PSI Variable Speed fluctuations

[Dustman]

I have a two year old Penn State variable speed lathe. I've used it quite a bit but like I said, it's only two years old. Lately I've noticed the speed fluctuates from approximately 1-200 rpm while working at about 1800 rpm. I only notice it when finishing. I don't notice a change while turning. Probably due to noise from dust collector. Does anyone have any idea why this is happening? Anyone else experienced the same thing?

Al

 

[derekdd]

Hi Al, I have a 10" lathe from PSI.

The friction of sanding and finishing slows mine down a bit, also. Those are pretty small motors so I think just the light pressure from those activities affects the speed.

Is this what you're talking about or something else?

 

[Dustman]

Almost. This is new. I've had the lathe two years and this just started a couple of weeks ago.

 

[jrista]

Any load is going to involve power. Without some kind of compensation mechanism, such as a PWM or VFD, increasing load on the motor will cause it to slow. With higher end lathes, a PWM (pulse width modulator) or better a VFD (variable frequency drive) will maintain power as a load is applied, according to the setting of the lathe. It is unlikely any lower end lathe would use such a drive mechanism.

Even with a PWM (I had a Laguna lathe for a while with a PWM), which is a pretty steadfast way to maintain power, applying a larger load would sometimes result in a drop in RPM, before the drive would respond and adjust the motor to get me back to my selected RPM. Momentary, usually, but, if it was just spinning a blank (notably with larger blanks), and then I applied the tool to the wood (i.e. a bowl gouge), there would be a momentary drop before the lathe adjusted.

Without a more advanced system to maintain power and RPM, applying load usually will result in an RPM drop. The Penn State pen lathe is only 1/5th of a horsepower, so it doesn't have much to start with. In contrast, my Wen is 1hp, the Laguna Revo is 1.5hp, and my big Powermatic is 2hp. There just isn't a lot of power behind 1/5hp.

 

[jttheclockman]

That should not happen. Should be under warrenty. Have them check it out.

 

[Curly]

Just for grins carefully pull the brushes from the motor and see if they are worn. If getting short order new ones to see if the problem get resolved.

Pete

 

[jrista]

.

 

[jttheclockman]

I have a two year old Penn State variable speed lathe. I've used it quite a bit but like I said, it's only two years old. Lately I've noticed the speed fluctuates from approximately 1-200 rpm while working at about 1800 rpm. I only notice it when finishing. I don't notice a change while turning. Probably due to noise from dust collector. Does anyone have any idea why this is happening? Anyone else experienced the same thing?

Al

What is the HP rating of the lathe motor? Someone said 1/5hp. What number lathe is it?

 

[rixstix]

Only the PSI PenPal is 1/5 hp

All the others are 3/4 or 1 hp.

 

[jttheclockman]

Only the PSI PenPal is 1/5 hp

All the others are 3/4 or 1 hp.

That is what I thought. They are not going to put a 1/5hp motor on a full size lathe. Most minis and midis are 3/4hp or 1hp. No way should a lathe slow down while turning or finishing pens. If so you are doing something wrong. To put that much pressure on a motor while finishing is quite unbelievable.

 

[monophoto]

We really need to know which lathe this is. If its the 'pen pal', then the problem might just be the natural variations in speed due to variations in loading on a seriously underpowered machine. But if it is the 10" or 12" Turncrafter, I would suspect a different problem.

Pete suggested checking the brushes, and that's one possibility. However, Al said that he's only had the lathe a couple of years. My 12" Turncrafter is over ten years old, and the brushes have plenty of wear left in them. But its easy to check brushes, and checking that off the list would eliminate one possibility.

On Turncrafters, the cable from the motor attaches to the speed controller via a IEC form C connector (that's the same plug that often appears on power cables for desktop computers and that plugs into the back of the computer case). I have had one or two instances where that plug has worked loose - and the symptom has been fluctuations in speed. If that's the problem, the fix is very simple - just push the plug back into the connector on the control box.

