Plane Mouths: How Perfect Must They Be?

[Joe Vincent]

I went to a flea market recently and saw a few adjustable mouth block planes that I passed on for various reasons, but a couple of them had some minor jaggedness around their mouths. I wonder how much unevenness or jaggedness is acceptable on an adjustable mouth block plane? And does it make it more or less acceptable based on whether the defects are on the front or the back of the mouth?

Thanks

[Mike Henderson]

For block planes roughness in the mouth usually doesn't make a lot of difference. Of course, it depends a lot of how rough it is.

For cutting end grain it doesn't make any difference.

For cutting face grain it could mean that you'd get a bit more tearout for certain kind of work. But for critical work, you could select a different plane. I've often grabbed a block plane and used it, only to discover later that the mouth was wide open because of the way I was using it earlier. And most of the time, I never noticed any difference.

Mike

[Joel Goodman]

The front of the mouth is what matters. On a adjustable block can't you just remove the knob at the front, and then lift out the cam adjuster and then remove the moveable section (I don't know the correct name) and then dress the back edge of it (which is the front of the mouth) with a file and/or a stone (or sandpaper on glass)? This takes longer to describe than to do.

One of the nice things about block planes is that they are easy to tune.

[Joe Vincent]

Thanks for the insight. Good point about fixing the adjustable plate in front of the mouth, Joel. I guess it depends on how much needs to be fixed so that the mouth can still get tight.