Lathe RPMs rising and falling a little

[TonyL]

Hi Folks:

My lather is less than two weeks old and had only turned 13 pens. I noticed yesterday and again today, that the RPMs fall and rise a little bit (not including when I apply tool pressure, of course).

For example, if I set it at 1500, it will drop to 1492 briefly then climb right up again. At 2500, it will drop to 2490 briefly etc.. These "cycles" of dropping and returning to the set speed last about 3 seconds. What do you think? My house is pretty large, but has ample electoral service. Nothing else was drawing on the outlet and possibly not the circuit. Thanks

I did call my local Rockler where I bought the lathe and they instructed me to tighten the belt. It was as tight though, and was not squeaking/slipping.

 

[ed4copies]

Tightening the belt will put more stress on the motor (IMO). I would not think this is a critical problem, but it is also not "normal". May be good to contact Jet (in writing) and be certain you are "on record" as having a concern, in case it gets worse.

FWIW,
Ed

 

[ashaw]

Check your live center. If it is older center like mine that could cause a +/- 8 rpm difference. Mine a general also goes through a cycle of +/- 8 rpms. Not an issue here. It's being doing this since I bought it 9 years ago.

 

[TonyL]

Thank you. I will. I did register it (twice!). I plug it into a different circuit to see if it was something else drawing on it. I only noticed it yesterday. I called Rockler (one of the guys there helped design it - I think his name is Jeff..(super nice guy!). He said if it's not the circuit; it's the controller unit. I will what and see. Thanks again!

 

[TonyL]

Live Center

Check your live center. If it is older center like mine that could cause a +/- 8 rpm difference. Mine a general also goes through a cycle of +/- 8 rpms. Not an issue here. It's being doing this since I bought it 9 years ago.

Thank you, but it happens with the mandrel saver. I only use the live center (with the point)...when I install the buffing wheel.

I seems to keep bending mandrels; could that be it?

 

[plantman]

Tony: Being a mech/elec trouble shooter for a large paper mill for many years, I can tell you that this is not an easy problem to pin down. I would give the lathe a little more time to break in all the moving parts. Your problem is either voltage drop, or ampereage increase. Voltage drop can be checked with an annalog voltage meter. A digital meter is not quick enough to catch and read out a quick change in voltage. With an annalog meter you can watch the needle move up and down. Same thing with amperage, check with an annalog meter, and watch the needle to see if you are increasing the load on your lathe. If not one of those, you could have a loose wire or solder connection on a printed circuit board, in which case the resistance in your circut will change. Not an easy thing to find. The changes you are having are within the + or - 1% of most factory specks. If, after a short time, the problem does not get better, make arrangements to return or exchange the lathe because they are only gong to get worse. When you start your lathe and just let it run, it should maintain speed within a few RPMs through all speeds. If not, your controller may not be working properly. Your controller is a DC output from an AC power supply that makes it possable to change speeds on an AC input. That little speed change should not bend mandrels. Jim S

 

[TonyL]

Interesting. I just tried it with the pointed live center an buffing wheel. It happens much less, maybe by 2 rpms at the 3200 setting; and more at the less than 2200 settings. Maybe I bent another mandrel (two in 10 days..possible a record!). I will check the center points (head to tail) and see.

 

[TonyL]

Possible voltage drop

Tony: Being a mech/elec trouble shooter for a large paper mill for many years, I can tell you that this is not an easy problem to pin down. I would give the lathe a little more time to break in all the moving parts. Your problem is either voltage drop, or ampereage increase. Voltage drop can be checked with an annalog voltage meter. A digital meter is not quick enough to catch and read out a quick change in voltage. With an annalog meter you can watch the needle move up and down. Same thing with amperage, check with an annalog meter, and watch the needle to see if you are increasing the load on your lathe. If not one of those, you could have a loose wire or solder connection on a printed circuit board, in which case the resistance in our circut will change. Not an easy thing to find. The changes you are having are within the + or - 1% of most factory specks. If, after a short time, the problem does not get better, make arrangements to return or exchange the lathe because they are only gong to get worse. Jim S

Thanks Jim. I just tested the lathe again, read above. It's definitely within tolerance at 3200 RPM, but not at less than 2200. That might rule-out voltage drop. You would know better than me.

