Back Bevel on bevel up planes

[Pedro Reyes]

Long ago I bought a nice little used 103 at a tool meet. Love the little bugger, enough that I got a new blade for it.

This is a fixed mouth plane, so I started wondering if I could close the mouth by using a back bevel.

I imagine that last statement, may confuse someone, but it would in fact close the mouth. It was immediately very clear to me, which may make it hard for me to explain in words. But here is a shot... if you take a bevel up plane and push the iron out all the way, eventually the mouth will close completely (with the iron projecting too much), now if you took this plane and planed a diamond plate, the iron would in time be shaved flush with the sole, creating a back bevel. Well imagine you do this but stop just before being flush, then back off the iron to have light through the mouth...:confused: ?

Anyway, I am trying to see what the more experienced think about the effects this has on the cutting dynamics. Basically having a very accute angle in the iron, and the trailing edge almost touching the wood, also the cutting edge is farther from the support of the back of the mouth.

/p

[Sam Takeuchi]

Blade will wear out very fast. Basically a large part of the blade is being constantly abrased against wood surface. Just to get rid of wear bevel, you'll have to take serious amount of metal from the back bevel before you even begin the normal sharpening procedure.

Edge being really far out of the iron bed, it might chatter as well, especially if there is any gap between the bed and blade.

Honestly I don't think it's worth doing all this just to close the mouth. You'll be using up your blade in a very short time. Unless you spend a lot of time sharpening to make sure all wear bevel is gone, it won't cut well either. For the price of replacement blade, you can pick up a 9 1/2 or 60 1/2 on ebay.

[Robert Rozaieski]

You will reduce the clearance angle by back beveling a bevel up plane. If you reduce the clearance angle by too much, the plane basically just won't cut. A bevel up plane is typically already bedded very low (20 degrees maybe). You need at least 10-15 degrees of clearance angle for the plane to function so back bevel any more than 5 to 10 degrees and the plane won't work. I wouldn't recommend it.

[Pedro Reyes]

Blade will wear out very fast. Basically a large part of the blade is being constantly abrased against wood surface. .... For the price of replacement blade, you can pick up a 9 1/2 or 60 1/2 on ebay.

Sam,

The explanation was just for some to visualize, you would sharpen the back bevel at something less than 12 degrees (the bed) say 10, which would give you a cleareance of 2 degrees.

I already have those other planes, I was looking to do somthing with this one.

But I can see the chatter issue potentially appearing, also the angle formed by the bevel and the back bevel is not 25 anymore, but something more like 35, which some think is harder to get "as sharp"

/p

[Tim Put]

Wood is more compressible than it might at first seem. You really do need at least 10 degrees of clearance angle. Two degrees is not enough.

[Pedro Reyes]

You will reduce the clearance angle by back beveling a bevel up plane. If you reduce the clearance angle by too much, the plane basically just won't cut.

Rob,

I trust what you say is true. But if I can push a chisel and cut, say at 1 degree tilt, it would cut, we all agree. The clearance angle here is well, 1 degree.

What is different on a plane?

/p

[Danny Burns]

The only time you need to have a tight mouth opening is when you are tackling very difficult grain. All the rest of the time, you can get the job done with a wide mouth opening.

I like to have a least 5 degrees of clearance myself, but have not tried to go any further.
All you have to loose is some time and abrasive, along with some steel. Go for it and let us know your results. Shouldn't be to hard if you need more clearance, to back off the angle a bit.

If you have a 20 degree seating on your plane, and then a 25 degree primary bevel on the blade, then a 10 degree back bevel should help with edge durability by increasing the total bevel angle to something in the area of 35 degrees.

One minor downside is that back bevels do involve faster wear on the blade, since more metal has to be removed when sharpening, and more abrasives.

Another option is to glue a brass shim into the plane to just advance the blade forward.

[Randy Klein]

For my LV LA Jack that I use for shooting, I put a 3 degree back bevel on bevel up planes that are bedded at 12 degrees. I do this so I can a low (23 degree) front bevel, but it will have the "strength" of a 26 degree bevel.

Like the others said, you get a back bevel for free by just planing. But when that happens, we call it a wear bevel. And from personal experience, when that wear bevel gets large enough to interfere with the clearance, the plane stops cutting. This is why I hone a back bevel on the BU planes, to get rid of the previous wear bevel.

[Michael Faurot]

Yesterday I did some clean-up and rehab on a 103 (see attached pictures) and got it working really well. So well, in fact, I was using it today to do some smoothing on Purpleheart. I was impressed that it was able to do the job with no tear out.

As you may notice in the pictures, the mouth on this plane isn't particularly tight, but it's not Mick Jagger big either. :) So having a really tight mouth isn't all that essential. What's doing the trick, is the blade. I made it from 1/8" thick O1 tool steel, and that seems to be a huge improvement over the original thin blade.

[Mike Henderson]

For my LV LA Jack that I use for shooting, I put a 3 degree back bevel on bevel up planes that are bedded at 12 degrees. I do this so I can a low (23 degree) front bevel, but it will have the "strength" of a 26 degree bevel.

Like the others said, you get a back bevel for free by just planing. But when that happens, we call it a wear bevel. And from personal experience, when that wear bevel gets large enough to interfere with the clearance, the plane stops cutting. This is why I hone a back bevel on the BU planes, to get rid of the previous wear bevel.
I agree with Randy. What he's describing is a "trick" that allows you to get a lower effective angle on your bevel up plane, while maintaining the strength of the bevel.

If I recall, a 103 is a "high" angle plane - the 102 is a low angle. So you should have lots of clearance angle on the blade unless you put a really heavy back bevel.

Mike

[I have a friend who puts a 5* back bevel on his low angle block plane, then sharpens the primary bevel to 20*. So he gets a 20* effective cutting angle and still has enough clearance angle - and his bevel angle is 25*, same as most low angle block planes. I haven't done this on my low angle but he claims it makes a big difference when working end grain.]