Question about avoiding cupping in thin stock
Farkel
| Posted in General Discussion on
I have a project that requires alot of 1/4″ hard maple, 7″ wide. I started with 3/4″ stock, form which I milled two 1/4″ boards, but the the milled boards immediately cupped making it all pretty useless. Besides going to 1/4″ plywood, how can I get stable thin stock. As to the cupped stock I have, I has thinking about gluing the two pieces together with the cupped sides facing each other, and then planing that down to 1/4″. Will this work?
Replies
The procedure you described in milling the 1/4" thick material often results in cupped wood I assume because the inner part of the board has a slightly higher moisture content than the outer surface. In my experience, each face piece cupped opposite () like this. Gluing two thinner pieces together () again like this, is probably the best way to assure flat, stable wood. I made a lot of exterior entry doors from various hardwoods. I always re-saw 1/4" thin stock for the facing and laminate it to a solid V.G. Fir core stock. A lot of milling and gluing but necessary to make the doors as flat and stable as possible. The results prove worth the effort.
" I assume because the inner part of the board has a slightly higher moisture content than the outer surface"
Assuming as the OP stated that he cut a 3/4" board down the middle from seasoned stock and the pieces cupped like you have shown () I would assume that the moisture content is higher on this >( side of each piece.
IF you take the two halves, wet the cupped sides and lay them face down they will soon go to flat and start cupping in the opposite direction. Just my two cents.
Tom
You are correct of course, my mistake. Thank you
I'm not sure what to tell you
I'm not sure what to tell you other than - would gluing the two pieces back together and then sizing (assuming you mean to take 1/8 off each side - not 1/4 off one) - would you not be creating a 1/4 ply out of maple?
Thus making a high quality ply?
I'm sure someone else will have a better suggestion or a suggestion in the first place - mine is more a question.
also, what is the project that calls for 7" wide non-ply hard wood?
>>> I'm not sure what to
>>> I'm not sure what to tell you other than - would gluing the two pieces back together and then sizing (assuming you mean to take 1/8 off each side - not 1/4 off one) - would you not be creating a 1/4 ply out of maple?
Thus making a high quality ply?
What gives plywood it's stability is then uneven number of plies. Making plywood by gluing two plies together with the grain running in the same direction will still lead to warping. Also, "plywood" made that way will have no more strength than a solid board that thick. After seeing what the original poster wants to do, real plywood is the best answer.
Yes, thank you for the clarification. Interestingly enough, there is a Howie by me who is also very knowledgeable about many things nearly all trade related, a good handyman and a good guy to talk with/learn from.
I wonder if it runs in the name?
First, what are you going to use the thin boards for?
Second, when resawing wood, it should be stacked and stickered as soon as it is cut. Keep it stacked and stickered for a week or so and it's best to not unstack it until you are ready to actually use it.
The thin stock is for lampshades for a Frank Lloyd Wright Taliesin 2 floor lamp. http://www.highbrowfurniture.com/lighting/products/S2308/?S2308.jpg. Frank Lloyd Wright used plywood. Based upon the comments here, I intend to use make 2 ply plywood out of the stock I have to ensure longer term stability. Thanks for your help.
Interesting design. However, it appears to me that the only way it will work is with real plywood consisting of uneven number of plies. For plywood to have stability, it MUST be made from an uneven number of plies. Attempting to glue two plies at cross directions will lead to the plywood laminations failing.
Are there lamps in each of the individual boxes? Are the thin pieces between the boxes solid plywood or are there some sort of translucent material? If there are lamp bulbs in each box, then there is going to be heat problems and solid wood or two ply plywood may fail.
Thanks for the additional information.
The thin pieces between the boxes are the lampshades, and they are made from the 1/4 inch material that I have been asking about. There are 25 watt bulbs in each box and they will generate heat. I will therefore look into plywood.
But, aren't most glues strong enough to prevent failing laminations where the laminated material is only 1/8" thick? And what is the secret behind an uneven number of plies?
By the way, I am self-taught hobbyist and have been reading your posts on various sites since I started woodworking about 8 years ago. I have learned alot from you, especially regarding finishing, and would like to thank you for that.
Go to the referenced URL and look at page 10-6. It will give you a good explanation about plywood.
