[GME]

Hello Yuri - Its good to work in plywood. You will need to make it quite a bit stiffer. Use Boxes for the gantry and the columns. Single plane pieces of PW are not stiff enough in transverse bending. Boxes can be stiffer than metal if big enough. There are many very good timber machines in this forum. Look for videos and info on the Mosquito airplane it was made from plywood and was an advanced machine at the time. I'm designing a mast for a large catamaran and it will be plywood and it will be lighter than the carbon fibre version so go for it.. Peter

Peter, when you say "boxes" do you mean "torsion boxes?" Given that Yuri is from Ukraine and English probably isn't his first language, he may not understand the term "boxes" to mean "torsion boxes."

IMO, torsion boxes are the best option for a build in plywood, assuming the boxes are built correctly. The inner grid members must be cut precisely, and the boxes need to be assembled on a perfectly flat reference surface. Any irregularity will be reflected in the finished product. It's very easy to induce twist, high stops and/or low spots, if one is not very careful. I'm a big fan of torsion boxes. Lot's of strength and rigidity.. However, very fussy to build correctly.

Yuri, If you are not familiar with torsion boxes, you should know that the greater the distance between the two outer skins, the stiffer your torsion box will be. So, a torsion box with an internal webbing that is 100mm in height will be considerable stiffer than one with 25mm webbing. I've read that if you double the thickness, you increase strength by 8 times. A dramatic increase.

Here's a link to ger21's wooden CNC build thread. Gerry has been working on his build for more than 10 years, so his threads are pretty long to wade through. Still, they contain useful information on torsion boxes. https://www.cnczone.com/forums/cnc-w...0-autocad.html The Internet also contains a much information on torsion boxes. Here is a thread showing an 8 foot (2438mm) long torsion box made exclusively of 3/16" (4.76mm) hardboard. https://www.popularwoodworking.com/p...a-torsion-box/ Loaded with 300 pounds (136 kilos) of bricks in the center, the deflection was only 1/2 inch (12.7 mm). Had the box made made of 18mm baltic birch plywood, I'd guess the deflection would have been measured in the hundreds of a mm or less. If thick enough, there may have been no deflection.

Here's another link to get you started on research: https://www.google.com/search?sa=N&r...w=1093&bih=530 The link is to a number of photos which are linked to threads, blogs or articles on actual builds.

To add some perspective, aircraft wings are built on the torsion box principle. If you think in terms of the gigantic military transport aircraft, you get an appreciation of just how strong they can be.

Hope this helps.

Gary