kiln dryed 8/4 birch is warping through the table saw and we can’t figure why, we’ve tryied flipping the material and different saw blades and cannot come up with a solution any concepts would be most appreciated.
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A band saw comes to mind.
T
Do not try this at home!
I am a trained professional!
Sounds like it may be case hardened caused by improper kiln drying. Ripping case hardened material on a table saw using all the guards normally employed on such machines in the US, i.e., none, is a dramatic, vivid, and memorable way of learning all about the causes of, and the results of kickback. I'd suggest you do the bandsaw test on a short length before you go any further. Take a piece about 4" wide by your 2" and use the bandsaw to create a pair of wide forks in the end by removing some material out of the middle across the width. If the forks close, it's case hardened, and you should take the lot back to your supplier for replacement as faulty goods. Slainte, RJ.
Edited 6/7/2002 6:10:07 AM ET by Sgian Dubh
I've heard of this, and heard it called "reaction wood".
The theory is that trees that grow at an angle will have some of the cells compresed more than on the downhill side. So every time you cut it, you release some of the pent up energy, and it tries to bend "uphill".
The only solution I know of is to make short pieces out of it, or make firewood.
When cheese has its picture taken, what does it say?
Boss, whether it's case hardened-- more likely by the description of its reaction to the saw, or 'reaction' wood caused by growth location, or other circumstances is neither here nor there as far as usability of the timber. In both cases it will be unstable in service so if, for example, it's door frames the rails and stiles can be expected to 'walk' all over the place, which wouldn't augur well for customer satisfaction. In either case, these are substandard goods and they should be returned to the supplier and exchanged. I should have said the bandsaw fork test in my earlier post. My error. Slainte, RJ.RJFurniture
I agree it's probaby not useable - Isn't that what I said?
BTW - What's a "bandsaw fork test"?
There was a power outage at a department store yesterday. Twenty people were trapped on the escalators.
Yes Boss, you did say it was unusable. I simply modified that to, 'Its only use being to take it back to the supplier and get the same amount of good stuff in replacement,' if you see what I mean.
I desribed the bandsaw fork test in my first post, but to elaborate a little, case hardening is caused if the wood is kilned too quickly then the surfaces dry out at a rate quicker than the rate of movement of the moisture by capillary action from the centre of the plank, with the result that dry outer layers are in tension, and the moist interior in compression. It can be cured by steaming and rekilning. A safe way of testing for the condition is to cut a short end off a plank, say about a 2' long, square it if possible, and stand one edge of this short section on the band saw table and cut a section out of the middle at the freshly exposed end about 1/4" wide, and about 2"-- 3" long to create a fork-- it looks like the female part of a bridle joint. Centre the cutout on the end. If the forks close, which can be measured accurately with a vernier gauge, it's case hardened. If it's very badly case hardened, there's no need to measure it, the forks will almost close up.
This is an infinitely safer method of finding out that a batch of timber is case hardened than using a typically unguarded US cabinet saw with all the potential for kickback that entails. Birch has to be dried slowly, and whilst I'm no expert at timber seasoning the tempation for the kiln operator must be to hurry the job to save/make extra money. I'd guess that 50%-- 60% of the kilned birch I've purchased in the past has been case hardened, so for this reason I've stopped buying and using it. I don't think I've used any of the birches in the solid for maybe seven years. Slainte, RJRJFurniture
well thank you all very much for your replies i find them most informative , with one additional question. how can one tell from the date of purchase at the supplier if case hardened is present in an order. and is this primarily a problem with birch or can/does it exist in other species. thank you from handcrafted cabinets
p.s. we have worked through building these bifold doors by only ripping in one direction and then using the planer for reducing the other , this has worked well
Edited 6/7/2002 8:48:10 PM ET by handcrafted
handcrafted, you can't. Purchase date is a useless determination for case hardened timber. It either is case hardened , or it isn't. It could have been kilned last month, or fifty years ago, but if it's case hardened, it's case hardened. In my experience birch is notorious for the condition, for it's a timber that has to be kiln conditioned slowly, which is diametrically opposed to drying properly and making a fast buck as directed by short termist bean counters. All timbers can be improperly kiln conditioned to be case hardened. Thick maple, oak, cherry, mahogany, pines, etc., are all notable for exhibiting the fault. Thin stuff can be just as badly seasoned, and it's all down to the skill, experience, and knowledge of the kiln operator, and the pressure applied to the kiln operator by the bean counters, and what the public are willing to pay. Slainte, RJ.RJFurniture
If you can't return the case-hardened wood, you may be able to relieve some of the stress causing the problem by ripping almost halfway through from both sides leaving 1/4" or so holding the board together. After doing this, let it sit for up to a week and then rip right through. It has worked for me more often then not, but not always.
Dick, if it's case hardened, running the board as you describe, i.e., burying the circular sawblade, is the very last thing I'd recommend. Your advice sets up all the right conditions for a potentially lethal kickback. Slainte, RJ.RJFurniture
You're right. This should probably have come with one of those on-screen captions saying 'Don't try this at home'.
Other than to say I never perform any task on my machinery unless I am in complete control, I won't try to defend the technique.
Dick, I've never been in complete control of a table saw. There is always the 'what if' factor, the wobbly, the piece of cast iron in the wood that we can't see or account for, the tooth that breaks off. Complete control never happens, and imperfectly evaluated risk is the best we can hope for. Slainte, RJ.RJFurniture
ya know you can never be to safe and even then you can never be to safe , saw kick is inherent in this trade and if you aint on your toes and expecting it every time you turn that saw on then dont turn that saw on and go get a desk job
Never had a desk job handcrafted, but I've come across a few kickbacks. Slainte, RJ. RJFurniture
Complete control never happens, and imperfectly evaluated risk is the best we can hope for.
That could be said for putting the first foot out of bed in the morning as well.
very well spoken
Indeed.
Slainte, RJ.RJFurniture
Agree with Sgian on case hardening being the likely culprit; if you have that kind of choice when buying material, lumber that has been dried with a dehumidification kiln or even a solar kiln often has less stresses than what you find out of a dry kiln, where the schedule often does get pushed.cabinetmaker/college instructor. Cape Breton, N.S