Haunted lathe

[Larry Dubia]

I bought a Grizzly G0766 wood lathe new. I recently had an issue with the rpm readout showing 1/.3 the normal speed. So on the slower speed belt, I should get 100 -1200 RPMs. I get a readout of 30-410. I have been going back and forth with Grizzly tech support on it and we are all scratching our heads. They sent a new potentiometer, I installed it...no change. They sent a new inverter, I installed it...no change. They sent the manual for the inverter and an email with the pages marked to show what the settings are supposed to be so I can check them, I checked them...they are correct and no change. Then yesterday and again today, while turning on the high range at mid speed (guessing), I made a few cuts, turned the lathe off to check my work, and the lathe would not come back on without waiting for a while. The error code suggests a too high voltage at high speed. But the lathe has been operational for a while with no problems.

So my question is...has anyone had any issues like this and what was the outcome or answer to the riddle.


Incidently, the lathe worked perfectly when I first got it then developed these weird problems.

[Roger Chandler]

David Roseman, an 0766 owner, mentions the magnets that allow the speed sensor to work correctly. If one of those 3 magnets came off, it would affect the rpm reading. There is some info on a thread in the Grizzly Green Monster Group that you can take a look at, and maybe David will see this and chime in. Your inverter may need a reset, but that should be determined by tech support.

[Matt Schrum]

I'd check the sensor inside that reads the RPM. As Roger mentioned, there are 3 magnets, so my guess is that somehow it is picking up one and not the other two. Check two things--
1) That all three magnets are there
2) That the sensor is about the width of a business card away from the magnets

These magnets are inside the lathe (behind the flap/door you open to change belts) on a pulley if I recall-- but nose around inside and they are pretty easy to come across.

[Brice Rogers]

Larry, I am presuming that when the display is reading 30 rpm, that the spindle is actually turning about 3X that number (i.e., 90 rpm). The slower speeds are easy to count with a watch and your eyes.

Roger and Matt are most likely correct in their assessment. It is a little surprising that Grizzly tech support had you swap out the potentiometer and the inverter. Perhaps they didn't realize that it is not a speed problem (you need to confirm that) but is a reading/measurement issue. Another possible explanation is that there is a problem with the digital readout board. This could be in the circuitry or could be something as simple as the electrical connection from the sensor to the readout board has a problem. So, if you confirm that there are 3 magnets still in place, are oriented correctly (polarity-wise) and has the correct spacing - - then I'd ask for a new digital read out board.

Please come back and report what you found.

On the other issue - not wanting to start up for a while and getting an error code - - I'm wondering if perhaps you were turning something very large and heavy and quickly turned down the speed control. I think that something really heavy might act as a flywheel and generate what is referred to as a back emf (electromotive motive force) - - kind of like a generator. So, if you turn down the speed control more slowly on the really big pieces it may help to eliminate that issue. I think that some people have installed braking resistors on the controller. There may be instructions or info on the Delta manual which is available on-line.

[Larry Dubia]

Thankls to all three replies.

Roger: I did check all the magnets to make sure they are there. They are all in place. I even cleaned them with acetone to remove dust, etc.
Matt: I will check the spacing and make sure the reader is spaced right.
Brice: It looked to me as though the machine was running slower than normal but has speeded up some. Still reads the same though. I usually just turn off directional switch to stop turning. It has never done this from when I first bought the lathe. I have the manual which thee emailed. They told me which settings to check and everything is correct. I did bring up the possibility of a bad digital readout. And lastly, I will double check the connections.

Thank you for these suggestions. I will report back after checking it out.

This lathe gets use all day, every day. So I need to count on it working for me lest I get bored and tear out my remaining hair. LOL

[Brice Rogers]

A second thought. If the magnets are set up right and you are reading the wrong speed, also ask Grizzly to send you the RPM sensor in addition to the digital readout. The sensor is a 3 wire device - - power, ground, and the sensor output (activated by the magnets). Most likely it is what is called a "Hall effect" device. It puts out a pulse when a magnet goes past it. It is a semiconductor and is an inexpensive device. On the G0733, it lists the readout as a part with sensor. On the Griz site for the G0766, it just says read out. So, I don't know if the sensor comes with the readout or is a separate part. I'm guessing that because of the low cost of the sensor that it is included in the readout assembly as I couldn't find it listed as a separate part. But it is worth asking.

[david privett]

I went threw this and believe it or not those magnets are directional even though they do not repulse each other when placed in the holder cups. what I did was to turn the lathe on (with no speed)and quickly rock the spindled magnet by the pick up the one that will not read is in backwards and the gap is .053 inch if you need to reset. hopefully this is clear enough it seems vague but at this moment I can not do any better.

[Brice Rogers]

David brought up a very good troubleshooting technique. Thanks - - I'm going to tuck this away in my memory.

Larry, you wrote: "...Brice: It looked to me as though the machine was running slower than normal but has speeded up some. Still reads the same though. I usually just turn off directional switch to stop turning."

This is confusing and a bit contradictory. Kind of like: maybe it was slower and maybe it is better now. Hmmm.... I think that if you are trying to isolate the source of the problem, you really need to know if it the lathe is running at 1/3 X or if it is running at the right speed but reading low. If you haven't already done this, chuck up a piece of wood and put a dark mark on it. Turn the lathe on to one of the lowest speed settings where it will reliably run - - for instance 80 rpms. Then count the number of times that the mark goes past during, say, a 30 second period of time or a 15 second period of time. If the number of rotations in 30 or 15 seconds is 40 or 20 (respectively), then your invertor and motor are probably running at the right speed. This isolates the problem to the readout and sensor circuitry.

For smaller items, you can certainly switch the direction switch to off. But if you have a really big chunk of wood, you may find it a better practice to use the speed control pot to slow it down. It has a lot of kinetic energy and that energy ends up needing to go somewhere. You mentioned that they sent you a new invertor and that you didn't have this problem initially (with the old invertor). Perhaps the new invertor is not working properly (technically, I can imagine that the transient protection circuitry could be bad or less effective). Or perhaps the repeated practice of stopping the rotation of a large piece, by using the direction switch could have fried that transient absorbing circuitry.

If you are unable to or not motivated to troubleshoot the problem(s) to a replaceable assembly, then you need to push to get a replacement headstock.

Just some thoughts to consider. Good luck.

[Roger Chandler]

I went threw this and believe it or not those magnets are directional even though they do not repulse each other when placed in the holder cups. what I did was to turn the lathe on (with no speed)and quickly rock the spindled magnet by the pick up the one that will not read is in backwards and the gap is .053 inch if you need to reset. hopefully this is clear enough it seems vague but at this moment I can not do any better.

David......you are correct about the directional nature [polarity of the magnets] If just one is in backwards, the speed will read 1/3 less than it should. This is probably a simple matter that has happened to Larry, but it could be more complicated than just the magnets....it might involve the circuit board as well. Brice and others here have given him good advice.....but I would double check everything I could, then have tech walk me through all steps again to confirm or make sure I did everything correctly.......if the problem persists, then a new headstock might be in order.