Plane Design

[custard]

Two questions that the engineers/designers amongst you may be able to answer.

1. Why don't hand planes have the blade in the middle of the sole? Machine planers have two equal length beds, so why are hand planes different?

2. Why is the sole on a hand plane flat, or at least supposed to be flat? Why isn't the sole behind the blade offset by the thickness of the average shaving? I guess that with the existing design of hand planes, where the edge of the blade is out of line with the sole, it would be impossible to ever plane a board truly flat, surely it will always be slightly concave?

 

[Philly]

Custard
For the first question - you normally need some space behind the iron to grip. The further back the mouth goes the less space is left for a grip.
Secondly - the age old question. :lol: I reckon its a lot easier to make a plane with a flat sole that a stepped one. Also you would have to set the iron perfectly every time you fit it or the thing wouldn't work. You'd have to have different planes for different thickness shavings.
Hope this makes sense,
Philly

 

[custard]

Philly,

thanks for the reply. I take your point about room for a grip on a number 3 or 4 smoother, but it's the same asymetric relationship between front and rear sole length on a number 7 or 8 jointer. Actually, thinking more about it, don't eastern wooden planes have the iron set more towards the back too? Maybe the wisdon of generations of woodworkers is that it's harder to end the planing cut than begin it?

 

[bugbear]

Custard
For the first question - you normally need some space behind the iron to grip. The further back the mouth goes the less space is left for a grip.
Secondly - the age old question. :lol: I reckon its a lot easier to make a plane with a flat sole that a stepped one. Also you would have to set the iron perfectly every time you fit it or the thing wouldn't work. You'd have to have different planes for different thickness shavings.
Hope this makes sense,
Philly

You might consider searching the OLDTOOLS archive for "manx jointer"

Add; Veritas did move the blade position back a little, compared with tradition, in their bench planes.

BugBear

 

[Digit]

My home made wooden jointer has the iron set well back. I made it that way as I find having a good length in front of the iron helps me keep it flat. Also I find that when planing thin stock there is less likelihood of the stock lifting in front of the plane.

Roy.

 

[Jeff Gorman]

1. Why don't hand planes have the blade in the middle of the sole? Machine planers have two equal length beds, so why are hand planes different?

When planing a full-length stroke, the forepart of the sole serves to set the entire plane in the same geometrical plane as the workpiece's surface. I think that tradition has established a distance about short enough for this purpose.

To work effectively, finish-wise against contrary grain, maximum pressure needs to be applied at the front lip of the mouth. The smaller the area over which the forward hand's pressure is applied, the greater the concentration of pressure at the mouth lip.

Hence putting the cutter too far back would decrease the mouth lip pressure because the forward hand's pressure is applied over a greater area.

2. Why is the sole on a hand plane flat, or at least supposed to be flat? Why isn't the sole behind the blade offset by the thickness of the average shaving? I guess that with the existing design of hand planes, where the edge of the blade is out of line with the sole, it would be impossible to ever plane a board truly flat, surely it will always be slightly concave?

I think this is based on the notion that while in use, the rear of mouth to heel area floats over the workpiece surface. However, I've demonstrated that a Record cast iron jack can deflect in use, so at least the heel of the sole can be in contact with the wood.

I think it can be demonstrated that the concavity is inevitable and is proportional to the square of the length of the plane, divided by the set.

Jeff Gorman