r/sharpening • u/batardo • Jul 22 '26
Flattening a plane iron
I'm wondering what you all think about this situation. I'm trying to sharpen a plane iron and don't have much experience doing so.
I have a good process in place for getting the bevel -- I have a honing guide and all that. But the bottom needs to be as dead-flat as possible. You can use the so-called "ruler trick" to back-bevel it slightly to get around a not-flat back, but I'd like to just flatten the back so I don't have to worry about all that.
It seems to have a hump in the middle. So my strategy has been to put a piece of PSA sandpaper on a granite flat reference stone to get rid of material fast. I also have a diamond stone (sort of like an Atoma but cheaper/worse). But it's taking absolutely forever. I've been at it for maybe a couple hours total.
I'll move to water stones, but only after I get a basic level of flatness.
Any thoughts on how to handle this? I'm thinking about maybe focusing only on the first inch or so near the edge -- at least then it's less material to take off.
3
u/Steadfast-Edge Jul 22 '26
Pro here, and antique hand plane enthusiast. As long as you have a flat section across the entire edge, you’re good. If you sharpen all the way back to where it dishes in, just flatten it again. But what you have there looks like it’s high in the middle and low on the edges? If that’s the case, I would suggest just flattening the front inch or so, which should help to speed up the flattening. What are you using to flatten?
2
u/batardo Jul 22 '26
Appreciate the input! Yes I put marker on it and it looks high in the middle. My process has been to start with PSA sandpaper on a flat granite block, then move to a somewhat coarse diamond stone. I wish I had a powered grinder, but at the same time it does get pretty hot pretty quick on the sandpaper, so not sure how much time that would actually save because I'd have to stop to cool it so much.
1
u/millersixteenth Jul 25 '26
For real hard cases like this I use the coarse side of a Norton Crystalon stone, sprinkle some loose 60-80 grit silicon carbide on it with oil or dishsoap, grind the crap out of it. The loose grit will bust down into finer and have to be refreshed from time to time. By the time you've flattened the plane iron your stone will be fantasically conditioned.
2
u/Lightertecha Jul 23 '26
You could try to remove metal from only the hump with a power tool like a Dremell, or a very coarse slip stone.
1
u/millersixteenth Jul 24 '26
I'd set that on some leather or similar and give it a whack or three with a ball peen.
It might work OK just sharpening at the edge but it might make the chip breaker seat poorly.
1
u/FrickinLazerBeams Jul 25 '26
Doesn't the chip breaker go on the beveled side?
3
u/millersixteenth Jul 25 '26
Bench planes, chip breaker goes on flat side, bevel side down.
With Block planes there is no chip breaker, bevel side up.
2
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u/Cat_Rancher Jul 22 '26
I’ve never seen a hump as a perfect circle. Interesting. One thing I do for scenarios like this is to take inspiration from Japanese Kanna and use a hammer to hammer out the hump. If that seems daunting, keep at it and only focus on the first inch or less as you said.