Replies

1. 
   jackiechan | Jan 09, 2003 06:03am | #1

   Bear,

   Here are the rules of thumb for lamination springback.  (1) The thinner the laminates, the less springback there will be.  (2) More layers means less springback.  (3) The larger the radius, the less springback.  (4) The smaller the degree of arc (distance around the circle), the less springback.  (5) The more flexible the material, the less springback (e.g. Poplar is more flexible than maple).

   The best way to control springback is by mechanically holding the bent piece in place.  Although lamination bending is extremely stable. 

   Warning! If you've done this type of bending before then you already know what I'm going to say.  The glues that you'll be using is toxic - protect your eyes, lungs, and skin!!  When you start to sand your project, the glue will be release in  a powder form.

   Remember that the glue lines will be visible in the finished project.  Also, the glue must be allowed to set up for an extended period of time.

   I do a tremendous amount of steam bending in the custom pieces of furniture that I design and build.

   Let me know if you have any questions.

   Dan Kornfeld, President/Owner - Odyssey Wood Design, Inc.

1. 
   UncleDunc | Jan 09, 2003 06:25am | #2

   >> The glues that you'll be using is toxic ...

   Could you identify which glues are toxic after curing. I've never heard of anything that suggests that dust from, for instance, hide glue or epoxy are any more dangers than any other kind of dust.

1. 
   jackiechan | Jan 10, 2003 06:18am | #11

   Uncle Dunc,

   It depends on what 'other' kinds of dust you're referring to. 

   Yellow, white, and other flexible glues tend to gum up or even melt slightly with heavy sanding or milling.  Setting aside the danger of inhaling the sanding dust, these "safety glues" are non-toxic to begin with and tend not to float in the air as lung damaging particulate.  On the other hand, the less flexible glues like plastic resins and epoxy can be very damaging to the eyes, lungs, and even skin if you come in contact with it.  When these glues are sanded or milled, the dust hangs in the air as toxic particles that will get on you, or all over the shop if one's not careful. 

   These types of glues are water resistant and are meant to not break down over time.  Having these toxic particles lodged in your lungs can lead to serious health problems.  If you can't touch a glue bare handed without consequence, then it definitely should not be inside one's body!  (Think of the old time ship builders with Asbestosis (Asbestos caused lung damage).

   Dan Kornfeld, President/Owner - Odyssey Wood Design, Inc.

2. 
   alias | Jan 09, 2003 06:29am | #3

   dan thanks for the reply, the piece is going to be painted and i'm pretty familiar with resorcinal dangers. i've done a fair amount of laminating prior to this. but i always like to have affirmation. i tossed around steaming but pine is not that well equipped to steam. or is it??? i tried casing once before and it didnt fair that well. had to switch to red oak and that took. i was wondering the rules if you will about laminations, which you have given me and that is a big help. the arc will be secured to a full 6/4 sill and i had planned to drill 1/2 holes in the end of the half round, and glue 1/2" dowels in those holes so when i'll position the screw into the pre-drilled dowel. i'm sure i'll have questions if you dont mind i'll take you up on the chance to ask you later, if you dont mind. thanks again....... bear

1. 
   bill_1010 | Jan 09, 2003 08:03pm | #5

   In all honesty pine isnt the best choice for bending, steam or bent lamintations.  Its fairly brittle.  It will work, id just make plenty of extra strips incase you hear a crack :)

2. 
   observer | Jan 09, 2003 08:20am | #4

   I pulled this off the forum a while back. I'd give credit if I could remember who posted it:

   Percent of spring back  = 100 X [1÷(N²-1)] 
   where N = the number of laminations..

1. 
   alias | Jan 10, 2003 01:30am | #6

   that what i was looking for thanks....... just to check my math the number of laminations is 9 so ... 9x9-1 divided by 1 x 100 i got 8000 is there a decimal i'm not moving? or is it on a Fb scale??. i am irish so i get points for thickness right or has my algebraic skills finally tanked, which is my suspicion.... hhhhmmm let me try it again.... any math teachers out there..... bear

   Edited 1/9/2003 6:08:10 PM ET by the bear

   Edited 1/9/2003 7:46:50 PM ET by the bear

1. 
   Marcello | Jan 10, 2003 03:46am | #7

   The formula is 100 x [1 / (N squared - 1)]  which yields the following:

   1.  81-1 = 802.  1 / 80 = 0.01253.  100 x 0.0125 = 1.25

   therefore your spring back is 1.25%

   Marcello

1. 
   alias | Jan 10, 2003 03:57am | #9

   T - that makes a little more sense, thanks for turning the light on..... happy new year... bear

2. 
   clampman2 | Jan 10, 2003 03:56am | #8

   Bear,

   I just finished some radius raised panel doors, face frame bends etc. out of cherry. The formula I used was one I got from someone at wood central which I had read several years ago, cut out of the magazine, and lost.

