# X-axis Servo 70 Power Feed Running Sluggishly



## Inflight (Oct 11, 2015)

My Bridgeport's Servo brand type 70 power feed is running very slowly lately.  Rapids are about 1/2 of what they've previously been and dial speeds are slow too. I know the type 70 is obsolete, but it's been working great for the last 10 years and I'm not about to replace it.

I can move the table by hand with no problem; handles spin nice and freely.
I removed the power feed and totally cleaned the leadscrew with solvent and re-lubed with fresh oil. I also pumped a ton of fresh oil into the table ways. Like I said, the table moves fine manually.

So I took apart the servo drive unit and cleaned everything inside and out. I used electrical contact cleaner to totally clean the armature and coil. I also cleaned and lubed the upper and lower gear assemblies.  With the servo still removed from the table, I ran the motor through its speed range and rapid too. That worked well, sounded great and was moving nice and fast.

I then put everything back together on the mill table and it still seems slow. A little better than it was before the cleaning, but nothing like it should be.

I should mention that I replaced the motor brushes last year and the drive was working fine after that. During my cleaning, I inspected the brushes and they looked fine. The servo unit does not run hot or anything obvious and the machine does not get used very much; maybe 4 hrs per month.

So, where should I be looking for the culprit?


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## David VanNorman (Oct 11, 2015)

If you can get a look see at where the brushes run I think you will see it needs cleaned. Take the motor apart get an armature stone and clean it up.


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## Black13 (Oct 12, 2015)

How did the commutator look when you removed the armature. The commutator can develop a glaze on the bars from airborne contaminants (coolant mist, cutting oils, even cigar smoke). As "DavidVanNorman" said a commutator stone and some careful cleaning between the bars may solve the problem. Contact cleaner will get rid of carbon dust, but will not remove the glaze on the bars. Most hobby shops with an R/C car section carry spray commutator cleaner that works good.

If the comm has any deep groves or pitting is should be turned on a lathe. Most motor shops will do this for a small fee.


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## Inflight (Oct 12, 2015)

Today I decided to inspect the commutator. It looked good but since I had it disassembled again I went ahead and turned it between centers, taking a very light skim cut with a sharp tool. I then cleaned out all the grooves and gave it a quick polish.  Reassembled and it runs the same.   I think I'm going to just live with it and see how long it lasts.  Thanks for all the help.


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## John Hasler (Oct 12, 2015)

Inflight said:


> So, where should I be looking for the culprit?


At the controller.  How is the supply voltage under load?   How does it perform at lower speeds?


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## Inflight (Oct 12, 2015)

John Hasler said:


> At the controller.  How is the supply voltage under load?   How does it perform at lower speeds?



 All the speeds seem 50% weak, like there is excess drag.  I didn't check the voltage at all.  Where should I connect the DMM leads to properly test voltage.


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## Riaan (Oct 12, 2015)

Have you tested for short circuits between commutator segments?


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## Inflight (Oct 12, 2015)

Riaan said:


> Have you tested for short circuits between commutator segments?


Yes, I checked between each bar and all was good.


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## John Hasler (Oct 12, 2015)

Is this a true servo system with a tachometer on the motor and a closed-loop speed control?   If so I would expect a weak motor or power supply to cause poor performance at high speed and high load but normal performance at low speed and low load.  I'd have see a schematic or the unit itself to know where to check the supply voltage.

That motor looks pretty good.

[Edit] I see that you found that it works normally off the machine.  That makes me suspect the power supply.


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## Riaan (Oct 12, 2015)

Could be a red herring, because the torque load when off the machine is obviously pretty much zero by comparison. But it does sound like supply problems. I was going to suggest taking a look at the bearings too, assuming it has bearings instead of bushings.


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## Inflight (Oct 12, 2015)

It's a "Servo Products" branded power feed from back when they were in Pasadena, California. Looks like just a standard universal motor to me, as I see no tach or  hall effect, etc.

Unfortunately the controller board is no longer available. The closest match would be the model 150, but the physical dimensions inside are different and the 150 board will not fit.

Yes, lots of bearings. Radial ball and needle type.  I think I might strip everything and just replace the bearings if it comes to that.


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## Inflight (Oct 12, 2015)

Ok, thanks for everyone's help but it's all for naught.  
The whole thing literally blew up in my hands this afternoon.  Must have been some kind of short when I reassembled.  After about 30 minutes of light use, there was a very loud POP! and the rubber plug on the side blew out and all I could smell was the magic smoke of an electrical nature.  It was powerful enough to blow my hand off the joystick and scared me pretty good while I counted my fingers to make sure I wouldn't be spending the evening in the ER. Luckily I was done with my milling job and I still have all 10 digits.

Don't feel like working anymore today but maybe I'll do a postmortem and show the carnage here soon.  

Again, thanks for all the help.


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## John Hasler (Oct 12, 2015)

Inflight said:


> Looks like just a standard universal motor to me,


A universal motor would be unusual in that application.


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## Inflight (Oct 12, 2015)

John Hasler said:


> A universal motor would be unusual in that application.


You could be correct.  Here is a current version: http://www.servoproductsco.com/html/type_150_power_feed.html
What type of motor does this unit use?


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## John Hasler (Oct 12, 2015)

That 150 uses a compound-wound DC motor, which would be quite suitable for that application.  It's a shunt-wound motor with a small additional series winding to improve regulation.


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## Riaan (Oct 13, 2015)

Sorry about your misfortune! When these things happen to me I look on the bright side - at least now you KNOW it's broken. In fact, I've helped many a piece of kit along with a BFH (computer equipment especially) in order to get it into proper non-working specification for my peace of mind.


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