Resaw cup on purple-heart ATTN: Bill Tindall

Re: Resaw cup on purple-heart ATTN: Bill Tindall

Arw01

>try misting the concave side to cause it to expand a bit, when it gets flat, then put it under some weight for a few days.

Alan

Re: Resaw cup on purple-heart ATTN: Bill Tindall

bill tindall

>If it sprung as soon as it was sawed then there was tension in the wood. I suspect this species is hard to dry and that leads to this sort of problem, especially in 8/4 stock. I don't consider it a supplier problem. If their profit is big enough they might entertain taking it back but there is no guarantee the next piece will be any different.

What has been suggested could work. What will definitly work is to steam it and then dry it, while restraining it to be flat. Steam will relax any tension. Simply wetting will not relax tension.

I have never tried this but in principal it should work to steam a small piece. Wrap in wet towel, then wrap/seal with foil and put in oven at about 250 F until wood reaches about 200 F throughout. It must stay wet to work. Remove and somehow restrain it to be flat while drying. It must dry evenly from both sides.

The wood cells are already collapsed so it will not take nearly as long to redry as it did to begin with because it will not take up much water.

Re: Resaw cup on purple-heart ATTN: Bill Tindall

Greg Sloop, Portland OR

>I just resawed a 24" long piece.

It sprung in the first 10" and nearly trapped the band. (I was unable to back it back out of the cut and just forced it through the rest of the cut.)

BTW, I measured the cup and it's a little more than 3/8" spring in the center from the edges.

I think I paid about $5 a board foot for it, but have no idea in comparative terms how that compares to others.

As for steam treating... Do I have to heat the whole board, or could I steam the one side till I get it flat.

I may just be out $30 or so for this board, I guess...

Any more ideas you have, I'd be interested.

Thanks again,

Greg

must heat throughout

bill tindall

>to relieve stress you will need to heat the piece throughout. the combination of heat and moisture will plasticize (as in make plastic) the wood which will enable any stress to relax. It requires both the heat and moisture. You could do this to the 8/4 piece, resaw it wet, and then dry, but of course it will take longer to heat the thicker piece. but that will cure the cupping.

The interior of this lumber is under tension, so it is the inside that needs the relaxing.

The reason your band dulled so quickly is

Garrett in Victoria

>that purpleheart is full of silica and very hard on cutting tools.

Cheers, Garrett

Re: The reason your band dulled so quickly is

Greg Sloop, Portland OR

>I know it's quite hard. It's heavy as heck too.

As for silica, it doesn't seem nearly as bad as Jatoba.

But, I think I'm going to end up with a Lenox Tri-master carbide band. The set of suffolk stuff I've currently got have been good to learn on, but for resaw, I'm not too terribly impressed.

(Yes, I know it's expensive. Yes, I know it may not last quite as long on a 16" bandsaw, but if they stay sharp I'm not sure I care.)

As for dulling... I'm not exactly sure it was getting so very dull, but the binding was probably a significant factor.

Thanks,

Greg

Re: The reason your band dulled so quickly is

Bruce, a MN Galoot

>I got the tri-master as a mix-up in an order from Fastenal, and they didn't want to mess around with it so they just gave me the blade for nothing! Heck of a Christmas present.

Anyway, I've cut bunches of stuff, mostly domestic hardwood, and it shows no appreciable difference in sharpness.

I would imagine it would last longer in a 16" machine than my in 14" neanderbuddy.

Bruce

Re: Resaw cup on purple-heart ATTN: Bill Tindall

Clay C in Miami

>Did you do a moisture check after the cut? Might be worth comparing the outside as-purchased-surface percentage with a freshly-revealed surface. One cause of cupping that severe (if it cupped such that the newly-sawn surface became convex) can be that the wood wasn't dry ... I remember resawing a piece of curly redwood that curled up like a potato chip as fast as it came off the saw, though it was visibly wet inside.

Clay

Re: Resaw cup on purple-heart ATTN: Bill Tindall

mikew

>Hi Greg,

First, do nothing other than stack it, dry stickers between the layers. Let it acclimatize for a few days. It will relax, how much can only be determined after a few days.

I have used a lot of purpleheart. Some has been under tension when the veneers are cut, some not. And btw, some I cut down to 1/32" (curly PH). Even on the thin pieces some went wonky. But they all have relaxed over a little time.

You can always steam/heat treat the stuff after a week.

Take care, Mike