# How to use limit switches in a project circuit?

#### LesJones

Joined Jan 8, 2017
4,007
You could try providing full information on the pipe. Wall thickness, tensile strength of the metal and maximum diameter and I would guess the radius of the bend in the hope that someone knows how to calculate the force required. A mechanical engineering forum would be a good place to ask this sort of question. One other way I would consider is to look at the specifications of machines sold for this purpose in terms of power rating and the speed of the final drive. In other words copy an existing machine.

Les.

Joined Jul 18, 2013
26,995
O/D pipe max to bend is 50mm and generally will be 32mm all 3mm wall.
What I have done in many instances in the past is put/operate an ordinary torque wrench on the input shaft, in this case, the motor input shaft to any G.B. etc, and operate the normal load with the wrench, while taking a reading.
This enables a pretty accurate requirement of any motor etc that you intend using.
I also prefer calculating electrical HP, no motion involved which as in this case can lead to misleading results.

To find the electric horsepower of a motor, use the equation:
Horsepower = (Volts x Amps) / 745.7 (does not take efficiency into consideration)

Example: The electric horsepower of a motor with 120volts and 10 amps is:
HP = (120 x 10) / 745.7
Calculated out this gives an electric horsepower of 1.6092.
Max.

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#### shortbus

Joined Sep 30, 2009
9,858
Your original request was to make a mandrel bender, but so far all of your examples are not even close to being mandrel benders. So I'll ask yet again, do you want the type you show or a mandrel bender?

I own and have used a JD2 bender, the manual type not hydraulic. https://www.jd2.com/benders And it is one of the type you show. They use a lever and movable pins to keep the leverage at the most force multiplying point in the movement. The ones you link too take much more force than the JD2 type because they are moving from the center of rotation, not the end of the arm. The shown machines I'm guessing are using a #100 or bigger roller chain, The #100 chain has an average tensile strength of ~12.5 tones, so you can imagine the force needed.

The JD2 that I have was used to bend many roll cages for Jeeps and dune buggies back in the day. Mostly from 1.75 diameter 1/8" wall mild steel tube.

#### fiftyv8

Joined Jan 29, 2018
223
Honestly, the simple answer is I will build a machine very similar to that shown in the first video attached.
If the motor shows that it is lacking HP, then I will find a larger one.
However, we stray away from my original request for a simple circuit if possible that I can run a pair of limit switches...

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#### shortbus

Joined Sep 30, 2009
9,858
However, we stray away from my original request for a simple circuit if possible that I can run a pair of limit switches.

Only two ways to do that, and it seems you don't like either. Limit switches are control circuit devices, not made for power use. So the only way a limit can be used is contactors(the normal way it is and has been done forever) or a VFD. I'd be willing to bet all of the electrical ones you've linked to use contactors.

#### LesJones

Joined Jan 8, 2017
4,007
I have since realised that there is a potential problem when I suggested using a double pole limit switch as a possible (BUT NOT RECOMMENDED.) solution. If both poles of the switch did not break at exactly the same time the motor could come to a halt with only one pole open leaving the motor with one phase connected to it which would probably burn out a winding, This is more significant as the TS would not be able to install thermal overloads as the NC contact has to be connected in series with the coil of a contactor for them to work.

Les.

Joined Jul 18, 2013
26,995
However, we stray away from my original request for a simple circuit if possible that I can run a pair of limit switches...
Limit switches and a 'simple circuit' may not go hand in hand for this project!
One, most commercial L.S. have a micro switch internal, these are rated around 1.5a.
Also they are made to switch a control circuit, therefore to control a 3ph motor with L.S.'s requires contactor control.
I could put something basic together but do you want to make it semi automatic?
i.e. , push a button and the bend takes place and the arm returns to the start position?
Or do you want purely manual control, i.e. Hold the button until bent?
Max.

#### fiftyv8

Joined Jan 29, 2018
223
I want two automatic stop points when tripped (limit switches). Other than that all motion in between would be manually controlled and no automatic return.

