Replies

1. 
   PlaneWood | May 09, 2004 03:49am | #1

   2nd page of table.

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)
   PlaneWood

   
2. 
   BobSmalser | May 09, 2004 03:18pm | #2

   Wow...terrific, Mike.  Easier than extrapolating from the USDA book.

   Boatbuilders have a real need for this but I'll have to try to run the upper limit to 20pct.

   Thanks

   “When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.

   
   

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   Edited 5/9/2004 8:25 am ET by Bob Smalser

1. 
   PlaneWood | May 09, 2004 08:20pm | #3

   Hey Bob -

   When your in the 6-14% range of EMC the relationship between dimensional change and EMC is pretty linear.  Above that there is a more pronounced curve to the line (progressively larger coefficient).  Probably need to increase the coefficients about 1 to 2 percent for each 1% rise in EMC above 14%.  Dimension doesn't change much for EMC's over 22%.  

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood

3. 
   HowardAcheson | May 09, 2004 09:04pm | #4

   Easier to use IMO is the "Shrinkulator" at: http://www.woodbin.com

   All you need to do input the species, range of either relative humidity or moisture content, and the initial width. The output is the change in dimension both for radial and tangential measurement.

1. 
   BobSmalser | May 12, 2004 05:14pm | #15

   I don't believe that Woodbin.com table is correct:

   It appears to be using a completely linear solution with the results not passing the common-sense test:

   It shows for 100 units of Coastal DF...

   The shrinkage from 30-25% is .85 Radial and 1.35 Tangential...

   ...from 25-20% is .86 and 1.37...

   ...from 20-15% is .88 and 1.41...

   ...and from 10-5% is .88 and 1.43.

   With a fiber saturation point of 28%, that data can't be correct....a lot more shrinkage will occur from 30-20% than from 15-5%.

   “When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.

1. 
   HowardAcheson | May 12, 2004 11:20pm | #16

   As I recall, the "Shrinkulor" uses the formulas in "Understand Wood" by Hoadley. I am still unpacking so I can't check now.

   But, I only use it to predict the expansion/contraction of wood that is already below 14-15% EMC. I don't think it is intended as a predicter of shrinkage during initial drying.

   The woodbin page contains the following at the bottom of the "Shrinkular" caluculator.

   *********

   References

   Forest Products Laboratory. 1999. Wood Handbook - Wood as an Engineering Material. Gen. Tech. Rep. FPL-GTR-113. U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WI.

   Understanding Wood: A craftsman's Guide to Wood Technology. 1980. R. Bruce Hoadley. This is an excellent resource for learning about wood movement, how to predict it, and how to measure moisture content using your oven. It also contains maps of regional and local EMC.

   *********

   It would appear that it is the same as the data that initiated this thread which was a lift from the Wood Handbook.

4. 
   jazzdogg | May 09, 2004 09:15pm | #5

   Planewood,

   As a rule of thumb, I was taught to use 4% for quartersawn and 8% for plainsawn. However, I can see where it would be worth the effort to perform the calculations or look up the data when constructing something very likely to succumb to the ravages of expansion & contraction.

   -Jazzdogg-

   Whether you think you can, or you think you can't, you're right.

1. 
   PlaneWood | May 09, 2004 10:20pm | #6

   Jazzdogg -

   8% is approximately the maximum shrinkage from totally green to totally dry (100% - 0% EMC).  When your working with the wood on a project, you will need to consider a max of about a 3% change in the across-grain dimension in the lumber over the lifetime of the finished piece, in average household conditions.  If quartersawn, then about half that much.  If air dried, then maybe 4%.

   So, a 50" wide red oak glue up could expand and contract as much as 1.5" across grain throughout it's life as a table top, for instance.  That's why one should use as close to quarter sawn as possible for wide glue-ups.  At least use straight grain lumber so the change will be consistent from one end of the glue-up to the other end.  Can you imaging what would happen if one end shrunk 1.5" and the other end only shrunk .75 inch!

   For grins, do this.  Cut a chunk out of a green limb about 4" long and 4" in diameter.  Peel off the bark and lay it aside for a year or so.  I did that with a piece of Sassafras and a 3/4" wide crack opened up on one side.  That's about 6% shrinkage from 100% EMC to about 18% EMC.

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood

1. 
   BobSmalser | May 10, 2004 12:27am | #7

   Thanks, Mike...I'll pursue it.

   Furniture is relatively easy in the grand scheme of things...pretty simple to make a button-in-groove connection to keep a wide top from cracking.

   But consider an expensive yacht with a planking M/C change in the neighborhood of 10 pct seasonally between haulout and use...either a new yacht where the owner wants solid q-sawn cedar planking sheathed in fabric/epoxy or (worse) a troller conversion of flatsawn DF planking where the surveyor's prescription is to fill those old cotton seams with epoxied wedges, creating a solid "panel" of sorts....

   ...the crossgrain width of those total planking systems can be anywhere from 8 to 15 feet and the potential movement against the fastenings considerable.

   With new construction, the potential wood expansion has to match the flexibility of the epoxy and the fastening system.  With old construction, the weariness of the planking has to be taken into account as the edges deteriorate as they crush during the swell cycle, losing considerable elasticity.

   My point is, that this is important, complicated (old, crushed planking doesn't move as much any more...but how much less?)  stuff and y'all might be surprised that even today how much expensive work is done on intuition and blind chance as opposed to engineering calculations and sure knowledge.

    

    

    

    

    

   “When we build, let us think that we build forever. Let it not be for present delight nor for present use alone. Let it be such work as our descendants will thank us for; and let us think...that a time is to come when those (heirlooms) will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, ‘See! This our father did for us.’ “ --John Ruskin.

   Edited 5/9/2004 6:16 pm ET by Bob Smalser

5. 
   davidh | May 10, 2004 08:14pm | #8

   Planewood,

   Thank you for publishing this data; it is really useful and I have tried to print the tables out but can not everything on to one page. Any advice for printing, perhaps without all Taunton press info on the page?

   David H

1. 
   HowardAcheson | May 10, 2004 09:18pm | #9

   The data and tables are from the Wood Handbook published by the Forest Products Lab of the US Forest Service. (Probably should have been an attribution in the first posting).

   You can go there directly and download the PFD file.

   Go here: http://www.fpl.fs.fed.us/documnts/FPLGTR/fplgtr113/ch12.pdf

   There is lots of great info in other chapters. Such things as coatings, adhesives, and composition materials.

   Go here for access to the complete handbook: http://www.fpl.fs.fed.us/documnts/FPLGTR/fplgtr113/fplgtr113.htm

   Edited 5/10/2004 2:20 pm ET by Howie

1. 
   davidh | May 10, 2004 10:18pm | #10

   Howie,

   Thank you for the information. I will follow up. Sounds as though the book is one that I should take a look at or possibly even purchase. Is it expensive?

   David H

1. 
   PlaneWood | May 11, 2004 03:29am | #11

   David -

   You can download the PDF file as Howie suggested.  Or, you can 'right click' on the file names in the 1st and 2nd messages.  The PDF will be the book. 

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood

1. 
   davidh | May 11, 2004 06:04pm | #12

   Mike,

   Thank you for the advice.

   David H

6. 
   GHR | May 11, 2004 06:08pm | #13

   You don't say the source for these numbers or formula. That makes them junk.

1. 
   HowardAcheson | May 11, 2004 06:14pm | #14

   That's a rather bizarre way of looking at things.

   In any event, the numbers are correct--see my post for the source. But, better not use them until you are satisfied with their validity.