 

[egnald]

A few days ago, my lathe seemed to be varying in speed according to how it sounded when I was wet sanding. The tachometer readout wasn't varying though. It turns out that I had forgot to lock the tail stock quill so the stuff wasn't being held tight enough on the mandrel. The sound was either coming from the parts slipping or the mandrel slipping in the mandrel saver. What a relief.

I hope you can get to the bottom of what is causing yours without a lot of grief.

Dave

 

[jrista]

Aye, I guess I made an assumption it was the Pen Pal. If it is a very low powered lathe, I think it could just be natural variation due to loading. If it is a 3/4 horsepower lathe...then maybe something else is wrong.

 

[Dustman]

What is the HP rating of the lathe motor? Someone said 1/5hp. What number lathe is it?

The motor is 3/4 hp. And, I didn't state the issue properly. The motor speed falls, goes back up and falls again etc. while working. I am aware it may fall slightly, less than 10-20 rpm when applying pressure on the work piece. I watch the readout. But going up and down 100-300 rpm with no change in pressure used for finishing is what I'm trying to figure out. I will find the paperwork and check the warranty as you suggested John. If it is no loner covered I may try checking the brushes as was suggested by Curly. But first, I will check the connections suggested buy mono photo. Duh, that's the first thing I should have looked at.

 

[jttheclockman]

When you talk about slowing down on a lathe especially when doing such a small item as a pen you will not get noticable deflections from rubbing of tools or even from rubbing of polishing a finish unless one you are using dull tools and are pushing harder against blank and two if polishing and you are doing a polishing technique that requires heat. Then you are pushing harder. if you are doing this and using a mandrel, then you run the risk of bending the mandrel.

When people talk about checking brushes what they are really saying is there is a disruption in power and there is a break in contact somewhere either from vibration or just plain wear. If checking brushes make sure the spring is pushing on them. If they were arcing you will see burn marks. Make sure you pay attention the way you take them out and replace the same direction. If not and you reverse or spin the brush then it now has to seat all over again and cause arcing.

Look for any other loose wires or connections as well. Blow out the controller. Many times dust can get cause problems and again break the circuit. I bet though the POT maybe breaking down and this is common. Call PSI and talk to their tech. Good luck.

 

[jrista]

The motor is 3/4 hp. And, I didn't state the issue properly. The motor speed falls, goes back up and falls again etc. while working. I am aware it may fall slightly, less than 10-20 rpm when applying pressure on the work piece. I watch the readout. But going up and down 100-300 rpm with no change in pressure used for finishing is what I'm trying to figure out. I will find the paperwork and check the warranty as you suggested John. If it is no loner covered I may try checking the brushes as was suggested by Curly. But first, I will check the connections suggested buy mono photo. Duh, that's the first thing I should have looked at.

Ah, thanks for the clarity.

I had this happen with my original lathe, a Nova Comet DR14. Same issue...RPM was not steady just with the motor on and no load on the lathe. Teknatool insisted it was the control board, which they sent me at least 5 of. After replacing the control board four times, I told them that definitely wasn't the issue. Took a couple months, before they finally agreed to take the lathe back on RMA. I didn't hear a thing from them until several months later (had written the darn thing off, and bought the Wen lathe I now use for my pens in the intervening time!!) They finally sent the lathe back and emailed me near the end of January 2021 (the problems started summer of 2020), and said they rebuilt the entire thing, replacing one part at a time in the headstock until they finally replaced the motor, which was the problem.

They sent it back with this incredibly loud scraping sound in the headstock. I've not used it since.

I had a wavering motor problem with my Laguna Revo 1524 as well. Again, I was told it was the control box. Replaced that. Ultimately they ended up agreeing it was the motor. Replaced that and it was fine.