   Take the height of the portion of the circle you are bending (in a 2' diameter arch that forms a half circle this would be 12 inches - it would obviously be less it it were not a full half circle). Divide that (12 inches) by the number of laminations squared. The result is how much EACH END of your bend will spring back. The accuracy of this formula increases as the number of laminations increases.

   I made my lams longer than necessary, my forms longer than necessary (which were concave of course), used shims to keep the lams elevated above the plywood which formed the bottom of the form. I had holes drilled through the plywood bottom to drain glue squeezout between the waxed shims. Lots of wax on the forms and the outside of the first ply and the inside of the last ply.

   Resourcinol was a major pain and didn't work for ####. I switched to West Epoxy and got a much better, faster, easier job. It is very greasy and allows each lam to slide easily on the adjacent one. Also their are no black lines between lams.

   I built my forms eliptical shaped so that the projected springback would reform into a circle.

   I have some pics of the forms if you are interested.

   Have fun. Good luck.

   Clampman

1. 
   alias | Jan 10, 2003 04:07am | #10

   clamp- thats a great idea about compensating w/ the form ....also pretty funny check this out 26316.4 on breaktime. under west systems/general discussion..... any pictures, advice, diffrent procedures etc., would be appreciated...... thanks again clamp..cheers

   Edited 1/9/2003 8:08:51 PM ET by the bear

   Edited 1/9/2003 8:10:03 PM ET by the bear

   Edited 1/9/2003 8:24:20 PM ET by the bear

1. 
   clampman2 | Jan 11, 2003 08:47am | #13

   Bear,

   Here are so pics, I think. I will try to describe them so you know what you're looking at. Formbend is a closeup of the form which I made using "routerjig". For a 15" radius, if the projected springback is 1/4" per end, I rout a 15" half circle. Then I move my pivot on the router jig 1/2" toward the half circle I just routed, and rout the other half of the circle. The center of the bending form will be where the two half circles meet. As you can see,I rout a dado into the ply which is the bottom of my form to make a glue channel and to aid in alligning subsequent layers of form.

   "Startbend" shows how three clamps can be used to keep plys from sliding all over. The form should extend beyond the plys if possible, and the ends of the plys should be square, otherwise the plys will split. Everything is waxed including the wooden blocks before each glue up and the edges of the blocks contacting the plys are radiused.

   "Lookdown" shows that I had a twist develop and used a barclamp from the base of the form to the outside of the top form which was twisting to remedy the problem. You will notice the skinny square I use to check between each clamp for square. You'll also see that I can eyeball the form base to check for twist. That base is screwed to a sturdy bench by the way. The wood resting on top of the clamps is a finished bend I just stuck in there for the picture.

   "Closeglueup" shows the bends down inside the dado in the form bottom. Once I get the plys beyond the edge of the dado with the three clamps (Startbend) I knock the plys down into the extrawide dado. Then I can relax somewhat, and start working clamps from the center out, one way then the other.

   "Paneljig" shows the glueup of the panel prior to raising, using the same rail/faceframe bending form and a couple scrap accessories. You will notice that shims are fatter in the middle and decrease in size to zero. That is why I make the dado in the bottom of the form extra wide from the get go. A little wider than (you guessed it) my anticipated springback. Then I can use the same form for the panels.

   You may notice the glue squeezout is titebond not epoxy. That is because the panels are not being bent, they are simply edge glued. I had already milled them to the radius I wanted, after cutting the edges to the proper angles for glue up.

   I don't believe there is any "right" or "proper" way to do anything. This is just how I do it. If it helps give you any ideas, great.

   Good luck.

   Clampman

   
3. 
   Petey | Jan 11, 2003 06:42am | #12

   I worked in a shop where we made custom round top windows, mostly out of sugar pine. we never worried about springback. We made the forms true to dimension. We just extended the legs and over bent them. Bending pine can be tough. We never had a steamer, we would soak the laminations in trough of hot water (thoroughly) bend them around the form, let dry, take them out of the form and hold the shape to dry even more, then put them back on the form for glue-up.! Sounds like a lot but we had consistent results. Good Luck

4. 
   Petey | Jan 11, 2003 06:04pm | #14

   Bear, clampman is right,there isn't any right or wrong way. I'll say one more thing then I'll get off this dadburn thing and try to get some work done! We would build our forms from plywood ( cdx ) stacked on top of each other to the depth of the frame,plus some extra. The forms were not mounted to a base. The Form was about 6" to the inside of the radius, that way we could put clamps on the top and the bottom. That eliminated any twist The only drawback is the amount of clamps and it was a two person job. Again, good luck    petey

1. 
   alias | Jan 12, 2003 02:43am | #15

   There is only one thing better than these taunton forums, and thats the people in it . you ladies and gentleman are an awesome resource. thank you all very much.. and may the new year bring you all nothing but health and happiness........ slainte.. bear