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sinjin
31st January 2014, 02:19 PM
Simple but tricky question. If i had a plank of timber 12mm thick and just by chance it had a 1mm bow right in the center.
Board lenght doesn't matter...say 1000mm for arguement sake.
I need to plane the board dead flat and also dead parallel what would be the maximum thinkness i could get the plank
when it is finished. This is a theoretical answer not from a practical point of view. Would the board end up being
11mm thick or 10mm thick.
Sinjin

Rod Gilbert
31st January 2014, 02:28 PM
In a perfect world you should be able to get 11mm thickness.
Regards Rod.

pommyphil
31st January 2014, 02:36 PM
!0mm, you must take 1mm off each side. Phil

sinjin
31st January 2014, 02:46 PM
So far...1 correct and 1 incorrect. Have no doubt this will get some good response

tore
31st January 2014, 03:46 PM
11mm

artme
31st January 2014, 03:54 PM
I had a plank like that once. Ended up with a veneer!!!!:doh::B

Oldgreybeard
31st January 2014, 03:58 PM
I am with Rod : 11mm. In the centre of the plank you remove 1 mm from the top, but nothing from the bottom.
Bob

artful bodger
31st January 2014, 07:15 PM
10mm in my books. If its 1mm out on one side it must e 1mm out on the other (concave/convex). Wood being wood though if you true it up it may well bow again. Quarter sawn is better than backsawn for thinner boards.

Treecycle
31st January 2014, 09:29 PM
11mm. You only need to take 1mm off at the centre area on one side. You take 1mm of the wings on the other side.

oldrose
31st January 2014, 10:16 PM
11mm. You only need to take 1mm off at the centre area on one side. You take 1mm of the wings on the other side.

FWIW Agree

elderly
31st January 2014, 10:27 PM
11mm

Dalboy
31st January 2014, 11:03 PM
If the board is PAR and warped after this then 11mm if rough sawn then it will probably be less.

This is in an ideal world and not taking into consideration of any other movement such as twist in length.

Hermit
31st January 2014, 11:23 PM
11mm. First you take 1mm from the high centre of the bow, making that section 11mm, then you take 1mm from the low ends of the bow, making those sections 11mm.

pommyphil
1st February 2014, 06:09 AM
Yes, you do take 1mm of each side but because of the bow the board is 13mm, from a thicknessers point of view:rolleyes: so 11mm

Mobyturns
1st February 2014, 08:35 AM
Dunno!

Q. how would wood turners know the answer to this? :?

Only a few strange ones own devices called thicknessers. :q

Dalboy
1st February 2014, 08:47 AM
Dunno!

Q. how would wood turners know the answer to this? :?

Only a few strange ones own devices called thicknessers. :q

That makes me strange:bleh: but they do come in handy it you want to prepare wood for segmented work:;:;

nalmo
1st February 2014, 10:13 AM
If you want only 1 side flat, then 11mm (either at the ends or the middle, depending which side you straighten - concave or convex).
If you want two flat parallel sides, then 10mm.

dr4g0nfly
2nd February 2014, 07:10 AM
10mm definitely.

Tim the Timber Turner
2nd February 2014, 11:23 AM
Consider this.

If you put the 12mm board on a flat surface with the cup side up, and measured the highest point it would be 13mm above the flat surface.

Remove 1 mm off the concave side to make it flat and measure again, the highest point is 12mm above the surface.

Turning the board over remove 1mm off the convex side to make this flat and you are left with 11mm.

By making both sides flat you remove the equivalent of 1mm x the surface area of the board.

So the answer is 11mm.

Of course this answer is theoretical and could be different in practice, depending on the skill of the operator.

Cheers

Tim:)

Hermit
2nd February 2014, 11:40 AM
This has been a good little exercise in clear thinking. :2tsup:
We should have one each week. :cool:

(And I'm sticking with 11mm.)

