Source of fin ply needed

[Banzai88]

The weight alone isn't the solution. It's usually a moisture issue. Weighting the sheet on a flat surface until the moisture content equalizes simply gives it a better chance of being flat

The OP steamed the sheets to try to straighten them out, probably introducing way too much moisture that didn't dry out evenly. Just a spray onto the convex side should be all it needs if weighting it down to even out doesn't do it

I've done this quite successfully more than a few times, thanks. Two of the warped pieces came out OK-ish.

The one sheet that was 2" warped on the 12" run is now dried to about 3 1/2" bowed and is as dry as it's going to get. It's firewood.

 

[Jay Rairigh]

I always have the same problem with 1/8 ply. I do look everywhere I go and buy any flat pieces I might find.
I asked sig to hand select some sheets (1/8 in.) but they came in warped.
I have been able to straighten sheets or fins using water,weight and heat/sunlight.

 

[heada]

Go to the stores and see in person. HobbyTown USA has some great ply (SIG brand for my 2 stores) but costs too much. Woodcraft and Rockler has some great ply but costs a good amount. Find out who your local hardwood supply store is and they'll have the same stuff but much less $$. For Indianapolis, my hardwood supply store is Northwest Lumber Company.

https://www.northwestlumberco.com/products#/plywood
Do some research, find the good source and go there in person.

 

[David Schwantz]

I also go to Rockler, that way I can hand pick the sheets.

 

[user 30299]

The plies have to be cut green when they are that thin. They are glue and pressed with no dry time.
As moisture dries out of the wood, the wood shrinks and causes warping.
This is the problem with plywood. Oriented Strand Board was introduced as a cheaper, more stable building material.
Do some research, I remember reading there is one company that kiln dried thin veneer sheets for making model aircraft plywood. But that has been several years ago. Who knows if that company exists. It could have closed doors or sold out.
But it would seam to me someone out there must make decent ply that is dried before gluing up that is stable enough for model air planes.

The "pressed with no dry time" is not correct. I service the Hardwood Veneer and Hardwood Sawmill industry. The veneer manufacturers have very large, very long and pretty sophisticated veneer drying machines (most made in Germany and Italy). The veneers have minimal moisture content because many of the adhesives are moisture sensitive. Also if the moisture content is too high when the plywood goes to the presses they will get a "blow" between the plies. Basically the water flashes, due to the high temps in the press, to steam and blows the plies apart.

 

[Tyler P]

Some people just get the short end of the stick, it seems. Out of the 8 LOC kits I've built in the last 2 years, I've had zero issues. Never missing anything, all my fins and centering rings were flat and true, no damaged tubes.

The shop I manage deals with SIG, Bud Nosen Models, Balsa USA, and a few others, for wood products. I would say that about 90% of the ply we receive is not warped. That leaves 10% that does arrive warped. After sitting in the rack in a climate controlled shop for a bit, probably another 5% or so actually flattens back to it's proper shape.

I agree that picking the best wood to ship out is best practice, but I know for a fact that our warehouse does that with the wood that gets shipped to our store, and it still arrives warped sometimes. Clearly, you've had some bad pieces and bad experiences. I'm not sure bashing one particular vendor when you said that all 3 had issues is a fair shake. Maybe mention the other 2 that you weren't happy with as well.

 

[Woody's Workshop]

The "pressed with no dry time" is not correct. I service the Hardwood Veneer and Hardwood Sawmill industry.

Thanks for clearing that up. I had the opportunity to tour a plywood mill once. This was construction grade through. They would bring the logs in by huge fork lift, and either roll or slice them. It was stacked on pallets and fork trucked to the next room and run through glue/press machines. Then the sizing cutters. The day I was there they were doing D/E grade. No plugging the knots or sanding. If they had drying machines, they didn't show them to me. But I was just there to put on a roof. They wanted me to see what was going on under the roof before I started so I didn't shut them down if it was an iffy day for rain.

 

[user 30299]

Thanks for clearing that up. I had the opportunity to tour a plywood mill once. This was construction grade through. They would bring the logs in by huge fork lift, and either roll or slice them. It was stacked on pallets and fork trucked to the next room and run through glue/press machines. Then the sizing cutters. The day I was there they were doing D/E grade. No plugging the knots or sanding. If they had drying machines, they didn't show them to me. But I was just there to put on a roof. They wanted me to see what was going on under the roof before I started so I didn't shut them down if it was an iffy day for rain.

Awesome that you got to see a plywood mill. That low grade stuff is boiler fuel if you ask me. We have a few hardwood veneer operation that now CAT Scan the logs before they peel or slice them. They use the scans to determine what is the best way to breakdown the log for the greatest value.

 

[DeeRoc29]

I've ordered from National Balsa with good results over the last several years.