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| Resawing some Ovankol - Question http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=18490 |
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| Author: | Goobie [ Thu Aug 21, 2008 6:26 pm ] |
| Post subject: | Resawing some Ovankol - Question |
Hello, I happened across some real nice 1/4 sawn, 4/4 thick piece of Ovankol (or Shedua as they like to call, it was 9 1/2 feet long and 11 1/2" wide. I started resawing them into back and side sets. With a nice thin 1/2" 3 tpi blade I was able to get 4 sides per piece but I'm can't get more than 2 back (plus an orphan) safely on the wider back pieces. I chicken out because there isn't much room for error being only 4/4 thick. One thing I'm trying to figure out is that the first piece I resaw (from the dressed face) always cups badly and instantly after resawing. All subsequent pieces stay nice and straight with no wapring or cupping. I'm hoping I can eventually flatten these out, but I'm still trying to figure out why this is happening... My best guess is that there is some differential in moisture in throughout the board. Also this didn't seem to be an issue for the narrower 5" side pieces I cut. they didn't seem to cup like the wider back pieces do. Any thoughts? Cheers, Chad |
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| Author: | TonyKarol [ Thu Aug 21, 2008 6:31 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
could be case hardening ..the wood was kiln dried improperly (too fast) and the outer layer has stresses in it, which of course release upon being cut. Fix ... I have successfully flattened warped pieces by using my heating blanket, and some wood and weights ont he table saw's table - its just like bending a side, only flattening instead. |
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| Author: | Don Williams [ Thu Aug 21, 2008 6:46 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
It's probably a combination of things. Case hardening is probably the main culprit as Tony said, but I've become convinced that surface tension / surface texture is another issue. If you have one side that is planed, and another that is rough coming off a saw, they two sides are going to react differently to moisture loss/gain due to the amount of exposed surface. I've seen it a number of times, and when I was able to sand both surfaces, it minimized the amount movement. Often I would take a thin slice off the outer surface so that both sides of the first real slice had a bandsawed surface. Perhaps it's just removing the worst of the case hardening. But it seems to help whatever it is. |
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| Author: | Goobie [ Thu Aug 21, 2008 7:07 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
Ah ha! Sounds like you might be onto something. It makes sense to me. Thanks guys, Chad |
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| Author: | joel Thompson [ Fri Aug 22, 2008 6:47 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
it does sound like case hardning a common prob in the denser woods such as coco lrss so with the mid range s.g.woods. i allways make sure the face is freshly planed on the jointer before resawing this usualy takes off the case hardend top layer and reduces the prob. also a fresh sharp blade will help as it will reuce heat build up. the only thing you can do if continues is to end seal with chestnut and sticker and stack for as log as poss which you should be doing anyhow. As for the yeild your getting its about right for a 4/4 peice of wood. when calculating my yeild i allways only allow for two backs from the wood as i usualy cut to 3.5mm for backs and three side sets at 3mm. this depends on the wood as some woods will allow me to cut thinner but i will not below 3.2 to avoid cupping etc. so i will often get three back and sides sets which is optimum. but i will not sacrifice quality over yeild. if you are cutting the sets for personal use and you are very accurate them by all means cut to 3mm but you have to be very good to cut that thin without having some thin spots. if you include the kerf of the saw you will find that two backs and an orphand peice is normal yeild unless you have a very good saw. I would like to know what yeild other folks get. Joel. |
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| Author: | fryovanni [ Fri Aug 22, 2008 7:23 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
Tony seems to have the right idea. Don's theory is interesting. I think Joel's resawing tolerances are pretty good, and as he mentions you can certainly consider going thinner if your saw is up to the task and it is for your personal use(can't usually sell sets if they are close to your thickness, but skinny for what someone else prefers). If you do go tight with the tolerance you do add that extra risk, you may get 3 sets, or you may lose sets. Rich |
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| Author: | Goobie [ Sat Aug 23, 2008 6:50 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
Yeah this is wood I plan to use myself. I didn't mind cutting the sides a little thinner than the backs. They are now at about 3.10mm after being cleaned up a little with a drum sander. The backs I will only get one set per. The saw seems to be doing an ok job, it's a generic taiwanese import 14" 10amp saw with a 6" riser (12" depth of cut) circa 1990. I bought it (barely) used about a year ago. I go real slow so and I'm using a 6" tall fence with a pivot block to help compensate for blade drift. I also seem to need to give the motor a break to cool off between cuts. It seems to get pretty hot and I worry about it... Is this normal I? The motor is currently set up to run on 110V would changing it over to 220V help any? Thanks for the help guys. Cheers, Chad |
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| Author: | joel Thompson [ Sat Aug 23, 2008 10:40 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
Its normal for a small bandsaw to get boged down when resawing as they are not designed for the job. your doing the right thing and taking it slow, let the saw do the work and you will get a smooth cut. you should get two backs from a 4/4 peice of timber. i would advise cutting thicker if you can becouse a small bandsaw will wonder and you will get thin spots if your not very carefull. 3.8-4 is a good target on a small saw, joel. |
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| Author: | Goobie [ Tue Aug 26, 2008 10:09 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
Thanks Joel, When you say 2 backs from 4/4.. You mean 2 pieces (i.e. one set) correct? Cheers, Chad |
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| Author: | fryovanni [ Tue Aug 26, 2008 11:35 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
You should be able to comfortably yeild two bookmatched back sets from 4/4(as long as it is a 7/8" or better, 4/4 does not mean a full 1" if it is planed on at least a face). Rich |
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| Author: | joel Thompson [ Fri Aug 29, 2008 2:03 pm ] |
| Post subject: | Re: Resawing some Ovankol - Question |
what rich said, Two sets for a 4/4 (1") peice of wood. Joel. |
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