OK, I have a project in mind and its going to involve steam bending some timber.
What I need is cheap ideas for building a small unit that I can steam stuff in!
I already plan on using a wallpaper steamer to provide the steam and the unit
doesn't have to be bigger than 4" across and 4' long.
Might grab a piece of 4-6" dia schedule-40 PVC pipe (schedule-80 is even
better), cap one end using PVC glue (do not use threaded pvc joints at
these temps) and slip cap the other. Drill and tap the center of the
pipe tube for a connection to your homemade steam genny. Drill a few
evenly distributed holes in the top (1/8 - 3/16) for pressure relief,
and add a ball valve at fixed end to serve as drain and added safety valve.
Open slip cap (cover), insert stock, replace slip cap, open steam input
valve for 30-40 minutes and check for doneness. Use heavy barbecue
gloves, tongs, and wear thick clothing and eye protection. Warning!! Do
not stand in front of removable slip cap while cooking or removing cap
Simple, cheap, can be varying lengths/ widths to accommodate stock
sizes. Easily mounted at slight down angle (to facilitate draining of
condensed water) on upright cinder block or just about any sort of home
brewed support. Should safely handle temps up to about 140 deg. F; steam
is much higher in temp, but with low pressures, adequate venting, and
ambient external skin temperatures the pipe won't exceed its maximum. If
concerned, add an inexpensive temp gauge and monitor aggressively.<G>
I've also been planning on doing some steam bending, and have no experience
whatever with the process. What I do have is a steam unit called a
"Ladybug". It is a semi profesional unit, which generates a smaller quantity
of very high temperature steam.
My question is....... Which is the better condition for bending wood, High
temperature with low moisture content, or lower temperature with more
moisture? What is the best temperature range for bending wood, and what is
the best moisture content? Should I pre-soak the wood before I place it in
the steamer, or just start with dry wood, and rely mainly on the temperature
to make the wood pliable?
Anyone have any thoughts or experience with this?
Offered in the spirit of friendship and respect :)
On 6/29/2011 9:47 AM, firstname.lastname@example.org wrote:
I am no expert!! So, I can only express an opinion based upon my own
My thought, and again I am not a fluid physics major, is that steam is
212 deg F, period! Unless one uses some sort of additional process,
pressure and super heating, to force higher temperatures (danger Will
Robinson), steam remains steam and the temperature is relative only to
the type and design of generator used. Water boils at a 212 deg, which
remains fairly constant in free space at sea level. Volume (or density)
of steam produced is a whole different discussion and would vary with
type and settings of burner combined with method of containment and
So, I would think, simply brainstorming for discussion, that given a
relatively fixed temp, moisture content and absorption rates become a
function of time, exposed surface area and pressure, variables easily
controlled. Rates will also differ based upon cellular density and stock
sizes; hardwood vs soft pine...open porous stock vs close grain etc.
One can soak stock in a body of water for months and probably achieve
almost the same capability of radius bend as steam, but the whole point
of using steam is speed. I see no advantage to pre-soak and would think
it might add weeks to fixing/ curing. Just my best guess, but I do know
it takes much longer for water soaked lumber to dry and become workable
again than simple steaming. My sense is stick with cured lumber.
at normal atmospheric temperature, but it is possible to produce steam
Another time proven method of bending wood is "hot pipe" bending - and
there you DO soak the wood - the roughly 300 F heat of the hot pipe
turns the water in the wood to steam. It is the heat, more than the
moisture, that allows the wood to bend, as it loosens the lignen? in
the fibers, allowing them to slip.
On 6/29/2011 10:11 PM, email@example.com wrote:
Never said steam could not be heated to higher temps, but, as stated
above, it would take additional effort to achieve elevated temperatures.
As water boils at 212, steam is (theoretically at least) immediately
directed to the containment vessel due to venting, without additional
heating or other post process. We are talking about the simplest form of
a steam genny aren't we? But, perhaps I am wrong.
