I would like to make some 360 degree hoops of either 1/2 EMT, or preferably 3/4
EMT for a model RR project ( helix construction). Would like to get approx 60"
dia circle. Can you tell me how I might best go about this??
A tubing roller works most smoothly, but a hickey is a lot cheaper.
How smooth do you want the bends, and how many of these are you
making? I'd suggest buying the tubing bender, making 3x the number
you need, and selling the rest to pay for the bender. Make sure the
tubing stays straight through the bender or you'll end up with a
spiral. And, whatever you do, don't tell us what you're making. We
love staying in suspense.
Show them to the local gardening club to get sales. Women love that
crap for their gardens.
"brian" wrote in
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If you can't justify the cost of a tubing roller
you could bend it around a plywood form. I'd start at full size to
measure the springback, then reduce the diameter accordingly. You only
need a half circle which is all you'll get from a 10' length. 1" pipe
will slide over 3/4" EMT to give you better leverage at the ends.
If you have a good eye for shapes it can be bent between closely
spaced tree trunks, using a circle on cardboard as the pattern. I
straighten bent antenna mast tubing that way and once made a spiral
handrail from EMT for a staircase for a theatre set.
Tubing bender is just two expensive for fabrication just a few (as little as 2)
hoops. Just yesterday I found a contractor friend who says he has a hand conduit
bender i can borrow. I figure I can just make small incremental bends and get my
circular hoops. Now I just have to figure out how to calculate those incremental
bends to get my 5 foot hoop.
If you google "model railroad helix" you will see imagines of what I am looking
to build,...but an alternative method/materials.
Here is a forum subject thread I started on the project...
these photos you will see a 4 foot dia metal ring I found at a junk yard
(likely a rim of of outdoor table). This would work for a 4 foot dia helix, but
I was looking for 5 foot dia,...hence my search for bending conduit into 5 foot
dia circles. One hoop at the bottom, and one hoop at the top,...then 8 vertical
pieces joining the 2 hoops. Inside this 'open style barrel' I would coil up a
spiral hoop(s) of PVC pipe onto which to lay the rr track.
Certainly, mate; fill the tubing with (possibly wet) sand and bend it as th
ough it were a solid rod; the peculiar "Poisson's Ratio" of the sand will m
ake your tubing behave like a solid. Loverly, eh, wot?
Admin AT Replikon DOT Net also keeps the spam way down
If you use that method, use *dry* sand and pack it as tightly as you
can. It requires stoppers on each end -- typically wooden plugs that
are held in place with bolts or pieces of rod through holes
cross-drilled into the tube. Expect some distortion here after you're
done. It's best to assume that the ends will be waste.
If the sand isn't really tight, it will get pushed away at the point
of highest stress -- your bend point -- and do no good at all.
Be aware that this approach tends to leave the outer part of the bend
somewhat thinned. Unlike a commercial pipe bender, it doesn't
distribute the displacement of metal equally on the comperssion side
(the inside of the bend) and the tension side (the outside of the
bend). At least, that was my experience, when I used it to make
aluminum tent frames.
But it does work well. I've had to drive the sand in with a hammer to
get it packed tightly enough.
Oh, yeah. That will do it. I didn't even pay attention to the early
posts, so I didn't note the radius you're working with. A single-side
rig like that, with no follower, is the way they have made big-radius
bends like that for many years.
That should work just fine. What I was thinking of was much tighter
BTW, just as I retired (last September) the publishing company I
worked for was starting up a new magazine just for tube and pipe
fabricating, including bending, of course. I think they got through
one issue before they realized it wasn't going to fly.
Anyway, in preparation for it, I was accumulating everything I could
find on tube bending. The basic fact is that nothing much has changed,
mechanically, for the past 50 years or so. But computer control now
allows them to make some wild and crazy bends.
"brian" wrote in
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In that case you could bent the conduit into the two halves of an
See "Offset Bends:"
The nominal OD of 3/4" conduit is 0.922", the ID is 0.824". If an EMT
compression coupling isn't rigid enough I don't know of another common
material to join the two halves unless you can turn down 1/2" pipe
from 0.840" to a snug press fit on a metal lathe (the R.C.M.
True, but if you did buy one, you'd have another =tool=.
Don't discount the possibility of selling extras, though.
Conduit is cheap, so trial and error isn't too prohibitive. Make a
pattern so you can physically lay the bent tube on it to compare? Did
you ask the electrician? Perhaps ask on an electrical newsgroup. One
of the many math wizards here should be able to give you a tip.
Good luck getting the spacing right. That would seem harder than the
diameter to me.
How will you fasten the track to it, on plywood screwed to the tubing?
OK, cool. I favor the more open models, and the inverted cone or
stadium style with the smaller lower diameters and larger uppers.