Cutting ply sheets

[Pete79]

Random question about cutting strips out of ply for all of the woodworkers out there.

I need to cut the sides for my new roof on the Finch.
My sheet of 12mm marine ply is 1220 x 2440. Unfortunately the long sides need to be 2500.

I’ve worked out how I can nest all of the pieces I need into one sheet, but my question is about the odd grain angles that will be in my strips.
My ply is good quality (not Bunnings) stuff and even after about 3 weeks laying on 2 trestles it’s still perfectly flat.
So I’m guessing it doesn’t really matter, but could I expect to see any weird twisting or warping of the panels over time if I cut them out of a sheet like this?

[GBC]

If there is, rest easy that there was no way of working out which way it would spring before you cut it. Usually cross laid ply will counter it’s own internal stresses and remain neutral. Non structural Bunnings hardwood ply - can go any which way but generally not straight haha. It usually springs straight away rather than over time. I wouldn’t worry too much, if it is good furniture grade gear you’ll be fine.
Ps always store sheet and doors on their long edge or dead flat if fully supported.

[DarWen]

Hi Pete,  For neat  edges  if using a circular saw, use a blade with as many teeth as you can find.  When cutting the long edge you will be able to rip straight up the length of the sheet.  When cutting the short edge if you don't use sacrificial board you will get break out. ( This is when the saw blade picks up the grain of the face and splinters the edges.)   if you use a sacrificial board remember to use some on the on the other side of the cut line so that the base plate of the saw sits flat.  I used to cut up to 2 tonne of ply a day using this method. Also the marine ply you have is possibly not twisting because of the way that it has been laid up, giving strength to both directions of the sheet.  Don't forget to seal the whole Broad once cut.  I hope this helps.   

Regards Darren.

[MB TD42]

Cut it how ever you like...its ply...the laminates are keyed 90 degrees to each other as long as top is same as bottom.

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[Spada]

and have the blade of the saw as shallow as you can so the teeth of the blade are ripping from an angle. A deep blade will be ripping almost vertically which causes more breakout from the top layer.

[Pete79]

Thanks for all of the tips and advise guys.

Just going to cut it on the angles as per my sketch and hope for the best.
I don’t expect it to bow or twist much, if at all.

At the end of the day whatever I do is going to be better then cutting the 2.4 length and stapling on a 100mm piece at the end like they do in the factory.

[Alan Loy]

Just for future reference and for others who need ply longer than 2400, you can get some types of ply that are over 3000.