 

[BayouPenturner]

Jim tightening the mandrel should not be the issue unless it is really loose. The mandrel being bent should mean it is too tight. This will cause other issues like out of round pens.


Now if you are being aggressive with the tools the lathe will change speeds. If there is no load on the unit and it will happens well that would be a different story.

 

[plantman]

Tony; Reread my first reply, I added a little to it. And as Jim said above. Your lathe should not change speeds with no load on it. Jim S

 

[Jim Burr]

It seems really simple...no load speed of, say 1500 rpm...add a load, say a gouge applied to the material in question. Take into account friction, resistance and pressure...why wouldn't it slow down? Your car goes slower up hill...doesn't it?

 

[plantman]

It seems really simple...no load speed of, say 1500 rpm...add a load, say a gouge applied to the material in question. Take into account friction, resistance and pressure...why wouldn't it slow down? Your car goes slower up hill...doesn't it?

Not with cruise controll!! That's what a DC controller is made for, to maintain speed under any load. Jim S

 

[low_48]

Put a piece of black electricians tape over the digital readout. If you can sense 8 rpm while you are turning, you are way more sensitive than I am. 1500 is way too slow for pen turning. Just turn and don't worry about the rpm. Bending mandrels is all about the way you tighten the tailstock. It should just meet the mandrel, and be just snug enough to keep from slipping. I mean like zero pressure on the mandrel! Do you have a 60 degree live center? Jet's stock live center is not and doesn't make using the mandrel work well. By the way, you can straighten the mandrel on the lathe. With a bare mandrel, run the lathe and sneak a pencil up to the middle of the spinning mandrel. I rest the pencil on the tool rest. You will see a pencil mark on the high spot. Rotate that over till the pencil mark is on top. TAP the mark with a hammer, and repeat the pencil mark. Continue till you see a pencil mark nearly all around the mandrel.

 

[Jim Burr]

It seems really simple...no load speed of, say 1500 rpm...add a load, say a gouge applied to the material in question. Take into account friction, resistance and pressure...why wouldn't it slow down? Your car goes slower up hill...doesn't it?

Not with cruise controll!! That's what a DC controller is made for, to maintain speed under any load. Jim S

Within 5 seconds? What planet did you grow up in? DC controllers take a few seconds to read data and spool up...common knowledge.

 

[plantman]

It seems really simple...no load speed of, say 1500 rpm...add a load, say a gouge applied to the material in question. Take into account friction, resistance and pressure...why wouldn't it slow down? Your car goes slower up hill...doesn't it?

Not with cruise controll!! That's what a DC controller is made for, to maintain speed under any load. Jim S

Within 5 seconds? What planet did you grow up in? DC controllers take a few seconds to read data and spool up...common knowledge.

Yes!! Within nanoseconds. Why must you always have a sarcastic answer for everything and everyone?? You may know more than I do about the medical field, but you better read up on the electrical field. It may be common knowledge, but it's not expert knowledge. Ask anyone who programs high speed machines what can be done with them. Does your heart/lung machine take 5 seconds to give out a change in data?? Jim S

 

[its_virgil]

I would be more concerned why you are bending mandrels using a mandrel saver. Something you are doing is causing them to bend. Analyze your process and figure out when the mandrel is being bent. I would think dull tools. Just a hunch.
Do a good turn daily!
Domn

 

[rherrell]

Same thing happened to me only it was my metal lathe. Try turning the speed control knob all the way in both directions, and do it kind of fast about 10 times, like you're "cleaning" the inside of it. That did it for me so MAYBE it will work for you.

Oh yeah, do it with the lathe OFF!

 

[Si90]

I have the same lathe, at 2500 RPM mine fluctuates between 2500 and 2504 and very occasionally 2506 for fractions of seconds under no load. If it's fluctuating does this not indicate that the controller is doing it's job . For a fraction of a second it determines that the lathe is spinning too fast and displays 2504 and then instantly the display drops back to 2500 ie the speed is corrected by the electronics, and the cycle of monitoring and adjusting continues hence the fluctuation. if the motor was capable of holding a constant speed with absolutely no fluctuation you would not need the controller surely. At 2500 rpm your lathe is doing 41.6 revs per second. To give 2490 rpm its doing ONLY 41.5 revs per second. I believe that over 14976° of rotation in 1 second (360 x 41.6) its a difference of only 36° (less than 1° per revolution) if it drops to 41.5 revs per second which gives 14940°. Bearing in mind that it seems to be constantly being corrected I don't know about you but thats close enough for me.

