# Atlas Forward/Reverse Switch



## D.Moon (Jul 20, 2021)

I was recently given an Atlas TV48 lathe. It seems to be in good shape, except that the motor was missing and the wiring cut off short. Does anyone have a schematic or wiring diagram of how the motor and forward/reverse switch are connected together? It has a Furness L143 C switch. It has 6 terminals labeled L1, L2, 1, 2, 3, 4.


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## markba633csi (Jul 20, 2021)

Do you have a motor, or are you shopping for one? 
Fractional horsepower motors have different wiring arrangements depending on brand and model
Dayton motors can be the most difficult to wire for reversing operation- try not to get a Dayton if possible
-Mark


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## D.Moon (Jul 20, 2021)

I have a 3hp DC treadmill motor. I could wire a DPDT toggle switch in about 5 minutes to do the job, but I would like to use the original switch if possible.


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## markba633csi (Jul 20, 2021)

You can't run a dc motor directly off the ac line. At minimum you would need to rectify the ac power OR provide a dc motor controller like KB electronics or the original treadmill controller if you have it.
Using just rectified ac power you would not have good speed regulation with varying load, so having a true electronic controller is recommended
-Mark


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## D.Moon (Jul 20, 2021)

I have variable speed DC motor controller. I'm just trying to see if the original switch can be adapted to the DC motor for forward and reverse


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## Ulma Doctor (Jul 20, 2021)

Directional control is as simple as reversing the polarity


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## markba633csi (Jul 20, 2021)

OK,  you can connect the switch as a DPDT to reverse the motor polarity. You just need to ring it out with a ohmmeter to id the switch contacts.
Be aware however:  switching the motor while under power could blow the controller's output stage, depending on the type of controller.  Old style SCR type units are more rugged.  Some of the older treadmills had those. They usually have five TO-220 power tab devices on a common heatsink.
On the other hand...
More modern mosfet types are more prone to voltage spikes and damage though, so you need to use caution with those.  A moment of forgetfulness and there goes your controller.
But, if you do have a mosfet type controller and blow it up, you can change to a SCR type like KB electronics or Dart controls


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## WCraig (Jul 20, 2021)

Because the chuck threads onto the spindle nose, there is a risk of it unscrewing if the lathe is run in reverse.  That is typically a Bad Thing(TM).  Are you sure reverse rotation is necessary?

Craig


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## markba633csi (Jul 20, 2021)

Often times for metric threading the spindle/carriage needs to be backed up repeatedly to the starting point without disengaging the half-nuts
In this case the backgears are used or the machine is set for a low speed so the risk of dropping a chuck is minimal


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## wa5cab (Jul 23, 2021)

If considering using a variable speed DC motor on the lathe, first thing that you need to determine is whether or not the drum switch that you want to use is suitable for 3-Phase and DC motor operation.  To determine this, fasten the switch to something either bolted to a bench or somehow fastened down so that you can operate the switch one-handed (not having to hold the switch down with one hand while operating it with the other hand).  Operate the switch to one of the two ON positions (call it Forward for the moment).  Now try to change the switch to Reverse in one continuous motion (without momentarily stopping in OFF).  If you can do this, do NOT use the switch on anything except a single phase motor.  It is NOT safe for use on either a DC or a 3-phase motor.  

The reason that this is so is that a single phase motor when running in either direction (assuming that the centrifugal start switch is working) will have the START winding disconnected by the centrifugal START switch and throwing the control switch directly from FORWARD to REVERSE will do nothing except momentarily remove power from the RUN winding(s).  The motor will continue to run in whichever direction it was running before you changed the switch.  The DC or 3-phase AC motor, on the other hand, will create much hate and discontent as it tries to go from full speed in one direction to full speed in the other without being allowed to momentarily stop before starting in the other direction.  A rotary, lever or toggle switch that is made to operate a reversible motor has a mechanism built into it that basically forces you to remove your hand from the bat/lever/knob while it is in the OFF position before you can throw the switch on over to the opposite setting.  Determine this before you even bother to try to figure out how to wire your drum switch.  If the switch came from Atlas, it is probably OK.

We have switch wiring diagrams for a lot of motor switches. but it isn't worth looking it up until you have tested the switch mechanically.


