Thanks everyone..
There's one inherent problem I think with the idea of sharpening from an already planed profile. I understand where the idea came from, and up to recently I thought the idea would work to. But, really I think the idea has to be abandoned.Quote:
Originally Posted by LineLefty
Unlike straight edged blades a profiled blade will change as the angle it presents to the wood changes. I'll attach some pictures to show my point.
Yesterday I managed(only just) to get a larger profile going. It has deeper valleys and hills than most, so it should show my point better. See picture 1.
In picture 2 I've removed the plane body from the picture and just braced the blade at 50 degrees, which is the bed angle for the plane. ie. the effective pitch ; the angle the blade cuts at. Right ?
However, we don't sharpen blades at their Effective pitches. We sharpen at about 30 (or whatever) degrees right ? So, I've dropped the angle to about 30 degrees. Braced it at that point, and taken a photo of it which is picture 3. In particular, look at that sharp spur part of the blade on the left. It no longer touches the wood.
If we were to coat a pre-cut profile with some abrasive, like a compound or sandpaper, and took our blade to it, we'd only get an edge if you were willing to accept sharpening it at its bed angle ! 50 degrees in this case. Try and sharpen it any lower and the hills (like that spur) wont get any attention what so ever.
And of course you can't sharpen it at its bed angle. It just won't work, because when you put it back into the plane you'll have no clearence between the bevel and the wood you planing. The blade will just skip all the time. It just wouldn't work.
Now, I reakon the idea of sharpening a blade off a pre-cut moulding may work but only if it was the profile you get when you lower it to 30 degrees. But how could you ever plane out a profile like that? Your plane only cuts at 50 degrees......get my drift?