Convex no. 4 sole — how to flatten?
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Does anyone have a suggestion about how to flatten a Stanley no. 4 sole that is convex (bulges out slightly) across its width?
I flattened it best I could when I bought it, but it’s never actually take a fine shaving the way I think a smoother should. I think what happened is that the sole rocked along this convex portion and so I never actually flattened it.
Now that I also have a 4-1/2, I can compare the 2 planes and I find that the 4-1/2 takes a finer, full width shaving. I inspected its sole with a straightedge and it has a slightly concave sole across its width. My no. 4 is the opposite.
I’ve already learned the hard way that trying to lap a convex surface to flatness is futile. So I assume there has to be a different technique for those surfaces. Does anyone know? 🙂 Thanks.
The only way I know is how I have done it before and that is the lap method. I have a piece of 1/2″ float glass: 6″ X 36″ and start off with 60 grit sanding belt cloth sand paper adhered to the glass. Then a lot of elbow grease. You could also use 3/4″ MDF instead of glass
You will need to adjust your stroke as it is fairly important to be perpendicular to the sides.
To help, you could have a straight wood runner attached along side the glass or MDF to provide some “guidance” for your stroke until you get flat and square.
Then switch to 180 grit to remove the heavier grit marks.
Thanks Brett. I’ve given it some thought and I think I have a method. But I want to try it first and then I’ll report here. But basically, I think the objective is to knock down the bulge first until there is a slight hollow instead, and THEN lap flat as usual. The trick is how to do that efficiently. I’ll post again when I have some results.
Ok, here is what I figured out. It worked pretty well. I think the pictures explain it all, but here it is:
The theory is that a slightly concave sole can be lapped flat, whereas a convex sole cannot. So I created a concave sole from convex, and then lapped as usual. It worked 🙂
I taped 2 guide rails to my granite slab for my #4 to fit in. Then I glued a 3/4″ strip of sandpaper down the middle. This created a concavity down the middle of the sole. Then I used a slightly wider sandpaper strip (about 1-1/8″) to lap that concavity and create a wider one. I repeated once more using a 1-3/4″ strip which gave me the full width concavity I needed (disregarding the 3/16″ or so of worn edge-sole on each side). Finally I lapped normally, giving me the correct wear pattern (wear on the left and the right, increasing toward the middle).
Things I’d do differently: just to use less strokes on the thinner strip. It would have saved time in the final lapping.
Looks like a good solution. Were you able to keep the bottom perpendicular to the sides?
I’ve actually never checked it for square before. I did check it since you asked. And it is out of square. BUT! I thought about it for a while and my honest evaluation is that it was always out of square. It’s my first plane and it’s always behaved the same way even before I fettle’d it. I’ve always had to move the adjustment lever the same amount (which is quite a bit to the right). I think that’s why. I think that if you keep steady, even pressure directly above the sandpaper strip, it’ll be fine. You could also layer up tape along the sides of the sandpaper to just below its surface to minimize rocking. Anyway it worked for me and I’d do it again for sure.
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