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Author Topic: Rip-sawing balsa  (Read 641 times)

Offline FLOYD CARTER

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Rip-sawing balsa
« 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.
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Offline pmackenzie

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Re: Rip-sawing balsa
« Reply #1 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.
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Online Dan Berry

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Re: Rip-sawing balsa
« Reply #2 on: May 08, 2022, 03:24:55 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.

This is correct.

Online Brett Buck

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Re: Rip-sawing balsa
« Reply #3 on: May 08, 2022, 03:43:39 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.

    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.


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Online Dan McEntee

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Re: Rip-sawing balsa
« Reply #4 on: May 08, 2022, 04:09:31 PM »
    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.
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Offline Dave_Trible

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Re: Rip-sawing balsa
« Reply #5 on: May 09, 2022, 10:37:27 AM »
I still use the equipment I built when I made kits.  Then,  I made a small router table with a fence and use a diamond cut router bit-  looks like a rotary wood rasp.  Just set the fence for width and the router depth for height.  Makes a lot of powder thin balsa dust but you can cut perfectly straight sticks. 

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Offline Dennis Saydak

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Re: Rip-sawing balsa
« Reply #6 on: May 10, 2022, 05:26:54 PM »
Floyd, here's the resaw blade you need, which I now use for making guitars.
https://www.highlandwoodworking.com/wood-slicer-resaw-bandsaw-blades.aspx

Way back when I used to scratch build I Beam models (Argus, Barracuda etc.) I had serious warping problems hand-cutting straight spars. Using a bandsaw completely completely eliminated warped spars. The wood slicer blades have a very narrow kerf.
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Offline BillLee

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Re: Rip-sawing balsa
« Reply #7 on: May 10, 2022, 06:49:46 PM »
Remembering what I saw at Lone Star before the fire....

Sheets are cut off the large blocks using a horizontal bandsaw., cut large and then sanded to proper thickness.

Sticks were made from the appropriate thickness sheet using a special table saw with multiple ganged blades set the proper width apart. As I recall, they were not large diameter blades, more along the lines of those used in a biscuit joiner.

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Offline FLOYD CARTER

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Re: Rip-sawing balsa
« Reply #8 on: May 11, 2022, 11:00:31 AM »
Thanks for the responses.  I have had some luck with a band saw and a long fence.  Problem was how to set the fence exactly parallel with the blade, which tended to wander and twist.  I fail to see how warps result from "unlocked" internal stresses.  If so, then each and every piece made by large commercial balsa manufacturers would have to be individually straightened.  I don't think they would do that.
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Online Dan McEntee

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Re: Rip-sawing balsa
« Reply #9 on: May 11, 2022, 03:03:37 PM »
Thanks for the responses.  I have had some luck with a band saw and a long fence.  Problem was how to set the fence exactly parallel with the blade, which tended to wander and twist.  I fail to see how warps result from "unlocked" internal stresses.  If so, then each and every piece made by large commercial balsa manufacturers would have to be individually straightened.  I don't think they would do that.

   But that is exactly what happens. It gets worse as a blades get dull. This is one reason for cutting the sheets a bit oversize and then sending them through a thickness sander or planer, and that tends to "settle" them down. It's the same effect as if you try to use a knife and straight edge to strip wood. It will always come off bowed.  Some band saws have better blade guides than others, and that is one part of the recipe, If the teeth with the set in ne direction get damaged or dull for whatever reason, that will cause a blade to wonder. Part of the recipe is to have brand new blades and don't use them for anything else. Those blades that Dennis Saydak put the link up for look like they are the answer. You do need to make sure that the blade isn't too sloppy in your blade guides since it is so much thinner. It takes practice and knowing what to adjust on your saw.
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Offline Dennis Saydak

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Re: Rip-sawing balsa
« Reply #10 on: May 12, 2022, 09:26:39 AM »
My Woodslicer blade works extremely well for me on my ancient Sears band saw. A proper saw setup is critical to eliminate blade drift. I also replaced the metal blade guide blocks as recommended on the W.S. web site. Along with proper saw setup it is critical that the blade runs on the center of the rubber tires. Too far forward and the blade drifts one way and vice versa.

Here's an excellent video about all of that from a guy who really knows his stuff:
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Offline Tim Wescott

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Re: Rip-sawing balsa
« Reply #11 on: May 12, 2022, 03:14:33 PM »
...  I fail to see how warps result from "unlocked" internal stresses. ...

When I'm building little planes and I strip a stick off of a sheet, I basically count on the strip being bent.

Half the time that I split a sheet in half the two halves bow -- sometimes inward, sometimes outward.

So -- I think the whole "internal stresses" thing is real.

  If so, then each and every piece made by large commercial balsa manufacturers would have to be individually straightened.  I don't think they would do that.

I have found that if I take a warped sheet of balsa and put it on a good flat shelf, with a bunch of other sheets of balsa on top of it, then after a few months of the humidity in my shop cycling (or whatever the actual phonomenon is that drives it), the sheet is flat.

So maybe every piece of balsa made by commercial balsa makers is individually straightened, by the simple expedient of proper storage.
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