It strikes me that if the controller was basing its display over say updating every 5 seconds that it would not deviate at all from 2500, just my thoughts, I may be wrong.

 

[plantman]

Same thing happened to me only it was my metal lathe. Try turning the speed control knob all the way in both directions, and do it kind of fast about 10 times, like you're "cleaning" the inside of it. That did it for me so MAYBE it will work for you.

Oh yeah, do it with the lathe OFF!

:RockOn: Rick; what you have done is clean off any carbon buildup on the wiper of your contoller. This may happen if you run a machine at the same exact speed for long lenghts of time, the electrical arc puts a carbon deposit on the wires. You could also use an (electrical) contact cleaner to make the wiper and coils bright and shiney again. This can be done with the lathe running, as the cleaner is nonconductive, That used to be one of the biggest problems with the old TVs with the manual tuners. Good Tip!!! Jim S

 

[plantman]

I have the same lathe, at 2500 RPM mine fluctuates between 2500 and 2504 and very occasionally 2506 for fractions of seconds under no load. If it's fluctuating does this not indicate that the controller is doing it's job . For a fraction of a second it determines that the lathe is spinning too fast and displays 2504 and then instantly the display drops back to 2500 ie the speed is corrected by the electronics, and the cycle of monitoring and adjusting continues hence the fluctuation. if the motor was capable of holding a constant speed with absolutely no fluctuation you would not need the controller surely. At 2500 rpm your lathe is doing 41.6 revs per second. To give 2490 rpm its doing ONLY 41.5 revs per second. I believe that over 14976° of rotation in 1 second (360 x 41.6) its a difference of only 36° (less than 1° per revolution) if it drops to 41.5 revs per second which gives 14940°. Bearing in mind that it seems to be constantly being corrected I don't know about you but thats close enough for me.

It strikes me that if the controller was basing its display over say updating every 5 seconds that it would not deviate at all from 2500, just my thoughts, I may be wrong.

Simon: You are correct on both maters!! There are 3 main reasons one uses a controller. 1st Is to controll the speed of a motor. 2ed is to maintain that speed at any point from zero to max, no matter what the load is applied to it. (not always possable) 3ed is to convert 120 volt AC household current to a stable, constant, DC output. And, a digital readout cannot detect a slight change in anything that happens realy fast, unless it's built by NASA. An annalog meter, however, will show any change in data if you watch the needle move. Jim S

 

[JP61]

Nothing to worry about in my opinion. If you can hear the motor ramp up and down then you have a problem. The display is going to bounce around a little even with no load on the motor. While turning there's no way anyone will notice +/- 8-10 RPM's at high speeds unless you're looking at the display. As far as bent mandrels.... probably from over tightening, too much pressure applied while turning with tools not sharp enough or poor quality mandrel.

 

[TonyL]

Thank you all. This is outstanding feedback. Considering two weeks ago, I couldn't spell "lathe" and didn't know pens could me made from acrylic, I am humbled by your knowledge and getting an outstanding education.

I made a pen last night, and the lathe behaved fine at all speeds - under-load, no load, and no mandrel.....so that's a good sign. Regarding my mandrels, that's another story...let's just say that after a they both have a slight arch to them. Interestingly, I have not produced any oval pens - at least when viewed with the naked eye (I will be ordering calipers today to improve my pen turning skills).

I do use the Easy Tools with the carbide blades, I would think they would still be sharp after only 13 pens AND I have already rotated the blades (I do hit the bushing every once in a while especially when turning my first few pens). I do experience, when removing the squared corners, from a new blank, the blank will get stuck (it will stop turning) unless I apply less pressure to the blank. However, I usually move the tail stock in closer to the head stock/mandrel/bushings etc. I also use a the pointed live center when using the buffing wheel and the mandrel saver when using the adjustable mandrel to turn pens. I don't have a separate lathe for buffing.

