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How do I know when my chisels are sharp enough

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Forum topic by Chris208 posted 09-02-2012 05:26 PM 2759 views 0 times favorited 19 replies Add to Favorites Watch
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Chris208

195 posts in 959 days


09-02-2012 05:26 PM

A couple months ago I bought a 6 piece set of Marples Splitproof chisels second hand. They were in pretty poor shape when I got them. I spent a ton of time working on them, and now I can shave my arm hair with each of them, but is this really a good indicator that they are sharp enough for woodworking?

What other tests are there for verifying the sharpness of a chisel?

Are my chisels sharp enough?

Thanks,

Chris in Boise


19 replies so far

View Tedstor's profile (online now)

Tedstor

1369 posts in 1322 days


#1 posted 09-02-2012 05:40 PM

If you can shave hair with it, I’ll venture to say its sharp enough.
In all seriousness, try to work some wood with it. That would be the “other” way to verify its sharpness.

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jmos

681 posts in 1059 days


#2 posted 09-02-2012 05:51 PM

Shaving the hair on your arm is a decent indication, and quick to test while sharpening. Try paring end grain; do you get a shaving? Is the surface left smooth and shiny? If so, it’s probably sharp enough.

-- John

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rwyoung

369 posts in 2161 days


#3 posted 09-02-2012 06:15 PM

You can shave with a dull razor, so the arm hair thing really isn’t that indicative of sharpness.

Sharp = two planes (think geometry, not woodworking) coming together at a single intersection.

Ideally, the working end would be one molecule of steel thick. In reality, the best you can do is one grain of steel exposed. In practice, if you cannot see light reflected from the cutting edge, you are likely done. It will look like a black line while the rest of the bevel and back reflect light.

Pairing end grain is a decent enough test, use pine. It should happen nearly effortlessly and create shavings with some body, not dust.

Alternatively, you can hold a sheet of typing paper (copy paper) LOOSELY and push the chisel/blade down through the edge. Don’t pinch the paper to form a curve and make it more rigid. This is a cheat and you can push a much duller edge down through a rigid sheet than a “floppy” sheet.

Another simple test is the finger nail test. Carefully try to slide the sharp edge down the length of a thumbnail. It should stick and not slide. If it slides, it is dull. You can also draw your thumbnail across the edge and feel any micro nicks in the blade. Again, it should stick a bit but feel smooth as you draw across. Be careful with this test and don’t slice things that shouldn’t be sliced. Also, if fingernails on a chalkboard bother you, this test will also make your skin crawl.

Don’t spend all your time testing for sharpness. The wood you are working on will tell you if the tool is sharp enough. It should cut and you shouldn’t need to fight the tool, just guide it.

Also, invest in a x5 to x7 magnifying glass or eye loupe to inspect the lapping marks. Once you look at these a few times you will learn when you need to lap more (make the marks smaller) on any particular grit regardless of the presence of a burr. The higher the polish, the smoother the steel (in general) and so fewer longitudinal gouges in the steel which form the start of micro-fractures which eventually let a little flake come off and this is how your edge dulls.

Just don’t obsess with the steel. Get it sharp and get back to work.

-- Don't sweat the petty things and don't pet the sweaty things.

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rance

4142 posts in 1849 days


#4 posted 09-02-2012 06:19 PM

They need to be at least sharp enough to shave arm hair with, but not so sharp that you are frustrated with the process of getting them to that point. Somewhere in the middle.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

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Chris208

195 posts in 959 days


#5 posted 09-02-2012 06:34 PM

Thanks for the great info (as always).

I already reached the point of frustration, but I took a break and came back to it after I watched a bunch of youtube vids to make sure I wasn’t the problem. As it turned out, the chisels were just beat up, and needed a lot of work.

Thanks!

View HorizontalMike's profile

HorizontalMike

6948 posts in 1603 days


#6 posted 09-02-2012 06:50 PM

IMO, no matter how sharp you think you have them, you should re-strop them frequently while in use. It only takes a couple passes each time but I do find that it really helps keep the edge.

-- HorizontalMike -- "Woodpeckers understand..."

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Chris208

195 posts in 959 days


#7 posted 09-02-2012 06:55 PM

Assuming I don’t have a strop (or know what stropping is, for that matter) can I just touch them up on my high grit stones?

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rance

4142 posts in 1849 days


#8 posted 09-02-2012 08:21 PM

No. :) Well, you could, but you should read up on making a strop. You can make one from an old leather belt. Google it. I think you’ll be happy with your new homemade tool.

-- Backer boards, stop blocks, build oversized, and never buy a hand plane--

View David Kirtley's profile

David Kirtley

1281 posts in 1687 days


#9 posted 09-02-2012 08:23 PM

Just make a strop. It can be as simple as a piece of MDF or nice leather. Something that will hold the stropping compound.

-- Woodworking shouldn't cost a fortune: http://lowbudgetwoodworker.blogspot.com/

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Tedstor

1369 posts in 1322 days


#10 posted 09-02-2012 09:24 PM

I bought a piece of leather off this guy (see below). Glued to a piece of maple. I use it with some green buffing compound. Works boo-tiff-lee.

http://www.ebay.com/itm/3-X-9-inch-Leather-Strop-By-R-Jones-use-as-is-or-on-your-block-/120976436094?pt=LH_DefaultDomain_0&hash=item1c2ac1eb7e

View HorizontalMike's profile

HorizontalMike

6948 posts in 1603 days


#11 posted 09-03-2012 12:36 AM

Mads has the absolute BEST explanation and examples of making and using a strop that I know of. Enjoy:

http://lumberjocks.com/mafe/blog/26468

-- HorizontalMike -- "Woodpeckers understand..."

View David Kirtley's profile

David Kirtley

1281 posts in 1687 days


#12 posted 09-03-2012 07:08 PM

Just be aware that you can strop too much and dub the edge over. There is really no right or wrong. It is a balancing act. Too sharp and the edge doesn’t last. Too dull and it doesn’t cut as cleanly. There are times you want to change up for what you are doing. Cutting some nasty endgrain? Make it wicked sharp and stop and sharpen it again while you are cutting. Chopping out mortises? The same edge won’t last two chops. A soft strop will give you a longer lasting edge. A hard strop will give you a sharper one. That’s why barber’s stops have different belts (of course most people now days have never seen a barber’s strop)

-- Woodworking shouldn't cost a fortune: http://lowbudgetwoodworker.blogspot.com/

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waho6o9

5086 posts in 1266 days


#13 posted 09-03-2012 07:30 PM

Leather + adhesive ( I like 3M 90 high strength adhesive) + Plywood = Stropping board

I charge the leather with oil, my preference, and green honing compound. Once in a while
I mix it up with Autosol for a change of pace.

I like to have the leather close to an edge to hone the back of chisels and blades
as well.

MDF and green honing compound works also.

HTH

View HorizontalMike's profile

HorizontalMike

6948 posts in 1603 days


#14 posted 09-04-2012 02:25 PM

Yeah David, but I sure do remember what that strop felt like! Especially after I misbehaved at home ;-)

-- HorizontalMike -- "Woodpeckers understand..."

View vipond33's profile

vipond33

1405 posts in 1187 days


#15 posted 09-04-2012 10:32 PM

Take the chisel into a quiet room. Breathe across the edge and then put your ear to it. If really sharp you will hear the germs scream.
gene

-- gene@toronto.ontario.canada : dovetail free since '53, critiques always welcome.

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