I've done extensive power tests in my home and workshop. I have a ROCK SOLID 125V, with minimal droop when powering devices and machines. I've done long term power usage measurements, and the power has always been incredibly stable and reliable. So I don't know why I had motor issues with two lathes. Since replacing those two, I have a Wen and a Powermatic, I've had no issues since. But, I have had exactly the same problem you described, wavering RPMs (and you can hear it in the motor pitch as well) without any load, and also even more significant drops when the motors were loaded. In the end replacement motors was what fixed the problems.

 

[Dustman]

Ah, thanks for the clarity.

I had this happen with my original lathe, a Nova Comet DR14. Same issue...RPM was not steady just with the motor on and no load on the lathe. Teknatool insisted it was the control board, which they sent me at least 5 of. After replacing the control board four times, I told them that definitely wasn't the issue. Took a couple months, before they finally agreed to take the lathe back on RMA. I didn't hear a thing from them until several months later (had written the darn thing off, and bought the Wen lathe I now use for my pens in the intervening time!!) They finally sent the lathe back and emailed me near the end of January 2021 (the problems started summer of 2020), and said they rebuilt the entire thing, replacing one part at a time in the headstock until they finally replaced the motor, which was the problem.

They sent it back with this incredibly loud scraping sound in the headstock. I've not used it since.

I had a wavering motor problem with my Laguna Revo 1524 as well. Again, I was told it was the control box. Replaced that. Ultimately they ended up agreeing it was the motor. Replaced that and it was fine.

I've done extensive power tests in my home and workshop. I have a ROCK SOLID 125V, with minimal droop when powering devices and machines. I've done long term power usage measurements, and the power has always been incredibly stable and reliable. So I don't know why I had motor issues with two lathes. Since replacing those two, I have a Wen and a Powermatic, I've had no issues since. But, I have had exactly the same problem you described, wavering RPMs (and you can hear it in the motor pitch as well) without any load, and also even more significant drops when the motors were loaded. In the end replacement motors was what fixed the problems.

Thank you. I've tried everything from checking all the connections on the outside to those I could access on the inside. All were tight. I haven't checked the brushes and am hesitant to do so .... yet. I'm going to take Clockmans advice and will call Penn State tomorrow and see what the tech has to say. My lathe is out of warranty so it will be interesting to hear their response is. I wonder what their charge for a motor is.
Thank you again for the information.

 

[Dustman]

When you talk about slowing down on a lathe especially when doing such a small item as a pen you will not get noticable deflections from rubbing of tools or even from rubbing of polishing a finish unless one you are using dull tools and are pushing harder against blank and two if polishing and you are doing a polishing technique that requires heat. Then you are pushing harder. if you are doing this and using a mandrel, then you run the risk of bending the mandrel.

When people talk about checking brushes what they are really saying is there is a disruption in power and there is a break in contact somewhere either from vibration or just plain wear. If checking brushes make sure the spring is pushing on them. If they were arcing you will see burn marks. Make sure you pay attention the way you take them out and replace the same direction. If not and you reverse or spin the brush then it now has to seat all over again and cause arcing.

Look for any other loose wires or connections as well. Blow out the controller. Many times dust can get cause problems and again break the circuit. I bet though the POT maybe breaking down and this is common. Call PSI and talk to their tech. Good luck.

Hi John, I am calling Penn State tomorrow. What is POT? I'd like to know before I call. Except for the brushes, I've checked everything else. For what it's worth, The variations in speed is not consistent. I've even turned on the lathe with nothing on it and it still happens but not as consistently. If/when I find out exactly what the cause is I will post it here.
Thanks everyone!

 

[jttheclockman]

Hi John, I am calling Penn State tomorrow. What is POT? I'd like to know before I call. Except for the brushes, I've checked everything else. For what it's worth, The variations in speed is not consistent. I've even turned on the lathe with nothing on it and it still happens but not as consistently. If/when I find out exactly what the cause is I will post it here.
Thanks everyone!

