Mouth of a Hand Plane

You can adjust the frog on some hand planes to make the mouth smaller when you are making fine strokes. My question: why does it make a difference whether the mouth of a hand plane is larger or smaller? Does it make the cut any smoother?
Thanks,
S.
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samson wrote:

It can help reduce tearout in some cases, but it's not strictly necessary and it needs to be pretty small to be effective at this. See this article by Chris Schwarz.
http://blog.lostartpress.com/default.aspx#a3f6a4a90-e2f4-4021-b0bb-a890659c6d1f
Chris F.
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says...

Thanks for the good info, Chris (and the good blog site). Much appreciated.
S.
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It makes a difference, the why is a bit complicated.
Yes, a "tighter" mouth "can" produce finer shavings and a smoother cut.
If you have the time take a look at
http://www.amgron.clara.net /
Jeff's Planing Notes will tell you more than youy want to know about the mechanics of the cutting action of a wood plane - it's a lot more complicated than most of us realize (or want to know).
You can also read
http://members.shaw.ca/petermichaux/workshop/BevelDownSharpening.html
which is really about edge angles but can help one understand waht's going on when the plane blade shears (or breaks) wood.
Regards.
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On Tue, 18 Mar 2008 16:20:33 -0500, Tom B

If planing doesn't interest you have a look at these dovetails from Jeff's site: http://www.amgron.clara.net/dovetails/moorishdovetails/moorishindex.htm
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snipped-for-privacy@nospam.mail.airmail.net says...

Good information, Tom. Thanks.
S.
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snipped-for-privacy@samson.net says...

The idea is that it a smaller throat should reduce chatter (and tear-out?) when going over knots and inter-locked grain.
In my experience holding the plane at an angle to the cut you're making and setting to an even finer cut is a lot more effective at stopping chatter than the most finely tuned throat. Maybe my technique is to blame...
-P.
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Yes. When working against the grain the tendency is for the edge to get under the fibres. The backface lifts the fibres so they are rived instead of being cleanly cut. The riving (splitting) and eventual breaking causes the rough tearout.
A very closely set mouth acts so that its front lip presses down on the fibres, preventing them from being raised and allows the edge to reach the fibres and cut them.
Jeff
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