axminster sieg c1 lathe & erratic rpm control

[rvt]

A couple of days ago I was happily working on something when something odd happened. The lathe was running around 400 rpm (I don't get exact readings with this model), I was very gently moving the Y axis in further and it was cutting cleanly. I just as I was moving it out, the motor seems to increase to what I can only guess was around 2000 rpm (which is what it's limit should be). My hand was nowhere near the dial. I then slowed it right down and moved everything out the way. When i turned it back on it sounded like it was going up to some rediculous rate when turned further up... then it went back to normal, and I carried on with the job.

Electrical problems? I'm a little concerned. I've only had it 4-5 months and it's still under a 12 months warranty.

[crabsign69]

warrenty problem send it back  its there problem

[rvt]

Hmm.. you would just get rid of it then, even if it 'appears' to be running okay now?

[andyf]

It might be worth taking the cover off the speed control board and checking if any swarf has found its way in there via the hole which the leadscrew passes through. I understand that Sieg mini-lathes are vulnerable to this. Of course, any offending bit of swarf must have shifted by now, or the problem would still be there. A brushing down with a soft paintbrush might help.

Another cause of high revs is failure of one or both mosfets on the speed control board; see http://littlemachineshop.com/Reference/DriveTroubleshooting.pdf . But mosfets are not known for putting themselves right again once they have popped. If things aren't consistently normal after a swarf check, contact Axminster under the warranty.

Andy
 

[dsquire]

A couple of days ago I was happily working on something when something odd happened. The lathe was running around 400 rpm (I don't get exact readings with this model), I was very gently moving the Y axis in further and it was cutting cleanly. I just as I was moving it out, the motor seems to increase to what I can only guess was around 2000 rpm (which is what it's limit should be). My hand was nowhere near the dial. I then slowed it right down and moved everything out the way. When i turned it back on it sounded like it was going up to some rediculous rate when turned further up... then it went back to normal, and I carried on with the job.

Electrical problems? I'm a little concerned. I've only had it 4-5 months and it's still under a 12 months warranty.

At the minimum I would report the problem to who ever holds the warranty so that if it acts up again they will be aware of when it first started acting up. This could be very beneficial if it doesn't act up again until just after the 12 month period. 

Cheers 

Don

[winklmj]

Since it's under warranty I'd at least contact the mfg/seller about it.

FWIW, my mill and lathe (both MicroMark/SIEG) have a similar issue from time to time. Neither have gone full speed so it's not like a mossfet short. Appears to be the speed pot. Before turning them on, if I rotate the pot back and forth a few times this seems to avoid the problem. Maybe some stray carbon buildup on the wiper? They sit in a humid garage--don't know if that has anything to do with or not. Others have used that spray terminal cleaner and even gone as far as taking the pot apart to clean them up.

[John Swift]

since  the speed control worked normally after adjusting the speed a few times
check the potentiometer is ok and you don't have any loose connections
do you use a lot of coolent that could have found its way into the speed control ?
control pcb idents starting FC .... use fet's   XM... types use thyristors

If the potentiometer is the same as in my lathe it will be 4K7 linear
and the interlock switch closed when fully anti clockwise !!!
contact axminster , if your lucky they may send you one free

a few months ago I repaired the control pcb in a 10 year  old CL300 lathe
as a result I have traced the circuit for the FC250/240v board
the board had two faults the relays buzzed and once a capacitor had been changed
the board needed adjustment to stop the bursts of full power with speeds over 60%

in my lathe I found the original crimp terminal are made from very thin brass
and made poor contact once disturbed

with your lathe being only  a few months old I would not expect any adjustments to be  required
for several years



     John

[jim]

i would contact the seller.

i did once have a similar problem with a chester conquest lathe, turned out to be a loose speed controler knob (just need the retaining screw tightening up!)

[cedge]

I had this problem  with my Micromark 7x14 lathe. Their tech support suggested tightening the motor brushes, which cured the problem straight away. Every time it happened, a quick adjustment set things back on the proper path. Sometimes it's the simple things easily overlooked.

Steve