Rebuilding a Bridgeport Variable Speed Mill from the 70s

[folkenheath]

I was requested by some to post a thread to show my rebuild of this Mill shown here before I purchased it. It is from the early 70s, an original Bridgeport 2J Variable Speed mill.

It was missing a quill handle and I was told it only needed electricity to run.

It had been repainted poorly with a paint brush at some point, and abused on the table surface, but it was cheap and variable speed so I took a chance.
It came with a Sony 2 axis DRO, that would not plug into the 2 scales that were on it.

I bought the mill for $1400 and sold the Sony DRO off it for ~$300 if I recall. I thought it was a deal, but it needed a lot of work.

Warning: I felt like I got ripped off after I found all the problems. I felt like I had $1100 in a pile of junk. Get some help and don't trust the seller, either spend more and get a good condition mill, or spend less to rebuild one. Don't do what I did and get ripped off.




I brought it back to my shop with help from my brother and his trailer and my father and his Skid loader.

 

[folkenheath]

After searching for a long time for a variable speed mill, I then bought a Lenze AC Tech variable frequency drive(VFD). This gives you full power vs a static phase converter only giving you 2/3 power. However, it also allows you to vary the frequency of the AC, which varies the speed of the motor! It's an inverter type model that is made in the USA and had a good price and quality. You need to buy it based on the current rating of your electric motor, this one was 7A at 230V rating max.

Perhaps you could buy an older mill with a pulley setup for lower cost, and use the VFD to vary the speed, however, you do not get the torque multiplication of the gearing with that method. I still turn it down manually for power tapping, etc. Keep that in mind.

You have to set the max current for the motor so you don't damage it, and you need to read the manual and set the parameters for your motor before you start it up. I think my 2HP motor was 5.6A max at 230V, 60 Hz from the motor plate on the motor. Don't skip this, it can cause a fire or injury/death!

Another option is a rotary phase converter, but they are more expensive and then you have to leave that motor running the whole time you are using the tool, but it does give you full power. They are supposedly smoother for the motor though than the digital drives.




One thing I learned later, that VFD works great, for one motor. However, when I went to buy a VFD for the old lathe I bought, they did not make this model with an 11A rating. So I had to find a different model, a Hitachi WJ200 fit the bill well, and after I got the Hitachi, I realized it has 2 control inputs, and 2 motor outputs. So although you can't control them at the same time, if I would of bought that first, I could of used the same VFD for both the mill and the lathe. So if you are getting a first one, get the Hitachi just in case, my 3 HP lathe motor was rated at 11A, get the biggest one you think you need, you still will set the max current for your actual motor rating.

 

[folkenheath]

Once I hooked that up the problems started....

The 1.5 HP motor base was cracked and bent, and the upper support bearing for the spindle was gone, and I don't mean wore out, it was literally gone, as in not even there!



I found a used motor plate from a parts source for $125, and put new quality bearings in it (no overseas junk bearings), was easier than I thought. A 3 PH induction motor has no brushes or wear items, so it was as good as new after I cleaned, blasted and painted the exterior case, then I sold that rebuilt motor for quite a bit, and bought a bigger 2HP motor that needed rebuilt and did it again. Be careful, you don't want to create any shorts with this much electricity!

The 2 HP motor and clutch are still serviceable from Hardinge, the 1.5 HP clutch and motor parts are only available aftermarket or used. But you have to change a belt and pulleys, etc, to complete the upgrade. This is one reason I sold the 1.5 motor, plus I made money on it because a fresh motor is worth a lot more than wore out one.

 

[Cucv_M1008]

Ohh those are so cool!

 

[82355]

Why would you think this deserved its own build thread???

Just kidding. Glad to see it. You did what appears to be a lot of quality work were.

Martin

 

[folkenheath]

Why would you think this deserved its own build thread???

Just kidding. Glad to see it. You did what appears to be a lot of quality work were.

Martin

If it got more than a 1 sentence response out of you that's worth something...

I'll add more pictures as I make time.

 

[Truckman4life]

All these quality older machines deserve saving. I watch a couple guys on YouTube and everything you can buy anymore is trash for quality (on anything for that matter). I'm becoming more and more a fan of rebuilding and restoring quality made things since they just don't exist anymore. Hate to see it when scrappers and those looking for a quick buck just trash stuff.

 

[folkenheath]

So after fixing the motor and replacing the upper support bearing, I started adding a DRO. I had sold the Sony since it didn't work with any of the scales I had.

Normally, I avoid anything not made in the USA, I prefer US made tools. However, with the DRO, I couldn't justify it. A new USA made DRO with 4 axis was going to cost around $3K! I found this "Ditron" model I got for about 5 hondo with glass scales and an RPM sensor that had positive feedback. The glass scales are more accurate than the magnetic scales, down to .0002" I believe. I have confirmed it matched the micrometer thread scales on the mill itself exactly, but more accurately, and the scales allow you to measure and account for any backlash in the leadscrews.

I ordered the glass scales with my exact length specs, which I can't find anywhere. I'll have to go look on the mill. The quill scale was a thinner, more compact version than the rest.
I made some brackets to mount the scales on the knee, the scale on the back of the table was super easy. I did have to drill and tap the knee and I then you have to "align" the scales so they don't vary more than about .001" when you run it through the entire length. This is why most mounts are "slotted" for adjustability. Making slots is a lot easier once you have a mill.



I used 5/8" thick x 1.5" aluminum bars to countersink and mount the scales to the knee. Those can be "shimmed to get the depth parallel, then the other direction can be adjusted with the slots in the scale itself.