There appears to be a fine line between too loose (blanks stops rotating) and too tight (mandrel bending).

I am just going to keep my eye on it. I average 1 pen a day which puts behind the lathe (now don't laugh), for close to 1.5 hours. I will just keep observing and apply your advice.

Here's some other general information regarding my rpm settings for various activities (still experimenting though):

Sanding: 1,000 (same speed for sandpaper, MM, and scratch polish)
Turning: 2,200 to 2,600
Buffy: 1,500


Thank you all again and have a great Sunday or Monday for those 12 hours ahead.

 

[mikespenturningz]

I run my lathe at full speed when I am turning. I use close to the same speeds that you are using for sanding. For finishing I usually apply doctors at about 1200 for application and full speed for drying and buffing.

 

[Janster]

.....IMO, the " brushes " have finally seated themselves.

 

[TonyL]

Regarding the brushes being seated.....that is good, right? Thank you

 

[JP61]

Regarding the brushes being seated.....that is good, right? Thank you

Yes, seated brushes is a good thing. Also, it's probably not a bad idea to maybe once a year, with motor disconnected from power source, unscrew a brush cap and blow out the motor with compressed air. Excessive carbon dust build-up can cause erratic speeds.

 

[TonyL]

Super.... thank you!

 

[shastastan]

I have a Jet 1014vs and sometimes it takes a few seconds to reach the new setting after I make a change. This is not a problem for me though. I have a new Jet 1221VS, but I have not used it yet since I'm still working on the stand/table and moving stuff around in the garage. You say your lathe varies from 1500 to 1492? I'm not a machinist or electrician but is that a variance worth worrying about? 0.533% ? Just asking....

 

[TonyL]

Thank you. I was concerned that there was a problem with the controller unit of a brand new lathe. To your point....I am not concerned about it any more. Perhaps, I am sharing the current with something else (water heater. etc.). Thanks for the feedback!

 

[plantman]

Regarding the brushes being seated.....that is good, right? Thank you

Yes, seated brushes is a good thing. Also, it's probably not a bad idea to maybe once a year, with motor disconnected from power source, unscrew a brush cap and blow out the motor with compressed air. Excessive carbon dust build-up can cause erratic speeds.

Jan and Joe, Both of you have good points there. When the factory test runs a machine or hand tool they only run it for a few seconds, or they do what is called a static test, no power. Therefor you have a flat brush running on a round surface creating a lot of arcing and carbon deposit buildup. After a while, as Jan said, the brushes will wear in and your machine will run a lot smoother. When we would change brushes on motors in the mill that ran 24/7 (checked and recorded once a month), we would have to do several things. Remove the old brush and check the wear compaired to a new one. There is a line printed on the brush telling you when the brush should be replaced. If it would make it another month, we would not replace it. Next, as joe said, we would blow out the brush holders and windings to remove any carbon dust. Carbon dust is like fine sandpaper and can wear out bearings if not cleaned out. Wear a mask when doing this as you don't want to breath in carbon dust!! Next we would take sandpaper or a file and put a concave shape on the brush end to match the motor. Last thing would be to clean off any carbon deposit on the armature. This is done with the motor running and the use of a nonconductive stone. Nonthing like sticking your hand in a running 440 volt 3 phase motor. Perfectly safe if you know what you are doing, but a little shakey the first time you try it. So, Yes, seated brushes are a good thing !! Your lathe should be running fine by now if the brushes are seated properly. Jim S

 

[Wood Butcher]

A few years ago when I was a part timer at the local Rockler store and doing demos there and we had a Jet that had this issue. It got worse with time and after horsing around with it, a lot, they got Jet to take it back. This lathe was a variable speed and we replaced that unit and the motor and just about everything else before they sent it back, never did know what to issue was for sure. I would talk with the Rockler manager and if he is reluctant to handle it I would go to Jet. That's my 2 pennies.
WB

 

[TonyL]

Thank you. It seems to be fine now. I have done all of the above except for cleaning anything. I think there may have been something else on the circuit. However, these are all very good things to keep an eye on. Rockler, the guy at Rockler that helped design it, and Jet have been notified. I will see how it goes. I am 22 pens into it, and see what happens over my next 20. Thank you for all of the feedback.

Best,

tony