# New To Me Atlas 3950: Questions About Motor Controller



## Brendan (May 22, 2015)

Hi gents! This is my first post. I'm an engineer by trade, and have long wanted a small hobby machine in my garage to make parts for my other hobbies (restoring motorcycles, machines, etc). I've recently been given a small Atlas/Craftsman 3950 (With the cast iron housing) that had been stored for many years. 
The ways were pretty rusty when I got the machine, but cleaned up ok. There is certainly some wear on them, especially close to the chuck. 

The idler pulley was very very worn, so I pressed out the bushing, turned the worn shaft down to the next available drill size, and put a new bushing on. It is nice and tight now, and I hope it lasts another 40 years. 
	

		
			
		

		
	




The coupling was also stuck, but I got it unstuck and the backgears seem to work well now. I still need to clean up the entire gear train, as they are coated in a grease that has dried to a tar-like consistency. I'll pull them off and clean them on a tank of diesel. 


Some items of concern:
One of the handles is broken on the carriage (crossfeed handle). Are there replacements available? Preferably something that isn't pot metal 



Is there a backlash adjustment for the crossfeed and the compound slide? There seems to be a lot of backlash (although I am spoiled by the lathes at work and I am not sure what to expect out of a hobby machine)

The automatic feed doesn't work/ work sporadically. The lead screw turns well, and the half-nut lever actuates the half nut correctly, but it only sporadically feeds forward. I think the half-nut has stripped threads, but I haven't had it off to check. 

When I got the lathe, there was a motor controller bolted to the top. I assume it is a DC motor controller based on what is inside. Can anybody help me identify the model # and the hp rating of this controller? There is a 2A fuse on both the "line" and "armature" fuses. 




The lathe also came with a motor, which I first thought was a DC motor (as it had brushes and I assumed it went with the motor controller). I tried powering it wit DC, and it just hummed at me. I took it apart, and it looks to be a very old RI motor. 

Thanks, and look forward to making some chips!


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## tomh (May 22, 2015)

Brendan
Yes the parts is still available from clausing.  
Call clausing and ask for the parts dept,  jo  will know what you need shes good on the small lathes.
Get their price on the half nuts and handle before going to the on line auction. 
Ask for  the parts break down, they used to give them for free don't about now.
Tomh


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## wa5cab (May 22, 2015)

Brendan,

Yes, or at least partially.  You can adjust the feed screw end float to very near zero by loosening the special nut retaining the handle, tightening the jam nut between the handle and dial, and then tightening the special nut without allowing the screw to rotate.  Tighten the jam nut until you feel a drag when you try to rotate the crank.  Then back off about half a flat.  On the cross feed, you can arrive at the best setting probably more quickly if you first crank the cross slide all the way to the rear until the cross feed nut underneath the cross slide runs off of the feed screw.  Or alternatively, remove the two screw holding the thrust plate and turn the crank CW until the screw comes loose, and do the adjustment off the lathe.  Hold the thrust plate in a smooth jaw vise.  Once you have made that adjustment, the backlash remaining (there will always be some) can only be improved by replacing the cross feed nut and/or screw.  You can tell whether or not a new screw will make any difference by checking the backlash in the common work area and then with the cross slide to the rear until only one or two screw threads are visible.  If the two readings are the same, a new screw won't make any difference.

To check the half nuts for wear, remove the lead screw.  Slide the tailstock off of the bed.  Slide the carriage about 1/3 off the bed and remove the two 1/4"-20 fillister head machine screws securing the guide to the back side of the apron,

The PDF manual on the Atlas 3950 is in Downloads.

On the controller, best way is to find the model number and look it up.  Second best is to look on the instruction sticker on the Variac for the current rating.  If it is there, multiply that by 120.  Divide that by 746 and you will have a ballpark HP figure.

On the motor, add a photo or three.  How many wires come out of it?


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## Brendan (May 23, 2015)

Thank you, I was eyeing those jam nuts previously and know I know. I adjusted the backlash and it is much better. 

Regarding the motor: I scraped the paint off the name plate so I could read it and it definitely says 60 cycles. I am not near my shop, but here is a picture of the same motor. There are two brushes, with only two wires going in. There are no permanent magnets. 




It's a 1/6 HP, which is pretty underpowered. I have a 1/3 HP 1750 RPM motor that will be much better suited to use on the lathe. 

