Old plane blade too hard?

[Shaun Mahood]

I've got an old wooden jointer plane with a blade that I have never been able to sharpen satisfactorily. I just bought a bench grinder and have given it another try. It seemed to take longer to grind than my other blades, and after that is taking much more time and effort to sharpen on my stones. I got it to the point that it was close enough to sharp to test, and had a ton of chipping on the blade when planing the long grain of a piece of cheap pine that I use to setup and test my planes after sharpening.

The same sharpening method I am using gets my Narex chisels nice and sharp with no chipping. I'm starting to think the blade is too hard - is there an easy way I can confirm this?

[David Weaver]

It sounds useless, so you don't have anything to lose with it. Put it in your kitchen oven for 45 minutes at 300. If it's still chippy, put it in at 350,...

Keep going in 50 degree increments until you get something you can use. if it's old, it's probably simple carbon steel and unless it was starved of its carbon in heat treating, it should temper softer at a temperature your oven can handle. If it's very low carbon, maybe it can't, but if that's the case, you wouldn't want it, anyway.

[Zach Dillinger]

I'd say you've done all the confirmation you need. Unless you are sharpening at a ridiculously low angle, the blade shouldn't do that.

[Shaun Mahood]

Thanks for the help. I've never had a problem like this and just kept going back and resharpening it thinking I screwed something up.

[george wilson]

I have actually had ADDIS vintage carving tools that were entirely too hard. I had to slowly heat them to a brown color in the musical instrument maker's shop. The only heating device was to lay them on top of the side bending setup. It consisted of an oval brass chimney about 4" tall,with a silver soldered on top. The chimney sat upon an open sided box,and we put alcohol lamps in the box to burn up into the brass chimney. It worked fine for drawing some temper from the carving tools. I also sometimes had to soften bundles of jeweler's saw blades which broke very easily. I did them the same way.


P.S.: These were a pristine set of PRE WAR(II) carving tools,too.

[Mel Fulks]

Interesting post on the Addis tools, surprising .Not a carver ,but aware of their good reputation .

[Steve Q Brown]

It sounds useless, so you don't have anything to lose with it. Put it in your kitchen oven for 45 minutes at 300. If it's still chippy, put it in at 350,...

Keep going in 50 degree increments until you get something you can use. if it's old, it's probably simple carbon steel and unless it was starved of its carbon in heat treating, it should temper softer at a temperature your oven can handle. If it's very low carbon, maybe it can't, but if that's the case, you wouldn't want it, anyway.

Good advice... I'

[Steve Q Brown]

It sounds useless, so you don't have anything to lose with it. Put it in your kitchen oven for 45 minutes at 300. If it's still chippy, put it in at 350,...

Keep going in 50 degree increments until you get something you can use. if it's old, it's probably simple carbon steel and unless it was starved of its carbon in heat treating, it should temper softer at a temperature your oven can handle. If it's very low carbon, maybe it can't, but if that's the case, you wouldn't want it, anyway.

Good call...incremental tempering adjustment

@OP, my recommendation would have been for re-tempering to an appropriate hardness, though I like Davids step-by-check process a little better- especially for one (presumably) not accustomed to tempering steel....

If the (re)tempering doesn't work for you, $30 for a new, thicker, known quality iron would be a good investment, IMO.

[Winton Applegate]

Ha Ha
Nah nah
Carbide tool bits for metal working and in the router bits etc., are harder than any plane blade that you will find (or make) and it is quite possible to sharpen them with home tools.
Are you using natural stones such as Arkansas etc ?
Try diamond plates.
Are you using one of the gray grinder stones that come with the inexpensive grinders ?
Try the white or pink power grinder stones (for the plane blade not for the carbides).
Chipping : Pine is weird stuff, there's that engineering term again. Some pine has really hard rings mixed in with really soft rings/fibers.
Use some walnut or straight grained hard maple to test the blades on.
I was thinking the same about the bevel angle being too shallow. When the angle is too shallow the "chipping" is just the edge folding over from hitting the hard growth rings.
PS: if you like soft easy to sharpen tools try the Sorbys from Woodcrap they are nice and soft. Not much use once a person gets them sharp though. A stern look makes them dull again let alone trying to cut a mortise with one.
PPS: I have made small plane blades out of old files I picked up at the local scrap yard. While keeping them wet to prevent tempering them I have ground the teeth off and ground a blunted bevel on one end then using my Shapton 120 white stone brought the edge up then using extra coarse and coarse diamond plates and the other Shaptons bada boom bada bing.
Alternatively one can anneal them, shape them and re-harden them, temper them, then do the final sharpening. Depends what mood you are in at the time.
I have made scraper tools that I use on brass brazed joints that still have some grit from sand blasting and the glass hard brazing flux inclussions still on the joint here and there. These scrapers I made from files, heated them red hot and shaped them then just quenched them and used them with no tempering (full hardness ) because I needed the extra hardness. These scrapers are so hard that they break in my hand while using them. But you know what ? I can still sharpen them using the above methods.
Just takes the right sharpening tools. One thing I discovered fairly recently : The Shapton white 120 stone cuts much better and faster than another white super coarse stone that was rated at 100 grit size. Quality is worth paying for.

[Kees Heiden]

There are three modes of edge failure. When the blade is too soft, it just folds over. When the hardness is just right, the edge wears gradually to a blunt round edge. And when it is too hard and brittle, it chips. And of course there are gray areas in between, depending on the honing angle and the type of wood. We all want the edge to be as hard as possible, so it doesn't wear as quickly, whithout it being chippy. Some smiths manage to create harder and tougher angles then others, through skill and secret trade pratices and what not.

In practice, when you happen to find a blade which is really too hard, I would first try a higher honing angle. Up to 35 degrees is practical. If the blade doesn't tend to chip with the higher honing angle, but it remains to be too hard for your sharpening system, you have (again) three choices. Tempering the blade to a lower hardness. Investing in a diamond sharpening setup and learning to use it (might be a bit excessive). Or sell the blade. The fourth choice of using the blade only in benign wood is not practical.

[george wilson]

Why would you use fully hard file steel scrapers?

[David Weaver]

Blades that aren't as hard as carbide can literally chip when you're sharpening them. That is, carbon steel blades that are overhardened or that are defective. In razors, it's described as microchipping. In plane blades like the one being discussed, the chipping is probably larger. In a microchipped blade, the blade chips while you're sharpening and it will not get sharp like what you'd expect from a better blade. If you look at a microchipper, you can see a glint of light across the edge. When a fresh blade is truly sharp, you will see nothing on the edge no matter the angle you look at it. If you strop it hard on a bare strop, you can see just a bit of wear on the edge (though the edge will perform as though it's more sharp if the strop is clean and good quality, because little microscopic bits of scuzz have been worn off).

Anyway, being able to sharpen carbide without chipping doesn't equate to being able to sharpen a softer than carbide but overhardened carbon steel without chipping.

[george wilson]

Plus,carbide blades are ground with an extremely blunt cutting angle on router bits. They cut by virtue of the very high speed of the router.

[jamie shard]

If you look at a microchipper, you can see a glint of light across the edge.

Thanks for that tidbit. It seems like I've encountered this in the past, not fully knowing what was going on.

[David Weaver]

Sometimes it happens on blades that aren't that hard, but not too often. If you go through enough vintage planes, you'll eventually find one like that - one that you can't ever seem to get sharp. A milder abrasive will sometimes not chip the edge while you're sharpening, but there's no reason to do that because the iron will probably just fail in use.

I've never seen it on a modern heat-treated blade, though.