New to me PM3520A

[John Hebdon]

Ok so here's the deal. I found a PM3520A on the facebook for $500 and thought I would go take a look. Turns out the thing had been dropped or knocked over and the VFD shell was torn up and the motor was not on the thing. I started to test the motor and all posts showed continuity so I thought it was fried. I then started looking at bearings and all of the controls. The speed control know is broken off and the on/off was a little cockeyed.

We got into the negotiations and of course I started pointing out all of the things that were wrong and missing. He said throw me a number... I started at $200 and he said $350. I hit back with $300 and he said take it and get it out of his shop. I got home off loaded it and starting cleaning up the ways. They cleaned up perfectly so I started cleaning all of the mating surfaces. As I started to put the headstock, banjo and quill on I noticed the tensioning rod that cranks down the headstock was broke so I tabbed one up and called that part done. Once I cranked the head down I noted a little crack on the headstock right around the rod. I guess I will get that repaired later, if everything fires up.

I rewired everything and got the motor mounted with some longer hex head bolts. I started by just hooking up the VFD and controls to make sure it fired up. As beat up as the housing was the VFD showed signs of life by illuminating the LCD. I reached around the pulled the switch, sure enough it showed run. I then cycled the FWD RV knob and all of that regestistered. Then I turned what was left of the speed control knob and it worked too. I thought surely this $300 deal I just got couldn't get better.

I wired in the motor figuring I would need to get it rebuilt, but no. Fired right up.

I am totally shook and shocked that it worked.

I threw a heavy faceplate on to see if anything gave me fits and the only things was an OV code when I turned the speed down to fast. I switched belts from speed to torque and the error does not reappear. Y'all think I should install a brake resistor?

Let me know the best place to find a new VFD housing (perhaps one of you have a burned up one laying around I can swap the good parts into) and a good spot to find the speed control knob.

 

[John Hebdon]

Here are some pictures.

 

[John K Jordan]

Looks like you are well on your way towards an incredibly inexpensive working 3520, as long as the headstock spindle is in good shape and the bearings are OK.

That Delta VFD is different from the Deltas on the 3530b and Jet1642 so what I have won't fit. I'd probably make something from plastic or aluminum and cover up the missing part.
A bit of paint and the motor should be fine. If you don't have the capability any welding/machine shop can repair the cracked casting.

If you need do double check any of the wiring Doc Green's website might be a good reference. I suspect the control circuit (speed, reverse) on that lathe is 10v DC. The switches, potentiometer, and knob are easily replaced if needed.

You are probably familiar with these lathes but if not note that when tightening the belts Jet/PM recommends not to use too tighten the belts too much. I'm not familiar with the "a" model but my "b" model and Jet1642s both have lifting handles to pivot the motor up to change the belts. Some people damaged bearings by pressing down on the lifting handle - just the weight of the motor is all that's needed. I don't see a lifting handle on that one, but again, I'm not familiar with the "a" model.

If it's been dropped and abused you might also check the headstock/tailstock alignment when you get to that point. Put centers in both and push the tailstock up so the points almost touch. If the bed is not twisted the points should be aligned both vertically and horizontally. If off a bit horizontally, it's usually easy to fix by adjusting one foot.

JKJ

 

[John Hebdon]

Looks like you are well on your way towards an incredibly inexpensive working 3520, as long as the headstock spindle is in good shape and the bearings are OK.

That Delta VFD is different from the Deltas on the 3530b and Jet1642 so what I have won't fit. I'd probably make something from plastic or aluminum and cover up the missing part.
A bit of paint and the motor should be fine. If you don't have the capability any welding/machine shop can repair the cracked casting.

If you need do double check any of the wiring Doc Green's website might be a good reference. I suspect the control circuit (speed, reverse) on that lathe is 10v DC. The switches, potentiometer, and knob are easily replaced if needed.

You are probably familiar with these lathes but if not note that when tightening the belts Jet/PM recommends not to use too tighten the belts too much. I'm not familiar with the "a" model but my "b" model and Jet1642s both have lifting handles to pivot the motor up to change the belts. Some people damaged bearings by pressing down on the lifting handle - just the weight of the motor is all that's needed. I don't see a lifting handle on that one, but again, I'm not familiar with the "a" model.

