Flattening backs

[Kees Heiden]

Mr. Sellers again :D
http://paulsellers.com/2014/05/does-plane-iron-flatness-really-matter-this-blog-could-save-you-hours/
I think he is onto something with this blog. I am surely going to try next time when I have a bellied blade with pitting and dubbed corners. The kind you always seem to find. Creating a slight hollow with a big blow from a nylon hammer should reduce a lot of lapping time!

I really like to read Paul Sellers blogs. Some things I vehemently disagree with, other times he has some very interesting things to say.

[Jim Matthews]

I will try this, with the vintage Coffin smoother that's giving me fits.

"Smack it with a hammer" always sounds good, about now.
(4 hours and it's sharp, but not straight!)

[Matthew N. Masail]

Seems like a good idea for old blades that will go in METAL planes. causing a hump on the back-side can be an issue if the blade needs to bed well in a wooden plane.

[george wilson]

A hammer blow can be effective IF you know what you are doing. Only skill and experience can provide that.

His bench is not flat at all, rendering a random hammer blow pretty experimental at best.and neither are most solid steel diamond stones particularly flat that I have seen. Some are downright concave. It's hard to tell if they are TRULY flat,even when selecting one,because the diamonds prevent the straight edge from actually touching the steel surface. They are only roughly Blanchard ground to begin with,before being plated and coated. I have the necessary precision flats to check a supposedly "flat" iron. I can pretty much guarantee that it will not check out flat with truly appropriate surfaces to check them on.

[Matthew N. Masail]

A hammer blow can be effective IF you know what you are doing. Only skill and experience can provide that.

His bench is not flat at all,and neither are most diamond stones I have seen. Some are downright concave. They are only roughly Blanchard ground to begin with,before being plated and coated. I have the necessary precision flats to check a supposedly "flat" iron. I can pretty much guarantee that it will not check out flat with truly appropriate surfaces to check them on.

Isn't that kind of his point? that it dosen't need to be THAT flat.

[David Weaver]

Reserve that for irons that have somehow been ground unevenly, or you'll just transfer the bump from the front to the back.

I wouldn't strike a harder iron that I really like, either.

[george wilson]

I read that in a hurry while cooking breakfast. There was a sentence early on that mentioned achieving dead flatness,which caught my eye.

When I want to make something flat,I make it flat,not pretend to make it half baked flat. I am coming from a background of both a machinist and a woodworker. So,I've gathered up my own little "Bureau of Standards" in my shop. It includes granite flats,straight edges and granite squares. These are my most accurate final authorities. Plus my lapped high precision laboratory grade flat plates. So,flat or straight,to me,means something entirely different from the person who is purely a wood worker.

Anyhow,there is nothing new about establishing a surface better,or a straight edge,with hammer blows before final grinding or lapping. It's been done for thousands of years already. No one wants to go to the trouble of lapping a really out of true surface,when it can be gotten considerably farther along with hammering. Blacksmiths do it all the time,even for their comparatively roughshod work(no insult intended,it's just a different class of work altogether).

[Kees Heiden]

I've done the hammer method with capirons that were very much out of line, or twisted or whatever. Never thought about trying it on a convex blade. And I haven't yet found the ultimate lapping method either, it usually takes up too much time to be considered fun. The only reason I want the face of the blade to be flat is to get rid of all pitting and dubbing and to get a good flat surface for the capiron.

Of course you don't want to introduce a huge belly on the other side of the blade, but I don't think it will move that much under a nylon hammer. Reworking the bed of a wooden plane isn't too much work though.

[Noah Wagener]

Does this pose any danger to laminations?

[Kees Heiden]

They are welded, so they can handle some stress. Biggest danger I guess is introducing too much stress in the steel bit. It's hard, so can't bend too much. But the Japanese have a similar tradition, hammering their plane irons so the edge bends down a little bit. This helps in the final shaping of the hollow of the back. They go at it much more systematically though. The steel bit in Japanese blades is harder then in Western ones.

[Steve Voigt]

Does this pose any danger to laminations?

I wouldn't pound directly on the lamination, but I agree with Kees that there is little likelihood of causing delamination.

On old tapered, laminated blades, you can easily bend the blade, because everything above the lamination line is just soft steel or wrought iron. I do this sometimes, especially if the bladed is twisted or warped from having been screwed to a chipbreaker for the last 75 years. But I don't just whack away like Sellers seems to be doing; I shim one side so I can control the max amount of bend. Often, I shim and then bend with a clamp, rather than a hammer. If the blade is corksrewed, I put it in a vise, grab the free part with a clamp, and twist the clamp.

All of the above, and what Sellers describes as well, has little in common with Japanese "tapping out." I don't see any way you could successfully tap out a laminated blade with a nylon hammer.

The only thing I agree with Sellers on is that the whole blade doesn't need to be flat. On a woody, just the part the contacts the bed (basically, the bottom half of the blade) needs to be flat or slightly convex. A metal blade can get away with even more convexity because the blade is thinner and the lever cap will force it flat.