Replies

1. 
   PlaneWood | Jan 03, 2003 04:38am | #1

   Mahogany -

   Drying and Shrinkage: The wood can be air-seasoned and kiln-dried easily without appreciable warping or checking. Kiln schedule T6-D4 is suggested for 4/4 stock and T3-D3 for 8/4. Shrinkage green to ovendry: radial 3.0%; tangential 4.1%; volumetric 7.8%. Movement after manufacture is rated as small.

   What difference in EMC can you expect between now and this summer?  I would think, based on the above data, that expansion would be less than 1% which would translate to 1/100" expansion for a 10" wide piece.  Like they say above - "small".

   Recon that was one of the reasons it was so popular as a furniture wood?

   PlaneWood by Mike_in_Katy
   PlaneWood

1. 
   Vterry | Jan 03, 2003 05:18am | #2

   Thanks for your help! First time I made anything significant in mahogany and it was a joy to work with. It was clear why the colonial furniture makers used it and now that you've filled me in on the stability issue it's even more impressive.

   Thanks again,

   Terry

2. 
   jonsherryl | Jan 03, 2003 06:39am | #3

   Mike, your stats are flawless...but I think your math needs some work. The worst case scenario here would be the tangential shrinkage of 4.1%, or a maximum expected shrinkage of just over 4 tenths of an inch on a 10" width, green to ovendry. Assuming the in-use EMC range will span about one third of this maximum potential (i.e., 5% to 15% MC), then, an allowance of about 13/100" might be necessary (about 1/8", if we assume the wood is put in use at it's driest EMC.) If it's quartersawn genuine mahogany, then only about 3/32" should do the trick.

   ...But then there's the question of which "mahogany" we're dealing with here? If it's not genuine mahogany (Swietenia), or the other "real" mahogany (the African; Khaya, which is almost as stable), most of the counterfeits like lauan and meranti experience much higher shrinkage...Don't mean to knit pick, but if he goes with a clearance of only 1/100", he'll need a crowbar to open that drawer come May.

1. 
   PlaneWood | Jan 03, 2003 07:22am | #5

   oops!  move the decimal to the right and multiply by 4!!!

   PlaneWood by Mike_in_KatyPlaneWood

2. 
   SgianDubh | Jan 03, 2003 07:30am | #6

   Gawd, Jon. You guys with your whacky, off the wall, decimal inches,--- and fractions of an inch too? I wish you Yanks would make up your mind what system you'd like to work in, ha, ha!  What is that 13/100th's"? I just tried using my Construction Master calculator to get a grip on how big (or small) that is. It blew out with a major brain fart, and that was the end of that.

   Hmm, let's see, 13/100ths. of an inch must be a bit more than a 1/10th".  About 2.7mm. Now we're talking numbers that make sense.

   As for drawer sides and fronts getting a bit tight, make the piece, and the drawers, put the lot inside normal interior conditions, drawers not installed, let it all acclimatise for about a fortnight, and trim the drawers to fit snug. Watch them as the seasons change and trim the drawers to suit as the summer approaches and passes. That should about do it. And if you polished the drawers with something at installation, add a bit of polish to the just planed edges, otherwise don't bother. Slainte.Some stuff I've made.

2. 
   HowardAcheson | Jan 03, 2003 07:20am | #4

   Terry, go to http://www.woodbin.com and click on the "Shrinkulator". Plug in the species, width, high and low relative humidity and it will calculate the expansion/contraction.

1. 
   Vterry | Jan 06, 2003 04:27am | #8

   Thanks Howie. I'll bookmark this for later reference.

3. 
   JeffKurtz | Jan 03, 2003 03:22pm | #7

   Terry and All,

   I believe the old timers used a method that was less scientific, but probably just as effective.  In the summer months allow the thickness of a dime all the way around.  In the winter months, use a nickle.  (Don't think inflation or the effects of an expanding or shrinking economy has any effect here.)

   Jeff

4. 
   Vterry | Jan 06, 2003 04:30am | #9

   Thanks to everyone. I got my answer and an interesting discussion as well.