If it's been dropped and abused you might also check the headstock/tailstock alignment when you get to that point. Put centers in both and push the tailstock up so the points almost touch. If the bed is not twisted the points should be aligned both vertically and horizontally. If off a bit horizontally, it's usually easy to fix by adjusting one foot.

JKJ

Thanks for all the information. I did not think of lining up the headstock and tail stock. So here is a picture.

 

[Dave Landers]

Wow.
Get that crack fixed and you've got a great deal.
Put what's left of the VFD cover together with epoxy and make something to cover the rest. (If it were me, I'd plan on doing that, but probably never actually get around to it )

 

[Kent Reisdorph]

Great find, John. I'm glad you took the risk, but for $350 it wasn't much of a risk.

 

[robo hippy]

My favorite of the 3520 models. I like the speed ranges better, almost zero to 1500, and 1500 to 3000. Slow range was ideal for turning smaller bowls and coring big bowls, and the speed would go slow enough so I could sand my warped bowls. Also, the headstock spindle is right on the face of the headstock tower, so I almost never used the tailstock. Great find! Another thing to check is the pressure plate on the bottom of the headstock. First ones were cast iron, and mine snapped when coring some black locust. They went to metal plate after that.

robo hippy

 

[Richard Coers]

I wouldn't spend a dime more on that machine until you get a quality fix on that headstock crack. Since it goes right through the hold down bar, it's going to see a lot of load when you crank down the tailstock or turn stock that maxes out the capacity. I really don't like turning cracked wood, but a major crack through the headstock puts it in a whole new world of catastrophic failure. The weld shop will want that head stock completely stripped so they can preheat before welding as well as putting it in an over to cool it slowly. You have a ways to go before you need a vfd

 

[Wally Crawford]

Sometimes you roll the dice......and win!

 

[Dean Center]

IIRC, the braking resistor is wired with a pair of white wires. See if there is a soft white wire coming out of the bottom of the VFD and running into the headstock. Then open the panel where you see the belts inside the headstock and look at the far, inside wall of the headstock housing. If it's like my A, the braking resistor is bolted on there, on the inside of the headstock where the VFD is bolted on the outside. It's a 3 dimensional aluminum box, taller than wide. My recollection is that there might be other locations for the braking resistor on some the the 3520s, but that's where it is on my A. (On the B, IIRC it's a fold of aluminum stuck inside the fins of the heat sink that connects the VFD to the lathe, and also wired with 2 white wires)

BTW, that lathe took a pretty good hit. As you have learned, the headstock is really, really heavy. Is it possible that just the headstock fell, somehow? If so, that's a good thing. IMO, the only irreparable injury to a lathe is if the bed gets cracked.

Those potentiometers and on-off switches are generic items and can be had for about $5-10. You don't have to get an official Powermatic model.

 

[John Hebdon]

IIRC, the braking resistor is wired with a pair of white wires. See if there is a soft white wire coming out of the bottom of the VFD and running into the headstock. Then open the panel where you see the belts inside the headstock and look at the far, inside wall of the headstock housing. If it's like my A, the braking resistor is bolted on there, on the inside of the headstock where the VFD is bolted on the outside. It's a 3 dimensional aluminum box, taller than wide. My recollection is that there might be other locations for the braking resistor on some the the 3520s, but that's where it is on my A. (On the B, IIRC it's a fold of aluminum stuck inside the fins of the heat sink that connects the VFD to the lathe, and also wired with 2 white wires)

BTW, that lathe took a pretty good hit. As you have learned, the headstock is really, really heavy. Is it possible that just the headstock fell, somehow? If so, that's a good thing. IMO, the only irreparable injury to a lathe is if the bed gets cracked.

Those potentiometers and on-off switches are generic items and can be had for about $5-10. You don't have to get an official Powermatic model.

Thank you very much for all the info. I looked in the headstock and there was not a box of any kind. I guess I could just order a brake resistor, right? What would I look for? Can you link?

 

[Dean Center]

Thank you very much for all the info. I looked in the headstock and there was not a box of any kind. I guess I could just order a brake resistor, right? What would I look for? Can you link?

I have read that contemporary VFDs do not need a braking resistor as they have built in braking. I'm not expert enough on them to know, but some of the engineers on the forum should know.

 

[Bud Goetzinger]

That’s a great deal! A good machine shop should be able to easily fix that crack.