Hi fifty8, that Youtube is what I pictured from your description. A reversing contactor is a simpler solution than a VFD. If I was doing it I am confident I could work out the connections on the contactor on ebay (Or similar.) without the documentation. If I had any doubt about the connections to the auxiliary contacts I could confirm them using a meter. From the connection labeling I can see in the picture I am fairly confident I could draw out a diagram that you could follow but I could not be 100% certain. The schematic in post #8 is exactly what I was proposing but I realise that you do not understand that. Even talking people on forums who claim to some electrical knowledge through doing simple continuity tests can be a problem as they very often say something has no resistance when they really mean it has infinite resistance. I think in your case I would consider it reasonable not to bother with thermal overloads as you would realise that the motor had stalled if the metal you were bending was too strong and remove power to the motor.

Les.

 

Les, I'd very much like to see your simple circuit diagram.
Are we talking using a lower voltage or would it be power taken straight of the mains to run the limit switches?
I'm all ears so to speak.

 

I don't understand what you are saying in post #22 The power for the motor will ALWAYS come from the mains.(Either directly from the three phase mains or a single phase supply converted to three phase by a VFD.) One point I forgot to mention is that most reasonably priced VFDs only supply 240 volts phase to phase so the motor must be a type that allows the windings to be strapped in delta configuration rather than star configuration. That is something that would have to be checked before considering the VFD option. The lower voltage is ONLY used on the control circuit. The SIMPLE circuit is made possible because the VFD removes the need to interlock the two contactors ( So there is no possibility of both contactors being actuated at the same time.) Using contactors the control part can work at many different voltages. For example 440 volts AC (Phase to Phase.) 240 volt AC. (Phase to neutral.) and at various low voltages AC or DC (For example 50 volts , 24 volts 12 volts.) The control voltage only drives the coils on the contactors and the contactor coils must be rated coils must be rated for the chosen voltage. From memory the reversing contactor on ebay had 24 volt DC coils so a 24 volt DC supply would have to be provided. One other point about VFDs is that you should use screened cable between the VFD and the motor and you should have a mains filter on their input to prevent electrical interference being injected back into the mains supply. (Some VFDs have this filter built in.)

Les.

 

The mains power was mentioned so folks know I have access to a neutral wire for any single phase requirements in a circuit since my motor is 3 phase. I will not be using a VFD to power this machine.

I am trying to keep this simple and practical, without the aid of a VFD, as I have used one in the past and I dont see a need for one on this project.

 

Your only real choice is to use a reversing contactor. Your idea of using a tumbler reversing switch (Posts #4, #11, #14) would work but I don't know where you would get a two or three pole limit switch suitable for the full motor current. And as I have said before I don't recommend that method. As you can't read the schematic in post #8 You would need one of us to do a drawing using pictures of the reversing contactor and limit switches with the wires drawn between them. so I think the next step is to find a reversing contactor at a price you are prepared to pay. (Or two contactors to the specification I mentioned in post #6).

Les.

 

It may better provide you with a better understanding of what I seek to build.

I thought you said you were making a mandrel bender? That bender is definitely not one.

 

I don't know where you would get a two or three pole limit switch suitable for the full motor current.

Why would you need them? Using the tumbler switch would be the interlock, simulating a reversing contactor. All of this would be low volt control to two contactors, one for forward and one for reverse. The limit switch voltages would be run through the tumbler switch, most of which are for three phase having three sets of contacts. Use one set for forward and another for reverse and center off. That would be only using 4 of the possible 9 contact terminals in the switch.

 

Hi SB, The TS seems to want to avoid the cost of contactors. I think he just wants to use a reversing switch similar to the Dewhurst reversing switch that is used on Myford lathes.

Les.

 

Check this out.
It may better provide you with a better understanding of what I seek to build.

As you can see from the video, the torque required is very high, especially for steel product.
Hence the very high ratio G.B. is required.
For automatic use, I don't see the any choice in not using a reversing contactor, especially for a fair sized motor as in the video.
The manual reversing switch of the right capability would also work, but the repetition accuracy would suffer, I would think?
Max.

 

fiftyv8, I have been looking on Ebay (UK) for "reversing contactors" and found a few at around £30.00 Most of them have clear pictures showing the terminal markings which would enable me (Or others. ) to draw a picture of how to connect them. I don't know if this is any use to you as I don't know which country you are in. If you decide to buy one I suggest posting which one you have chosen so we can confirm that it is suitable. (If I was doing it I would choose one with a 24 volt AC coil.)

