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reversing a milling machine

trying to reverse a milling machine but unsure of obstacles

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James fortin01/12/2010 12:38:37
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i am at the start of putting a reversing switch on my mill using a DPDT switch. (so i can reverse taps e.c.t)
 
the diagram goes like this
 
 
 
 
 

am i right in thinking that this should reverse an AC motor or will it still run in the same direction- because i know most motors have capacitors on them but don't know if this affects the direction
 
any help would be appreciated
 
many thanks
james 
john swift 101/12/2010 13:04:06
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318 forum posts
183 photos
Hi James ,
 
what type of motor do you have ?
 
your circuit will only work if used to reverse the connections to the armature or field winding of a universal motor , as in a mains power black and decker type of drill
 
or reverse the connections to the main or start winding of a single phase
capacitor start , ac motor
 
   John
 
ps - if you need , i'll upload a diagram for you

Edited By john swift 1 on 01/12/2010 13:09:05

Nicholas Farr01/12/2010 13:55:55
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Hi James, I doubt that your idea will work on a single phase ac motor. Like John has said, you need to change the armature/field winding relationship. Most motors allow you to do this inside the connection box. To do this with a remout switch you will have to bring extra wires out of the motor to the switch.
 
Regards Nick
James fortin01/12/2010 14:05:54
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hi thanks for the advise
 
a diagram would be appreciated john-its a 4pole induction motor if this helps
 
 
many thanks james 
 
 
Jeff Dayman01/12/2010 14:08:18
2356 forum posts
47 photos
Hi James,
 
Your switch wiring will work perfectly for a DC motor but will not work for an AC motor.
 
You need to ID the type of AC motor you have to be able to figure out how to phase shift the field  to reverse the motor.
 
If it is a shaded pole AC motor it will be difficult or impossible to do this, as these motors have a heavy copper shunt winding that influences the direction, which is built onto the stator lamination pack.
 
If it is a common general purpose AC motor for washing machines etc. which reverses the field by altering connections in the wiring box, a simple drum switch will be able to reverse it. The key is to find an AC motor with a wiring box and 4 to 6 connections in it.
 
JD
James fortin01/12/2010 14:17:44
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46 forum posts
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when i got it and rewired the mill it did have 4 connexions. ill post a pic when i get in the shop.
 
many thanks 
James fortin01/12/2010 14:38:09
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46 forum posts
12 photos
 ive put some pictures up and i also found a diagram inside the cover that looks like this but unfortunately couldn't photograph it because it is to small.--- the 1234 are the connections to the 4 poles and the 2 wires going towards them is the supply- i don't fully understand this diagram, any opinion on it is welcome.
 
 clockwise      anti clockwise
  CW                     CCW
 
  1  2  3  4         1  2  3  4    
   I   I   I   I           I   I   I   I    
    \ /     \ /             \ /     U
     I       I               I       I
 
 
 
many thanks
 
james 
 
James fortin01/12/2010 14:44:20
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46 forum posts
12 photos
sorry the formatting has changed maybe this is better
 
 
clockwise       anti clockwise
     CW                 CCW
 
  1   2   3   4         1  2   3   4    
   I   I   I   I           I   I   I   I    
    \ /     \ /             \ /      U
     I       I                I       I
  

Edited By James fortin on 01/12/2010 14:44:42

Edited By James fortin on 01/12/2010 14:45:09

Edited By James fortin on 01/12/2010 14:45:28

Edited By James fortin on 01/12/2010 14:45:43

NJH01/12/2010 14:45:42
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2314 forum posts
139 photos
Hi All
 
This is a probably a really silly question - Why is there a need to reverse the motor?
 
Regards
Norman 
James fortin01/12/2010 14:52:20
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46 forum posts
12 photos
its not a silly question 
 
i need i reverse it because in the future i am going to us it as a tapping machine and for other things that require reversing 
 
by the way its single phase. 
 
many thanks
 
james 

Edited By James fortin on 01/12/2010 14:58:17

Jeff Dayman01/12/2010 16:14:58
2356 forum posts
47 photos
James I don't want to burst your bubble, but unless your mill has LOTS of torque and very low speeds, you may find you will not be able to tap much under power. For non powered alignments ie tapping immediately after drilling without moving the table, you can't beat doing that in the mill.
 
In my experience  taps larger than say 1/4"-20 need a LOT of torque, and taps below #10-32 will break easily in steel if power tapping.  I have not had much luck power tapping in my RF30 Taiwan mill. My old South Bend lathe is great for tapping though.
 
When I first started work the shop I was in had a jig borer with a 20 HP motor and spindle speed down to 2 rpm. On that unit, we tapped from #2-56 up to 3/4"-10 under power regularly. It weighed about 8 tons and was super heavy cast iron construction though.
 
JD
KWIL01/12/2010 16:19:16
3681 forum posts
70 photos
I would not use it as a tapping machine without the use of a properly constructed tapping drive unit. How would you stop the rotation instantly?
James fortin01/12/2010 16:21:20
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46 forum posts
12 photos
thanks for the advice - i think i should be able to tap quite things easy as in the lowest gear the reduction is 1450 / 120 . the torque is 12 time more than at the motor(hence 12 times less speed)- thats a total of 12 horsepower 
 
when i am out in the shed next i will try my biggest tap and see how it copes
 
many thanks
 
james 

Edited By James fortin on 01/12/2010 16:23:05

Jeff Dayman01/12/2010 16:33:08
2356 forum posts
47 photos
Sorry KWIL, I assumed James would be using a tapping head like a Procunier unit or a Tapmatic. These are driven by the spindle James and are instantly reversible for tapping by means of internal cone clutches. You will need something like these units for power tapping or at least a clutch on the motor or spindle.
 
JD
James fortin01/12/2010 16:47:14
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46 forum posts
12 photos
thanks ill look this up and buy one of these instead
 
many thanks
 
james 
john swift 101/12/2010 16:48:45
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318 forum posts
183 photos
Hi James ,
 
does this diagram help with the wiring ?
 
 

as I understand tapping machines have two counter rotating drives
 
when you pull down on the handle
one clutch is engauged to drive the tap in
 
when you release the downward presure the drive stops
 
letting the handle up engauges  the reverse drive to remove the tap
 
  John
James fortin01/12/2010 16:56:28
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46 forum posts
12 photos
thanks for the diagram john, it makes sense now  , i might still use this method if i cant afford a tapping head. but at the moment the the tapping clutch sounds sensible.
 
thank you all for your input 
 
many thanks
 
james 
Andrew Johnston01/12/2010 16:57:54
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7061 forum posts
719 photos
Errr, assuming that the motor in question is 1hp, you'll still have 1hp at the spindle, whatever the speed reduction? It'd be a neat trick otherwise, and would have the Nobel prize committee winging it's way to your door post haste!
 
Power is torque times angular velocity, so if the speed is reduced by 12 then, as you say, the torque goes up by 12, but the power stays the same.
 
Regards,
 
Andrew
James fortin01/12/2010 17:01:44
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46 forum posts
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oh, thanks for that. now i think of it horse power isn't torque at all its just another unit of power as torque is in ft/lbs and n/m
 
many thanks
 
james 

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