This is the RPM sensor and also under that retainer is where the missing bearing was, I just countersunk a magnet into the drawbar, and a bracket from aluminum angle channel. It only works when its all the way up, but you don't really need the RPM sensor anyway, but it did allow me to calibrate the clutch so the RPM is pretty close, and I can see if I turn down the VFD how much.



I also made a bracket and a control panel to interface with the VFD remotely. The switches are ABB, I think made in Europe. They have a much more positive feel than the cheap junk. I enclosed the VFD in a box to protect it, with air vents that don't allow dust to just fall in via gravity.





However, the mill was still super noisy and the power down feed didn't work, etc. So I ended up taking it apart further before I added the quill scale.

 

[jimmyleetn]

So all I'm gonna say is once you get this running I'll send you my NP208 tail housings and you can me some SYEs. Don't say "no" just think about it.

 

[folkenheath]

So all I'm gonna say is once you get this running I'll send you my NP208 tail housings and you can me some SYEs. Don't say "no" just think about it.

It's been running for a few years now, I use it often, I just haven't made the time to create a thread about it, I also can't find the pictures I thought I had of the upper head tore apart.

I do machining on occasion for customers, so I won't rule it out, but what is involved in that? Just milling and boring? I also have an old lathe from 1957 I use, 12 x 30 Hendey.

 

[JoshHefnerX]

No pics of the lathe?

As a slight bit of hijack, anyone have any thoughts on replacing a 220v brushed motor with a 110v brushless with a speed controller of supposedly the same output?

 

[folkenheath]

No pics of the lathe?

As a slight bit of hijack, anyone have any thoughts on replacing a 220v brushed motor with a 110v brushless with a speed controller of supposedly the same output?

What is the amp rating of the 220V motor?

I didn't go a complete rebuild on the lathe, just a couple little upgrades and cleanup and an amateur paint job. Eventually I will add the DRO to it as well.

Before:



After:

 

[JoshHefnerX]

Old: 220v 8.5a 1725rpm cap start.

New: claimed 1500w 2hp - doesn't have actual amp but should be in the 12-13amp range I imagine. Being brushless would have some better efficiency per amp..

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Didn't think it was a terrible price.

And, that's a beautiful lathe.

 

[folkenheath]

That's a 1870W motor according to your numbers, is it single or 3 phase? What kind of motor is it?

I believe all true "induction" type motors are brushless. The VFD is basically a speed controller for the brushless motor.

A nearly 1900W motor at 1725 RPM may have a lot more torque than a 1500W motor at 3400 RPM or something, you may also need to gear it accordingly?

Some VFDs can be used for single phase motors too.

 

[jimmyleetn]

It's been running for a few years now, I use it often, I just haven't made the time to create a thread about it, I also can't find the pictures I thought I had of the upper head tore apart.

I do machining on occasion for customers, so I won't rule it out, but what is involved in that? Just milling and boring? I also have an old lathe from 1957 I use, 12 x 30 Hendey.

That lathe is a beauty too. I wish had the shop space and the time/need to have those tools. Below is a link to a guy using a lathe and a bridgeport to do a SYE. He makes it look easy which in turn makes me wonder why more people aren't doing it.

 

[JoshHefnerX]

That's a 1870W motor according to your numbers, is it single or 3 phase? What kind of motor is it?

I believe all true "induction" type motors are brushless. The VFD is basically a speed controller for the brushless motor.

A nearly 1900W motor at 1725 RPM may have a lot more torque than a 1500W motor at 3400 RPM or something, you may also need to gear it accordingly?

Some VFDs can be used for single phase motors too.

This would be for a gearhead lathe, so gearing could be adjusted. At present its 220v single phase, no vfd's ect. My best understanding is going to brushless/induction does make up some w/ it's efficiency - the old motor doesn't put it to the ground so to speak. But it's still a net loss. Not sure it it would be noticed.

Right now just looking at options, I know this had a problem, and I don't know if it was ever figured out - but am in a holding pattern picking this up to diagnose it. But it could have a bad motor or contactor in there. Which will add up quick vs a replacement.

 

[folkenheath]

That lathe is a beauty too. I wish had the shop space and the time/need to have those tools. Below is a link to a guy using a lathe and a bridgeport to do a SYE. He makes it look easy which in turn makes me wonder why more people aren't doing it.

I'll have to watch the video later to confirm, but it looks like from the screenshot he is shortening both the tailhousing and stock shaft a little and bolting a flange on it. This may work fine if you don't need the even shorter length with the aftermarket shaft to reduce your driveshaft angle further yet. I wonder how hard the tailshaft is, it seems he would need to drill and tap it. I'll check it out later.

This would be for a gearhead lathe, so gearing could be adjusted. At present its 220v single phase, no vfd's ect. My best understanding is going to brushless/induction does make up some w/ it's efficiency - the old motor doesn't put it to the ground so to speak. But it's still a net loss. Not sure it it would be noticed.

Right now just looking at options, I know this had a problem, and I don't know if it was ever figured out - but am in a holding pattern picking this up to diagnose it. But it could have a bad motor or contactor in there. Which will add up quick vs a replacement.

The VFD hooked directly to the motor, no contactor or anything in between. So it's a valid option assuming the motor itself is good.

 

[imiceman44]

That lathe is a beauty too. I wish had the shop space and the time/need to have those tools. Below is a link to a guy using a lathe and a bridgeport to do a SYE. He makes it look easy which in turn makes me wonder why more people aren't doing it.

I am doing the same thing.
I had a deal a member here 15 years ago to make and sell them but his wife killed herself and he moved away.
I still want to do it, and I have a few cases ready

 

[jimmyleetn]

I am doing the same thing.
I had a deal a member here 15 years ago to make and sell them but his wife killed herself and he moved away.
I still want to do it, and I have a few cases ready

Do it!!!!!