Thread: Flattening the backs

The quickest method I've found is sandpaper.

Get yourself some wet dry paper, if it's really bad I start with 80grit. replace every 5 mins or when you feel it's no longer biting. Shouldn't take longer than 15 mins or so to flatten a 3/4" chisel. Once flat work your way up the grits till you can use sharpening stones.

Obviously still takes a reasonable amount of effort, but is the quickest. If you're feeling lazy and are happy to wait, then the side of whetstone grinder.

You can use the side of CBN wheels but I'm not brave enough to risk a chisel being flung out of my hands at full speed. If you have a slow speed grinder and rest it might be ok, but given that flattening the backs is a once off I'm happy to take my time.

Thanks - I remember trying this method some years ago but just found that I was dubbing the edges (and it was more like hours than 15 minutes). I might have another go and see how it works for me.

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It also occurs to me I could put the CBM wheel on my hand cranked grinder (the ultimate variable speed technology) - it should fit. So that would deal with the flying chisel risk...

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PSA backed sandpaper on a granite surface plate. Change it as soon as it slows down.
Technique is important to avoid rolling, making everything wonky, and ruining the geometry.

Yes to the dremel to work backs that are badly humped... But honestly, I'm sort of tired of doing that. I would rather get tools that don't require hours and hours of flattening. I'm probably more likely to pitch it in the rejects box and just move on to the next one if it's *that* bad.

I have a Stanley #289 in excellent condition except the blade, which is terrible - but I figure it's worth the effort for this one. I'll try the glass / surface plate and sandpaper option again, I might put together a blade holder with rare earth magnets or similar.

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I sometime think of this - primarily as Im making very small planes (Japanese style) for making cups and pots.

I was thinking that one could use a belt sander? 240 grit roll?

Another was to send it to a mate (service?) that has a metal shop and a surface grinder. These magnetically grip the material and a spinning stone zings back and forth skimming the surface.

I found this guy on Gumtree: Lathe, Milling, Machining, Fabrication and General Engineering. and wrote to him. It might be an interesting option to send up everything you want done in a box, he does the job/s and posts them back?

Yet another I considered was to make up a disk, akin to a record player, with a large sheet of high-grit paper glued nice and flat. Power this disk with a suitable "thing".... router, drill, etc. I've a small battery powered Makita router (RT700 or something) and its a powerhouse. On low revs, one could make a pulley and a belt to rotate the disk.... just like the excellent record players of old. This is not some super sonic device, but a slower revving platter that the blade is press down to, then started up.

Hopefully no dubbing.... but it may be all in my imagination and I'm an idiot

Originally Posted by woodPixel

Yet another I considered was to make up a disk, akin to a record player, with a large sheet of high-grit paper glued nice and flat.

That's called a Worksharp.

Yeah, but the worksharp is such a little thing. A bit hard to get a whole chisel or plane onto.

I was thinking more along the size of 40cm, perhaps 60 rpm and something where the piece can be lain down, held, THEN turned on.

Nothing worse than applying the thing to an already moving surface! No accuracy


I do remember one image of a guy using a drill press in this manner. The sanding plate was chuck mounted. The quill was lowered and sssss, zing!

I was thinking with the CBN wheels....

I have a mate (Evan!) who makes a thing called a Noob-grinder for knife makers.

There is an attachment that a knife is magnetically attached to a jig and the item is slid back and forth until the desired finish is obtained.

A knob on the front is wound that moves the jig microscopically back/forth on an screwed inverted trapezium.... this raises it an absolute minute amount... most accurate.

Ive two mates that are kniffy-types and they use their Noob's for almost everything. Very versatile.


I was thinking a jig could be made with drawer runners and a metal threaded bolt to give something similar? Mount the jig under your belt sander, CBN wheeled grinder, or a lathe attachment?

This would be a bodge-up surface grinder

I have a Worksharp and have tried using it to flatten backs with mixed results. The big trick some have with it is placing the blade on it so big gouges don't happen but that is not my problem. What I find is that taking the blade to a stone to finish it off gives a different pattern every time and I don't know why and wonder if it is a problem at all because I have to ask how flat does the back of a chisel really need to be. If you want really flat then the only way to get that is on a lapping plate but I don't think it is necessary and yes I have one sitting in the corner gathering dust. If anyone wants surface grinding done on a new machine by a toolmaker I might be able to arrange it. My brother in law is a toolmaker and I am sure he would do it.

A home made surface grinder? CBN wheel laid on its side driven from a drill press sitting inside a sub table level with the top of the wheel. You would have to run it very slow I guess but it is an idea.

Originally Posted by woodPixel

I was thinking with the CBN wheels....

I have a mate (Evan!) who makes a thing called a Noob-grinder for knife makers.

There is an attachment that a knife is magnetically attached to a jig and the item is slid back and forth until the desired finish is obtained.

A knob on the front is wound that moves the jig microscopically back/forth on an screwed inverted trapezium.... this raises it an absolute minute amount... most accurate.

Ive two mates that are kniffy-types and they use their Noob's for almost everything. Very versitile.


I was thinking a jig could be made with drawer runners and a metal threaded bolt to give something similar? Mount the jig under your belt sander, CBN wheeled grinder, or a lathe attachment?

This would be a bodge-up surface grinder

I think I might pass on that idea. For any sort of accuracy you need a bed on well machined ways, it gives a nice finish though.

Have you tried the ruler's trick?

Originally Posted by justonething

Have you tried the ruler's trick?

The ruler trick is to create a clearance angle and clearance angles are debated here as well as other things that are useful to know.

Astounding video especially with the "wear bevel" and the finding that the sharpness is almost irrelevant, but the presentation of the wear bevel is far more important.

Makes me think that plane blades should be sharpened on the plane itself... in order to grind this wear bevel off, thereby sharpening it to an optimal angle....


edit - it explains the unicorn methods longevity as well....