Plane Blades: Camber vs. Rounded Corners

[ExCrusader]

Hi everyone. Yesterday I had some red oak to smooth, about 6 inches wide. I bought an extra 25 blade for my Veritas Bevel Up Jack that I am using as a higher angle blade for smoothing. I know how, and why, you put camber on a plane blade (it took me a couple times, but David Charlesworth's explanation from his videos finally sunk in). But I have also read somewhere that you can round the corners to eliminate plane tracks as well (I think Leonard Lee's book). I tried that yesterday, the blade was sharpened strait with rounded off corners. Worked great for me, not a plane track in sight.

Basically that rambling story was my way of asking if there are any advantages to rounding or cambering a smoothing blade and why you would choose one over the other? Unless there is a super compelling reason, I am thinking of sticking with rounding, because it is extremely easy.

[JimT11]

When you get to smoothers, the thickness of the shaving is so thin that a very small camber is required. The radius required to give that camber is large and so hard to do with a jig. The jig would have to be very, very long. Rounding/dubbing the corners is easier and works fine, maybe better. For an indepth study on camber see..

http://www3.telus.net/BrentBeach/Sharpen/camber.html

Jim

[Jayked]

You might want to check out p.12 of the October PW, where Chris Schwartz answers a reader's question about camber on a BU plane. His answer is more or less do what works.
Jim

[Frank D.]

I agree to do what works for you.
Giving a camber to a smoothing plane blade is not difficult though. As Charlesworth show in several of his books/articles/videos, you don't need a special guide. Finger pressure on various spoints of the blade for the appropriate number of strokes on any sharpening guide works. A little trial and error, and you can easily learn how to get a camber of less than one thousandth of an inch. You don't measure blade camber by mesuring the blade...you measure the shavings. When you have, say a shaving of one thousandth, and the shaving disappears into thin air towards the edges of the blade, you know you have a camber of about one thousandth. I aim for a camber of slightly less than this. I find that visually, rounded corners might do the trick when planing, but if you sand film finishes after each coat like I do, the differences in depth of cut tend to reappear as you sand the finish or as the surface becomes glossy. I've never had a problem with a cambered blade.

[ERic In Nova Scotia]

I think the benefit of rounded edges is a wider shaving but requires the blade PERFECTLY squarely set blade. A cambered blade will give a narrower shaving, but is more forgiving since there is no such thing as squaring to a round edge so long as edge of the blade is not cutting into the wood.

[Frank D.]

I think the benefit of rounded edges is a wider shaving but requires the blade PERFECTLY squarely set blade. A cambered blade will give a narrower shaving, but is more forgiving since there is no such thing as squaring to a round edge so long as edge of the blade is not cutting into the wood.

Hey Eric,
Shavings from a cambered blade on a smoother aren't like the shavings from a cambered blade on a jack or scrub. The shavings on a smoother should go all the way to the edges of the blade (in other words, they should be full width). If you look at them out of the plane, they appear to taper off to zero, but at a few ten-thousandths, more or less, at the edges, they are still full-width, or so close as to be just about full-width (when you think of it, rounded edges reduce the shaving width too, although, similarly, not very significantly). If all this doesn't sound too precise, that's because it's not; all you need is some relief toward the edges (a shallower cut) so the next overlapping cut will not leave a track. This works exactly like rounded edges, but it's simply a more gradual transition. I also think that a slight camber is more demanding when it comes to squaring the edge, because when you have a shaving that's only a few tenths at the edges, it doesn't take much for part of the shaving to disappear (forcing you to make an adjustment). With rounded edges, you can still be a little off and the shaving will be full width.

[ERic In Nova Scotia]

Interesting point Frank. I could be guilty of over cambering a little at times, under cambering at others. You've got me feeling I should/could be a little more demanding of myself.

Often times I'll be happy if I get a shaving half the width of the blade. Ha ha shame on me.

[KenL]

Darren,

I just take the smallest amount off the corners as you describe. I use my BU smoother exclusively as a smoother; my jack for shooting mitres, so I do not want a camber on the jack. I find that a straight blade with rounded corners does a good job smoothing with minimal issues with "tracks" the only cambered blade that I have is in my scrub plane!!

Ken

[michaely]

The only plane on which I scribe the desired camber with a marker and compass is my scrub plane; with everything else I just 'ease the corners' with fingertip pressure on the final grit waterstones, and get sufficient easing with using the standard/straight roller that comes with the mark 2 Lee Valley honing jig.

This is practice I've just fallen into and not researched the pro and con on.

But I am particular on making sure I am sharpening an edge that is 90 degrees to the sides of the blade and that the projection of the blade in the plane is not skewed to either side.

good luck

michael

[derekcohen]

For what it's worth, I camber the blades of smoothers (as well as most other bench planes). I have tried a straight blade and rounding a corner - even quite markedly - and the plane will still leave tracks. Look in raking light to check for yourself. These show up later when you finish. Run your hand over the surface. The other aspect I dislike about straight blades is that one must keep the blade perfectly parallel to the surface - more set up - while a camber is much less fussy.

A fine camber is far better. The aim is a full width shaving, so you are only removing the thickness of a shaving at the sides of the blade. Note that this only works to the depth of the camber - if you take a rank shaving you expose the straight side of the blade, and then leave a track. So consider the depth of the shavings you plane to make with the blade when you hone a camber on it.

Regards from Perth

Derek