Edit: If it didn't have to be planed, it might be possible to steam-bend it and keep the original 12mm thickness.

robo hippy
3rd February 2014, 04:41 AM
Well, first you run it through the thickness planer to remove the hump on one side. Then one very light pass to make sure it is all gone. Then you turn it over and remove the dip from the other side. Again, one very light pass to make sure it is all gone. Then you let it sit over night to 'adjust'. Next, run it through the drum sander to remove all planer marks. Again. let is sit over night to 'adjust'. By now you will have removed about 4 mm. Hopefully the weather will have been constant, and the board will not have adjusted to humidity changes and warped again.......

robo hippy

Mobyturns
3rd February 2014, 06:44 AM
That makes me strange:bleh: but they do come in handy it you want to prepare wood for segmented work:;:;

Where is PowderPost when you need him? He would know the answer. :D I'm also becoming stranger by the day. Up until recently I have hand planed everything that came of the table saw. :wink:

My answer theoretically 11mm btw. RoboHippy has the practical answer - what it ends up as! or more like 10mm in practice.

Given the few segmenters I thought this was a left field trap question to catch out woodturners masterminded by a dastardly flat worker masquerading in wood turners clothing. :D

RETIRED
3rd February 2014, 07:48 AM
Well, first you run it through the thickness planer to remove the hump on one side. Then one very light pass to make sure it is all gone. Then you turn it over and remove the dip from the other side. Again, one very light pass to make sure it is all gone. Then you let it sit over night to 'adjust'. Next, run it through the drum sander to remove all planer marks. Again. let is sit over night to 'adjust'. By now you will have removed about 4 mm. Hopefully the weather will have been constant, and the board will not have adjusted to humidity changes and warped again.......

robo hippyRobo, a thicknesser would only duplicate the bow. A pass across a jointer would flatten one side, then thickness.

A segmenter would not worry about the bow as small pieces would not be affected. If the board were being glued to another board, different story.

sinjin
3rd February 2014, 07:29 PM
The answer is 11mm..i did ask for theoretical answer..but i did think it would get answers of 10 or 11mm.
Sinjin

Hermit
3rd February 2014, 07:50 PM
The answer is 11mm..i did ask for theoretical answer..but i did think it would get answers of 10 or 11mm.
Sinjin

Have you proof?
I expected that having posted the question, you would show definitive proof rather than just ask us to take your word for it.

Edit: I agree though, the answer is 11mm.

Sturdee
3rd February 2014, 07:56 PM
That makes me strange:bleh: but they do come in handy it you want to prepare wood for segmented work:;:;

Makes me even more strange as I have, in addition to the thicknesser, a jointer and drum sander as well. :U

Peter.

jefferson
3rd February 2014, 08:02 PM
The correct answer is not 11mm.

I would suggest that the thread be posted on the general woodworking section. You will hopefully get some correct answers there.

Depending on your planing skills - and the depth of the crook - the best you can hope for is around 10mm. You take 1mm off the bottom with planing, another 1mm when thicknessing. If a board is 1mm out on the top, typically it will be 1mm out on the other side. If you are skilled, you can reduce the waste somewhat, but you still need to face both sides of the board.

This is not a wood turner's question. It should be placed elsewhere. Only segmenting turners will an idea. Perhaps.

I have plenty of boards that are twisted. Prepared to send them if needed. 11mm advocates can pay the postage when wrong.

Again, this is not a wood turners question. I would doubt that most wood turners have a planer and thicknesser.

Hermit
3rd February 2014, 08:21 PM
The correct answer is not 11mm.

I would suggest that the thread be posted on the general woodworking section. You will hopefully get some correct answers there.

Depending on your planing skills - and the depth of the crook - the best you can hope for is around 10mm. You take 1mm off the bottom with planing, another 1mm when thicknessing. If a board is 1mm out on the top, typically it will be 1mm out on the other side. If you are skilled, you can reduce the waste somewhat, but you still need to face both sides of the board.

This is not a wood turner's question. It should be placed elsewhere. Only segmenting turners will an idea. Perhaps.

I have plenty of boards that are twisted. Prepared to send them if needed. 11mm advocates can pay the postage when wrong.

Again, this is not a wood turners question. I would doubt that most wood turners have a planer and thicknesser.

This was double-posted in the General Woodwork section at the same time it was posted here, with similar conflicting answers.

