?? on Powermatic 3520 b. VFD

[Joe Meirhaeghe]

Does anyone here know how I can adjust the VFD on my Powermatic 3520 b so that I can get it to run about 20 to 25 RPM's ??
It's set from the factory at 50 RPM.
I know that the older models 3520 & 3520 a models could be turned all the way down to zero RPM"s.
I would really like to get down to the 20 to 25 Rpm range for finishing, not for actual turning.
Thanks Joe

 

[robo hippy]

I answered this in a pm before I saw your post. When I stepped up from the PM to a Robust, one of my concerns was having a slow speed of 10 or so rpm for power sanding my warped bowls. Brent English assured me that the conveter could be adjusted to do that, and he walked me through the steps. You need a technician to help you do that. Apparently there are a number of adjustments that can be made for more or less torque, and different speed ranges. The converters are different for the Robust and PM, but the PM I think still uses the same brand as they did on the A model which I had, and it went down to almost 0 rpm. Call PM/Jet/WHM Tool group.
robo hippy

 

[Jeremy Williams]

Whatever you learn on this topic, I hope that you will post it to this thread. That's a great question and one many would likely want to do.

 

[robo hippy]

I called WMH tool group and asked a technician. No one ever asked that question before. He is looking into it, and will let me know. He was going to talk to supervisors, and try it out on an in house model.
robo hippy

 

[robo hippy]

Well, I got a responce back from Powermatic. It left me with more questions. I talked to David Gentili (1-800-274-6846 ext 1332#). He said that it could be done, but it would void the motor warrentee (gosh, how do you spell that?). Reason being that there is an excess build up of heat. I told him about my experiences with my old PM, and my Robust, and how there was never any heat build up, and that was sanding out 8,000 or so bowls, and he couldn't explain that. He said that in order to do it, you would have to remove the converter, and send it back to the factory so they could unlock it, and reporgram it. He said that the 3520A models shut off at about 50 rpm, and I told him that mine went down to almost zero before shutting off, and that I had the braking time increased and did it over the phone, and my converter wasn't locked out. He said it hadn't been that way in a long time. My PM is about 9 plus years old now. He also said that it is still the same motor on the lathe, and virtually the same converter. The converters are locked out to protect us from ourselves I guess. I have no explanation as to why he got heat, and I didn't.
robo hippy

 

[mike lipke]

David Gentili is living in a theoretical world, and you live in a practical, real world.

I heard once that aeronautical engineers cannot explain how a bumblebee can fly, therefore, they must not.
But they do.

The motor will build up too much heat, according to calculations. But it doesn't, if used reasonably. He is a bumblebee cannot fly kind of guy.

 

[Richard Baker]

Reed,
How long do you run the lathe at very low speed when sanding? Mine would get warm (about 125-130F) when left at 50 rpm for 1/2 hour or more. The TEFC motor gets little cooling from fan at very low rpm. One could always mount a small fan at end of the motor, I suppose.

 

[robo hippy]

I seldom sand more than 2 hours at a stretch, up to about 6 hours in a day. Extremely boring. Did the same with the PM. Brent Welch of Robust told me to check the temp with my hand. His comment was if it gets so hot that you can barely keep your hand on it for more than a few seconds, then it is too hot. Never gets even close to that. I never put a thermometer on it, but it never got hotter than my hot water from my kitchen faucets, and that is less than 130 degrees. I have an older Delta 13 1/2 inch industrial planer, and ran it for a couple hours straight, planing out a bunch of oak, and it got almost to the point of not being able to keep my hand on it. Never hurt it a bit. I am guessing that the 'official' PM responce is a liability thing (thank you lawyers and insurance companies), not a 'real' thing.
robo hippy

 

[Bill Turpin]

40° C. Rise

Any motor worth owning is rated at 40° C. (104° F) rise. That is the rise above ambient, while running, that is considered normal and non-harmful. You can touch 130° F for about thirty seconds. You can not touch 180° for more than an instant touch. You will probably get first degree burns for any longer. If you can touch at all, it is OK. The rise rating should be on the nameplate. I believe that PM's response is bogus.

 

[Steve Worcester]

I am guessing that the 'official' PM responce is a liability thing (thank you lawyers and insurance companies), not a 'real' thing.
robo hippy

It probably a warranty thing. If you run electronics hotter, they don't last as long. As temperature goes up, MTBF goes down. (Mean Time Between Failure)

 

[robo hippy]

Steve,
Are you saying that the electronics will get hot as well if you run your motor slow, or that a motor that runs hot will wear out faster? If the motor on my PM had worn out, I wouldn't have been surprised as I abused it severly, but it showed no signs of slowing down.
robo hippy

 

[ssinner]

PM has had this request before, because I asked it a few years ago (on my then new model A), and I'm not the first or the last. I finally got the same answer after spending too much time getting the run-around.

So, I called the VFD manufacturer. Their engineer was more than cordial, and helped me reprogram the drive. Since then, I've run it often at very low speeds for extended periods, and the motor is still fine. In fact, I've forgotten it was running and let it run overnight (I use it to apply and dry finish at low speed, about 20-30 rpm).

