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bending wood with steam
26 oct 1996
"brendan a. niemira"  writes:

>i seem to recall... a simple steam tank that is used to make wood really
>pliable.  basically, a pipe (or round air duct, i forget which), about 12"
>in diameter, is attached to a steam source at one end, a removable cap at
>the other and wrapped in insulation.  slats (for the boat hull) are piled in
>the pipe, and steamed for a long time (24h? 36?).  these are removed and
>bent to the proper shape while hot; as they cool, they get quite rigid.

thanks for the tip, brendan. i'm trying to think how to do this. seems like a
steel 55 gallon drum on its side with a wood fire underneath might make a good
steam generator, with 6 more deheaded steel drums in series, all bolted or
welded together and surrounded by strawbales or leaves. grainger's $55 1a122
steel drum deheader looks like a large can opener... 7 drums and 48 bales... 

                                   21'

                    bale   bale   bale   bale   bale   bale
            ------ ------ ------ ------ ------ ------ ------
           |                                                | 2'
            ------ ------ ------ ------ ------ ------ ------
  _________  fire   bale   bale   bale   bale   bale   bale _____________

           cross section:      

                          |   --~52"--   |

                           ---- ---- ----  --- ~52"
                          |    |    |    |
                          |     ----     | --- ~38"
                           -- /      \ --
                          |  |        |  |
                          |   \      /   |
                           ---- ---- ----  --- ~14"
                          |    |    |    |    
                          |    |    |    |    
                  -------- ---- ---- ---- --------

but it seems simpler to just use one drum, and make the steam chamber a
strawbale trench lined with epdm rubber, like this... 

           cross section, not to scale:      

                          |   --~54"--   |
                             | - 36"- |      
                              --------     --- ~42"
                             |sideways|    
                             |  bale  |    (quantity 16'/18" ~ 12)
                              -------- 
                                rebbure 
                              plywood b
                           rubber  erub   
                           ---- u  b ----  --- ~28"    
                          |    |b  b|    |              endwise bales
                          |    |beru|    |              (quantity 4x
                           ---- ---- ----  --- ~14"     16'/36" ~ 22)
                          |    |    |    |    
                          |    |    |    |    
                  -------- ---- ---- ---- --------

the sheet of rubber has to be at least 46" wide, and 16' + 14" + 14" long,
so a 10' wide x 20' long sheet of rubber roofing material would allow bending
1x3s up to 16' long, with 2 sheets of plywood or some strings stretched across
the top, and about 40 straw or haybales around it, and all this could be taken
apart and reused, or left in place, with the rubber draped over the top and a
poly film vapor barrier between the strawbales and the ground. 

the screw-in plugs in the drums (bungs) are about 2" diameter, but us plastics
("god is our partner!") and others sell bungs with smaller threaded holes in
the middle, and plumbing supply stores have bulkhead male garden hose fittings
that screw into the smaller hole in the bung, to get the low-pressure steam
from the drum in the fire to the trench, via a hot water garden hose (?) with
the other open end inside the trench. if something plugged up, the garden hose
would likely pop before the drum exploded.

but if the drum had a fiberglass insulation cozy on top, it might lose about
25ft^2/r20 x (212-52) = 200 btu/hr, and the trench surrounded by 85 ft^2 of
r50 strawbales might lose another 85ft^2/r50 x (212-53) = 300 btu/hr, so the
whole thing might use 1/2 pound of water per hour, or 12 pounds of water or
1.5 gallons in 24 hours, since it takes about 1,000 btu to evaporate a pound 
of water (or 144 btu, if you come from andy m's planet.)

so the steam generator might be an electric teakettle, or a bucket of water
with an immersion heater sitting inside the trench, controlled by a 190 f
thermostat at the other end of the trench. we might restack the bales later
and make a sauna.

nick

confusion is like fertilizer:
it feels like shit, but nothing grows without it. 
                                                    --carl whittaker



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