Gary Wolf wrote:

Paul,
   The cerrobend or other alloy will definitely fill the tube to minimize
nwcking and parting on the OD and I think you will have success with the
smaller diameter on the 2" centreline radius. Make it easy on yourself and
use as thick a wall as you can. Bend it into a die that fits the tube well
(+.002 -.000)
and ensure that the tube does not slip through the clamp while the other end
is formed. You may have a bit of wrinkling on the inside of the bend but
this should not be a problem for water plumbing.

   The intake runner is a very different animal. On this you cannot afford
any wrinkling but you are into the critical range of the OD/ radius of bend/
wall thickness relationship. If you choose to try bending this part I would
again suggest using as thick a wall as possible.

   Nxt I would suggest increasing the Centreline radius (CLR) of the bend to
the absolute maximum possible for this application. With your current
requirement of 1.5"CLR the nominal tube length for 180 degrees is 4-3/4".
The inside of the bend must be compressed to a length of 2" and the outside
of the bend must be stretched to 7-1/2".

   The more critical area is the stretching of the outside by more than 50%.
If you begin with .100" wall tube it will be less than .050 here. The inside
will be more than .200" after it has been compressed. It is more likely that
it will corrugate ahead of the bend to get rid of the extra material. I am
not sure that this will be acceptable for an intake runner.

   There are three ways I would attack this part. If it has to be aluminum
and on this CLR, I would e-mail Tools for Bending in Denver, find if anyone
is bending this already, and order from them.  If not I would give up on
bending and look at hammerforming.

   Kent probably has a video on this technique. Basically you carve a
hardwood pattern, clamp a blank of aluminum to it, and begin caulking the
sheet down over the form. It takes a lot of skill and patience but very
simple tooling. You make two halves and seam weld them together. My local
metal guru made all of the engine covers for the early Ilmor engines this
way. Kent has a video on the welding of aluminum that would help here.  as
well. If you choose to do it this way, you can incorporate any taper or
D-shape you may feel is suitable for the runner.

   The other way is to pass on the aluminum completely and lay composite
over a wax form. The University of Waterloo students made a beautiful intake
manifold using this technique for their Formula SAE Honda 600-powered slalom
car. It had all of the taper, d-shape, inlet radius, necessary to optimise
flow.

                                                                Gary Wolf

PS. The Burns online catalogue offers 1-3/4 16 ga on a 2.5"CLR. These guys
are as good as you will get in the bending business and they are no fools.
There is a good reason why they don't bend tighter than 2.5"CLR on 1-3/4" tube.

 
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