Nothing ventured, nothing gained they say. I think the best time to catch this is right after it comes off the lift at the lumber store, before it has a chance to pick up moisture and warp. The one I used was actually in the back of my van since early March, so I'm sure that didn't help. Of course, some warpage is unavoidable, but I do believe sanding the rough side smooth would make a big difference. Also, since the good side of this plywood has been sanded, the veneer is substantially thinner than the veneer layer on the back, which would add to this problem slightly. You can help support the work I do in making these videos: Plans for sale: www.ibuildit.ca/plans.html Support this channel on Patreon: www.patreon.com/user?u=865843&ty=h Did you know I have other KZfaq channels? My main channel: kzfaq.info My home reno channel: kzfaq.info My "Scrap bin" channel: kzfaq.info Website: www.ibuildit.ca/ Facebook: facebook.com/I-Build-It-258048014240900/ Instagram: instagram.com/i_build_it.ca/

John, I always enjoy your videos because you give the ideas that don't work as well as the ones that do. That way we don't waste our time trying the ones that don't work.

I love how you experiment with stuff like this and just show it how it is, whether it works or not. I like the idea of your theory, and I'd be curious about adding moisture to the smooth side, say, wiping it down with a damp sponge or misting it with a sprayer. Can't wait for the router table!

Thanks for taking the time to do this. Your work background in conjunction with what you're doing here, now, is very informative and interesting (to me at least) and there are many insights to be gleaned from just you going about your project/work, even those as subtle as eye movement or how the hand reaches for a tool. I mean, it's nice to see a competent person exercise their skill. There are many other people that cater to us woodworkers (on YT) and I think that you definitely fill a niche regarding the practical side. It's good stuff John. Cheers from here. Thanks. (Damage control: drippy/mawkish, can't a person just express their appreciation?!?)

Cool idea, I'm interested to see you try other options

I'd love to see the same experiment with a torpedo/salamander heater. Of course that doesn't fit well with an already hot, humid workshop...but it's certainly a very dry heat. Good thought process with moisture collecting on the one side...brilliant actually.

i cant believe I watched this whole video lol. Not that i haven't spent quality time in my shop doing less than nothing

I've heard that laying the cupped side down on a concrete floor will increase the moisture uptake of that side and help take the cup out.

Didn’t have a heat gun or an iron handy so I used a torch and it really made a difference, thanks for the *hot* tip!

hi John, nice video mate! love the content u put out! makes me think out the box to,

I used an old small cast iron table saw top plate as a router table and spent time flattening it only to find it was a little raised in the middle. It was only when I read that Trend router tables are raised in the center just in front of the cutter where the business happens, that I let it be. Maybe a little warp in the middle is beneficial.

I had three ply Baltic birch plywood which I sanded all the way down to one ply.I know ridiculously time consuming and unnecessary work,but I needed thin wood for a cajon faceplate and Home Depot and lumber shops in my area did not have it.When I got to the last very thin portions of the second ply,I noticed the more the imbalance of thickness was the more extreme the bow.the wood it was glued to was keeping it straight and or bowing it depending on how it was being sanded off.Hope this helps someone.

Just wet the other side with a cloth, you will see the board get flat in 5 minutes. It worked for me a few times with 40 mm plywood doors..

My guess is that warpage is mostly caused during the manufacturing stage when the plys are still a little more wet than they should be and inconsistent from one ply to the next. It gets pressed straight with these inconsistent moisture levels and then as the moisture equalizes over time the warping occurs.

Down here in my part of Texas we have big changes in humidity especially on the high side. I straighten out plywood by taking a spray bottle and putting a fine mist on the concave side with more in the places where it is worse. Then I lay it concave side down and put some weight on the bowed places. If it is a big sheet and really bad I might shim up the corners. If it is hot and sunny outside I will lay it on the driveway. If not I will lay it on my shop floor. Sometimes it works in a just a few minutes outside so you have to watch it. Even inside I rarely have to do it over a couple of hours.