Les.

 

My preference is for 24vdc coil, you only need a small bridge to use on 24vac, and they don't burn out or chatter like AC versions.
Also most DIN style contactors now have custom O/L that connect directly to the bottom of the contactor.
This may also help.
Max.

 

I'm in Australia.
Here is a 2nd machine using 2 foot pedals with limit switches.

เอ็นทีเอ็นจิเนียริ่ง #เครื่องดัดแป็ปคอยาวราคา75000 #สนใจเครื่องดัดแป๊ปคอยาวติดต่อเลย - YouTube

 

Hi Max, I agree with your reason for a preference for DC coils. I suggested the AC version to save the TS having to connect a bridge rectifier to the output of a transformer and there seems to be more reversing contactors with AC coils on Ebay (UK) at the moment. (I know it would probably be cheaper to buy a 24 volt DC switch mode power supply than a transformer but I consider transformers much more reliable. I still have a few WW2 surplus transformers that have never given any problems.)

fiftyv8, You will have to look on ebay (Australia) to see if you can find a suitable reversing contactor within your budget.
Have you done any calculations to check the the motor you have provides enough torque to bend the material that you plan to bend. (See Max's post #29) If you are bending 15mm copper water pipe I think your motor would have enough torque but for the materials shown in the videos (My guess is 25mm square tube with a 3mm wall thickness in the first one and 30mm diameter steel bar in the second.) I don't think it would be powerfull even with the extra reduction in the chain drive in the videos.

Les.

 

Obviously, these projects are not for the faint hearted, but one must start somewhere I guess.
I will be running two reduction gearboxes. I only need to rotate at my preference of 2 rpm. I note bigger stronger machines are more than double and some triple that speed.

That is a lot of force and I am hoping the 3 phase option will help out.
There are hand operated machines with not so long levers that will bend many of the small to medium sized sections.

Run of the mill hydraulic pipe bend machines bending upto 50mm pipe have a 10 Tonne ram, whether all that effort is required I am not sure.

 

Is the unit intended for some kind of production machine? Or just for your occasional use for one-off units?
Max.

 

My feeling is that you will not be able to provide enough torque.
You have 0.75 HR at 2 RPM final speed
1 hp is 33000 ft lbs per minute
So 0.75 HP is 0.75 is 33000 x 0.75 = 24750 ft lbs per minute
If we consider a one foot long lever on the output shaft the end of it will travel a liner distance of 2 (RPM) x 2 x 3.142 (pi) feet per minute = 12.6 feet.
24750 (ft lbs) /12.6 = 1964 lbs
This is not as bad as I thought it would be. It is like about 200 pound hung of the end of 10 feet of your pipe. It think that might bend it . I do not know how to calculate the force required to bend your pipe.
You could try applying that sort of force to a 10 ft length of your pipe before building the machine.

Les.

 

Les, Is the increased torque for the rate of the ratio of reduction in that calculation?

 

Dobladora manual de tubo TM-025 - YouTube

 

Hi Max, My simple calculation ignores any loss in the gearbox. I chose to base the calculation on using a point 1 foot from the axis to make the calculation simple. The distance traveled in one revolution one foot from the axis would be 2 x Pi x R
(2 x 3.132 x 1) feet. As the output speed is 2 RPM then that distance is 12.6 feet. So if you think about it as a rope wrapped round a 2 foot diameter drum in one minute it would have lifted the load 12.6 feet. As we know 0.75 HP is 24750 feet pounds per minute we just divide that by the distance traveled by a weight on the end of the imaginary rope. The result is 1964 pounds. As I chose a 1 foot radius the torque is also the same number in units of pounds feet. Strangely I had correctly remembered from when I was at school that 1 HP was 33000 foot pound per minute. (I did check that I had remembered this value correctly as it was over 60 years ago.) If I had not remembered that conversion I probably would have done the calculation in metric units. The TS had originally said the output of the geared motor was 25 RPM And that would have made the situation much worse if that was the final speed.
If I was building the machine I would do some tests to find the actual force required to bend the tube (Or find someone who could calculate it.) and then choose a motor that could provide about twice that force.

Les.

 

O/D pipe max to bend is 50mm and generally will be 32mm all 3mm wall.