Jet 1642 stop on a dime, need some input....

[Dave W]

About a two weeks ago I was roughing out some wet bowl blanks and was really having issues with bogging down the motor. Using my 3/8" bowl gouge I was literally bringing the motor to a stop taking about a 1/4" cut, and no the belt was not just slipping. I opened the door to verify the motor pulley was actually coming to a stop, it was. Fast forward to this past weekend and I'm back in the shop turning some stoppers and other smaller things. While sanding one of the stoppers at around 500 rpms I reached for the hand wheel to bring it to a quicker stop, and boy did it ever. The following is done at 3 times the stopper speed and with the belt on the high setting.

https://www.youtube.com/watch?v=W9VvQQd7cpQ

I have since taken a meter to one of the power supply lines on the motor to check the amperage. Upon running the motor at around 1000 rpm it was registering 2.7amps. As soon as I grab the hand wheel and bring it to a near stop or total stop, it jumps to just over 4 amps. Being a wood worker and not a electrician I am guessing that the VFD is doing what it should by supplying more power to the motor and that the motor has an issue internally. Now if I switch the belt over to the slow side I am not able to slow the speed by any more than 100 rpms by hand. I haven't thrown a bowl blank on yet to try the gouge on that setting, but it is where I had it when roughing the other week.

I also know that the bearing inside the motor housing is clicking along pretty good. I discovered this after having taken the belt free of the pulleys. Changing the bearings inside is doable, but if the motor is shot a waste of time.

I know I should open the motor and take a look at the windings, but this will have to wait until I finish up X-mas.

Any input would be much appreciated.

 

[Don O. Jr.]

I have the same lathe only older. I can easily stop it when roughing bowls and cutting aggressively. Trying to slow it down with the handwheel is counterproductive since the VFD has a ramp down time preprogrammed into it. It will slow down to a stop on its own and grabbing the hand wheel is really not a great idea. It's only a few seconds from spinning to stop. Grabbing the handwheel at speed as in your video is not my idea of a good thing to do either. However if you can stop the lathe that easily then there may indeed be a problem. I have no idea what that problem might be though as I am not an electrical engineer. A call to Jet Technical might be in order.

I have never had this trouble with my machine but it is one of the earlier models which seems to have better controls and motor as there has been several issues in the later models.

 

[Dave W]

Don,

Jet was called, said they would replace motor based on the clicking noise alone if it was under warranty. As far as stopping it at full speed, it is that easy. I can do the same with the lathe at running at 500 or 2500 rpm.

 

[Bill Boehme]

When you said that the pulley was in the high speed range when you could stop it by hand, I was not surprised. For comparison purposes the high speed spindle torque would be roughly a quarter or less of the low speed torque for any given speed that falls in the range of both pulley settings. That particular lathe isn't exactly overpowered, so it would be a good idea to use the low speed range whenever possible. Pen turning and maybe bottle stoppers would be about the only critical need for using the high speed range.

If you can hear a ticking or other noise when slowly turning the motor shaft by hand then it is possible that a bearing is starting to wear out, but that would not account for loss of power unless you have to apply muscle to make the shaft turn.

The current measurements that you made don't really tell you much about the health of the motor unless something would be drastically wrong. You didn't mention if your meter is capable of measuring PWM voltages and currents, but unless it is an expensive one (in the $400 and up range), the answer is that the readings wouldn't be even close to actual current. If, on the other hand, you measured line current to the VFD, the readings should be valid. In general, unloaded motor current is fairly light compared to FLC. Your assumption about the reason for the motor current increasing when you applied your "hand brake" is valid. However, with the simple VFD used on that lathe, It really is not able to provide much recover torque with a sudden increase in load torque.

It is hard to say whether the motor is failing, but it certainly is within the realm of possibility. I don't recall what motor is on that lathe, but it is probably one with a Jet nameplate which means that you may not be able to find the really pertinent information about its insulation class. Motors that are used in inverter duty really ought to have an insulation class rating of F or greater, but I have seen a number of lathes that use motors with an insulation class rating of B which means that their life expectancy will be adversely affected when operated with an inverter drive.

