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  1. #1
    Hi , i have a denford triac atc ,im going to give it some love . i currently have it running with a 24000 rpm water cooled spindle geared down . 5/6000 rpm is good when cutting aluminium which i mainly do . But i would like to cut steel at lower rpm . this spindle loses all torque at slow speeds.
    I've recently retired so i have time now for an upgrade . i would love to be able to tap, cut steel and aluminium at reasonable rpm . so is this a pipe dream and i have to have 2 machines or is there a motor/setup i can use that will do a half decent job and not be extremely expensive .
    im quite prepared to build a new spindle motor mount as i have some hiwin linear rails for x,y.z i have already bought .

    cheers

  2. #2
    What happened to the original motor?

  3. #3
    its in a box under my bench still

  4. #4
    Well the original motor is probably a Baldor DC commutator type as used in other Denford machines - like my little Novamill. Max spindle speed is 5000rpm which is OK though I'd like higher for engraving. Power approx 0.5hp I think. The mills don't have reduction pulleys for more torque at low speed. OTH DC motors have good low speed torque. I think you should at least try replacing the original motor/spindle and see how well that works - the Novamill is fine for cutting steel with this type of motor, the triac should be too. If you don't have the drive I can recommend KB Electronic types.

    If you really want to replace the motor there are DC brushless servo motors and controllers around designed for sewing machines, e.g. https://www.college-sewing.co.uk/jk5...rvo-motor.html . Several people over on the ME forum have used these for machine tools.

    Do you mean rigid tapping? For that you need coordinated Z feed & spindle which needs a spindle encoder and a controller to suit - more like lathe control. I do a lot of power tapping on my big manual mill which has a VFD so I can turn the speed right down. I've thread milled on the Novamill which works fine.

  5. #5
    the original motor was a sem, 4000 rpm but would stall sometimes so i converted it to the Chinese spindle. the sprint board has got damaged in storage. ideally a motor and vfd or controller with low down torque would be good .if there is nothing out there then im ok with swapping belts on pulleys

  6. #6
    Well as I said a DC motor has better low speed torque. Or a modern induction motor with a constant torque VFD which adjusts the drive voltage and current as well as frequency to give good torque at low speeds. These exist but I don't know much about them except they exist. You might also have to provide a cooling fan.

    TBH I'm not sure why you want to use low speed except for tapping? With manual mills the argument for having a low speed is to use big cutters and carve out lots of metal so you don't spend hours twiddling handwheels, but with CNC you can use smaller cutters at higher speeds (with cooling if needed) as the machine does all the boring stuff. Actually since I got the Novamill I started to use higher speeds on the big mill too and deeper cuts and the cutters are happier for it.

  7. #7
    Thanks for the info . it would be prudent to refit the sem dc motor and try it for a while . the original sprint 1200 board may be toast if i still have it . i had a quick look around the net . does anyone know if this is suitable ? as dc motor control is above my paygrade
    https://www.aliexpress.com/item/1005...8dam51Nmy&mp=1

    if not can anyone recommend a suitable control which is not 1000 .


    any help greatly appreciated

  8. #8
    An important question is whether the original motor is a wound field type or permanent magnet. My Novamill is a PM type. How many wires go in to the motor? If only 2 then it's PM, if 4 then wound field.

    The controller you link to is I think OK but may not have the supply terminals for a field winding, the data is very sparse. Lots of these "generic" Chinese controllers do but if you need it and this one doesn't then it wouldn't be suitable. The other question is whether you want to control start/stop and speed? As supplied it looks as if this drive just has a manual potentiometer control. I believe these drives have an isolated control input (that is, not connected directly to mains voltage) but if it doesn't then it isn't safe to connect to the usual 0 - 10v speed control output, an isolator is needed.

    In the UK KBE motors are stocked by Axis Controls and this one has the right rating:

    https://www.axiscontrols.co.uk/produ...eed-controller

    This does support a wound field (or PM) but does not have an isolated control input. KB also make an isolator:

    https://www.axiscontrols.co.uk/produ...ard-kbmm-range

    Together these cost ~240 which is a lot less than 1000 but you do get proper industrial rated products.

    This is on eBay:

    Claims to be fully isolated and can be driven by PWM input. What CNC controller are you using?

  9. #9
    it was previously and still with the vfd speed managed by 0-10v
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  10. #10
    Right, so appears to be a PM type with an inbuilt tachometer. I'm not sure what the K1 and K2 terminals are for. Do you mean 0-10V from a pot or the controller? I have seen on here a Sprint drive on I think a Novamill where someone was proposing to connect it to a 0-10V supply from a breakout board (part of a Mach3 conversion?) and the drive had a big CAUTION label on it warning against gounding either side of the 0-10V input - does yours have that on it?

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