Thread: Skew plane bedding angles explained.

Back in 2009 I made a little skew throat plane based on a gunmetal plane Rob (auscab) has.
It was a lovely fit in the hand, and was a delight to use. I decided to make one, and add the skew mouth to get the shavings to spiral out the side.
This isn't a step by step on how to make the plane, more an explanation of how I solve the skew throat geometry without complicated calculations.

more pics of the plane seen here



These edge and red boarded triangles are the key to knowing how to make the plane.
I decide on the important specification for the plane, draw the plane up, sides, base etc.
Then lay out on the metal and start cutting.






In another thread the skew came up for discussion, and I've seen many plane makers baulk at attempting it.
I'll try and explain it with pictures and not mathematics.
Because we are talking about planes & planes, I thought I better distinguish between the imaginary planes, and the HANDplane.
The base, the bed, the sides are all planes, and they meet forming lines.
The sides are two parallel planes, with another plane, the bed, passing through them at a skew angle.

This picture might go towards greatly simplifying it, and explaining why the bedding angle on the sides is common whether the throat is at 90* or at say 70* to the sides.
Why should 90* think he's so special?
A couple of 60-30 set squares. One smaller than the other to represent the 2 sides of the handplane.
Separated a few inches, with the left vertical edges aligned square, and the front points skewed like the handplane throat.
The top edges are parallel. So an imaginary handplane with a bed at 30* will have the same bedding angle, 30* angle on both sides...just like the set squares.




To understand how all the planes relate to each other without going into complicated stuff, I"ll make a model.
Since it was easy to use the set square to make the cardboard triangles, I'll use that 30 degree as a bed angle, and a nominated 70mm as the base width and a 70 degree throat angle.
That's all the dimensions I need to make my model. NO trigonometry or programing a machine. Just a knife, cardboard and tape.
Starting on the left - a triangle with a nominal 120mm length along the handplane base - done
Cut the base - left side 120mm - throat angle drawn and cut, and right side length of the base found, BUT no need to measure it.
Transfer that RHS base length to the RHS triangle. That gives the height of the base on that side.
70mm wide back piece. The height on each side is the two corresponding triangle sides. swing them down and transfer those lengths. No measuring!



Tape it all up.
looking down into the base with the throat at the left.



Below - from the back looking towards the throat .... has to be parallel to each other.
Looking across the sides, has to be parallel as well!
The angle at the back is unknown, it is just a line between two points. I can lay it out without ever measuring it.



NOW, looking at the plane to see where it all applies.
The model above represents the part under the blade, and also the part under the red lines I've drawn showing the bed on the handplane below.

1/8 inch sides are cut out, base line created on each side, sides clamped over base insert 1/4 inch . throat scribed across, and bedding angle (your choice) transferred up to the back. Escapement length along the bed marked and transferred around the bottom to the other side.
It's important to see these are all points, lines and planes that are intersecting and creating the geometry of the working part of the plane.

Knowing all that above means you can do a complete drawing of the plane you want to make.
On the plane I've shown the layout lines for cutting and filing that will get the escapement, the throat and bed right.
You need to allow sufficient metal to file away, the cut isn't at right angles to the sides. Looking at the back there is a slight angle where the blade seats.




Cheers,
Peter