Coffin smoother and vintage iron - am I missing something?

[Jim Matthews]

I picked up a nice "coffin" smoother from the Auction site that shall not be named;
complete with original wedge, cap iron and tapered blade stamped Sheffield steel.

I can get the blade sharp, but not flat.

It appears to be curved along both the length and width of the back.
Every time I mark out the back, and worry at it on my coarsest stone,
it appears that the blade takes on a subtle curve.

I wonder if it's the threads of the cap iron screw pulling things out of alignment.
Is that even possible?

I've verified that the cap iron is flat, but it doesn't meet the back of the blade.
It's all-too-easy for shavings to pack into the corners and jam the works.

I'm into this for not much money (more in domestic shipping than the final price)
but I don't want to abandon the effort just yet.

What steps can I take, without machine tools?

I've got files, a lapping plate and a sandpaper library.
The files just skate off the blade, it's so hard.

Flummoxed in Taxachusetts....

[David Weaver]

80 grit high quality PSA paper, like a mirka gold roll.

Presuming your lapping plate is fairly long.

If it's not, then i'll wait to suggest something until you mention the size.

Fresh al-ox is super aggressive, like diamonds, but it dulls a lot faster.

Old woodies are usually a chore.

[Charles Bjorgen]

I had the same problem with the cutter on a woodie that I got on the auction site. I was able to verify with a straight edge that the back or non-bevel side of the iron had a slight crown causing the jamming of chips along the outside edges between the iron and the cap iron. Lots of work later I managed to work the crown down but not completely. It still needs work. I had the most success using my Tormek grinder on the crown although I wouldn't hesitate doing this with a power grinder and I will probably do that next.

[Jessica Pierce-LaRose]

Am I correct in understanding that it appears the curve, on the back of the blade, is convex? These are hard to lap. On blades I don't care too much about, I've taken to using a method that Garret Hack mentions in his hand plane book; hitting the back with a small grinding wheel in a drill or a dremel, sort of making a poor-mans version of a hollowed back tool like a Japanese blade. Nothing dramatic, just enough so that you're not spending a lot of time lapping where it doesn't gain you much. Besides speeding up lapping, it gets you a couple of points of contact, helping to lap convex blades without rocking and continuing to make it convex. The trick is to grind too much, and alternate between the grind and your coarse stone to keep track of what each is doing.

[Jim Matthews]

Am I correct in understanding that it appears the curve, on the back of the blade, is convex? These are hard to lap. On blades I don't care too much about, I've taken to using a method that Garret Hack mentions in his hand plane book; hitting the back with a small grinding wheel in a drill or a dremel, sort of making a poor-mans version of a hollowed back tool like a Japanese blade. Nothing dramatic, just enough so that you're not spending a lot of time lapping where it doesn't gain you much. Besides speeding up lapping, it gets you a couple of points of contact, helping to lap convex blades without rocking and continuing to make it convex. The trick is to grind too much, and alternate between the grind and your coarse stone to keep track of what each is doing.


Thanks for this. It's confirmation of what I suspected, and this is a manageable method.

I'm tantalized, as the steel seems to be high quality but my results disappoint.

[Steve Voigt]

Jim,
I've flattened a lot of old irons like this, some of them in pretty bad shape. I usually start by gluing an 80 grit belt (with the seams cut out) down to a piece of granite sink cut-out. I lay the bottom 3" or so of the iron on the belt and move it sideways (parallel to the cutting edge). It's good to use a holder for the iron, or a mag base, to save your fingers. Once I've established a good scratch pattern, I do exactly what Josh says above--I use an angle grinder and sweep the high spots, always staying away from the edge, and trying to make the blade a teeny bit convex. Then I repeat these steps until I can flatten the whole thing.
I think it's important to move side-to-side, not up-and-down, because if the blade has any twist, you'll never get it flat doing the latter. Also, you don't have to get the entire blade flat, just the part that contacts the bed.

[Jim Matthews]

I think it's important to move side-to-side, not up-and-down, because if the blade has any twist, you'll never get it flat doing the latter. Also, you don't have to get the entire blade flat, just the part that contacts the bed.

I believe this is the base failure in my first effort.
I couldn't fathom how I could have a uniform scratch pattern, without flattening the back.

I gain appreciation of what Ron Hock makes, with each passing hour.

I suspect that this is why there's so much steel remaining on the blade...
I avoided "closet horns" when buying and selling saxophones for the same reasons.

Never trust the old ones that are still pretty.

[Kees Heiden]

Each and every old plane I have was like that. It takes a lot of love to get them in a usefull shape again, and backflattening isn't really my hobby. I find that sandpaper never creates a real flat back, quite a bit of extra work on flat benchstones is neccessary after the sandpaper. Grinding a slight hollow is indeed really helpfull.

I don't know how the old guys used these planes. I guess they had the capiron a full cm from the edge to avoid jammed shavings. No wonder the art of using the capiron got lost.

[Charles Bjorgen]

I don't know how the old guys used these planes. I guess they had the capiron a full cm from the edge to avoid jammed shavings. No wonder the art of using the capiron got lost.

That was exactly my feeling after trying to get my old auction site woody working. Fortunately it was only less than 12 bucks including the shipping.

[Jim Matthews]

This inexpensive education has revealed what it is I'm paying for when I buy from today's plane makers.

[Zach Dillinger]

That's good... more vintage wood planes for me :)

Anyone who buys them and doesn't love them can feel free to send 'em my way. Depending on what you have, I'll even pay shipping :)

[Kees Heiden]

You certainly need a lot of love to be able to enjoy old planes. Luckily the somewhat masochistic act of flattening blade backs is a one time affair. After that, the planes are very nice.