Building Tips and technical articles. > Building techniques
Rip-sawing balsa
FLOYD CARTER:
I sometimes need balsa sticks, or smaller x-xection balsa strips. With table saw or band saw, the pieces often come out warped from heat generated by cutting. I wonder how balsa strips are cut commercially. Maybe I need a special saw blade? Or slower cutting speed? I cant slow RPM on my tools. Thin balsa sheets can be cut with sharp knife and straight-edge, but in thicker pieces, the cut doesn't always result in completely rectangular or square strips.
pmackenzie:
Not sure it is the heat of the cutting that causes the warping.
More likely it is internal stresses in the wood that are released when the piece is cut out.
Dan Berry:
--- Quote from: pmackenzie on May 08, 2022, 01:55:10 PM ---Not sure it is the heat of the cutting that causes the warping.
More likely it is internal stresses in the wood that are released when the piece is cut out.
--- End quote ---
This is correct.
Brett Buck:
--- Quote from: FLOYD CARTER on May 08, 2022, 01:45:14 PM ---I sometimes need balsa sticks, or smaller x-xection balsa strips. With table saw or band saw, the pieces often come out warped from heat generated by cutting. I wonder how balsa strips are cut commercially. Maybe I need a special saw blade? Or slower cutting speed? I cant slow RPM on my tools. Thin balsa sheets can be cut with sharp knife and straight-edge, but in thicker pieces, the cut doesn't always result in completely rectangular or square strips.
--- End quote ---
It's much less prone to do this if you use a jigsaw, so, I think both the heat and the impact make a big difference. And certainly heat will also dry the wood, causing it to shrink on the hot side.
Brett
Dan McEntee:
Most commercially cut balsa wood is cut with special blades of one kind of another. When I was trying to cut some of my own sheet wood years ago, it was suggested to use a meat cutting blade in a band saw. This type of blade has little to no set to the teeth. If using a circular saw, a similar type blade with no set to the teeth is used,, but it is also hollow ground soo it is thinner behind the teeth. To keep heat from building up you need a kerf behind the cut, and that is what the set in the teeth is for. A hollow ground blade achieves the same thing. Thicker sheets and blocks are cut close, then run through a thickness planer or sander to finish them off. This works for sticks down to a certain size. Smaller sticks can be cut off sheet stock with a balsa stripper. This works up to about 1/4" square. If you remember building Guillows sand Sterling rubber power kits, they had 1/16" square stick that were connected at one end. There were cut is some sort of gang saw, and if you look at the end where the kerf stops you can see evidence of that. When SIG first started cutting balsa in large quantities and volume, Glen SIG had blades made with a sanding type surface on both sides and no set to the teeth to try and get a smooth , warp free cut, and I think he had a patent on that, but more modern technology took over from that before too long. I tried using a jig saw for cutting wood, thinking that the narrow blade would avoid a lot of heat build up but even with a dead steady fence, the blade can hit hard spots and twists in the wood grain and twist the blade. After a while I gave up unless I was just cutting wing tip blocks and such. Finding the special blades for home use was very difficult. The late Carl Frieze of NFFS fame had a hollow ground circular saw blade made for his saw at great cost, and did not try to cut anything longer that 18 or 20 inches. Some other guys in the Thermaleers free flight club figured out how to surface grind balsa sheet for indoor model use and could g down as thin as .015" on smallish sheets. I don't remember how they did it but the finished wood was pretty nice.
Type at you later,
Dan McEntee
Type at you later,
Dan McEntee
Navigation
[0] Message Index
[#] Next page
Go to full version