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Planing bowed boards on PT

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GrahamF

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On a recent thread, it was said that when planing a bowed board on a planer, it should be done convex side down. I have always done it concave side down. If the job allows, will cut in half (2 shorter lengths) before planing. If twisted as well, I use the thicknesser with the board wedged and fixed on a sled board.

What do you do? (I see Matt Estlea also recommends concave side down) Not interested in arguments about how the board is held/fed across, just which way up.
 

Jonathan S

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For the last 35 years I've been doing it concave side down .....have I been doing it wrong?

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Jacob

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GrahamF":1qk9hhlq said:
On a recent thread, it was said that when planing a bowed board on a planer, it should be done convex side down. I have always done it concave side down. If the job allows, will cut in half (2 shorter lengths) before planing. If twisted as well, I use the thicknesser with the board wedged and fixed on a sled board.

What do you do? (I see Matt Estlea also recommends concave side down) Not interested in arguments about how the board is held/fed across, just which way up.
First I'd always cut to length according to the cutting list, before planing.
Then if very bowed or twisted put convex side down with pressure in the middle, to keep the middle flat on the bed as you plane (whatever system you use! :roll: ) This gives you a flat in the middle and subsequent passes extend this until it reaches both ends.
It works because the middle of an evenly distorted board is going to be parallel with the best flat face you can get out of it (just geometry) so working from it automatically produces a good result.
You can't do same from the hollow side - has to be from ends instead.
It really helps with bigger pieces difficult to handle, but doesn't matter so much for short pieces.
No you haven't been doing it "wrong" JonathanS it's just a little wheeze to make it easier on some bent pieces.
 

Doug71

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I do a bit of both!

Sometimes if a board is bowed and you just flat one side then put through the thicknesser it comes out bowed again. If you keep flipping the board taking some off the middle of convex side and off ends of concave side any tension is equalled out and hopefully it stays straight.

Speeds up thicknessing also, nothing worse than watching a 6' length of wood going under planer that is only getting 4" planed at each end, I have work to be getting on with!
 

GrahamF

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Jonathan S":hkvysthi said:
For the last 35 years I've been doing it concave side down .....have I been doing it wrong?
I hope not, as that would mean I'm wrong as well but maybe as I only have 3 years experience with PT, I would have more of an excuse :D
 

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I guess the answer could be either depending on all sorts. However in many years of using surfacers I would say concave down as default.
 

DodgyLogic

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I can't say I'd thought about it until now and in truth I've no idea what I've been doing up until now.

If you're dealing with stock of a similar length to the bed of the planer, it makes sense to me to do it convex side down as you keep the reference surface on the bed throughout the cut. If you plane concave side down, then one of the reference surfaces is off the end of the bed by the time you're cutting the end of the board.

I'm going to have to be more observant next time I fire up my PT.
 

Inspector

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DodgyLogic":3plc9gdz said:
I can't say I'd thought about it until now and in truth I've no idea what I've been doing up until now.

If you're dealing with stock of a similar length to the bed of the planer, it makes sense to me to do it convex side down as you keep the reference surface on the bed throughout the cut. If you plane concave side down, then one of the reference surfaces is off the end of the bed by the time you're cutting the end of the board.

I'm going to have to be more observant next time I fire up my PT.
When you do it concave down you turn it around and take the other end off. Then you flip it back and have another go and again turn it around. By now when you do the full length it cuts it flat the full length. If you don't flip it around you make a nice wedge. If you lead with the end it dives into the opening cutting too much.

Pete
 

Jacob

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See rough sketch below. Bendy bit of wood exaggerated, starts on infeed table, sitting on the middle of the bend.
1,2,3,4 = first second third fourth pass over the cutter. The bendy bit of wood stays horizontal, the planed surface develops with each pass. It'll take out twist at the same time. Difficult to describe but it does work! Helps with difficult big pieces as you don't have to force it down - it's held by gravity.
Concave is more common, not least because the best face with many timbers is on the concave side, but convex down is sometimes really useful. More than one way to skin a cat.
PS I've been doing it all day with some 2.1m x 150 x 45 sycamore. Get one face flat enough, then through thicknesser, then first face through again as the thicknesser produces a cleaner cut.
IMG_3215.jpg
 

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scooby

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I was taught concave side down (same as Matt Estlea) so the ends get planed first. Cant say I've ever tried convex down.
 

Noel

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It it rocks take a hand plane until it is stable, then machine, generally concave down. Works for me.
 

Jacob

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Re: PT planing convex side down, with weights as poor man's power feed.
There was a bad tempered thread on this, seems to have disappeared, so I tacked this on here.
Up date; I got an old fashioned 5kg cast iron weight for christmas :ho2 so now have three weights (2 at about 3.5kg).
Having 3 weights is even better. I can strategically move them about on the workpiece, stopping and starting as it goes over, with much finer control. I'll do a thread on it.
Doug mentioned an interesting further justification for convex face down - it removes wood from the middle first where it is most stressed and hence relieves tension and proneness to movement - before the board is thicknessed.
 

Jacob

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Nope - for me at least - and quite a few others you find if you cruise the net a bit.
It's ease of handling and release of tension thing which excites most of them, my added weights is another idea which seems to be mine alone so far.
 

Trevanion

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Jacob":238bwhju said:
Nope - for me at least - and quite a few others you find if you cruise the net a bit.
Have you come back to this just to start another argument?
 

Trainee neophyte

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I am very excited by the idea of Jacob using a planer to launch a 5kg weight into low earth orbit. I only hope that the great event is on video - that sort of technological innovation should be documented for future historians .

 

Jacob

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Trevanion":1b9epzha said:
Jacob":1b9epzha said:
Nope - for me at least - and quite a few others you find if you cruise the net a bit.
Have you come back to this just to start another argument?
Moi? Argue? As if! :roll:
No it's just that I'm developing the idea a little and have a lot of planing to do shortly, so will post some snaps. Doug's suggestion of tension release before thicknessing made particular sense. The better control of convex down and the tension relief both add up to better yield i.e. a thicker board planed square all round.
 
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