1. ## torque question

I have built a wire bender, that I am bending 3/16" wire.

I want to build a cnc bender.

how do I measure how much force (torque) it takes to bend the wire with my hand bender.

My handle is 10" from the center of the pivot.
the wire is .1875"

Do I need a scale or something to measure how much force it takes to bend the wire?
Is it as simple as using a scale to push on the handle.

Thanks
EZ

2. ## measured

I did use a scale and pushed against the end of the handle.
It seemed to be almost 14 lbs.

EZ

3. ## forgot part of the equation

the distance from the center of the pivot to the center of the push pin
is .5"

the distance of the handle is 10"

So the force applied to the handle about 14 lbs.
Using these figures, I put them into a torque calculator on the web

F = 14 pound force = 62.27510268 newton
D = 10 inch = 0.254 meter

torque (T) = 15.81787608072 newton-meter

So about 16 newtons of force or 11.8 lbs ft or 141.6 lbs in

How do I calculate the torque needed to push the wire at the
.5" mark

EZ

4. It appears you already have calculated the torque. Is force what you need to know? If .5" is the point the force is applied then 10" / .5" = 20 20 X 14lb. = 280lb. applied at .5" distance will bend the wire as tested.

Reverse the equation: 280lb. of force @ .5" = 140lb. of force @1" = 140 lb.in of torque / 10" = 14 lb. of force.
So, 140 lb.in. of torque = 280 lb. of force @.5"

Either that's true or senility has set in. LOL

Dick Z

5. No I don't think senility has set in.

cncfoam here is a suggestion based on making several benders, not CNC, hydraulic and manual. Your calculation sounds realistic based on my experience but when you make the bender put in an overload factor. Nominally 300lb is adequate but make your bender for something like 600lb. You can easily bend something that is below the bender capacity and if you have excess capacity it does not matter if you get hold of a batch of wire that has a slightly higher yield strength.

6. ## re - check

I took your formula and entered it into the torque calculator.
and came up with the same answer

F = 280 pound force = 1245.5020536 newton
D = .5 inch = 0.0127 meter
torque (T) = 15.81787608072 newton-meter
after digesting it. it makes sense.

So how does that relate to finding a suitable motor.

Im assuming that I will have to calculate the gear ratio too.

lets assume I have a pinion of .75" on my motor and a gear(final drive) of 6"

I would have to take the torque rating of the motor and apply a formula
to see what the final torque is.

Does this sound correct?
I will look this up right now.
EZ

7. EZ, I recalculated. It should be 140 in.lb. per my edit above.

Geof's correct, you would want more torque available than required for the bend.

Also, the motors torque is at what motor rpm? Permanent magnet servo motors can deliver full torque at near zero rpm, others have to reach a rated rpm in order to deliver full torque.

Also, if a gear train is added, it's efficiency must be accounted for. Spur gears are in the 95+% range while worm/worm wheel can be as low as the 35% area. However, the worm type gearing can have a greater speed reduction and torque multiplier.

ex. A 35 in.lb. perm. mag. servomotor with a 20:1 worm gear reduction @ 50% efficiency would result in: 35 in.lb. X 20 = 700 in.lb. X 50% = 350 in.lb @ rated speed.

Personally, I'd use an air cylinder. LOL

Dick Z

8. I would look at something like a Bayside planetary, they go up to 100:1 and you could drive the bender right at the rotary axis using a servo motor.
Other than servo motor, servo valve operated hydraulic is often used on pipe benders, I think air would be a bit 'soft' and very imprecise for positioning?
Al.

9. Al, Yes the air cylinder is not very precise. But I'd use the air cylinder to push against an adjustable hard stop. Easy speed and pressure adjustment.

But, that's not the question he asked. I wasn't trying to change the discussion, hence the LOL

Dick Z

10. ## Score !!

Went down to the local surplus shop.

found a servo with a gear drive attached.

Best thing... \$40

this thing is torquee. The shop owner hooked it up to
24v dc.. there is no way I was even coming close to
slowing it down.

I will look up the specs on the motor and gear box.

EZ