Shooting edges true...

[Pete Howlett]

I've just converted a try plane for novices so they can bookmatch thin sections for musical instrument backs and fronts... see: http://www.youtube.com/watch?v=FRC_QZv0-3A

I flatted the sole of this plane and the shim makes the sole dead flat and yet I still get slight crowning when I am preparing each edge. Granted it's easier to sweep the centre a few times to get the joint perfectly shot but this is a subtlety that is perplexing me. To rectify this with this setup the plane should surely have the toe end lowered by the height of the blade like a surface planer?

So the question is, why do we insist obsessively that the sole of our planes be flat? In theory, it should not work - we will either plane a hollow or a crown wouldn't we?

BTW it takes a minute to shoot edges using this thing...

 

[wizer]

That's a very simple solution Pete. There was me convinced I'd never need a jointer plane!

 

[Paul Chapman]

Hi Pete,

Neat set-up 8)

If you keep planing a piece of wood along its length, you will eventually plane it into a convex curve. As you suggest, this is because the sole of the plane is the same height either side of the blade. The only way to correct this is to take a few "stop shavings", starting and finishing an inch or so in from both ends, and then finish off with one or two full length shavings.

Cheers :wink:

Paul

 

[Pete Howlett]

Granted Paul - so why insist on the flatness of the sole of a plane?

BTW I used the knop and handle to make a sander plane - you do a huge amount of sanding in musical instrument making....

 

[Paul Chapman]

Granted Paul - so why insist on the flatness of the sole of a plane?

Because if the sole isn't flat, you can't produce very fine shavings.

Cheers :wink:

Paul

 

[Pete Howlett]

If it's concave, yes. If it's convex?

 

[Paul Chapman]

It doesn't have to be flat all over. Where it needs to be is at the toe, heel and around the mouth. A few hollows elsewhere don't matter too much.

Cheers :wink:

Paul

 

[tnimble]

If the plane was convex from toe to heel it would plane very fine shavings, but it would only if held just correctly with the mouth as the lowest point. A bit more pressure to the heel or to the toe and the plane stops making shavings.

A convex plane is only handy for planing inside curves of the same radius.

Therefore there's so much to do with the flatness. A slightly concave sole would plane easily but the fineness of the shavings is limited. A slightly convex plane is hard to handle.

 

[Karl]

A convex plane is only handy for planing inside curves of the same radius.

I have a cheap plane (silverline?) which has a convex sole, and I mean really convex.

It was destined for the bin, until I discovered another use for it - preparing softwood cauls for glue-ups. It quickly gives a nice curve to a piece of pine!

Cheers

Karl

 

[Jeff Gorman]

Pete Howlett wrote:

>I flatted the sole of this plane and the shim makes the sole dead flat and yet I still get slight crowning when I am preparing each edge. Granted it's easier to sweep the centre a few times to get the joint perfectly shot but this is a subtlety that is perplexing me. To rectify this with this setup the plane should surely have the toe end lowered by the height of the blade like a surface planer?<

With respect, and with admiration for a nice jig, I'd like to point out that this popular theory about plane sole configuration is countered by an investigation I made and is reported at:

http://www.amgron.clara.net/planingpoin ... nindex.htm

Naturally, this will hardly apply in Pete's case where the worker's weight is applied to the job.

So the question is, why do we insist obsessively that the sole of our planes be flat? In theory, it should not work - we will either plane a hollow or a crown wouldn't we?

Using a bit of maths, it can be shown that even when correctly operated a perfectly flat plane can cut a concave curve whose radius is proportional to the square of the length divided by its set. Something we all make us of l of course, when shooting rub joints.

To my mind, the principle reason for having a dead flat sole is that for a good finish when working gnarly grain, the front lip of the mouth must be in firm and close contact with the wood.

Jeff Gorman