Not familiar with "hot pipe" process as such -- perhaps an aka might
ring a bell -- and have only played with the simplest forms of steam
bending. Sounds logical though, but more like a commercial process
rather than homebrew backyard project. However, never too late for me to
learn something new.<g> Keep in mind, yours truly is only a hobbyist at
best, not a pro or expert.
A little basic heat transfer.
To raise temperature of 1# water 1 degreeF requires 1 BTU.
Thus 180 BTU/# of water are required to raise the temperature from 32F
To convert 1# of 212F water to 1# of 212F steam requires 144BTU/#.
This is known as the "Heat of vaporization".
To raise the temperature of steam above 212F requires 1BTU/#, and
requires the steam to be above atmospheric pressure.
This is known as super heated steam and forms the basis of every
fossil fueled electric steam powered generating station.
(Damn, you never forget that stuff.)
More the 50 years ago, passed the Ohio PE exam solving heat transfer
All of which has very little to do with most steam bending rigs for
The steam in the steaming chamber is at atmospheric pressure and will
BTW, I have always been told to use "green" lumber for steam bending.
According to the Uk Forest Products Wood Bending Handbook, 'wood at 25% -
30% moisture content contains enough moisture as is necessary to render it
compressible when heated.'
'Wood is in the best possible condition for bending when it has been heated
right through to boiling point.'
'........for the most part the effect of steaming is to heat the wood, not
to inject steam into material as is sometimes supposed.'
Jeff Gorman, West Yorkshire, UK
email : Username is amgron
Armed with all this new information, I contacted the manufacturer of my
LadyBug Steam Cleaner. I was assured that the steam leaving the boiler is at
290Degrees, but cools slightly as it travels through the delivery hose. The
main question now is the amount of thermal gain required to heat a given
size chamber, the efficiency of the chamber's insulation, and the method of
distribution within the chamber. I had no idea I was entering into a physics
dilemma! I was also told that the machine is intended for cleaning with
superheated steam, rather than what I plan to use it for. Does a good job
cleaning, so why not see if the little "Bug" is up to the test.
I'm just going to make a test chamber with pvc pipe, insulate the heck out
of it, measure the temperature of the exhaust, and do a few trial runs.
Nothing ventured, nothing gained. I'll try to remember to post my results
when I get around to doing the test. If it works, I can imagine that more
than one Steam Cleaner is going to find it's way out of the vacuum cleaner
closet, and into the workshop! :)
"TrailRat" wrote in message
OK, I have a project in mind and its going to involve steam bending some
What I need is cheap ideas for building a small unit that I can steam stuff
I already plan on using a wallpaper steamer to provide the steam and the
unit doesn't have to be bigger than 4" across and 4' long.
You wife always wanted one of those hanging clothes steamers anyway. They
work like a charm!
I was going to say! How big are the double boilers in where you are?
Thank you for the suggestions. Most useful.
A question though? Is it OK just to leave the timber on the bottom of the pipe
or should it be raised so it doesn't sit in any water/block steam input/block
water run off?
My own experience is just use a sacrificial piece (or scrap pieces) as
the bottom layer, mostly because it is then easier to retrieve other
layers. However, anything wider than a half inch would not be of concern
anyway due to the rounded nature of pipe -- I did once try wire mesh and
the adjacent wood became discolored and took an imprint of the mesh.
Real pain to remove all of that after bending.
As suggested earlier however, I would tilt slightly downward at valve or
relief end and if water becomes an issue, perhaps you may add a large
reducer between ball valve and vessel to act as a temporary reservoir.
Just as a precautionary note, try to avoid steaming dissimilar woods in
the same batch as it can cause spotting, streaking or minor
discoloration through leeching.
You could use 4' sections of snap-together galvanized round ductwork
with a couple of end caps. Wrap the duct in scrap rebond carpet
padding for insulation. You want the steam to circulate around the
wood, so use some scrap wood to make a ladder-arrangement that will
slide inside the duct and raise the wood to be steamed so it's not
touching the duct.
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