Lapping the back of a plane blade - help requested

[Christian Castillo]

Hi,

I began lapping the back of a plane blade for a wooden jointer plane that I recently purchased. I have the back flat, I just need to get through some pitting at the edge. Now that the back has an even scratch pattern across the back, I noticed that there is a small margin around the edges of the back that are very shiny colored steel, and a patch in the center of the back that is of a slightly duller color, what does this mean?

Christian

[Jack Curtis]

Sounds like you might have a slight hollow on the back. Is this a western plane blade?

[Christian Castillo]

It isn't a hollow, the blade has an even scratch pattern, it is flat, but the color is different in the middle, the shape of a hollow in size, but its just discoloration, the steel is all equally lapped. This is a vintage laminated western plane blade. I'm starting to fear that it is the same thing that happened to Carl Stammerjohns plane blade as seen here:


http://stammerjohn.com/2011/08/21/plane-tune-up-8/

http://farm8.staticflickr.com/7139/7458713710_3d9052e81c.jpg (http://www.flickr.com/photos/50072175@N07/7458713710/)
IMG_1366 (http://www.flickr.com/photos/50072175@N07/7458713710/) by Christian Castillo1 (http://www.flickr.com/people/50072175@N07/), on Flickr

http://farm8.staticflickr.com/7117/7458800852_51d09fdd45.jpg (http://www.flickr.com/photos/50072175@N07/7458800852/)
IMG_1369 (http://www.flickr.com/photos/50072175@N07/7458800852/) by Christian Castillo1 (http://www.flickr.com/people/50072175@N07/), on Flickr

[Christian Castillo]

Okay, I used my scratch awl just like Carl did to check... it is just as I feared, I managed to scratch the middle dull area and the awl felt like it just wanted to dig in, but I cannot get the awl to scratch into the shinier side margins, the awl feels like its skating on ice in those parts, bummer.

Christian

[Matthew N. Masail]

sorry to hear that.

[Jack Curtis]

[QUOTE=Christian Castillo;1948194]Okay, I used my scratch awl just like Carl did to check... it is just as I feared, I managed to scratch the middle dull area and the awl felt like it just wanted to dig in, but I cannot get the awl to scratch into the shinier side margins, the awl feels like its skating on ice in those parts, bummer.[/QUOITE]

I'm way out of my depth here. Why is this a bummer?

[Matthew N. Masail]

I know very little about this too, but according to this link (if I understand correctly), and it makes sense, it mean the blade is not hardened in the middle, hence it needs to be tempered or it's useless.
http://stammerjohn.com/2011/08/21/plane-tune-up-8/

[David Weaver]

Just use it until it doesn't seem like it's hard enough and then if it's a hardness issue, reharden it then, first in quenched in oil, and if that doesn't work, then in water.

It looks like you've got a good length of iron to work through before you get to that middle.

[george wilson]

If the blade is too soft,tempering is NOT what you need to do. Tempering is what you do to SOFTEN the blade AFTER hardening,so that the blade is not so hard that it has no mechanical strength and the cutting edge crumbles.

The blade needs re hardening,BUT,with the bevel on it,you are guaranteed that the blade will warp because each side of the iron has different amounts of surface area. The bevel should be ground away till the end of the blade is just square. Then harden it and lastly,temper it.

First,do as David suggests and see if the blade cuts alright as it is.

[Christian Castillo]

Everyone, thanks for the help and support, thanks for the clarification George, the only problem is that I am currently not set up for re-hardening and tempering, my oven doesn't even work, and I dont have more than 45 dollars in the plane, the time and money spent to get it working is just not worth it to me. I'll try to see what I can work out with the person whom I purchased it from.

Christian

[Pat Barry]

Can't this just be used as is, that is assuming the cutting edge itself is consistent and the harder material? If the cutting edge is soft then you will need to re-harden it.

[Jack Curtis]

I know very little about this too, but according to this link (if I understand correctly), and it makes sense, it mean the blade is not hardened in the middle, hence it needs to be tempered or it's useless.
http://stammerjohn.com/2011/08/21/plane-tune-up-8/

Thanks, Matthew, makes sense. If I wanted to save the blade, I'd probably create a hollow by scooping out the unhardened middle stuff, just use the edges. That's what I do with Japanese blades, but the situation is different, the hollow in Japanese plane blades is made of hardened cutting steel, and the edges are actually tapped out.

[Tom Vanzant]

As this is a "vintage laminated Western plane blade" I don't think trying to re-harden it will do anything other than de-laminate the iron... ruining it. Help me here George.