3 winding sticks?

[swb58]

I'm currently having a go at flattening a face on a piece of reclaimed timber nearly 12" x 6" and 6' long. Using windings sticks now because it's a bit out.
This reminded me of how they used to set up drains many years ago, fix a 'T' at point A and at point B then move a 3rd along the line and by sighting along the tops giving intermediate heights.
Using two winding sticks will achieve a will flat surface side to side but there still could be great hump somewhere along the length.

Thoughts?

 

[MusicMan]

Not only drains, our Roman Road network was surveyed in much the same way.

Yes you could have a hump and detect this using a third stick. But I think most people use a straight edge. 6' is quite long for this but you don't need a super precision straight edge; I have a 2.5 m carpet fitters' edge, which proved good enough to use in jointing some 7' yew boards.

A decent spirit level will work, also, Big metalworking machines are set up this way.

As usual, we have plenty of ways to achieve the same end. Jacob of course, would just squint along the plank .

 

[AndyT]

You can tell a lot by squinting at a piece of wood, as << this photo shows.
But winding sticks can be moved along the whole piece, not just stood at either end.
If you have three the same, I reckon that would work fine too.

 

[bugbear]

I'm currently having a go at flattening a face on a piece of reclaimed timber nearly 12" x 6" and 6' long. Using windings sticks now because it's a bit out.
This reminded me of how they used to set up drains many years ago, fix a 'T' at point A and at point B then move a 3rd along the line and by sighting along the tops giving intermediate heights.
Using two winding sticks will achieve a will flat surface side to side but there still could be great hump somewhere along the length.

Thoughts?

The theory of winding sticks is that any particular line down the board, parallel to the sides, will be flat, achieved via planing technique and/or a straight edge.

The only possible fault remaining is twist, which is what the winding sticks detect, and allow you to remove.

If each stroke is flat (via planing), and the ends are parallel (per the winding sticks) the board is flat.

BugBear

 

[custard]

The only possible fault remaining is twist

Cupping?

 

[swb58]

I know that there are the looking along the length and the straight edge options, I just wondered if a third stick can be used. They come in pairs normally so I don't suppose it's the done thing.
But it does work, I knocked up another this afternoon and reckon I've got a 10mm tump in the middle on a fairly even curve.
It's an oak solebar destined to become part of new benchtop

 

[Biliphuster]

I just move the far stick down the board towards me, usually in a few steps for longer boards. If a board is way out I sometimes map it out with winding sticks first so I only have to do the minimum amount of planing.

 

[thetyreman]

straight edge is how I check, once the twist is removed.