Flattening plywood


Meatwad
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I don't have access to good plywood. Home Depot is my best source and I always wind up with some slight warping. This is only a problem when I try to make jigs/sleds for my table saw or drill press. I've seen different tricks around the net for warping/de-warping plywood but they all look pretty extreme. So I was wondering if anybody has any tricks they use when they get a piece of plywood with a slight warp or one that warps after they get it home. Seems like you could just wet it down a little and smash it?

I can't be the first person to think of this, hence my topic!

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On 7/21/2022 at 9:29 PM, Coop said:

Maybe use mdf if possible?

That's been my solution so far. But I have decided to try out some of the Microjig matchfit dovetail products so I need something that can take the clamping pressure. I will test MDF, too. It's certainly cheaper now.

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On 7/22/2022 at 4:53 AM, curlyoak said:

What grade go plywood are you buying at home depot? The stuff they put on roofs is for roofs only.

https://www.homedepot.com/p/Columbia-Forest-Products-3-4-in-x-4-ft-x-8-ft-PureBond-Birch-Plywood-165921/100077837 

Yes, birch is usually what I get. It's not terrible in most cases but it's hard to tell until I get it home. Sometimes there's a twist in it.

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We have a McCoy’s Building Supply here in Houston that I buy bb ply from. I see that they have stores in Arkansas. Might look them up to see if there is a store near you.

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On 7/22/2022 at 11:48 AM, Coop said:

We have a McCoy’s Building Supply here in Houston that I buy bb ply from. I see that they have stores in Arkansas. Might look them up to see if there is a store near you.


If they still have BB available at a reasonable price you should buy it all! It’ll probably be several years before BB prices and availability normalize unless a good alternative becomes available. 

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Most of the finish type plywood at HD! Menards, Lowes, etc  the veneer is really thin and brittle. I've bought MDF , oak, birch 0ly from the big box in a pinch....

At one time HD was selling Chinese birch for $24 a sheet. It was excellent for shop projects etc. Later the price climbed and has disappeared...

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On 7/22/2022 at 1:07 PM, BillyJack said:

Most of the finish type plywood at HD! Menards, Lowes, etc  the veneer is really thin and brittle. I've bought MDF , oak, birch 0ly from the big box in a pinch....

At one time HD was selling Chinese birch for $24 a sheet. It was excellent for shop projects etc. Later the price climbed and has disappeared...

It's normally around $27 here in Arkansas for a 2 x 4 ft sheet of 3/4 inch. Yesterday it was $ 40.

I got some scraps around here to test with so I'm really hoping MDF will suffice for my needs.

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Particle board, MDO, masonite, MDO and melamine make excellent jigs, etc for around the shop. MDF is good for small jigs , but PB os better for larger ones. PB has picked up a bad rap from the hobbyist, but is an excellent product..

 

I've worked at shops with PC cabinets and drawers. If constructed correct, they will last a long time..

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Well believe it or not I bought a cheap 2 x 4 3/4 inch plywood sheet from HD and got it home and it was dead flat. I cut it basically down the middle. After I routed a dovetail grid on one piece I decided to put some wipe on water poly on it. I left it overnight and that turd had a 1/16 inch bow in it this morning.

So I wet it down and have it smashed flat. We will see if that does anything at all.

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I bought a sheet of ply from Menards for flower boxes. It's still sitting in the garage acclimating. As soon as I cut it I'm sure it will do its thing. Maybe I'll get lucky, maybe not but I prepare..

 

Biggest thing with ply or lumber is to keep the project moving till complete. Many will cut parts come back the next weekend and ask "why".... Same with clamping up boards to make tops. Leave it in the clamps till your ready to do something with it. Leave the "why" out..

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On 7/28/2022 at 10:13 AM, curlyoak said:

Meatwad, what are you building with the plywood?

I'm making a sled for my router table and another for my table saw so I can use my matchfit clamps.

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On 7/28/2022 at 1:19 PM, Meatwad said:

I'm making a sled for my router table and another for my table saw so I can use my matchfit clamps.

Then you will attach other pieces on edge to the bottom. And hardwood runners. Look for bowed wood and apply the runners to help flatten. You can countersink lag bolts in the runner bottoms. Do you have a drawing or plan for the sleds?

PS I think baltic birch might be a choice...

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