POT short for Potentiometer which basically a variable resistor. It is what will vary the speed. That knob to control speeds They may send you a new board before they send motor. They will be able to tell you where to start looking. Checking brushes is easy. Just watch the way you take out is all I am saying.

 

[Dustman]

I have a two year old Penn State variable speed lathe. I've used it quite a bit but like I said, it's only two years old. Lately I've noticed the speed fluctuates from approximately 1-200 rpm while working at about 1800 rpm. I only notice it when finishing. I don't notice a change while turning. Probably due to noise from dust collector. Does anyone have any idea why this is happening? Anyone else experienced the same thing?

Al

Everyone, here is the answer I received from a PSI Tech: "It's a DC motor. All DC motor's speed fluctuate until they are warmed up." So, I told him mine fluctuates by 3-400 rpm even after turning an hour or so and the motor itself is warm to the touch. Now, here's what pissed me off; "These lathes are for hobbyists. If you want an accurate, precision lathe, you'll have to go to another brand." He then mentioned a few you can find in any wood working store or catalogue. That was a response I certainly did not expect.

 

[jttheclockman]

Well without getting into a lot of technical speak all motors AC and DC can fluctuate with heat and humidity as a cause. DC motors more so. But there is much more to fluctuating speeds in DC motors. Copper windings are effected by heat in forms of magnetic function and amperage. Then you have friction or mechanical losses because of bearings and brushes, then you have magnetic losses due to eddy currents and things like this. Again without getting in the weeds here. most mini and midi lathes are built with cheaper DC motors with brushes for sales but hp plays a role and the higher hp the better the motor. But there are more metrics to determine a better motor too. Your better lathes have electronics to balance out speeds and fluctuating voltages. Speed in a DC motor is controlled by voltage. Your torque/ speed ratio can be controlled by the pulley position. I guess the bottom line is yes there are better motors out there and using a reputable company can help in that area. A lathe should not vary speed in a noload constant speed situation. If so then there is something wrong.

 

[monophoto]

John is correct - there are many factors at play here, but the bottom line is that a speed fluctuation of 200 r/min when turning at around 1200 r/min does seem a bit excessive.

But as I understand the situation, this only occurs when sanding - there is much less fluctuation when cutting/slicing. That suggests that the torque associated with sanding is significantly greater than the torque associate with cutting/slicing, and that begs the question of how the sanding is being done? It almost sounds like either the abrasive is being wrapped around the workpiece so that a significant fraction of the circumference is being sanded at the same time, or that significant force is being applied while sanding. Neither is ideal, and wrapping the abrasive around the workpiece is potentially dangerous (there is a YouTube video out there that illustrates this rather dramatically).

What happens if the sandpaper is lightly held against the workpiece - does the speed drop as much? Applying too much force generates excessive heat and causes the surface of the workpiece to become burnished such that it won't accept finish as well. The best way to sand it to slow down the lathe (to 100-200 r/min), and only lightly press the sandpaper against the turning. And never wrap the sandpaper around the workpiece.

(Side note: the comment by the PSI rep that if you want better speed regulation you should buy a better lathe was stupid - PSI management needs to have a discussion with him about how to talk with customers.)

 

[Dustman]

Everyone, here is the answer I received from a PSI Tech: "It's a DC motor. All DC motor's speed fluctuate until they are warmed up." So, I told him mine fluctuates by 3-400 rpm even after turning an hour or so and the motor itself is warm to the touch. Now, here's what pissed me off; "These lathes are for hobbyists. If you want an accurate, precision lathe, you'll have to go to another brand." He then mentioned a few you can find in any wood working store or catalogue. That was a response I certainly did not expect.

I have good news from PSI. Not long after my October post I received a letter from PSI telling me they were going to send me a new motor and control box. I was also told it would be up to several months due to supply issues. Well, about three weeks ago I received the new motor and control box. Everything is now working just as it was when new. So, I have to thank PSI and I also thank this association for giving all of us this forum to exchange information.