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Variable speed control died on Jet 1221vs

N

Nicole Curry

Joined
Oct 2, 2021
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Location
Saint Augustine, FL
Hello, I just started turning over the summer and I am 100% addicted. I found what I believed to be a "great deal" on ebay for a new jet 1221vs, but when I got it, the base was cracked and the spindle threads damaged. Also the electronics were not secure because the plastic bracket holding them was broken. None the less, I taught myself the basics on it and believe it or not, everything still lined up and after a new spindle it worked perfectly. Unfortunately, without the electronics being properly secured, some how I have lost the variable speed. When I turn it on, it turns at 30 rpm and the controls do not increase the speed at all. I have checked all of the connections to the variable speed control circuit and I think the variable speed module is the issue, not the entire circuit board, (hopefully)Is there anything I can do to to verify this?

Fortunately, I have since upgraded to a Revo 1836, so I am able to turn, but I would like to either repurpose or maybe get my friend or son started turning (when he's big enough). Right now it is just sitting covered and protected from the elements outside my workshop and it kind of breaks my heart since I had so much fun on this little, broken lathe :-)
 
In my case, it would be very hard to do any troubleshooting without test equipment. But being an electrical engineer means that I am not quite normal. The first thing that I would look for is something mechanical that is out of whack. Sometimes the plastic speed control knob has a setscrew to hold it onto the shaft of the speed control potentiometer. If the setscrew is loose then the knob wouldn't be able to turn the potentiometer. Also, the potentiometer should have about 300° stop-to-stop rotation. If the shaft is fluted or half-round then the loose set screw scenario wouldn't apply.

Most potentiometers used for speed control are either carbon film or conductive plastic. Both types are very good because they have a high MTBF (mean time between failure). There have been some lathes that used wirewound potentiometers which is a poor choice because of their low MTBF. I don't know what type of potentiometer is used in the Jet 1221, but the failure mode that you described is a possible indication of a bad wirewound potentiometer.

The Jet 1221 uses a DC motor so the speed controller is just a variable voltage source. Lacking a voltmeter and circuit diagram I suppose that the next best thing would be to call Jet tech support. The quality of their tech support seems to be better than average, but somewhat dependant upon who you get on the other end.
 
Thank you for your response. I will look for a set screw tomorrow and hope that is the case. If not, I am willing to purchase a new variable speed control module from Jet, my only hesitation is I'd like to know this is where the issue lies and not waste money on a part that I don't need. I have contacted customer service because technically it is still under warranty, but because I purchased through Ebay, it is officially null and void. I was under the impression that the Jet has an AC motor since there is no VFD, but im a chemist and certainly not an EE! Thank you again for your advice
 
I understand your concern. Shotgun troubleshooting isn't much fun.

You would need a three-phase motor to work with a VFD and that's just too expensive for a midi lathe. All of the mini and midi lathes with electronic speed control use DC motors since that is a much lower cost solution. The main disadvantage of electronic variable speed on small lathes is the lack of power at low speeds. That usually isn't a problem since small lathes are typically used to turn small things.
 
If the lathe was new, you should still be under the 5 year warranty. Perhaps Jet would be able to help.

From your description, though, this lathe was not pristine and the problem may have originated from the damage done before you bought it. The seller appears to have misrepresented the lathe and possibly you have still recourse with him or through Ebay.
 
We had a VS problem with one of our 1221's in 2019. After checking all of the easy stuff (dust, sensor collar, etc.) we swapped the control unit with another 1221 to verify it was the control unit. Made no difference. Tried brand new controller. Nope. Called Jet, turns out there is also a sensor in the motor unit. Called it quits and replaced the lathe.
 
The most common failure on DC lathes is the potentiometer. Second is resistors on the control board. When 46-460 Delta lathes started crapping out and Delta had no parts, people went to this controller. Be sure to read the full information as the unit also needs a plug in horsepower resistor. https://www.amazon.com/KB-Electronics-KBMD-240D-Multi-Drive-Variable/dp/B00RW7LSXM/ref=sr_1_46?crid=1MDXVMAURZNRM&keywords=dc+controller&qid=1640367326&sprefix=dc+cont,aps,88&sr=8-46#descriptionAndDetails

My opinion only, but eBay is not a place to buy good used equipment. It's there because it won't sell locally.
 
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