Bevel-up smoother question

[Paul Cahill]

I just received the June FWW and in his review on smoothing planes, Chris Gochnour made the statement that for bevel-up smoothers the blade requires more camber to eliminate tracks. I don't have enough experience with planes to have noticed this, and I haven't read about it anywhere. Also, I can't visualize why this would be so.
I figured this is the perfect place to get to the heart of the matter.
Thanks.

[Adam Cormier]

Hey Paul,

There will be some subject matter experts responding in due time I'm sure. I am by no means one of them but have experience with several hand planes, including 3 bevel up planes. I am not sure I fully understand your question though. Are you just asking about cambering a blade to eliminate tracks or asking why a bevel up smoother would require more camber than a bevel down smoother?

Personally, I put a good camber on my jack plane which I use in lieu of a scrub plane. I do this because I am removing more material in less passes and this avoids those deep tracks that you are talking about. On my jointer and smoother plane though (1 is bevel up and 1 is bevel down) I use much less of a camber due to the fact that I am only removing small amounts of material on each pass.

[Paul Cahill]

Hey Paul,
I am not sure I fully understand your question though. Are you just asking about cambering a blade to eliminate tracks or asking why a bevel up smoother would require more camber than a bevel down smoother?


My question is the latter - why would a bevel up smoother require more camber than a bevel down smoother?
Thanks

[Andrew Gibson]

Think about the blade in relation to the surface. You have a camber on your iron. In a bevel down plane the iron is at 45* or so to the work surface. In a bevel up plane it is at say 12*. the lower the blade is bedded, the effective camber is reduced. In other words as the bevel gets closer to parallel to the work, the corners also get closer.

take a clock. now start laying it flat on a table. as the clock gets closer to laying flat, 3 and 9 O'Clock get closer and closer to the table... 6 O'Clock is the middle of your cambered iron and 3 and 9 O'Clock are the edges.

hope that makes sense.

[Greg Wease]

Derek Cohen has the complete answer here:

http://www.inthewoodshop.com/WoodworkTechniques/TheSecretToCamberinBUPlaneBlades.html

[Paul Cahill]

OK, I get it now - nicely explained.
Thanks,
Paul

[Steve Elliott]

Andrew and Derek have it just right. In addition to Derek's analysis of how much metal is removed, here's a piece of dry technical stuff that shows the math that links the amount of blade camber to the maximum thickness of shaving the blade can take without leaving tracks. As you already know, it depends on the bed angle of the plane.

In the drawing below, the term “actual camber” refers to the distance the center of the blade extends past the corners of the blade, in this case 1/16 of an inch. The term “effective camber” describes the thickest shaving the blade will be able to take without leaving tracks. For the bevel-up smoother in this example, its 12 degree bed angle results in a maximum shaving thickness of thirteen thousandths of an inch.
http://planetuning.infillplane.com/assets/images/BUS_Camber04.gif

[Will Blick]

great stuff Derek and Steve....

just to be clear, if you use a jointer plane for edge planing priror to glue-up, you NEVER camber these blades, right? I did not read that on Dereks site, so just making sure...

Also, for smoothers, I never noticed any tracks, and I don't camber intentionally.... but I do apply a bit of extra pressure at the edges to prevent sharp corners... I assume this was cambering enough to prevent tracks, cause I have never seen them.... is this what was occurring?

[Andrae Covington]

great stuff Derek and Steve....

just to be clear, if you use a jointer plane for edge planing priror to glue-up, you NEVER camber these blades, right? I did not read that on Dereks site, so just making sure...

Actually some people do camber their jointer plane blades; I have done both, currently mine is cambered. While edge jointing with a cambered blade, you can adjust an out-of-square edge by shifting the plane laterally relative to the edge. If, for example, the edge is too high on the left side, offsetting the plane to the left will put the middle of the camber at the place that needs the most removed, taking the thickest shaving there. Hope that makes sense, a diagram would be clearer. Once the edge is square all along and you have taken a pass with the plane centered, a slight hollow through the middle of the narrow face is not going to matter in a glue-up. The visible edges will be tight.



Also, for smoothers, I never noticed any tracks, and I don't camber intentionally.... but I do apply a bit of extra pressure at the edges to prevent sharp corners... I assume this was cambering enough to prevent tracks, cause I have never seen them.... is this what was occurring?Sounds right. Another approach is to file a slight radius on the corners. I have found with my bevel-up smoother that I need to file a larger radius than what most people talk about with bevel-down planes. This seems to correlate with needing a larger camber for the same effect.

[Will Blick]

> a slight hollow through the middle of the narrow face is not going to matter in a glue-up. The visible edges will be tight.

true....but I edge plane both edges at the same time, bottoms touching, then any planing errors are self correcting during glue up, so I prefer straight edge jointer blades... so I guess different applications for planes, different camber strategies...

I think I will round my corners though on my other planes vs. cambering them... I like the flatness of a straight edge for sharpening....

[Mike Holbrook]

I believe there is another factor that can come into play with some planes. We know that hand held card scrapers can be bent into a slight arch such that the edges are slightly raised reducing or eliminating visible edges. As a matter of fact I believe some use card scrapers to remove the edges left by planes.

Gary Blum makes a little different plane. He has designed his own "frog" which holds a much smaller, thinner, more flexible blade. The blade is reinforced by the very stout frog. Gary will make his frog with a little camber in it so that when pressure is applied to the blade with the tightening mechanism the blade is slightly bent like hand bent scraper blades. Gary even offers a special scraper frog that can be used with his planes.

I wonder if it is possible to place a little arch in some of the thinner plane blades simply by tightening up on them with the frog? Plane blade adjustment/tightening systems that run a bolt into the back of the blade might do this when used with thinner blades, for instance. Chip breakers may very well prevent this from happening with some planes. I think many Japanese planes/blades are designed with tapered edges, sort of "hollowed backs" and two different steels. The unique features of Japanese "blades" may also affect how much, if any, edge marking they leave.

[george wilson]

Simply camber the BU blade till the corners of the blade don't leave tracks when set to take a fine cut. The finer the cut,the less camber needed.