I love this question because I'm a geek.
The speed you can theoretically bend at is a function of your motor horsepower and the output torque required to bend your tubing. Let's say you have a 1hp motor and it takes 3,900ft-lb of torque to bend your tube (FWIW that's what I measured on my machine for 1-3/4x.120 chromoly). If you were able to match your gearing perfectly you would get:
[ 3,900ft-lb / (1hp * 550ft-lb/sec*hp) *2*3.14rad/360deg]= .12sec/deg = 11sec/90deg or 22sec/180deg
Now in the real worked we tend to deal with fixed displacement pumps and non-variable gear/machine ratios, so we really have to design around our worst case torque. In my case I designed a bender for 5,000ft-lb of torque and it uses a 1hp motor. I was able to size the cylinders, pump, and mounting points to optimize for that power output, so I theoretically get:
[ 5,000ft-lb / (1hp * 550ft-lb/sec*hp) *2*3.14rad/360deg]= 0.16sec/deg = 14sec/90deg = 28sec/180deg
I got pretty close to this when the machine was completed. If you look at this video, you can see I do a 45 in about 7 seconds which is pretty close to the calculation above. http://www.myspace.com/video/vid/1441790523
That machine was designed from scratch so I had a lot more flexiblity to put the cylinders where I wanted and match them to the pump/motor/power unit.
Ways to get faster bends:
- Increase power
- Make bender variable so smaller tube (lower torque) can be bent faster with the same power
- Reduce variation in geometry/leverage during cylinder stroke
- Do the homework to match components, geometry, etc
- Have someone else do it for you :)