Any one ever had this problem?

[Bruce Lewane]

About a week ago I was in the process of turning when all of a sudden I would hit the start switch and the lathe (Nova Comet 2) would hesitate or require me to turn the piece to get the motor going. Then I noticed that under a load the motor would slow down more than seemed right. Then-- just listening to the motor while under no load the speed would vary.
Called Teknatool service and the tech there decided, with out a shadow of a doubt the variable speed control was the culprit, or to be much more particular a wire to the speed controller was the problem. Now, I'm not an electrical engineer but it would seem to me that controlling the speed on an electrical motor requires resistance which creates heat so---chances are the wire is going bad due to heat build up. Basically it's frying. I haven't pulled the thing apart yet seeing as though the tech promised me a new control switch but it seems to be kind of slow forthcoming. Just wondering about the logic of all this and whether I want to schedule the exploratory surgery just to take a look. With the snow and cold weather down here not being able to spin wood is making me cranky.

[Steve Schlumpf]

Bruce, first off, I am not familiar with your lathe but after checking online I see that it is DC and is electronically controlled. That means your variable speed control provides an input to a microprocessor and most likely has minimal current running through it. So, in my opinion, it is highly unlikely that one of the wires is frying.

The speed control is nothing more than a potentiometer (pot) and that is a variable resistor. They have a thin film of carbon or other resistive material inside that will eventually wear out. So, that begs the question - how much do you use the variable speed control?

Without knowing the history of this model of lathe, I have to admit I am suspect of determining that a wire is the problem. I can see it if works lose that it would cause an intermittent problem but the symptoms you describe make me wonder if you only need to blow out the controller with some compressed air and see if that doesn't change things.

Good luck!

[Dan Hintz]

About a week ago I was in the process of turning when all of a sudden I would hit the start switch and the lathe (Nova Comet 2) would hesitate or require me to turn the piece to get the motor going. Then I noticed that under a load the motor would slow down more than seemed right. Then-- just listening to the motor while under no load the speed would vary.
Called Teknatool service and the tech there decided, with out a shadow of a doubt the variable speed control was the culprit, or to be much more particular a wire to the speed controller was the problem. Now, I'm not an electrical engineer but it would seem to me that controlling the speed on an electrical motor requires resistance which creates heat so---chances are the wire is going bad due to heat build up. Basically it's frying. I haven't pulled the thing apart yet seeing as though the tech promised me a new control switch but it seems to be kind of slow forthcoming. Just wondering about the logic of all this and whether I want to schedule the exploratory surgery just to take a look. With the snow and cold weather down here not being able to spin wood is making me cranky.

You don't vary a large motor's speed by adding resistance for the exact reason you mentioned... heat. A simple control would be an SCR which chops the incoming waveform (and will build up a bit of heat, but not nearly as much as a pure resistance), whereas the opposite end of the spectrum is a full-blown VFD. I don't know what the Comet has, but my quick Google of it says it's midi lathe, so I'm guessing it's a 1hp, give or take. It's unlikely to be a burnt wire due to heat.

[Bruce Lewane]

Thanks for your replies.
Like I said I am not that good with electronics. Just good enough to keep this 120 year old house from burning down. (So far.)
Guess I just have to be a boil on the butt of Teknatool till I get some action. It is under warranty after all. But stuff like this moves soooooo slooooowly and I've got all this beautiful wood to work.

[Bob Mezzatesta]

Wait a minute! You're in Texas. Snow? Cold? Try Ontario. 15 below EVERY DAY this winter. Sorry, I had to rant, cheers.

[Paul Williams]

Sounds similar to how my Delta 46-460 midi acts if I don't keep the dust out of the control box. I would blow out the potentiometer before trying anything else.

[Bruce Lewane]

I'll give that a shot and
thanks for the tip.
Oh and Bob. I lived in Colorado for 35 years.
The wife and I don't do cold anymore.

[Thomas Canfield]

Bruce,

I had to replace the on/off switch on my Nova Comet II about a year back when it would not start. The replacement switch was start/stop button switch with dust covers and I thought that was an improvement. Yesterday morning early when sanding and removing the tenon on a hollow form, the unit would not start. It was too early to call the service center so I used my air compressor to blow the exterior of switch and electronic controller. It started working again so guess I will have to wait for another malfunction to determine if it is switch or something else. Your problem may help then. My only problem was getting unit to start and not a speed control or power issue.

[terry mccammon]

As it happens I had 40 years of experience with drives of all sorts and I suspect dust/contamination in your speed control/potentiometer etc. In general anything you can do to help keep dust away from the controls/electronics package is a good thing. Wires can break or come loose but I sure can't picture one "failing" from heat at the range that one would find in the control box.

[Bruce Lewane]

Well I took the bottom plate off and blew the whole thing out.
No change.
I lit a bit of a fire under the service techs yesterday.
Maybe I'll get some action.
Thanks for all the replies.

[Thomas Canfield]

I am happy to report my little Comet performed well today. I turned and sanded 10 little 3"+/- bowls using a recess and expanding collet from PSI. The lathe must have been started/stopped at least 50 times with no switch issues. Must be a different issue from Bruce's. My Comet is located in a section of shop where shower curtains help hold in the heat from little heater and outside temperature stayed 28 to 33F today, a real icy day with ice on trees all days.

[Bruce Lewane]

Now don't get me wrong here. I've been very happy with this lathe. It's worked flawlessly from the get-go and is located in an area that never drops below 60 degrees.
I'm just a bit frustrated seeing as though I use it everyday. I personally feel it's a great tool for it's price. (Currently on sale including a chuck in many places.) Which brings me to another current thread here. I've easily spent twice the price of this lathe in the last nine months on tools, accessories, finishing stuff, etc. A real consideration when jumping into the vortex. I'm totally hooked. I miss this lathe. Quite a bit less than I would miss my wife but only a bit less than I'd miss one or two of our dogs. A bit more than I'd miss the cat.
I'm beginning to start shopping in case I can't get this issue settled.

[Thomas Canfield]

Bruce,

A word caution if you change the switch yourself. Teknatool did not use different color wires in wiring up the switch. I tagged the wires and made a diagram for reference, and then removed and moved to new switch. There was also some little trick that the tech told me in removing the switch from box but a senior moment has set in and I cannot remember what it was. I did use the low powered slow speed range today to sand a Mesquite bowl my grandfather turned about 50 years back that the old glue ha failed and had to be re-glued. The 250 rpm was handy since the bowl was not round and hard to center on vacuum chuck, but bowl has a lot of meaning knowing that it was done with a lot less equipment and quality tools that I have today.

[Bruce Lewane]

I noticed that when I opened the box up to blow it out.Should not be a problem but thanks for mentioning it. Now if you could only remember that little trick.
I have to add that over the weekend I ordered a Jet 1221VS. Didn't need more size but a bit extra horsepower won't hurt. I turn a lot of very hard kiln dried exotic wood.
I figure if I ever get this Nova working I can always sell it.

[Bruce Lewane]

Just a little update. I did light a fire under the Customer service guys at Teknatool. Got a replacement speed control this morning. Problem is it's not the right one.
This might go on for a while. Glad I ordered the Jet.
A cautionary tale. Even though a machine get's glowing reviews from it's users, when push comes to shove it's the customer service record that should be looked at with just as much attention.