# Shunt wound DC motor on Clausing 8530 mill



## calstar (Jul 13, 2014)

I recently bought the Clausing mill and need help understanding exactly what and how the DC motor and controller work. I googled and read some on shunt wound motors but would like info from the perspective of machinists. Hoping to better understand how much torque loss I have at any given speed, etc. The OEM power switch is disconnected, the 240(238v at line side of main meter) goes directly into the controller to the motor. Check the pics, input always appreciated.

thanks, Brian


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## John Hasler (Jul 13, 2014)

The data plate says it all: 25.2 in-lb at 1250 RPM, 15.2 in-lb at 150 RPM.  It'll be pretty much linear in between.  With a closed-loop controller you could have nearly full power over the full range, but that's a lot more electronics.


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## Muzzer (Jul 15, 2014)

IIRC, you connect your 200Vdc across the stationary field winding and a variable zero to 180Vdc across the armature (brushes). The control electrics can be quite simple, like a simple bridge rectifier fed by 120. Vac for the field and a 0-120Vac Variac feeding another bridge rectifier for the armature. I expect that's what you will find inside the control box. 

The speed regulation won't be amazing but it's a simple system. 


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## Muzzer (Jul 15, 2014)

Now that I've bothered to look closer I see it runs off 240Vac. Not quite sure how that works out cos the numbers don't look right for the motor. It obviously isn't original and isn't really the ideal sort of motor for driving a spindle open loop either. Does it still work?


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## Terrywerm (Jul 15, 2014)

As already mentioned, the DC motor is not original to the 85xx series of Clausing mills, and it was added later on by another owner as a method of introducing variable speed for this machine. The motor is 1 HP, and should work well on this machine also, but keep in mind that 1 HP will not be available at lower speeds. You may find it necessary to gear down a bit with the belt system, but a little experimentation will answer that for you. The top speed of the motor is 2500 RPM, whereas the original motor only ran 1725, so you should be able to do some speed reduction with the belt system, and still get a full range of speeds without seeing too many problems with loss of power.

The input voltage to the speed controller is 230/240 VAC as shown. The controller converts AC to DC and feeds it to the motor at the proper voltage for the required speed. This type of controller often uses an SCR for speed control, sending a pulsed DC current to the motor, and they work quite well, but the variac style mentioned by muzzer is common also, though not as good at speed control. The SCR type tend to whine or hum in use, particularly at lower speeds, but are quite a bit more expensive than the variac type.

DC motors come in three basic varieties: permanent magnet, shunt wound, and series wound.  

Permanent magnet motors use magnets for the field, and power is fed only to the armature through the brushes. They are inexpensive and work well in low power applications.
Series wound motors use a wound field coil that is connected in series with the power that is fed to the armature. These motors are typically used in high speed applications, such as car starter motors. Speed control is poor, and the current draw is usually rather constant regardless of voltage or load. Motor speed will change significantly with the load at a given voltage. To keep the speed constant, the voltage must be varied with the load.
Shunt, or parallel wound motors wire the field coils in parallel with the armature. They tend to run at a constant speed for a given voltage and the current draw will change with the load.
 
As you can see, a shunt wound motor is the ideal type for machine tool use, as the speed will remain fairly constant even as the load changes. Granted, there will be some change in speed, but it will generally not be great.

There is much more technical information that could be posted, but the information posted so far in this thread should be enough to answer your question. As always, if you have more questions, feel free to ask!

Good luck with that Clausing mill, I think you will like it, as it is a very robust machine for its size. The 8530 has a heavier knee than the 8520 plus it has a few other improvements including the power feed on the X axis. Problem areas on these machines include the power feed and the gears for the fine spindle feed, they are easily stripped of their teeth. From what I understand replacements are available but come at a hefty price. It is sad that the belt guards are missing on your machine. The front guard also included a brake that allowed you to lock the spindle for tightening or loosening the drawbar. Make sure you keep your hair, hands, and fingers away from those belts when it is running!! Personally I would start hunting for a guard for at least the spindle pulley, or better yet, make a temporary guard that can be used until you can find an original one.


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## calstar (Jul 15, 2014)

terrywerm said:


> ........ It is sad that the belt guards are missing on your machine. The front guard also included a brake that allowed you to lock the spindle for tightening or loosening the drawbar. Make sure you keep your hair, hands, and fingers away from those belts when it is running!! Personally I would start hunting for a guard for at least the spindle pulley, or better yet, make a temporary guard that can be used until you can find an original one.



Not to worry, I removed it for safe keeping during transit(6 hr round trip), also has the head pulley guard but not in pic, and as can see the optional belt guard between the motor and head pulley .




I'm pretty sure the lever/knob on the head casting below is the spindle brake/lock, yes?



I'm getting away from the electrical subject, I'll post more info in the clausing threads forum. I was really lucky to find/purchase this mill on CL, $1100(thats including the $100 for gas on the 6hr drive). And yes the motor and controller work fine although I did not get to try it under a cutting load.

thanks for the info guys, Brian


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## Terrywerm (Jul 20, 2014)

Ahhh, sweet!!  It's great to see that you have the guards.

As for the brake, it normally is fit into the bottom of the front guard (on the left side as you are facing the mill), and extends up into a gap in the brake plate. I guess I don't understand what is holding in place on yours at present, but I can wait for you to post more about it in the Clausing forum.

Congrats on a great buy at a decent price!


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## amuller (Jul 22, 2014)

calstar said:


> I recently bought the Clausing mill and need help understanding exactly what and how the DC motor and controller work. I googled and read some on shunt wound motors but would like info from the perspective of machinists. Hoping to better understand how much torque loss I have at any given speed, etc. The OEM power switch is disconnected, the 240(238v at line side of main meter) goes directly into the controller to the motor. Check the pics, input always appreciated.
> 
> thanks, Brian
> 
> ...


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