Replies

1. 
   floman47 | Jul 02, 2002 04:21am | #1

    Hi rick

   I was hoping someone new of a book, but I guess not.

   I do a lot of bent laminated work myself. I just keep a mental note of how much spring back. I know that for a 10r @ 8’ long I add ¼” in pecan, walnut a little more. Maybe I should right it down from now on then put it on the forum. Good idea we should all do that! Then can do are own book.

    

   Jeff in so cal

1. 
   rms101 | Jul 02, 2002 05:07am | #2

   Thanks for the info Floman. After posting my message I searched the net for more info on radius's Check out this site . http://www.homestead.com/DaveWoodshop/coldbending.html This guy claims there is a formula for spring back.Which is:

   Percent of spring back  = 100 X [1÷(N²-1)] 

   where N = the number of laminations.. I wrote him back this question:It's hard to believe that there aren't any other variables than the number of laminations in the spring back formula,like species of wood or size of radius.Can you confirm. Also I'm looking for a good book on radius work glue ups etc.Can you help? Thank you Rick.He E-Mailed me back this message:

   Rick...

    

       Looks like we are nearly neighbors (I'm east of Holly).. to answer your questions..

    

       Well sir.. as far as other variables than the number of laminations in the glue-up effecting the spring back I'm not aware of any.. perhaps that is taken up in the fact that certain species of wood bend with more difficulty that others.. my experience has been with western red cedar, PT southern yellow pine, and white oak.. the cedar and pine were larger radius projects using four 3/8" thick laminations to achieve the 1½" thickness and four 1/4" thick laminations  for the 1" thickness.. in the white oak I used four 1/4" thick laminations to achieve the 1" thickness in the larger radius.. whereas.. the tighter radius of the chair back was achieved with eight laminations of 3/32" for a 1½" finish thickness.. the spring back formula seemed to work the same in all applications.. however.. the cedar and pine did seem to be more flexible when finished.. and the white oak was much more rigid even with the 4 laminations .. I suspect due to the nature of white oak..

    

       This formula was given to me by a woodworker that was working with the guy who does my turnings.. as to where he got it I don't know but it seems to work.. at that time I was building the pergola using the cedar and he didn't mention that the formula would be different with different species of wood.. so that is the best I can do to confirm.. other than.. it works..

    

       As to pointing you to a good book on radius work..? I haven't found one.. seems to be nothing written on the subject of cold bending.. even R.Bruce Hoadley's book "Understanding Wood" is silent on this subject (perhaps he didn't understand it).. lots on steam bending however.. which is the main reason I included my experiences with bent-laminating on the web site.. it is my opinion that the finished product is more stable than steam-bending.. sorry that I've not been more helpful.. 

    

       I'd be interested to know how you were able to fine my web site..? I visit and comment of a few wood forums.. usually in the early morning..

    

   Dave²        Hpoe you get something out of this .Thanks again for your reply Micro.

1. 
   floman47 | Jul 02, 2002 07:02am | #3

   I can’t knock it til I try it. I’m skeptical like you.

    One thing I noticed on his site was planning the pieces. I always have the off-fall pieces the ones I wont to glue, that way the edge against the fence is the same. And you don’t need to plane them. You have to move the fence each cut but most of the time I move it a ½” for each cut, which gives you 3/8” pieces.   

    Thanks Jeff

1. 
   DKowlasky | Jul 02, 2002 02:00pm | #4

   Jeff...

   Skeptical..? try it you'll like it..

   The secret to a successful glue-up is that the mating surfaces come into "intimate" contact with each other.. to accomplish this in hardwoods I plane the surfaces and run them through the drum sander (to remove the planner ripples and to make them absolutely flat).. for the projects in pine and cedar I was using 6" wide materials and re-sawing on the table saw from each side.. so there was a need to plane that surface (no sanding)..

   I agree.. a very good glue joint can come directly from the table saw without a jointer for edge gluing (I know this will spark some responses from the opposing camp).. however.. in this case the need to plane and sand was very important to the success of the glue-up..

   As to the source of the formula..? It must be written someplace (but I haven't found it) cuz the guy I got it from wasn't clever enough to think it up himself..Dave²   http://www.homestead.com/DaveWoodshop/     

1. 
   Elcoholic | Jul 02, 2002 10:31pm | #5

   At least the formula is intuitive - the more plys the easier it bends therefore the less springback.  All the other variables are accounted for in the bending which is either go or no go.  So if you can bend it you can predict the amount of springback.  Cool.  I wonder if it holds for tapered-bent laminations?John O'Connell - JKO Handcrafted Woodworking

   Life is tough.  It's tougher if you're stupid - John Wayne