This is my thinking. (I'm on the 11mm horse.):

302868


Edit: If it can't be done with a power planer or thicknesser, it can be done with a hand plane.

powderpost
3rd February 2014, 08:35 PM
Simple but tricky question. If i had a plank of timber 12mm thick and just by chance it had a 1mm bow right in the center.
Board lenght doesn't matter...say 1000mm for arguement sake.
I need to plane the board dead flat and also dead parallel what would be the maximum thinkness i could get the plank
when it is finished. This is a theoretical answer not from a practical point of view. Would the board end up being
11mm thick or 10mm thick.
Sinjin
Theoretically, one would run the board over a surfacer with the cup side down to remove the 1mm cupping. Then one wold run the surfaced board through a panel planer to make the second side parallel to the surfaced side. The board would end up 10mm thick, theoretically, that is. The correct answer, theoretically, would be 10mm..

Jim

jefferson
3rd February 2014, 08:37 PM
Steve, get some crooked boards out and tell me you come up with 11mm. My best advice is to avoid boards with crooks. Typically, quarter sawn boards won't twist the same as rift sawn boards.

And if a board is 1mm out on one side, it must be 1mm out on the other. Low or high on one side, same on the other.

Again, do you want me to send some boards? At your cost if you are wrong.

What sort of machines are you running? I assume both a buzzer and thicknesser. Which makes we wonder why you are saying 11mm. From my experience - and it follows industry standards - a rough sawn 25mm board comes down to 19mm when dressed.

That's not a deviation of 1mm.

Perhaps you can educate us all.

Hermit
3rd February 2014, 08:48 PM
Theoretically, one would run the board over a surfacer with the cup side down to remove the 1mm cupping.

Which leaves the board 11mm thick in the middle and 12mm thick at the ends.


Then one wold run the surfaced board through a panel planer to make the second side parallel to the surfaced side. The board would end up 10mm thick, theoretically, that is. The correct answer, theoretically, would be 10mm..

Jim

This would take the 1mm from the 12mm ends but nothing from the 11mm middle, leaving the board 11mm thick.

OR

Hand-plane 1mm from the middle where it bows upwards, tapering out to nothing at the ends.
Next, flip the board and hand-plane the ends by 1mm, tapering out to nothing at the middle.
We are talking theoretical, and theoretically it should be possible to take 1mm from one part of a board but not from another.

It's perfectly clear to me, and I thought my drawing was too.

Actually, in my opinion, the onus is on the OP, who provided both the question and the answer, to prove his case. It's not up to me. I'm just another 'guesser', and my guess is 11mm.

Tim the Timber Turner
3rd February 2014, 09:03 PM
Simple but tricky question. If i had a plank of timber 12mm thick and just by chance it had a 1mm bow right in the center.
Board lenght doesn't matter...say 1000mm for arguement sake.
I need to plane the board dead flat and also dead parallel what would be the maximum thinkness i could get the plank
when it is finished. This is a theoretical answer not from a practical point of view. Would the board end up being
11mm thick or 10mm thick.
Sinjin

I think some of you missed the question.

"This is a theoretical answer not from a practical point of view".

It's not a wood working question.

It's a mathematic theory question.

The answer is 11mm.

Cheers Tim:)

Hermit
3rd February 2014, 09:11 PM
Steve, get some crooked boards out and tell me you come up with 11mm. My best advice is to avoid boards with crooks. Typically, quarter sawn boards won't twist the same as rift sawn boards.

And if a board is 1mm out on one side, it must be 1mm out on the other. Low or high on one side, same on the other.

Again, do you want me to send some boards? At your cost if you are wrong.

What sort of machines are you running? I assume both a buzzer and thicknesser. Which makes we wonder why you are saying 11mm. From my experience - and it follows industry standards - a rough sawn 25mm board comes down to 19mm when dressed.

That's not a deviation of 1mm.

Perhaps you can educate us all.

Forget the planer and thicknesser if they can't do it. If you take a hand-plane and do it exactly as shown in my earlier sketch, you'll end up with an 11mm board. (In theory, not practice. In practice none of us could do this because we don't have enough control over the plane.)

Don't forget, we're not looking at what you get 'in practice', using a buzzer etc, but the 'theoretical' answer. 'In theory', under 'ideal' conditions, you should be able to remove the exact amount of wood that's needed.

