Problem with Lee-Valley low angle block plane

I bought one of the Lee-Valley low angle block planes a year or so back. In general, I'm very happy with it but lately I've started to have an interesting problem with it.
I generally keep it set for a very small cut, with the blade just barely sticking out and the mouth closed down to a sliver. What I've started noticing lately is that after I've used it for a while, the mouth tends to close down until there's no slot left at all (at which point it stops cutting). I tighten up the mouth adjuster knob as tight as I can (by hand), but it keeps slipping closed slowly.
Anybody seen this before?
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Take off the sliding mouthpiece and make sure that there is no crud in there or file off any burs on the mouth puiece or the mating surface.
Idunno, but that is the first place I would look.
-Steve

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Roy Smith wrote:

I've had a similar problem with block planes before, but I finally realized that I was causing the problem with how I gripped the plane. If you put your index finger on the knob, it's possible in use to actually loosen the knob.
If that's not the case, you should contact Lee Valley. They have such oustanding customer service that I'm sure they can figure out a way to help.
Chuck Vance
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Hmmm. Interesting thought, and that may indeed be exactly what I'm doing. But, isn't that what the knob is there for? It's even got a nice index-finger-tip-sized depression machined into the top of it to encourage such use.
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If you haven't already put a slight bevel on the leading edge of the bottom of the mouth, that might help.
JP
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wrote:

Yes, it is the best pace for your index finger to go (and I assume it is intended that way). You just need to be aware of the fact that you can wind up torquing it enough to loosen it. Play around with your grip and notice what your finger does when it's in position.
Chuck Vance
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Good advice in many circumstances ;)
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