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Wood panel cupping on mdf

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Forum topic by Johnny24 posted 05-09-2016 10:18 PM 509 views 0 times favorited 11 replies Add to Favorites Watch
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Johnny24

8 posts in 241 days


05-09-2016 10:18 PM

Topic tags/keywords: tip trick question

Hello all,

Another wood cupping question.

I glued a wood panel (striped maple and walnut) to an MDF board.

For a few days the panel was complete flat. Recently it has cupped in the last few days. It has been cold and rainy for the past week to 10 days non-stop. The convex side (the crowned side) is the wood side. MDF side if the concave side.

It is currently under the warm sun going under the “un-cupping phase”.

Questions:

1.) How do I prevent this from happening? Since only one surface of the board is exposed to the elements (the reverse side glued flat to a piece of MDF) I assume I should place it in a bad or place plastic over the side.

2.) How do I prevent this from happening again in the future to the board I am currently working on? I would hate to have flatten it and finish the project only for this panel to cup again breaking joints and popping out of alignment.

Will it just keep cupping every time it gets wet and rainy outside? or does the board have to “re-acclimate” and will eventually settle since I have now exposed only 1 side to the elements?


11 replies so far

View rick1955's profile

rick1955

258 posts in 897 days


#1 posted 05-10-2016 12:18 AM

You need to treat both sides the same. This is in all the veneer textbooks. There isn’t anything really new to basic wood working for 99.9% of all woodworkers.

-- Working smarter with less tools is a true crafts person...

View TheFridge's profile

TheFridge

5765 posts in 952 days


#2 posted 05-10-2016 12:24 AM

Im not sure but it doesn’t sound like a recipe for success.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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isotope

146 posts in 1090 days


#3 posted 05-10-2016 12:51 AM


You need to treat both sides the same. This is in all the veneer textbooks. There isn t anything really new to basic wood working for 99.9% of all woodworkers.

- rick1955

What Rick is trying to say is that your panel needs to be balanced. You need to glue a wood panel on both sides of your MDF board. You can use a different, less expensive, species but you should have the same thickness. Also, your solid wood layer needs to be thin. Otherwise, it’ll crack as changes in humidity cause it to expand and contract; whereas the MDF core won’t.

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rick1955

258 posts in 897 days


#4 posted 05-10-2016 01:18 AM

https://www.google.com/?client=safari#q=balanced+veneer+construction

They make plain laminate for laminated panels.

-- Working smarter with less tools is a true crafts person...

View Ger21's profile

Ger21

1047 posts in 2597 days


#5 posted 05-10-2016 01:27 AM

As has been mentioned, if you glue a wood panel to MDF, it will constantly be warping with changes in humidity, as the wood will always be expanding and contracting, while the MDF remains relatively stable.
If you’re going to be gluing wood to both sides, it really shouldn’t be much thicker than about 1/8”. If it’s thicker, it may eventually crack, especially if you glue it on when humidity is high, and it dries out.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com

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Johnny24

8 posts in 241 days


#6 posted 05-10-2016 01:41 AM

Thanks, Isotope and rick.

How thick does the panel usually have to be in order to glue it to MDF? Max thickness? From my google search people recommend no more than 3/16”

Does the thickness of my panel change if I would glue another wood panel on the other side?

Meaning, after my panel flattens, and if I glue a board on the opposite side would I still have to worry about expansion with the mdf or cupping?

Should have used some spare cheap would around. Could I use pine, birch or Douglas fir? would gluing it with the grain of the panel or going across the grain be best in a surface to surface gluing?

I’ve seen some people recommend when gluing thick stocks of wood to MDF to place a sheet of cork (1/16 to 1/8”) between the two. Does that really do anything for the wood expanding?

After my panel flattens, going to chuck it in the drum sander or slice it off with the band saw and glue a new backing board from wood.

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Johnny24

8 posts in 241 days


#7 posted 05-10-2016 01:42 AM



As has been mentioned, if you glue a wood panel to MDF, it will constantly be warping with changes in humidity, as the wood will always be expanding and contracting, while the MDF remains relatively stable.
If you re going to be gluing wood to both sides, it really shouldn t be much thicker than about 1/8”. If it s thicker, it may eventually crack, especially if you glue it on when humidity is high, and it dries out.

- Ger21

Ah, 1/8” is the max then…

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Johnny24

8 posts in 241 days


#8 posted 05-10-2016 01:50 AM

Does the same effect of warping, cracking and expansion occur if you use plywood that wood has when glued to MDF has?

Would it matter what type of plywood? The high quality smooth sanded finish or Oriented strand board (OSB) or Rtd Sheathing?

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isotope

146 posts in 1090 days


#9 posted 05-10-2016 01:16 PM



Does the same effect of warping, cracking and expansion occur if you use plywood that wood has when glued to MDF has?

To ensure that I understand this question correctly, you are asking whether you need to worry about warping, cracking, etc… if you glued a panel of solid wood to plywood instead of MDF? If so, the answer is yes. The alternating grain direction in plywood drastically limits it’s tendency to expand and contract with changes in humidity; “it won’t move”. Therefore, you still need to keep your glued on wood layer thin.

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Johnny24

8 posts in 241 days


#10 posted 05-10-2016 07:10 PM

That is the correct assumption Isotope! and thank you!

Watched a ton of videos on veneering and properly gluing wood face to face, etc. Picked up a book on veneering at Barnes and Noble today, skimmed through it.

Though my project is not a veneer per se, it is being glued to another material. I would like to do some veneer work in the near future. Something simple at first.

To recap:
When gluing a piece of natural wood to MDF, plywood etc, the wood should never be more than 1/8”

If I want to face glue a piece of wood that is larger, I should use another piece of natural wood same species or not.

Should the 2 pieces be of similar thickness to create “balance” in terms of the amount of area each side would be exposed to?

When gluing face to face, is there ever a time I can glue 2 pieces of different thickness? Say glue 1/4” of cherry to 1” thick pine or maple?

My high school shop teacher from 10 years always told us to glue with the grain when gluing face to face. This is Correct?

Does this hold true if you are using veneer on a piece of wood? should grain direction match?

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isotope

146 posts in 1090 days


#11 posted 05-10-2016 08:30 PM


If I want to face glue a piece of wood that is larger, I should use another piece of natural wood same species or not.

If you want to glue a piece of wood that is THICKER (?) than ~1/8, then you need to glue it to a substrate that will expand and contract in the same manner as your solid wood. For the most part, this means face gluing to another piece of solid wood.

Should the 2 pieces be of similar thickness to create “balance” in terms of the amount of area each side would be exposed to?

I don’t think it has much to do about surface area. It’s more about tension/stress. The solid wood you are gluing will expand/contract with changes in humidity. This will tend to put tension on the substrate (causing warping). If you have solid wood on both surfaces, then the tensions cancel out, and the laminated panel has a good chance of staying flat.

When gluing face to face, is there ever a time I can glue 2 pieces of different thickness? Say glue 1/4” of cherry to 1” thick pine or maple?

If you are gluing two pieces of solid wood, face to face, with the grain running the same direction, you can pretty much use any thickness you want.

My high school shop teacher from 10 years always told us to glue with the grain when gluing face to face. This is Correct?

Yes…... though there could be some exception when gluing thin pieces, such as veneers.

Does this hold true if you are using veneer on a piece of wood? should grain direction match?

As mentioned above, I think in some instance you could get away with gluing with grain perpendicular to each other. But, I would avoid it.

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