Back bevel plan mouth, only 1 way?

[Tim Reagan]

This is a bit of a follow up question from http://www.sawmillcreek.org/showthread.php?t=85107. The picture from Johnny at Rexmill shows the bevel going toward the front top of the plane at 12 degrees. Couldn't you also make the bevel point towards the front bottom, because thats where my blade hits? Also, why 15 degrees is recommended? The picture is from Johnny's website: https://home.comcast.net/~rexmill/planes101/tuneup/tuneup.htm
thanks.

[Robert Loss]

Couldn't you also make the bevel point towards the front bottom, because thats where my blade hits?

If your blade hits, it sounds like the mouth needs opening up but still keep the same 15 front top mouth bevel. BUT before recommending you do this it would be worth finding out why it hits? Assuming the blade is correctly fitted, are you using a new or different blade? If so did the old blade fit correctly?

A top front orient bevel is important for proper chip clearance - a bottom front bevel will tend to clog easier especially when tight curlies are being formed.

[Brian Kent]

Here is another plan with a mouth as you described.

http://linuxplane.awardspace.com/Plans.htm

I have also used a front mouth straight up.

Maybe the choice is affected by the chip breaker shape in your drawing.

Brian

[Tim Reagan]

The blade is hitting I think because the Stanley #4 I have is known to have a small mouth I'm told and I bought a thicker lv blade. The original blade only has about 1/4 left of usable steel. The chip clearance reason makes some sense.

[Jim Koepke]

Another reason is the sole in front of the mouth is supposed to hold the wood down in front of the cut.

Having the mouth's edge bevel facing down would in effect make the tight mouth, wanted for fine work, unobtainable.

The mouth would be open but the throat would be closed.

Draw some pictures, if need be, go to extremes and it may be come clear what is happening with the geometry.

If you file a bevel on the front, you will likely find you have knocked a few thousands off the front of the mouth in the process.

I just worked on a plane doing this. The mouth was not square. This plane is my tight mouth No.5, so it was a little troublesome at times. I secured it in a vise at about 75°. Then using a single cut smoothing file it was given about ten strokes and checked. this was done with the frog mounted so a blade could be popped in to check how it looked.

Now, the mouth is square and beveled. The gap between the blade and the front of the mouth is parallel when the lateral adjustment is set almost center to take shavings that are even from side to side.

I had minimal tear out when going against the grain on some cedar and pine even though the blade needs a bit of honing.

jim

[Eddie Darby]

The problem with a plane is that it is easy to open a mouth, but real hard to shut it! Uh that not be for planes only! :-)

I have an old LV Paragon Jack plane that I put a LN extra thick blade in, and I had to open up the mouth so that the blade could make contact with the wood.

I made sure that the frog was fitted well, and seated correctly with the plane blade resting on the plane sole for maximum support, before opening up the mouth.

One of two options I had was that I could really open the mouth so that I could get some rough work done, or I could leave it as a small opening to do fine work. I decided as a first step to just open the mouth up enough to do fine work, since that is the planes primary use for me. So far I haven't had to open it any more further, but if need be then out will come the file. I just like the extra support that the blade gets by being nested up a little bit against the sole of the plane as well as that from the frog. If I need to do more rough work then I will open up the mouth, and then move the frog forward, to tighten-up the mouth for fine work, but loose that little extra support. No big deal.

The 12 degree slant to the mouth in the diagram you provided is for the mouth of the plane to allow the chips to clear-up that area, rather than choking the plane. If the chips clear o-kay, then it is not needed. In the diagram you can see that the leading edge of the mouth is not touched, so as to not open up the mouth. The top edge is beveled so that there is clearance for the chip-breaker hump to throw the shaving forward into the beveled area. The new style chip-breakers by LN and Hock don't have this hump, and so require a little less clearance in this area.

I should add that the plane is used for curly maple, and so having the mouth close to the blade aids in compressing the tear-out prone wood, to keep cracks from wildly getting out of control ahead of the cutting edge. I guess you could say that it tames things down. In regular tear free wood, I do not adjust the mouth opening finely for fine shavings, and open it up for bigger shavings. I use one mouth opening for all regular wood requirements.

This is the critical role that the leading edge of the mouth plays, and is why when flattening/lapping a planes sole, the leading edge of the sole, the trailing edge of the sole, and the leading edge of the mouth of the plane are the 3 critical areas. Missing on getting the leading edge of the sole or the trailing edge of the sole right will change the planes length, reducing it, but missing out on the mouth will affect the ability to handle various types of woods that pose this tear-out problem.

Hope this helps.

Now to hurt: If chip-breakers break shavings, then why aren't they called shavings-breakers?:confused: ......:eek: ......:D