The typical failure mode for insulation breakdown is gradual loss of power over an extended period of time. Generally the loss of power is so gradual that it goes unnoticed until things get really bad. Whether this is your situation, I can't say, but if a new motor shows a significant increase in power then that is a pretty good indication of what may have happened. BTW, opening up the motor is unlikely to tell you much because without doing a failure analysis, there may not be anything that a visual inspection would reveal. If there is any wire to wire insulation breakdown going on, it would be most visible at the point of tight bends in the windings.

Good luck!

 

[Dave W]

Bill,

I know that in the past if I had attempted to stop my lathe in the same manor I probably would of wound up with my hand pinned between the hand wheel and the motor. It has definitely lost power since I bought it, as to how much I couldn't say.

On the motor name plate it states it is an E class.

The measurements that need to be preformed are out of my range of ability. The meter I was using is a fieldpiece unit in the lower end. All I was really trying to determine is whether or not the VFD was kicking in like it should when the motor was brought to an abrupt loss of speed.

I called on our 2 local repair shops to see what they would charge to change the bearings. One came in at $80 if I brought him just the armature, the other was $180 and he did it all. Forget about having it rewound, they both wanted well over what I could buy a new motor for.

I'm leaning more to just going with a new motor at this point.

 

[Bill Boehme]

Dave,
I remember when nobody threw away a motor that could be repaired (even an electric drill), but that was then. Now, the only motors that are rewound are expensive industrial motors. Buying a new motor is the only way to go. If you need bearings replaced, it might be worth paying a machine shop to do it because it is too easy for the average guy to score the motor shaft and wind up with a bigger headache.

Our club bought a Jet 1642 with a 1.5 HP motor to replace a Powermatic 3520A lathe that developed a crack in the casting of one of the legs. Maybe we didn't really need a Powermatic-class lathe, but it pains me to watch demonstrators always stalling the motor with what appears to me as minimal effort. I think that part of the rationale this lathe was that 120 VAC power is more readily available than 240 VAC.

I suspect that in some cases, the pulley might have been in the high speed range when turning something substantial that could have worked better using the low speed range.

 

[Michael Mendelsohn]

I have a 1.5 hp 1642 that is about a year old. The only time I have been able to significantly slow or stall the lathe is when taking an aggressive cut on the outside of a large bowl (13-14"). Otherwise, the lathe keeps spinning.

 

[john lucas]

I demo frequently on 1642's and have never found them to be underpowered. Your lathe definitely has a problem somewhere. I would definitely contact Jet.

 

[R Henrickson]

I've had and used a 1642 (1.5 HP) for 6-7 years. It takes something substantial, such as roughing a really large bowl to slow it down much. For all the talk there is about it being underpowered at 1.5 HP, I have rarely found it to be so (even roughing a 15" diameter, 7" deep bowl). I may not be the most aggressive turner, but 'delicate touch' is not my foremost trait.

 

[Dave W]

John, I'm out of warranty on it. But Jet did take a listen with my phone jammed up inside the headstock. As soon as I got it back out he agreed the bearings are bad, and would have sent me a new motor if I was under warranty.

I too in the past had a hard time slowing my jet down, usually with the largest of bowl blanks. Even then, I was turning and not stopping.

Well after a lot of consideration and knowing the bearing(s) need replacement, plus the lack of power I decided to bite the bullet and I order a new motor. It's not what I was wanting for X-mas, but if it does the trick I'll be happy.

 

[Bill Boehme]

Since our club lathe is fairly new, I suspect that somebody is keeping the belt in the high speed range. I agree that there should not be a reason for bogging down a good 1.5 HP motor unless using the wrong speed range.

 

[john lucas]

If its just bearings your local motor repair shop can replace them at a very reasonable cost. I would think if bearings are the issue you would hear a lot of noise. The motor with good bearings should just make a fan noise