I'm not getting any model number that matches anything on the Boston Gear web site, but I have an email in for support. The Variac is rated at 2 amps, and everything is fused at 2 amps. This is about 1/3 HP using your estimate.


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## wa5cab (May 23, 2015)

OK.  1/3 HP is about the max for a 6".

My guess would be that the controller is for a 1/4 HP DC motor, currently wired for a permanent magnet one.  Probably if you put a meter on the two terminal strip screws with no wires on them, and turn the controller on, you will find 115 to 130 VDC that does not vary when you rotate the Variac.  If so, they would be for the shunt field on a shunt-wound motor, and not used with a per-mag one.

I don't know what to make of the motor.  I just went through a late 50's vintage textbook on alternating current machines and didn't find anything with slip rings.  Just for grins, try putting 120 VAC on it and see whether or not it starts.


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## master53yoda (May 24, 2015)

Couple of thoughts.  the speed control looks like a vary simple Early DC drive for a DC motor with a parallel fields and stator   It would also work on a series motor but there wouldn't be any limit on the speed besides the load.    It looks like the drive is a variac transformer with full wave rectification and a choke circuit.   If it was me I would get a treadmill motor and drive  and not fight the old motor as it is a little on the small side for that lathe and doesn't have any torgue controll circuitry.   If you use one of the small tread mill motors they will deliver a real 1/3 to 1/2 HP at 1750 and will also reduce torgue as they slow down.     I have power taped 1/2 in steel with mine and can still stall it on a 1/4 tap and not break it.

As far as the back lash is concerned,  I use DROs and with them the backlash isn't an issue because the DRO tells you where the cutter really is.   There is backlash on almost any manual lathe and with the DRO it doesn't make any difference  if you are always working in the loaded position of the backlash as the cutter location is known.  I use the IGaging DROs on both my mill and the lathe,  the cost is about $90 for a lathe your size.  I also use the Android DRO app on my Phone to comunicate with them.

Have fun and enjoy your machine

Art B


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## John Hasler (May 24, 2015)

The motor looks like a repulsion-start induction motor.  If so the controller is not for it.


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## Brendan (May 26, 2015)

Tried the motor on AC, and it does work. I then proceeded to take it apart and damaged one of the bushings due to a burr on the output shaft. Maybe my first lathe project will be to repair this motor 

Anyway,  I got the machine set up with the 1/3 hp 1750 RPM AC motor that I had laying around and made a few small parts. I am still waiting on a new belt before I really run the machine through the paces. The good news is that the spindle is true with no wobble. 


That's great feedback about the treadmill motor. I'll take a look.  
Thanks for all the help. 


-Brendan


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## wa5cab (May 27, 2015)

Sounds like you are on the way.

I would like to get the headstock casting date (partially hidden behind the large back gear) and the serial number of the machine.


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## emasbury (May 27, 2015)

Brendan said:


> Hi gents! This is my first post. I'm an engineer by trade, and have long wanted a small hobby machine in my garage to make parts for my other hobbies (restoring motorcycles, machines, etc). I've recently been given a small Atlas/Craftsman 3950 (With the cast iron housing) that had been stored for many years.
> The ways were pretty rusty when I got the machine, but cleaned up ok. There is certainly some wear on them, especially close to the chuck.
> 
> The idler pulley was very very worn, so I pressed out the bushing, turned the worn shaft down to the next available drill size, and put a new bushing on. It is nice and tight now, and I hope it lasts another 40 years.
> ...



These are some good folks, they will be a great help to you. With their help I got my Atlas/Clausing 8520 up and running.
http://www.clausing-industrial.com/partsService.asp


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## Brendan (May 27, 2015)

Would the serial number be on a plate near the tailstock? If so, mine is missing. 

here is a picture of the casting info!


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## wa5cab (May 27, 2015)

Yes, the nameplate should be on the right end of the bed.  It shows both model number and serial number.  If it has no nameplate, how did you know that it was a 3950 and not a 101.21200?  Can you add a front view photo of the entire machine?

FWIW, this may be the first sighting of a green one.


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## Brendan (May 29, 2015)

To be honest, I am not entirely sure of the difference. I thought they were the same in all but nameplate. The Atlas was the first one I stumbled across in my research, so I was referring to it by that name. 

Here is a picture of the entire machine, and the missing badges.


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