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## wa5cab (Jul 23, 2021)

The Atlas machines all have threaded spindles.  So, unless your chuck is one of the more expensive ones with the added split locking sleeve, do NOT try to machine in reverse.  But on the other hand, I have had an Atlas lathe with a reversable motor and switch since 1981.  And I have never had a chuck or face plate come loose simply by reversing the motor.


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## Shotgun (Jul 24, 2021)

wa5cab said:


> The Atlas machines all have threaded spindles.  So, unless your chuck is one of the more expensive ones with the added split locking sleeve, do NOT try to machine in reverse.  But on the other hand, I have had an Atlas lathe with a reversable motor and switch since 1981.  And I have never had a chuck or face plate come loose simply by reversing the motor.



I recently made up a draw bar for holding my ER-32 MT-3 . . . ???. . . thingy.

High on my list is to make a part that will fit inside the chuck, below the jaws, that will allow the draw bar to hold the chuck in reverse.

I have the reverse switch, which is tied to the VFD that handles the "forward to reverse without stopping" problem, but haven't used it because the chuck isn't locked.  I tried using it for threading once, so that I wouldn't have to bother with the threading dial, but that destroyed my carbide threading insert.


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## wa5cab (Jul 24, 2021)

You need to re-read the instructions for cutting metric threads on a lathe with an inch lead screw.  You are supposed to stop the spindle and back the cross slide out before re-starting the motor in reverse.  All lathes have some backlash in the half nuts, even if the machine and all components are brand new.  Even if cutting inch threads.  You are supposed to cycle the cross feed between one setting for cutting and another setting for returning the carriage to the start position.  DOC is set  and increased only by the compound feed.


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## Bi11Hudson (Jul 24, 2021)

Seems to be a lot of 'foo fah rah' about doing a conversion to DC. Which is fine if that's what you decide to do. All of my stuff has induction motors because I've worked on DC motors in years past and don't want fool with them any more. Just being old and obstinate. . . 

If you are mounting a single phase motor at 120 volts, the basic premise is there are two windings, a start and a run. To reverse the motor, you swap the relationship between the start and run. The usual practice is to reverse the start winding, but is not an absolute. There are a half dozen or better switches so I can't give terminal numbers, nor can I specify motor leads. Together, you probably have half a hundred different combinations. Then there are 240 volt connections, which add another dozen or so combinations. All, well most are doable, the biggest issue is knowing which one to do.

*Most* switches will have six terminals, three sets of contacts. *Most* of the time, the lower of the three contacts is basically an on-off switch, switching on in either direction. The other two contacts, 4 terminals, make up a reversing switch. Connect the run winding through the on-off contact. Connect the start winding through the reversing contacts. I can't be more specific without writing a book, well at least several pages. There are too many variables, this will have to do. And I'm not sure where some of my drawings are after crashing last year. But this is the basic idea, you dig out the terminals.

.


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## markba633csi (Jul 24, 2021)

That's my aim eventually, to write a few pages on how to connect any reversing switch with any motor.  One of these days...
Easier said than done 
-M


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## Bi11Hudson (Jul 25, 2021)

Realizing up front that you are not dealing with a Sq.D reversing switch, I include the documentation more as a guide for the different types of motors, with the switching terminals as secondary. The circuits shown will be, of one sort or another, what  is used. The terminal definations, the terminal numbers will vary from switch to switch. As will the physical location of the contacts. But at the bottom line, this is what a reversing switch does. There are different diagrams depending on whether the line cord comes in to the switch or the motor. My personal preference is to bring the line cord into the motor and run a six conductor cable to the switch. But that's just my personal preference, it keeps several points clear(er). And keeps down the number of wires in the switch enclosure, which is crowded enough as it is.

.


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## wa5cab (Jul 25, 2021)

I found this wiring info for the Furnas L143 in another post from about 2014 and edited it.

The six terminals on the switch should be called L1, L2, 1, 2, 3, 4.

The motors "RUN" winding or windings if the motor runs on both 120 and 240 VAC connect to terminals 2 and 4. The "START" winding is fed from terminals 1 and 3. If the motor rotation does not agree with the switch markings, reverse the connections to the start winding on 1 and 3.

The remaining two terminals on the switch should be labeled L1 and L2.  Connect the Line and Neutral (if 120 VAC) or the two Line wires (if 240 VAC) from the line cord to these.   Connect the Ground wire (should be green in all cases) from the line cord to any available screw or bolt that is electrically connected to the switch body, lathe frame, headstock, etc.


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