Bridgeport Motor Replacement or Fix

B

bcfoster89

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Hello! I've been a reader of Hobby Machinist for a long time but this is my first post so I'll try to keep it from getting too long!

The backstory is: I recently bought a very used 1959 Bridgeport mill. To get it running quickly I purchased an cheap VFD, which I wired up and it seemed to work fine (although I never ran it for more than a few minutes). After reading many posts about how the cheap import VFDs weren't safe and lacking complete confidence in my electrical skills I chose to buy a new static phase converter from a US company. At first it didn't work properly so the company sent another capacitor to wire in parallel. This seemed to work but after running the mill for about 5 minutes it began billowing white smoke (hopefully not too toxic since it filled by garage).

So I have two questions: What was the cause of this and what is the best route for getting the mill working?
My thoughts on the cause are that it's an old motor (pancake style) and most likely has lots of wear/friction combined with running on two phases which caused the motor to overheat (insulation breakdown was the smoke?) I plan to test continuity between the three phases and ground to see if there are any shorts now.

Assuming there are no shorts to ground, I could: Try to switch back to the VFD and see if the issue was the motor running on two phases. Or, try to find a larger three phase motor to turn my static phase converter into a rotary.

If there are shorts would it be better to send the motor to a local shop to rewind it? (But then I'm back to the same question as above, just with a newer motor.)
Or buy a new 1 phase motor from H&W, looks like it would be about $1000 but it sounds like turn key solution.

The mill ways are very worn looking and it has quite a bit of backlash in the lead screws so I don't know if its worth putting too much money into. This is also 100% used for learning/hobby and doesn't make any money.

Thoughts? Thanks for any input to help me decide a path forward!
 
Do you have anyone with enough electrical knowledge to check the windings on the existing motor? It is a simple task, but you need to know how to use a VOM meter.
 
The elephant in the room here has to be the static converter... Doesn't seem like that was a great solution, or possibly just plain faulty.

I have some experience with the pancake motors... Is yours a 2 speed unit? Having a switch to change the motor speed?
 
Personally, I would remove the motor and do as much testing as you are capable of. If you can't find the problem, I would take it to a motor rebuilding shop and ask them to diagnose it. Once you have an answer as to what's wrong with the motor you can decide whether it's cost effective to rebuild it. You might even luck out and find the shop has rebuilt replacement motors in stock. In this area Bridgeport's are so popular the last time I checked there were several shops that had them in stock.

If the static converter was from a major brand, I doubt it was the cause of your problem. I have 4 machines in the shop running on static converters. The longest running is a Bridgeport mill. It's been running on a Phase O Matic static converter for over 20 years. It's run as long as 60 hours per week with no overheating or other problems.

I have a Sheldon lathe that's been running on an American Rotary static converter for over 6 years. It's run as long as 45 hours a week with no problems. I also have a Racine power hacksaw running on an American Rotary static converter for about the same length of time. Again no problems.

The latest machine to run on a static converter is a Black Diamond drill grinder. This one is powered by a North America static phase converter. I was originally going to purchase another American Rotary static converter, but they stopped building them before I purchased the machine. They decided to only manufacture rotary converters in their current facility, so they purchased the North America Phase Converter Company to continue in the static converter business.

I've had excellent performance from all 3 brands of static converters for many years. I also do business with an equipment dealer who sells Phase O Matic static converters. He has several machines in his own shop powered by them and has sold hundreds over the years. While they are probably the most expensive on the market, they are dependable and have a long lifespan.

Full Disclosure: I did not purchase the Phase O Matic converter from this dealer and have no affiliation other than having bought used equipment, tooling, and metal stock from him.
 
Welcome to HM.
IMHO a static converter is a downgrade from a VFD unless, as you said, you use it to build a RPC.

According to the NEC, a VFD must be housed in a NEMA rated enclosure. If so, it shouldn't be a safety issue.

Can you post some pictures of how you have the static converter wired?
 
While a static converter only allows the machine to run at about 2/3 it’s rated power it’s far less expensive than a vfd takes only minutes to install and allows the use of the original control station.

I opted for them on my machines to avoid having to rework them and for the convenience of using the factory installed control consoles.

I do have 1 machine that came from the factory with a built in vfd. The Baileigh cold saw has a vfd but also has a conveniently positioned control console.
 
projectnut said:
While a static converter only allows the machine to run at about 2/3 it’s rated power it’s far less expensive than a vfd takes only minutes to install and allows the use of the original control station.

I opted for them on my machines to avoid having to rework them and for the convenience of using the factory installed control consoles.

I do have 1 machine that came from the factory with a built in vfd. The Baileigh cold saw has a vfd but also has a conveniently positioned control console.
Click to expand...
I have a VFD on my Bridgeport and it works flawlessly. You can still use the factory control with a VFD, you simply wire the VFD to use a remote switch that you wire to the original Bridgeport Switch. Instead of the switch controlling high voltage, it is being used to control the VFD's low voltage remote switch.
 
Agree with @projectnut, get the motor diagnosed first.

I am also using a very economical SPC from WNY in a sort of hybrid situation. The SPC is configured for the 2hp mill, which runs perfectly. The only drawback is, having only two hot legs, you lose the instant reversing of 3 phase. The belt drive 1hp SB lathe doesn't seem to like operating with an SPC. It may be the older style motor or it may be becaue it starts under load. To get around this, I start the mill with the spindle disengaged and leave it idling, allowing it to function as an RPC for the lathe. Been doing it that way for 5 years now without a problem. I've considered going to VFDs, but can't find enough advantage to justify it.
 
If using a static converter and the starter circuit does not drop out, it can cause an over voltage/over current scenario and smoke the motor. At the cost of VFD's these days, I see no reason to use a static converter on the motor of this size, providing you do not dial up the VFD overload parameters and do not use a high carrier frequency. You could try to hook it back up to the VFD, most mainstream VFD's have output detection for shorts or motor issues. I have had two cases over the last 14 years where a new VFD would not run on a motor and showed and error message, both cases the motor had a winding short. As far as rebuilding the motor if needed, cost is all over the place, and depends if you have a local motor shop. Installing a VFD on a mill is about as simple as it gets, some of the basic VFD's like the Teco L510 have very few parameters to adjust and the manuals are very easy to follow. There is also technical support from the vendors (like Wolf Automation, Automation Direct, etc) as well as the company and these forums. We all need to learn new things through life, one should not be intimidated to try.
 
It's possible that the cheap VFD damaged the insulation of the motor- The cheap ones can generate enough voltage overshoots to punch through
old insulation, but the motor may have been on the way out anyhow. Hard to say. Vibration, moisture and heat can all take a toll.
You would want to check the motor windings with an ohmmeter for equal readings between the three phases and for shorts to ground.
You need an ohmmeter that has a wide ohms range, very low to very high. Or take it to someone who can test it for you.
Hopefully you could find a good used motor without spending an arm and leg
-M
 
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