extra course to course … is that a good starting sequence?

... and after that how polished do i need to lap the backs … i have a set of norton water stones … 1000 … 4000 …. 8000 … how far into those grits do i need to go?

Thanks!

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ElChe

630 posts in 796 days


#7 posted 11-22-2015 09:06 AM

Put some sharpie marks on the chisel surface and use the 1000 and see if it needs to be flattened. If the marks disappear evenly then you are fine. If slightly off I think you are fine too. If the chisel is crooked then you will need a coarser grit to get it flat. Sandpaper works well. As to the bright and shiny, I only do the last 1/2” of a chisel. Your grits are OK for getting a nice sharp blade. I don’t polish past 4000 usually. I think it is a waste of time to take it last 8000 unless you use your chisel as a mirror. :)

-- Tom - Measure twice cut once. Then measure again. Curse. Fudge.

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rwe2156

2187 posts in 940 days


#8 posted 11-22-2015 03:14 PM

Pierce:

keep in mind you’re dealing with a low quality chisel and they can be awfully out of flat and require lots of work, which you are obviously discovering.

As one poster said, you don’t need the entire back of the chisel flat, just a couple inches back from the cutting egde.
If not, you’re creating alot of unnecessary work for yourself.

The sharpie is indispensable, as is an lighted magnifying lamp or visor.

Ramone:

That’s a good sequence. I’ll disagree a little with the previous poster in that you won’t get a polish until you go to 8000 or use a strop. 4000 will get you close enough, but not if you really want a truly polished edge.

Also, I don’t see how you can only polish the last 1/2” without risking a back bevel because you won’t have enough purchase on the stone.

Its really the same amount of more work to polish a couple inches vs. 1/2.

If you’re using waterstones, make sure they are dead flat. I use a coarse DMT stone for this but any flat coarse surface will do. I have found the “flattening” stone Norton sells is not actually flat.

-- Everything is a prototype thats why its one of a kind!!

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Tedstor

1625 posts in 2092 days


#9 posted 11-22-2015 03:21 PM

Your technique is probably fine (hard to do wrong)......its the chisel you’re working with that sucks. Don’t drive yourself crazy trying to get a $5 chisel to look like a $50 masterpiece, and expend $10 worth of sandpaper in the process. Just get the area immediately behind the cutting edge reasonably uniform, sharpen the tip, and practice chopping a lap or mortise. Your time will be better spent.

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bandit571

14527 posts in 2143 days


#10 posted 11-22-2015 03:39 PM

$1 chisels, after a trip over 600 grit oil stone, 1000 to 2.5k grit paper ON the stone, “air tool oil” by 3in1 as the lube

I hold the chisel with a finger or two right over the area on the stones. I have to watch as I slide side to side, that I do not rock the chisel. I try to keep it flat on the stones.

Other than the Aldis chisels, the rest are yard sale finds.

Even the skinny ones.

$50 for just one chisel is a complete waste of money, after all.

-- A Planer? I'M the planer, this is what I use

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TheFridge

5764 posts in 945 days


#11 posted 11-22-2015 03:40 PM

I want at least 3/4 of the back flat. I like a big area to register my chisel against for some things.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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TiggerWood

271 posts in 1066 days


#12 posted 11-22-2015 04:35 PM

With a chisel like that, I would grind off the top and reshape it. Seems like a very hard steel and will be a good chisel once you get it shaped and sharpened.

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Tim

3110 posts in 1421 days


#13 posted 11-23-2015 05:03 PM

When I flatten chisels on sandpaper my fingers always hurt from pressing on the edges of the chisel. So now I take a small piece of scrap wood and make a dado in it that will fit tight over the top of the chisel. Then I can hold on the that instead of the top of the chisel. Sorry, probably harder to explain than show, but I don’t have a picture handy.

But since I hate even doing that, I try to eliminate it as much as possible. I use a grinder instead. I mark the back with a sharpie then find the high spots by what has been removed with a trip over the sandpaper. Then I carefully grind those a little bit more on the grinder. Then mark with a sharpie again to find the high spots, then grind again. rinse and repeat. You’re spending so little time on the grinder there’s little risk of heating it and drawing the temper, but it saves so much time on one that’s badly out of flat. Once you do it a couple times you get better at it. I’ve made a couple mistakes that made a little more work for myself, but still less than doing it all on sandpaper.

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waho6o9

7166 posts in 2036 days


#14 posted 11-23-2015 05:14 PM

A scrap block with magnets saves your fingers and can be used for

plane irons etc..

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rwe2156

2187 posts in 940 days


#15 posted 11-23-2015 09:57 PM



When I flatten chisels on sandpaper my fingers always hurt from pressing on the edges of the chisel.

A scrap block with magnets saves your fingers and can be used for

plane irons etc..

Question: Is there a difference between a man and a guy?

Let me rephrase that: a real man and a man?

Just kidding…....lots of guys with no calluses are making a whole lot more money than most of us.

-- Everything is a prototype thats why its one of a kind!!

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