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch10.pdf
Yes, adhesives are stronger than the force that would cause delamination. However, the cross grain 1/8" ply is not strong enough to resist the warping force. With an uneven number of plies the outside plies counteract each other in the direction that they want to warp. Therefore, the plywood sheet tends to stay flat.
If you take your stock (before machining), saw it into narrower strips, glue the strips back together, flipping every other one, it might result in flatter stock. In stock that thin and wide, it's a tall order. Another alternative might be quartersawn wood with the grain perfectly perpendicular to the face. Either way, "sneak" up on the final dimensions. Joint and plane the stock, then let it sit for a few days and acclimate. Then do it again, sit for a few days, then joint and plane to final dimensions. Occasionally on projects where I want the stock really flat, I might joint and plane as many as four times.
When I thickness thin boards (nearly always with handplanes, so they have waste removed from both sides), I clamp them together with cauls (to keep them flat), and leave them to settle. This may be overnight if I am, for example, about to dovetail them into a box or drawer - in other words, use them before more movement takes place. Otherwise I might leave them to sit for a few days to a week. Make sure that the air evenly circulates around the boards so that moisture loss is able to end up balanced.
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Regards from Perth
Derek
Farkel,
As Derek advised, taking equal amounts from each side of the stock minimizes the wood movement caused by removing material only from one side down into the (slighter) wetter interior.
The process can be done by hand or with a thicknessing planer. How did you mill your stock?
For a small project, getting 1/4" inch stock from 3/4" is not too wasteful. But it becomes a real problem when you need a lot of 1/4" material. In that case, it pays to get it sawn to size from the log before the drying process. When it's done that way the problem you've run into is minimized.
But you should be able to carefully moisten the 1/4" stuff on the cupped surface, and clamp it flat, allowing adequate air circulation until it dries at its new equilibrium.
Rich
Farkel ,
My guess is the stock you are actually re sawing may be already KD material . It seems air dried stock often re saws in a more relaxed way .
regards dusty
Dusty,
I don't think that's
Dusty,
I don't think that's the case. It doesn't matter how wood is brought into moisture equilibrium with the atmosphere. Once it has reached an equilibrium moisture content (with the ambient conditions at the time), that's that. Until the ambient conditions change slightly, which they always are doing, resulting in some moisture exchange, one way or the other.
Unless case hardening has occurred (and that's a whole other ball of wax) it just doesn't matter how wood has been dried.
I re-saw guitar sound boards, backs and sides from billets of softwood (sound boards) and tropical hardwoods (backs and sides). The re-saws are 0.18-0.2" thick from 2-3" thick billets. Sometimes I have to re-saw the billets into half or third thicknesses.
Such billets traditionally have been air-dried for years if not decades. But in recent years much more kiln drying is used. Some samples cup, twist and warp without warning. But for the most part, the wood behaves.
Problems with movement during re-sawing have always been a known factor and don't seem to have gotten any worse since kiln drying has increased.
Rich
Hi Rich ,
Well maybe it depends on the region we are located and the grain and specie play a huge factor imo .
When you start out with VG or other QS types used for instruments I think they behave more when resawn .
In general here in the PNW I have observed air dried boards and stock getting worse with time in many cases and not remaining as stable as kd will , thats just my experience .
There are a few problems from kd as you said , case hardening , cell collapse , checking , cupping , warping to name a few.
regards dusty,a kd guy
If you take the 1/4" wood, slightly dampen with a sponge, put "stickers" inbetween and clamp for a few days, they should be flat again. However, this advice is based upon the assumption that the pieces are large enough to handle in this fashion.
patience is one item that is needed. as with resawing most larger boards into smaller segments the outside boards are always going to cup more than the inner boards . there are several alturnatives to this and it does relate to the expediency of it's use. if you are in a hurry and one should be using nice straight grain material first. discard the outer pieces and only use the centre cuts. the other is to cut the pieces a little more oversize than you usually do as as you cut them immediately stack them back to the same relationship that they enjoyed before the cut. bind them together so that they are straight and set them side for a couple of weeks and the moisture releasing slowly from the wood will relax the strain. you will have to machine them again to remove what movement is left
ron
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