You might be able to download the drive manual from the mfr's site, but you'll probably need someone with some knowledge of the subject to explain all the terminology. As I recall, there are around 60 programmable items in the drive, and more than one of them may need to be changed to get the result you want.

One thing to remember is to not program it to go all the way to zero speed, because that may result in using the speed control to stop the machine (that's a no-no), or you'll inadvertently leave it on when you do not intend to.

 

[Richard Baker]

That's a lot of (yawn) sanding at a time. Got to admire your dedication.

 

[Nate Hawkes]

PM has had this request before, because I asked it a few years ago (on my then new model A), and I'm not the first or the last. I finally got the same answer after spending too much time getting the run-around.

So, I called the VFD manufacturer. Their engineer was more than cordial, and helped me reprogram the drive. Since then, I've run it often at very low speeds for extended periods, and the motor is still fine. In fact, I've forgotten it was running and let it run overnight (I use it to apply and dry finish at low speed, about 20-30 rpm).

You might be able to download the drive manual from the mfr's site, but you'll probably need someone with some knowledge of the subject to explain all the terminology. As I recall, there are around 60 programmable items in the drive, and more than one of them may need to be changed to get the result you want.

One thing to remember is to not program it to go all the way to zero speed, because that may result in using the speed control to stop the machine (that's a no-no), or you'll inadvertently leave it on when you do not intend to.

Did you also program it to slow down faster?? I just got my 3520B, and I'm already finding its limits (or, rather my limits with the machine). It is really a pain to wait several seconds for it to slow all the way down; this must be set on the drive, as even when you use the red button to turn the lathe off completely, using the handwheel doesn't really slow it down. I mean, on my (very modified) delta that I was using, I could stop the lathe very rapidly with my hands after turning it off, and it was using a 1.5HP motor; not that much more inertial forces to stop spinning.... Anyway, its really somewhat annoying if you're trying to turn and core out lot of bowls in one sitting...

Is changing the cycle time going to wear out the motor or headstock bearings more rapidly?? I know that this parameter is easily adjusted, I just don't want to do anything that might hurt the lathe, as I plan on using and abusing it for quite some time....

 

[mike lipke]

Let's say your VFD is set for a 4 second stop time. If you try to "help" the spindle slow down by putting friction on the hand wheel, the VFD will actually send power back to the motor to cause it to stop in 4 seconds.

 

[robo hippy]

The factory set time used to be 5 seconds. I had problems with bigger pieces tripping the converter and turning it off at that speed. 7 seconds prooved to be better. If you have too heavy of a piece on and try to stop it too fast, the brake can't handle it, and it trips the converter, then free spins till it stops, then you have to reach around to the back of the lathe and restart it.
robo hippy

 

[Steve Worcester]

Steve,
Are you saying that the electronics will get hot as well if you run your motor slow, or that a motor that runs hot will wear out faster?...
robo hippy

Yes. Most of the motors are TEFC, totally enclosed fan cooled. They have a fan on the end that runs at the same speed as the motor. With the motor at low RPM, the fan is at low rpms and does not cool as efficiently. The fan cooled part is the reason you don't want to block the ends of the lathe bed off too much, need the airflow. A lot of motors are finned to act as heatsinks and wick the heat away from the internals.

The VFDs usually have a fan on them that is thermo controlled. That is why you hear noise out of the "box" after you have shut the motor off, but with power still to the lathe.

Electronics are designed to run within a designated temperature range, usually 0-55c lets say (motor case temperature is probably higher), over that and the lifespan declines, sometimes dramatically as the bearing lube gets too thin and runs out or doesn't do it's "lubing" job anymore, or things warp or melt.

 

[Mark Ebert]

Sorry to go slightly off topic, but I have a jet 1642 with the Delta controller in which I just attempted to change the brake time from the default of 5 seconds to something a bit faster. Unfortunately, the people at Jet have a password set so changes cannot be made. It is a 1-3 digit code, so until I can figure it out I'm stuck with the factory settings. If anyone happens to know the code, please send me a pm. In the mean time, I'm going to start entering random numbers to see if I can conquer it (I only need up to 999 attempts).

 

[robo hippy]

Mark,
You don't want a faster brake time. It will trip the reset button on your lathe, especially if you have some thing larger on it. I acutally had mine set slower because of that problem. Stopping an 18 inch bowl blank that is spinning at 800 or so rpm will trip that sucker every time, and you will spend a lot of time resetting it rather than turning.
robo hippy

 

[john lucas]

Faster brake times can also cause the chuck to come unwound. When I added a VFD to my Nova lathe I had to program all the settings and this is one I experimented with. To slow and you get bored especially on small items, waiting for the darn thing to stop. Too fast on larger items and you either trip the shut off or the chuck comes unwound. I can easily see why the manufacturers pick a safe speed and lock it out, litigation is not worth the hassle.