Tuesday, May 13, 2014

Edge Failure

Ugh. This is not a fun post to write. I did say, at the beginning of my skew mitre project, that I might fail…and I have, at least temporarily. Or, to be more precise, steel failed me.
So: I intended to use a vintage W. Butcher iron, that I'm pretty sure was never used. It took a lot of work to grind it to the proper shape and coarsely flatten the back:

You can see that the back is slightly concave, so there is a silver-dollar-size area above the cutting edge that is not flattened. But that's OK. There is a good 3/4" of flat steel above the cutting edge, probably enough to last a lifetime, and the sides where the wedge prongs make contact are also flat.

Next, I polished the back with successively finer grits of sandpaper, then moved to my oil stones, working the back until it was smooth enough to take a selfie in the reflection:

Then I made the wedge. At this point, the plane is not finished--the wedge is not shaped, and the plane body hasn't been shaped and chamfered--but the wedge fits great.

Now I was ready for some test cuts, and this is where everything went south. After just a couple passes on end grain, I started to get ugly scratches. What happened was that the cutting edge was folding over, microfracturing. I increased the bevel angle to about 27°, which is as high as I can go in this low angle (38°) plane before I start to have clearance angle problems. This helped a little, but the problem remained. The blade is simply too soft.

So, for now I am stymied on this plane, but all is not lost. I'm determined to make some lemonade from these lemons. Last summer, I started building a small brake drum forge for basic blacksmithing operations…like hardening steel. I never quite finished, but this blade failure was just the kick in ass I needed to get back to the forge. I've got it done, and in a week or so I'll give it a test run. If all goes as planned, I'll see if I can re-harden this iron. And if that doesn't work, I'll try making a new iron from scratch. Stay tuned!