Back Bevels on LA Planes

Re: Back Bevels on LA Planes

Denis Ch�nard, Orl�ans, Ont.


>I do the ruler trick. The 1-2 degree bevel it creates has not caused any problems.

DC

Re: Back Bevels on LA Planes

Frank D. in Montreal


>Just for the sake of discussion,

I'm no expert, but I agree about the clearance angle on LA planes; at 12 degrees I find it a bit too low sometimes, even with no back bevel; couldn't see making it any lower that's for sure.

However on a 20� bevel-up plane it could be an advantage to put a back bevel on for shooting end grain of really tough woods. That way you could keep a relatively low planing angle but increase the bevel angle for longer edge life.

Re: Back Bevels on LA Planes

Derek Cohen (in Perth, Australia)


>Hi Vlad

These are my thoughts, based on my logic, which can be quite perverted at times, so you are warned!! < grin >

As I understand it (so I have been told), the clearance angle needs to be about 7 degrees. Therefore, on the worst case scenario, a 12 degree bed, you have about 5 degrees to play with because a problem occures.

I routinely hone a 1 degree micro backbevel, ala David Charlesworth, on all my blades, both BU and BD. There is no problem with this at all.

There is no point in honing any other type of backbevel on a BU blade since the cutting angle is obtained from the bed angle + bevel angle. You cannot alter the cutting angle with a backbevel. It is the same as attempting to alter the cutting angle on a BD blade by grinding a steeper or shallower bevel. Whether the BD bevel is 25 or 30 degrees will not alter the cutting angle.

So in one way the question of a backbevel on BU planes is moot. Add a microbevel (which ensures a clean edge, or aids in removing the wire edge) as long as it is 5 degrees or under and you are fine. Anthing else is a waste of effort and harmful to boot.

Regards from Perth

Derek

Re: Back Bevels on LA Planes

Dave Mount


>In his second techniques book, David Charlesworth has an article that talks about using substantial (like 10 degree) back bevels on BU planes in order to achieve lower cutting angles; e.g., the primary bevel is made 20 degrees and the back 10, so the edge is an effective 30 degrees for edge retention, but the cutting angle is reduced because the primary bevel is lower. Because of minimum clearance issue you mention, this might be more effective for getting a BU bedded at 20 degrees (e.g., standard block) to perform like a low angle plane.

Caveat: I'm speaking only from what I've read, I've never actually used anything other than a very small backbevel (small as in 1-2 degrees).

Best,

Dave

Re: Back Bevels on LA Planes

Blaine Hollis


>I keep seeing references to the "ruler trick" but don't really know what it is. I'd be interested to know.

Re: Back Bevels on LA Planes

David Charlesworth


>David,

Spot on. I used the 10 degree back bevel in a 20 degree mitre plane to lower effective pitch. Bevel honed at 20 degrees.

Not sure it was worth the effort in hard and very hard woods.

It might be of benefit for very soft woods.

Re: Back Bevels on LA Planes

paul womack


>I used the 10 degree back bevel in a 20 degree mitre plane to lower effective pitch. Bevel honed at 20 degrees.

OK - this still gives 20 (bed) - 10 (back bevel) = 10 degrees relief or clearance.

The effective pitch is 29 + 20 = 40.

Of course, in a 12 degree bedded tool, this effective pitch can be achieved with a 40 - 12 = 28 degree bevel, which gives an almost identical edge strength to the back bevel example cited.

BTW, guessing, was the "mitre plane" a Karl Holtey A11?

BugBear