Better work with hdpe... Nice experiment. You might be on to something. Plenty of moisture changes here in the Netherlands too!

Great video.. going throught the various techniques very useful. I love the shirt too! :-)

I wonder if the grain pattern has an influence on the cupping as well. usually the good side has fairly tight smooth grain and little if any knots. where as the back has knots and grain that wraps around those knot and just a worse quality of grain in general. maybe it also comes from a different part of the tree. like the cleaner face from the core and the back side from the outer most veneers. I have no idea just thinking out loud.

Saw the British Steel Tour in Asbury Park on the Boardwalk.

Nice experiment weather it works or not , one can still gain knowledge from this video. My view (and I’m nobody ) as a career in laminated composite fab is : 1- laminates need to counteract the force of the other. I.e. first ply down at 0/90, next at 0/45 deg, however , if the plywood was purchased flat, then the factory that assembled the plus got the bonding pattern correct. 2- it’s true where by sanding ( removal of thickness ) to one side should be performed to the opposite side of bonded stack , so be aware of what grit , rate of change-out to fresh piece of sandpaper and pressure applied to the sanding block or sander so you can repeat that process in opposite side of bonded stack. 3- it’s my feeling that yes moisture is 50 to 80 % of the issue, but and lastly 4- I’ve been told once warped always will be warped. There may be a way to temp remove the warp but it will return. I’ve tried various experiments with misting and weights to no avail.

Hi, can you help me to straighten some woods without cutting or sanding. I searched but could not find.

Also, the glue(s) used to bond the layers, depending on what they are, can show various amounts of "creep". So it can warp over months, and it'll tend to take a similar amount of time to get it back, unless you heat it (assuming the glue responds correctly to heat, obviously). And unfortunately the heat used to dry the wood is sorta working against you in the short term.

will this work with a 1.5" thick piece?

Love the shirt man

Not exactly useful. I got batch of bent plywood (3 mm thick), and not able to put it flat on the laser cutter. Is there anything I can do to make it flat?

you could try putting packers under the 4 corners THEN put a weight on the board to try to bend the board back to a straighter form sort of like bending a spring you over bend it then it springs back to a straighter board

Anyone know the story behind the $20 USD on the tool wall?

Interesting experiment. Recently I glued and screwed a 1.3 metre length of 2" x 1" timber to one face of a similar length of OSB3 board (the moisture resistant grade) which was cut 72 mm wide from an 18 mm thick sheet. The timber and the OSB board had been stored together for some time so the moisture content should have stabilised. The following day the pair had bowed dramatically with the timber on the concave side which suggested the effect was not due to moisture absorption. It had been a very warm day when I joined the two but the next day was a good 10 degrees C cooler so I suspected temperature change was the cause. I placed it in the airing cupboard which was about the same temperature as when I joined the two and it straightened out. Within minutes of it cooling it had bent again - had to be temperature - moisture content of the timber would not have changed that rapidly. I'd inadvertently made a wooden 'bi-metal' strip! I've since remade the item using two lengths of OSB cut from the same sheet with no further bowing. The lesson: don't mix your materials if you want them to stay flat.

I put the question of warping to P J White Plywood here in BC, and was told that for all but premium grades, the problem is that to keep prices down(?), low grade cores are sourced in Asia and only the face veneers are laminated in North America.

Big sheets of plywood have some internal forces because of the manufacturing process and deviations in the wood grain. Moisture variations in air and wood can also affect this force balance. When you cut the panel, internal forces are released and cut pices bends slowly one way or another. Thinner the panel, bigger the problem. Plywood also has a small design flaw, you should have always same amount of layers on both grain directions. This one has same direction on both sides and this makes unstable construction. I have cut several ply and particle boards with same results. Bad batch or wrong storing conditions is to blame. I live in Finland and seasons affect strongly in humidity in shop air. T. Carpenter from Finland

Hey John, i know this is an old vid... I wonder if it would be helpful if you put your weight on it, like in the vid, but also put a fan blowing over it over night? Might help with drying it out? Just a thought...

