Why you need a well cambered blade on a No7

[Corset]

i bought an oshio odate cambered diamond stone on the cheap off ebay to see what the deal with is a very slight cambered blade. i have always done it a bit by hand for a few extra stokes on the edges, but its nice to have stone that does it easily. I can concur that i am a fan of a slight camber. i personally prefer a number 8 over the 7 as its like a battleship of plane. But i wont be going back to a flat iron. This stone and a strop have really improved my jointing. I am not into the gurus but this seems to work for me! Once the camber is done i tend to use oilstones and then periodically use the diamond stone. Very happy. Not sure it will suit the sharpening gurus but it works for me

 

[Trafalgar]

All my irons tend to develop a little curve on the end over time. I have to work to keep the smoother straight across with the corners taken off. I don't want to take 3/4" wide shavings (off the nose of the iron) with a smoothing plane when it's set to take very light passes. I'm not necessarily in the camp that says a No. 7 needs to be 'well cambered,' a little is certainly useful, but the curve really needs to be a very regular one -- not shaped like an amoeba, lopsided, etc. It can't look like a lancet-head window. Has to be a section of a circle. If not, then even match jointing mating edges is going to be more problematic than it should be.

 

[thetyreman]

I don't bother with a curve on the blade on a no7, I just very slightly round the very outer edges, it works fine that way.

 

[Phil Pascoe]

... the curve really needs to be a very regular one -- not shaped like an amoeba, lopsided, etc. It can't look like a lancet-head window. Has to be a section of a circle. If not, then even match jointing mating edges is going to be more problematic than it should be.

This is what I don't quite get. If the edge of your blade is a very, very shallow perfect arc it would be fine for an edge to edge joint, it would allow you to compress the two outer edges for a perfect joint - but only if you used the dead centre of the blade. Why not just use a straight grind in the first place?
I am thinking of use on a shooting board rather than freehand where the planing tends to take place in the centre of the blade anyway.

 

[Trafalgar]

This is what I don't quite get. If the edge of your blade is a very, very shallow perfect arc it would be fine for an edge to edge joint, it would allow you to compress the two outer edges for a perfect joint - but only if you used the dead centre of the blade. Why not just use a straight grind in the first place?
I am thinking of use on a shooting board rather than freehand where the planing tends to take place in the centre of the blade anyway.

Parts of the arc are used to take down the high side of an edge, otherwise, you're right. The curvature is very slight in my world. Not really detectable without offering it to a straightedge for comparison.

 

[bentontool]

This is what I don't quite get. If the edge of your blade is a very, very shallow perfect arc it would be fine for an edge to edge joint, it would allow you to compress the two outer edges for a perfect joint - but only if you used the dead centre of the blade. Why not just use a straight grind in the first place?
I am thinking of use on a shooting board rather than freehand where the planing tends to take place in the centre of the blade anyway.

Yes...

 

[pe2dave]

Sure I read a 7" arc gave a fair curvature.

 

[Phil Pascoe]

A 7" arc would give you a scrub plane, and quite a vicious one at that.

 

[pe2dave]

A 7" arc would give you a scrub plane, and quite a vicious one at that.

I was going to say where I heard it, and yes, it was for a scrub. Unsure what purpose a lesser curvature would serve Phil?

 

[Phil Pascoe]

Many people use very slightly cambered blades to avoid the edges digging in and leaving tram lines, others just round the corners very slightly.

 

[pe2dave]

Yes @Phil that's what I do on my planes, just lift the corners each time, takes the sharp edge off.

 

[Trafalgar]

Yes...

It's easier to fix a sloping edge with a cambered iron if shooting freehanded. If you're jointing on a long shooting board, dead straight is fine. You can keep more of the plane's sole on the edge of the board with a curved iron.

The radius of the curvature is significantly wider than the width of any edge you are likely to shoot, yet it is still effective and does not produce scalloping within the width of the edge that some posters are envisioning/imagining. In other words, you get mating surfaces. What you are thinking of would only happen if the radius were very small -- like a scrub plane or something similar. Remember, Earth is a giant ball but seems flat locally. For all practical purposes is flat locally.

 

[highwood122]

It's easier to fix a sloping edge with a cambered iron if shooting freehanded. If you're jointing on a long shooting board, dead straight is fine. You can keep more of the plane's sole on the edge of the board with a curved iron.

The radius of the curvature is significantly wider than the width of any edge you are likely to shoot, yet it is still effective and does not produce scalloping within the width of the edge that some posters are envisioning/imagining. In other words, you get mating surfaces. What you are thinking of would only happen if the radius were very small -- like a scrub plane or something similar. Remember, Earth is a giant ball but seems flat locally. For all practical purposes is flat locally.

this has probably been said before, but i,ll say it anyway, slight curve on the blade on edges helps for edge joining of boards as its got some where for the glue to be. i am only relaying what i was told by an old shipwright 50 years ago

 

[Jacob]

Forgot to add: the one big overriding benefit of a cambered plane blade is that it enables finer planing, and on more difficult wood.
This is because as you retract it you also reduce the effective width. Taking a very fine but narrow shaving becomes much easier with less likelihood of tear out etc.
A very fine but full width of blade cut can be impossible