bending 5 foot dia circles of 1/2 or 3/4 EMT pipe

Tubing roller.

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 message news:%OU8B.365369$ snipped-for-privacy@fx15.am...

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.

-jsw

replying to Larry Jaques, brian wrote: Hi Larry, 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? Cheers, Doug 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.

replying to Ed Huntress, brian wrote: How about this relatively simple bender, ....with no sand involved? Lady bends 3./4 EMT conduit _

To get it all up yer arse?

And you wouldn't want that if you seek a helix. (Sorry, I can't read.)

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 bends.

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.

In that case you could bent the conduit into the two halves of an octagon.

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. solution).

-jsw

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.