Interesting experiment, it's a shame it didn't work out or maybe it just needed more time? Why don't you run a dehumidifier in your workshop, if you ntry and keep the humidity in the 40-6-% range then you should get a lot less movement in the wood due to humidity over the different seasons. Just make sure you get a dehumidifier with a compressor as they work a lot better than the desiccant based ones or at least that's my experience. I haven't tried the enthalpy wheel ones yet though... I have found it to be a lot more important to control the humidity than the temperature in my garage when I do any woodwork in there.

I have found the best way to store plywood in any size is laying flat with weight on top of it to ensure no bowing happens. I made the mistake of laying plywood up on its Edge and it ruined the entire sheet by the time I was able to use it. I soaked it in water laid it flat and let it stay that way with weight on it for about 3 weeks to dry out that helped a lot.

The cheap chinese version of baltic birch always warps, unfortunately it's dry clean only.

Did you try the steam feature on the iron? It works great on my pants.

My thought on the warping is when you glue ply of wood together you need to have equal amounts on each side...when you sand one side you have changed the balance..Sanding both sides would balance it out, but of course suppliers are not going to do that...

Not sure about your moisture theory. I brought a sheet of very similar 18mm [3/4"] ply yesterday and it rained on it on the way home. The sheet was laid best side up on the trailer bed and it went hollow by several inches on the wet/best side in under a 1/4 of an hour journey! I'm going to lay it across two edge battens in the sunshine with the convex B side up to see if it makes any difference.

hehe... I could have used this a couple weeks ago :)

You can control the humidity in your shop by moving to Nevada.

Heating it up then weight combo.is where u got it.. the longer the more weight the better. More heat moisture. Weight time. You would get it straight as a nail

Nice push stick XD!

I Build It , it’s very easy to know why it’s bent .... as you say one side is good and the other not so good . Now in marquetry , or in veneering , if you put a layer of veneer on one side , you have to do so on the other side .If not it will worp ! So in my theory , it’s missing a layer of veneer on the bad side !! Try it and let me know . 👍🏼😉🇨🇦

I'd like to know how to unwind a 2x4.

Oh wow wrinkle free plywood!

To flatten cupped wood, wet it down until it's soaked through. Clamp edges to a flat surface (ex. workbench) and add clamped cauls across the board. Let it dry and unclamp your flat board.

If you are relying on the structure below to keep it flat i recommend making a few shallow score cuts on the table saw on the underside to make it more flexible so it doesn't apply weird stresses. Its a dirty trick but it works :p

Wipe the other side with water, as well.

Bring out the old spray bottle and spray the concave side

I warped some inch baltic ply when i varnished it on only one side. Strong stuff that varnish. so maybe you could varnish the bottom and pull it straight.

👍

Sweet Judas Priest t-shirt John!

Judas Priest 🤘🤘🤘🤘🤘🤘🤘🤘

Just wipe some oil on the other side so it swells until straight! lm kidding!

Spray the cup side with water then weight it down overnight.

For the first few minutes I though it said John Heisz on you T-shirt, not Judas Priest (yes, I did go to school)

John you ever heard Primal fear? They are a Judas priest clone (singer sounds the same)... freaking awesome, check out "Metal is forever" on youtube

Great ironing technique John - you'll make someone a lovely wife 😉

Him only here to see the concert t-shirts

l

Pour hot water on it and clamp down

Came here for timber, found Priest\,,/

Your videos are great,but please try and upload all your videos on a single channel, Cheers!!

Nice Judas Priest t-shirt !

Paint both sides of it.

Cool Judas Priest shirt.

One way to dry electronics is by using rice. Maybe order a Chinese takeaway and eat it on the ply wood? Worth a try

Your wife will kill you when she finds out what you did with her iron. God Bless my friend.

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