Joined Jul 18, 2013
26,995

View attachment 232089
Incidentally That practice of placing the O/L on that side of the coil is now considered a no-no in most jurisdictions, particularly where L2 is usually a grounded neutral, N.A. U.K. and the op's location, Australia.
It would be placed next to the Stop P.B. in this case.

Joined Jul 18, 2013
26,995
Here is one method similar to @GetDeviceInfo , if you use AC for the relay circuit, disregard the diodes across the coils.
Max.

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#### fiftyv8

Joined Jan 29, 2018
223
Thanks Max, I will take some time to digest it.
It appears that I can follow most of it at first sighting.

Russ.

#### LesJones

Joined Jan 8, 2017
4,007
I'm pleased to see that you have now agreed to use contactors. If you are not sure about reading the schematic if you post pictures clearly showing the marking on the connections of the contactors, limit switches and motor connection box we should be able to make up a pictorial wiring diagram that you should understand.

Les.

#### fiftyv8

Joined Jan 29, 2018
223
Les and Max, your time and efforts are much appreciated.
Right now, I need to catch up to the electrical progress I've made by getting some of the mechanical and physical stuff manufactured and worked out.
I am on a mission to find sprockets and chain etc at the right price.

I will post progress once I have something worth showing.
So more later,
Russ.

#### fiftyv8

Joined Jan 29, 2018
223
Well folks, I have a bit of progress to report.
I found a 1.1kW motor which had a matching flange to my reduction box which was a bonus.
However the shaft size was larger so I had to remove the amateur and turn the end portion of the shaft down to fit the drive gear.

That has been done and the new motor mated up to the reduction box.
This a STAR configuration motor and I know need to complete my motor and box mounting platform which will be hinged for easy adjustment and removal of drive chain coming later.

The new motor is noticeably larger and heavier than my previous choice.
This unit will with a chain, will drive to another larger heavier reduction box which will then rotate an arm that pulls the tube around a selected circular form.

Well that is the plan, fingers crossed as I near closer to the big day.

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#### fiftyv8

Joined Jan 29, 2018
223
Got my 2nd reduction gearbox.
It is a monster 32mm input shaft and 50mm output shaft, that should tame the tube I need to bend...
It will need to be mounted horizontally in my frame so 90 degrees rotated to how it sits on the ground right now.
I am not sure what its original purpose was but it look sturdy, weighs a lot and is probably early post WW2.

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Joined Jul 18, 2013
26,995
Probabally pay to open it up and clean and re-grease the worm and pinion.

#### fiftyv8

Joined Jan 29, 2018
223
Yep, gets grease tomorrow.
Was oil filled, but since I have laid it on its side, grease will do a better job and no chance of leaks thru the bearings.
It is going to be a lot of grease, 4 to 5 ice cream containers at first estimate.
Lucky I got a buddy who inherited a relatives workshop contents and good or bad it included a 80+ litre drum of grease, perfect for my needs and boy he is happy to give it away.

#### fiftyv8

Joined Jan 29, 2018
223
Well, I got about 6 litres of grease into that huge gearbox, maybe once the weather warms I will require a couple more litres after it settles.
I got the frame mostly together albeit not fully welded in parts but enough so I can do a mock up of how the mechanical and electrical components will fit.
This is no joke weight wise and the overhead gantry crane I built in my shop several years ago has well and truly paid for itself and saved my back heaps.

#### fiftyv8

Joined Jan 29, 2018
223
My frame was rotated to stand on the wheels and electric motor with reduction gearbox is also installed now.
I need to calculate a sprockets size to mate with an existing sprocket that I have that came with one of the other components. Just trying to keep the expenses down but shoot for a 2 rpm final output speed.

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#### shortbus

Joined Sep 30, 2009
9,858
With the frame on wheels like that and the way the welds look on the worm gear box brackets, please, please make a video of your first test bend. It will be a Youtube viral.