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Real Bull controller, adjusting the trim pots

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Gazz292:
Brilliant, thank you very much  :bow:

yes, i have a DC ammeter, got a current clamp type (Uni-T UT210E... very handy little thing, does 100A DC)  and the usual multimeter  wire it in line type... then forget you had the leads set for current and go and do a voltage reading and blow the fuse  :doh:  or is that just me :)

Somewhere i've got a set of mains testing meters including a megger, but don't think i want to subject a chinese lathe motor to that kind of test.

I presume it's mainly the IR trimpot i need to play with, and assume it's been wound too far round,
i just had the lathe running, taking a light cut on some alli bar, speed set at ~650 rpm, as soon as i took a cut the speed went up to ~720 or so, take a deeper cut and it goes even faster, no load and it's back to 650.


It'll be nice to get this little lathe running how it should again, i've just put angular contact bearings in the spindle, and a set of metal hi - lo gears... i've not had low speed for a few years,
Whilst i had the headstock off i added extra jack screws to align the motor properly, when i first got it the motor was sitting at a right old angle, only the side of the drive gear was keeping the belt from coming off, and that's chewed up pretty bad... so got a new one coming, and a slightly longer belt so i have more room to adjust the motor and not have the belt as tight as a guitar string.

John Rudd:
From memory, if you look at the IR pot, the notch in the screw slot should be about the 9 o'clock position...
Failing that a good starting point is at 25% of the travel of the pot.

RussellT:

--- Quote from: gazz on December 21, 2020, 02:36:26 PM ---multimeter  wire it in line type... then forget you had the leads set for current and go and do a voltage reading and blow the fuse  :doh:  or is that just me :)

--- End quote ---

It's not just you.  I wanted to make some current measurements last week, first, wonder why the meter shows nothing, second, spend half an hour searching for a fuse somewhere near the right rating, third, make the measurements. :doh:

Russell

Gazz292:
Thankyou for this great info John.

I spent a little time setting my controller up and have got the lathe running better than i ever remember it.

It will spin reliably at 60 rpm in low gear and has just enough torque down there to actually use it gently,
In high gear with the max trim pot set for 180 volts on the motor, the chuck was turning about 2800 rpm, so i wound that down to 2500, and about 165 volts, it's quite rare i use this lathe in high gear tho except for polishing something.

And once IR pot had been twiddled with with informed reason (i'm not sure if this was just set up badly from the factory, or the last owner had a blind twiddle in there) it's now holding it's speed properly, i get maybe a 15 rpm change from it spinning free to taking a slightly deep depth cut for this little lathe, and it no longer speeds up when i engage the lead screw gears.


Not sure i have the overload set right tho,  as in likely too low?  i had the chuck spinning around 80 rpm and using a length of ratchet strap webbing, made a loop around the chuck and pulled it tight till the chuck stalled,
i saw no more than 2.5 amps with the motor stalled.

Should i have the overload current higher? or is that the controller cutting the current down (thought it would cut power in an overload condition tho) and should i reduce it?

There's no markings on my motor that i can see, i think the lathe was new in about 2008 or so, the motor is just a simple cylinder shape... like a vw beetles dynamo with flat silver end caps, and not the belled end caps, or plastic looking ones i've seen on sites showing how to adjust the motor position for belt tension...

The belts tension is done via 2 jack screws under the headstock bearing on the top of the motor, one slightly to the right of the middle of the motor and one above the right hand end, 
I've added 2 more jack screws, 1 at each end of the motor underneath it, and using these i was able to get the belt running straight for the first time ever.

awemawson:
i had the chuck spinning around 80 rpm and using a length of ratchet strap webbing, made a loop around the chuck and pulled it tight till the chuck stalled,

Blimey - do that with either of my lathes and you'll end up wrapped round the chuck  :bugeye:

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