Not trying to get into arguments, by the way, but can't help supporting my view.

Hermit
3rd February 2014, 09:12 PM
I think some of you missed the question.

"This is a theoretical answer not from a practical point of view".

It's not a wood working question.

It's a mathematic theory question.

The answer is 11mm.

Cheers Tim:)

Thanks Tim, We were making the same point at the same time, but you pipped me. (And you explained it better, I think.)

Sturdee
3rd February 2014, 09:16 PM
Simple but tricky question. If I had a plank of timber 12 mm thick and just by chance it had a 1 mm bow right in the centre.

Sinjin


I think you should stop buying your timber from the big sheds and buy it from a proper timber yard, then you won't have this problem.


Peter.

Tim the Timber Turner
3rd February 2014, 09:37 PM
Thanks Tim, We were making the same point at the same time, but you pipped me. (And you explained it better, I think.)

As my old maths teacher used to say.

Read the question.

Then read it again before you answer.

There are no marks for a correct answer to the wrong question.

But it's been a good debate.

Cheers

Tim:)

Hermit
3rd February 2014, 09:41 PM
As my old maths teacher used to say.

Read the question.

Then read it again before you answer.

There are no marks for a correct answer to the wrong question.

But it's been a good debate.

Cheers

Tim:)

In this case there are no marks for the right answer to the right question either. Just a good exercise in logic.
I still think we should have one a week, but I'm not putting my hand up.

powderpost
4th February 2014, 09:43 AM
I think some of you missed the question.

"This is a theoretical answer not from a practical point of view".

It's not a wood working question.

It's a mathematic theory question.

The answer is 11mm.

Cheers Tim:)
Agreed... but..... theoretically speaking, a board 12mm thick with a 1mm cup in it is now not 12mm thick but theoretically 13mm thick. So the answer is still 10mm.

So the answer of 10mm is still theoretically and mathematically correct.
Jim

Tim the Timber Turner
4th February 2014, 10:23 AM
Agreed... but..... theoretically speaking, a board 12mm thick with a 1mm cup in it is now not 12mm thick but theoretically 13mm thick. So the answer is still 10mm.

So the answer of 10mm is still theoretically and mathematically correct.
Jim

Sorry Jim that doesn't make sense.

Don't you agree with Hermit's drawing?

As one of your famous Queenlanders once said.

"PLEASE EXPLAIN"

Cheers

Tim:)

powderpost
4th February 2014, 10:48 AM
No I don't agree with Hermits drawing. With a 1mm cup in the board, the board now becomes 13mm thick not 12mm thick, theoretically.
Been an interesting exercise. Perhaps the moderators can see fit to include a "Conundrums" component to the board?

Jim

Sturdee
4th February 2014, 10:55 AM
If we look at it theoretically I'm wondering why you would plane it all. To retain the full 12 mm you would steam bend it back dead flat and dead parallel by clamping between two straight pieces. Bit of work but it saves the one or two mm. and is easier then planing. :roll:

Of course that would be a flat work exercise and real turners don't do that kind of thing. :U:U



Peter.

Hermit
4th February 2014, 10:56 AM
No I don't agree with Hermits drawing. With a 1mm cup in the board, the board now becomes 13mm thick not 12mm thick, theoretically.
Been an interesting exercise. Perhaps the moderators can see fit to include a "Conundrums" component to the board?

Jim

Jim, the board is not 'cupped' or 'twisted', only 'bowed'.
Second, it can only be 13mm if you include air. Air doesn't count as part of the thickness of a board.
I don't know how you can disagree with the drawing. It says it all.

This isn't a conundrum - it's a plain logical exercise, with only one possible answer - 11mm.

Forget thicknessers, buzzers, etc and look purely at the logic of removing unwanted material only where necessary as shown in my sketch.

Hermit
4th February 2014, 11:00 AM
If we look at it theoretically I'm wondering why you would plane it all. To retain the full 12 mm you would steam bend it back dead flat and dead parallel by clamping between two straight pieces. Bit of work but it saves the one or two mm. and is easier then planing. :roll:

Of course that would be a flat work exercise and real turners don't do that kind of thing. :U:U

Peter.

