[TheForge] Sheet Metal Bender

[Bruce Freeman]

Daniel,
 
First of all, why do you want to make this yourself? 
To have stainless steel instead of galvanized?  Or
because stainless steel isn't available in 12"
diameter?
 
Next, correct me if I'm wrong, but isn't 24 gauge
pretty light stuff?  Like you can easily flex it by
hand?  If so, then bending pipe shouldn't be too
difficult - roll it around a slightly undersized
mandrel (maybe 10" or 11") and let it flex back to
12".  Lock seams are nice for the prefab stuff, but it
would be a deal easier just to drill and pop-rivet the
edges and ends.  Or even use self-drilling screws if
you like them.
 
Someone else advised 45 degree elbows, and I second
that.  Whatever you choose, odd shapes can be made
according to diagrams available in any text on sheet
metal work. Visit a used_book store and peruse the
contents.  The Audel's series should suffice, but
there are text books for metal shops that are fine
too.
 
You can also fake it by means of a clever device Clay
Spencer showed me, and which I've since used:  Imagine
you want to make a pipe with a 12" diameter end on a
vertical axis, and goes to a 12" diameter end on a
15-degree-off-vertical axis.  (Three of these would
make a 45-degree bend.)  Construct a device as
follows:  Cut two (~1/4") plywood circles, 12" in
diameter.  Drill three holes in each, oversize for
available threaded rod.  String the two circles on the
threaded rods:  nut, washer, circle, washer nut, (then
a lenght of threaded rod), nut, washer, other circle,
washer, nut.  You'll end up with the two circles
separated on the three threaded rods by some distance.
 Now adjust the distance as you prefer, and adjust the
angle to 15 degrees between the planes of the two
circles.  You want the closest approach of the circles
to be some reasonable amount (say 2") because this
will be the narrowest sheet metal  you'll have.
 
Now roll this pattern along a piece of paper, and it
will describe a pattern to be used in cutting the
sheet metal. When actually cutting the metal, be sure
to leave tabs to overlap the next pipe section so that
you can join them with rivets or screws.
 
I have used this technique to develop a pattern for a
side-draft hood of unusual shape, and found it worked
quite well.
 
Bruce
NJ

>>> "Daniel Kretchmar" <dan at irontreeworks.com>
9/18/2006 11:17 PM >>>

Greetings,
           I need 12" diameter chimmey pipe for my new
side draft hood.  I 
looked into menards.  They have galvanized 12"  24
gauge chimney.  I looked 
into having some custom stuff made but it's too
costly.....so the next 
question is.....can I make it myself?

What kind of bender would I need to make 12" diameter
pipe/tubing out of 24 
gauge stainless steel?  I want to make it in 2 ft
sections. which means 
investing in a crimper a bender.....and what about
elbows?  I'll need two 90 
degree elbows.  How will I make them?

Advice is appreciated

Dan 


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