This was fun
A "Big" Conduit Bender

© Frank Ford, 2006; Photos by FF

The idea was to bend some 1" thin wall EMT conduit to make arches for a roof over Joy's big outdoor pottery kiln.  The arches needed to be 66" long, and as identical as I could make them without undue effort.  So I thought about the tiny little bender I use for fret wire and figured that if I had a really big one, I'd be all set.

Here's that little tool:

It's powered by a small hand crank, and has adjustable roller spacing to vary the bend.

First, I set about making some rollers to handle the conduit, which has an OD of 1.18."

I figured the easiest way for me to cut the radius on the rollers would be to make up a quick form tool, so I turned a section off the end of a piece of 1.5" W-1 drill rod I had lying around:

I made a little chip breaker groove in the end, parted it off, heated it to bright red and dunked it in water to harden it.  Since this would be a one-use tool, I didn't bother tempering or cleaning it up:

The stock already had the half inch hole in it, by the way.

Here's the tool mounted in a regular tool holder:

I stuck a piece of two-inch mystery steel in my chuck, center drilled the end, and mounted it with my heaviest live center in the tailstock:

I roughed out some grooves to make three pulleys, switched to my form tool, and finished the nice round grooves to match my conduit:

I parted two off, and drilled them.  I flipped the other one around, chucked it and turned a 3/4" shaft  so it could be my driving pulley:

Outside, I found a piece of heavy steel angle on which I mounted the two pulleys around three feet apart, using a couple of 1/2" bolts and some white grease for lubrication. With the angle clamped in my mill vise, and the drive roller in the quill, I stuck the end of a ten foot piece of conduit between the rollers, and cranked the table in to achieve an appropriate bend.

My lowest speed is 50 rpm, and that worked perfectly to send a curved section of conduit right out the back door in just a few seconds:

All I had to do was repeat the operation with the same Y-axis setting and I had three  more bent pieces, each with identical curves, kinks and straight sections at the ends.

Cutting out the nice curved center parts, I had my four ribs:

The completed roof, on top of the kiln:

Joy uses this kiln for soda firing, so in addition to the intense heat coming out of the top, it also exudes corrosive fumes that rust everything in sight.  Even stainless gets to looking pretty wiped out.  I made the entire roof modular so I could replace parts as they get eaten up, using stainless screws and brass inserts in the conduit.

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