Yep - that's what I suggested in an earlier post. If it was reasonably short that would be easy.
Unfortunately, though, the question stated that the timber must be planed, so that rules out this method.

Sturdee
4th February 2014, 11:04 AM
Yep - that's what I suggested in an earlier post. If it was reasonably short that would be easy.
Unfortunately, though, the question stated that the timber must be planed, so that rules out this method.

Great minds think alike but the examiner is posing the question asking about planing because he doesn't realize there are more ways to skin a cat.


Peter.

Tim the Timber Turner
4th February 2014, 11:28 AM
No I don't agree with Hermits drawing. With a 1mm cup in the board, the board now becomes 13mm thick not 12mm thick, theoretically.


Jim

I agree 13mm.

Theoretically you remove 1mm off each side to make it flat.

13 minus 2 = 11mm

The answer is 11mm

Jim I know you can add up because you have to count all them little bits of wood before you stick them back together.:roll:

I think you are not serious and just having a stir?:2tsup:love it!

Just to change track.

Isn't it great that we can all be in different parts of the country and have a debate like this.

Even if half of you are wrong.:D

Cheers
Tim:)

Hermit
4th February 2014, 11:44 AM
Just to change track.
Isn't it great that we can all be in different parts of the country and have a debate like this.
Cheers
Tim:)

Sure is. Technology has come so far in our lifetimes. What next?

Personally, I'm not planing my board. As said, by the time the 1000mm length is cut into segments the bow will virtually disappear. (0.025mm bow per 25mm segment)

Tim the Timber Turner
4th February 2014, 12:18 PM
I don't know why I'm participating in this debate,

I haven't even got a board like that.

Cheers

Tim:)

ubute
4th February 2014, 12:54 PM
My theoretical answer to the theoretical question is 11mm.

I'm more of a pictures kind of guy so here's my proof, in sketchup.

Original 12mm bowed board in the back, 11m planed straight board in the front, with the top and bottom 1mm thick waste sections in grey.

302915

(I drew it 100mm long instead 1000mmm for better clarity of the bowing)

Tim the Timber Turner
4th February 2014, 01:15 PM
Hey Jim!

You should grab them 2 offcuts from Ubute's great drawing and glue them together.

You would then have a 1mm thick piece that you could cut up and use in your laminations.:2tsup:

Please post a theoretical picture of your finished piece.:rolleyes:

Cheers

Tim:)

jefferson
4th February 2014, 01:39 PM
Like quite a few others, I mis-read the original post. I thought we in fact had a board that needed fixing. It seems not. So....

If you wasted your time and built a decent sled for your drum sander, you could sand the hump out then reverse the board over and then take the high corners out. If you were very careful. And I think that would give you an 11mm board. Why anyone would do so is beyond me. All for the sake of 1mm. I could also get the same result on my woodwizz. I'd have to pack under the cup in both cases.

How to do it using your jointer-thicknesser is not something I would even try to do. Clearly, the board has moved and I would simply start again from scratch. It happens. You could try to joint the board but the pressure you exert on the jointer table would most likely flatten the thin board and make the entire process quite difficult. Assuming you started with the board cup up as you would normally do. Cup down? I am yet to meet a tradie that good.

Hand plane? Possible but who owns a jointing plane anymore? Who has a length of plate glass long enough to get the sole flat in the first place?

So in theory, 11mm is possible using the methods noted above. I think.

But in practice, 12mm is what 99% of woodworkers would achieve in less than 5 minutes with no stuffing around. Assuming you correctly started with one straight edge of a seasoned board at the break-down stage and went straight to the thicknesser from your bandsaw. Speculating, the original board would probably be meant for boxes, so a 1mm variation over a metre would pull out straight anyway.

I hope that answers the question in a roundabout way.

powderpost
4th February 2014, 08:51 PM
I agree the correct answer is 11mm, but it was fun.. :D The correct term for a board with a hollow surface is 'cup', different from bowed or twisted. The drawings suggest, technically, the board in question was cupped.

Jim

sinjin
7th February 2014, 12:09 PM
Anyway the answer is 11mm is the final thickness.