Squaring a boards edge with cambered plane iron?

[Pat Barry]

I have heard that people typically use an 8 inch radius camber on their plane blades. Does anyone know how much this means as to the convexness of the iron? I can't quite wrap my head around this math. In other words, how deep of groove does the blade cut?

[Steve Voigt]

An 8" radius might be appropriate for a jack plane. A jointer plane would have maybe .005" camber; I have no idea what the radius is.

[Joel Thomas Runyan]

The difference is that with a cambered iron you can make extremely small and extremely controlled adjustments, which not only allows you to dial in an almost perfect edge, but also allows you to do it in fewer passes and remove less material.

You can make extremely small and controlled adjustments, perfect edges, few passes etc. with a straight blade... it's easy. The principle of a camber removing less material at the edges of the blade is exactly the same as the edges of the mouth removing none.

[Steve Voigt]

You can make extremely small and controlled adjustments, perfect edges, few passes etc. with a straight blade... it's easy. The principle of a camber removing less material at the edges of the blade is exactly the same as the edges of the mouth removing none.

I don't think it is the same. A cambered iron, placed off-center, removes a shaving that is tapered in thickness across its width. planing only one side of the edge creates a step that will need to be removed in a subsequent pass. For my money, the former method is a more direct route to a satisfactory edge. But I agree that both methods work.

[Pedro Reyes]

I have heard that people typically use an 8 inch radius camber on their plane blades. Does anyone know how much this means as to the convexness of the iron? I can't quite wrap my head around this math. In other words, how deep of groove does the blade cut?

about a 16th

0.06275 to be exact according to the math. This is an 8" radius on a 2" wide iron.

@Steve, according to the math, 5 thou projection (i.e. 0.005") is equivalent to about 141" radius, this on a 2-3/8" blade.

Pedro

[Steve Voigt]

about a 16th

0.06275 to be exact according to the math. This is an 8" radius on a 2" wide iron.

@Steve, according to the math, 5 thou projection (i.e. 0.005") is equivalent to about 141" radius, this on a 2-3/8" blade.

Pedro

Hey Pedro,

Nerdy math question. For the 8" radius, I just did the math and I get the same .06275 that you got. But this is the amount of camber, not the depth of groove. For the depth of groove on a 45° plane, I'm thinking we would divide by root 2 to get around .044. Is that right?

Not that it matters on a jack. But I think it's relevant to the jointer. People often think that the hollow produced by a cambered iron will weaken the joint. But if my #'s are right, an .005 camber turns into an .0035 max depth of hollow when the iron is bedded. For a 1" board and a 2 3/8" iron, that would result in about an .0015 hollow, surely nothing that would compromise the strength of the joint.

[Pedro Reyes]

Hey Pedro,

Nerdy math question. For the 8" radius, I just did the math and I get the same .06275 that you got. But this is the amount of camber, not the depth of groove. For the depth of groove on a 45° plane, I'm thinking we would divide by root 2 to get around .044. Is that right?

Not that it matters on a jack. But I think it's relevant to the jointer. People often think that the hollow produced by a cambered iron will weaken the joint. But if my #'s are right, an .005 camber turns into an .0035 max depth of hollow when the iron is bedded. For a 1" board and a 2 3/8" iron, that would result in about an .0015 hollow, surely nothing that would compromise the strength of the joint.

I have not done the maths on the angled iron, but you are absolutely correct, I should have clarified that, the projections I provided are the height of the arc as measured on the blade, for depth of cut I believe you are also correct (for the 45 degree case).

Pedro

[Pat Barry]

It's an old technique, but I don't see it written about anymore. If an edge is a bit high you can square the edge by shifting the camber to the high side of the board.
Frequently some one would write about it, but I don't hear much about it.

I sharpen my irons pretty flat across, just relieving the edges to prevent plane tracks. I think I will go back to a more pronounced camber. I'm sure Pop Wood wrote about it back in the day.

What say yea?

Seems from the info Steve and Pedro provided you won't want a very pronounced camber at all. Maybe something around .005 to .010 or so. There mus be some methods of grinding and sharpening to keep the camber that low.

[david charlesworth]

Methods for producing a slight camber are demonstrated and explained on my Plane Sharpening DVD. (From L-N or me!)

The grind is 22 to 25 degrees, the shaping is done on an 800g stone at 30 or 33 degrees and the polish is done 2 degrees steeper.

NB wide roller honing guides not helpful. Eclipse , L-N and barrel roller on Veritas all work well.


Jet made a camber grinding jig for their Tormek clone but this is not essential.

The Odate crowning plate will produce a consistent hollow when dressing waterstones. Again not essential but nice!

.best wishes,
David Charlesworth

[Joel Thomas Runyan]

I don't think it is the same. A cambered iron, placed off-center, removes a shaving that is tapered in thickness across its width. planing only one side of the edge creates a step that will need to be removed in a subsequent pass. For my money, the former method is a more direct route to a satisfactory edge. But I agree that both methods work.

Have you tried the method to which I'm referring?

[Steve Voigt]

Have you tried the method to which I'm referring?

Joel, I started with your method when I learned to joint by hand, in about 1996 IIRC. I used it pretty continuously until about three years ago, when I started experimenting with the cambered iron method. So yeah, I tried the straight iron method for about 16 years. It works great. But it didn't take me long to decide that I preferred the cambered iron.

I don't think these methods are mutually exclusive. If an edge is badly out of square, I tilt the plane. If it's moderately out of square, I plane half the edge. For the finest adjustments, I use camber.

I have no interest in converting anyone. Lowell started the thread by asking for people's opinion on jointing with a cambered iron, so I gave mine. If you're happy with the way you work, that's great.

[Patrick Harper]

I believe that squaring an edge by tilting the plane is fairly difficult to control. The added benefit of a slightly convex edge is that it makes a spring joint across the width of the edge when making panels.

[Derek Cohen]

There are several pros and cons, but overall a straight edge appears to me to edge out the cambered blade.

A cambered edge suits if you plan to joint the edges of boards individually. However, a straight blade can do this just as well - just a different technique.

On the other hand, one cannot use a cambered blade for jointing if you match plane. A straight blade is preferred.

Shooting an a long edge is something I would rather do with a straight blade.

Similarly, if cleaning up an edge off a power jointer, a straight edge is preferred.

Regards from Perth

Derek

[Derek Cohen]

I believe that squaring an edge by tilting the plane is fairly difficult to control. The added benefit of a slightly convex edge is that it makes a spring joint across the width of the edge when making panels.

Squaring an edge by tilting a blade is straight forward. One always follows up with a full shaving along the length of the board.

A spring joint is helpful, but this need to be slight - very slight - and is not across the width but along the length.

Regards from Perth

Derek