1. #1
    CNC direct stepper motor drive Lathe Idea. If anyone knows of anything similar please let me know.

    Task required its required to do take 12mm to 15mm plastic for drilling and cutting.

    Task it would be nice if it could do is to take 4-6mm brass and do the same (thinks the power required would mean Direct drive requires too much torque).

    As an Electronics Eng I have no Idea of the torques required to do these tasks.

    Mechanical concept the Chuck is moved 0-20mm forward on Rails (cheap drill press bars as rails as i have a matching pair) thru a Fixed bearing linear bearing mounted in shaft bearing on to the a Fixed Drill in a fixed stock and back 0-20mm after drilling. A cutoff cutter mounted on another set of rails very close to the linear/rotary bearing (or sliding chuck) the raw material is then feed forward 0-20mm after cutting for the next item.

    Sequence is then repeatable for maybe 10 items then new material is put in the chuck..

    I can imagine a lot of Mechanical engineers cringing now.. at the stupidity of this Idea/concept

    First Problem to solve is mounting the collet chuck to the stepper motor securely. Stepper shaft 10mm Collet mounting plate thread 14mm. (thoughts grind the stepper shaft to a D shape) or some other method?

  2. #2
    Direct drive Stepper motor won't have the speed or the torque to do this job.!

    Really you need a DC motor and speed control from something like tread mill or a servo motor.
    Typical Servo motor spins at 3000rpm with linear torque thru the speed range, best steppers will top out at around 1500-2000rpm MAX with very little torque left at this speed.

    Collet chuck mounting should be easy enough if you access to lathe, most steppers have a flat portion on the shaft just bore collet shaft and use grub screws and locktite.

  3. The Following User Says Thank You to JAZZCNC For This Useful Post:


  4. #3
    With 3.5NM or 35 Kg CM torque at slow speed is there any kind of Graph calculation showing how to calculate the Torque loss at higher speeds of rotation?

    Currently I'm using a SEIG Micro lathe set at about 50% of maximum speed to do this drilling operation so lets say its around 1k5 RPM as the Micro lathe max is only 3K rpm using a 6.1mm drill.

    For machining plastic like PTFE what would the ideal speed be?

    Unfortunately I'm working on using only things that I have in my collection of bits and Bobs.

    What level of Torque is needed to drill into plastics like PTFE with this size of Drill is there a way to calculate this?

    The option I was trying to avoid was gearing up the stepper motor as Lathes appear to be geared down, so without spending much money.
    It could be driven by T5 belt in a geared up configuration to minimise the Torque loss at higher speeds.

    Reasons why I'm trying to avoid gearing up is my ability to produce accurate STIFF mountings / rock solid to do this.
    This would need Aluminium machining ability. Though I did just see a concrete lathe configuration here that could work possibly from laser cut MDF or light cnc cutting.

    The shaft is a smooth 10mm with out a D ground into it but I have made a Jig for grinding 6mm an 5mm Stepper shafts so its not to hard to convert it to 10mm shafts was asking to see if there are any other recommended methods.

  5. #4
    PS I do not have a collet shaft to bore so I need to make one with a 14mm x 1mm Spindle Thread on it or find a 14mm x 1mm bolt to modify.

    The previous long post prior to this has vanished into the ether..

    basic questions were:-

    How do you calculate torque loss as the speed is increased?

    Speed required to machine PTFE ie drill a 6.1mm hole?

    I'm currently using a SEIG micro lathe at about 1.5k rpm to do this.

    The stepper is a 3.5NM or 35KG/CM torque

    Is it worth gearing the stepper up using T5 belt maybe ?
    I realize most lathes are geared down..

    was trying to avoid needing to make Stiff mountings as no ability to machine Aluminium but the concrete lathe looks like an interesting idea that could be used with laser cut MDF or light CNC machined MDF.

    This was better worded in the original that was lost this is a dyslexic quick reply.

    Trying to make this from my bits and bobs boxes as no money to spend on very much.

    I do have some cement and sand left over after installing my solar array..

    The 10mm shaft is smooth I do regularly grind 6mm and 5mm stepper shafts with a laser cut Jig was asking to see if there are any other recomended ways to do this.
    Last edited by Bodge; 14-04-2012 at 06:09 PM. Reason: lost reply prior to this

  6. #5
    Go check Irvings spread sheet out this will give you what you want.

    http://www.mycncuk.com/forums/showth...otor-do-I-need

  7. #6
    Might have this concept wrong so bear with me.
    What about scrapping the chuck, fit a collet chuck and just nip it on the work.
    Push the work thru the collet with a pneumatic cylinder or even lever feed, stop on the LH outboard end so you feed the same every time.
    Drill in a block on the cross slide.
    Part off tool in another bock.
    Write a program to start spindle, position drill and drill, retract, move to part off, feed new length, wash and rinse.

    Basically you have re-invented the sliding head lathe.
    John S -

  8. #7
    Great thank you just down loaded it... I got the torque wrong on reading the spec as I'm running windings in series the torque has increased from 3.5 Nm to 5Nm os its roughly 50 kg/cm.

    I just do not know how much torque is required to drill PTFE with a 6mm drill.
    Then how much torque is lost by running at 1K5 RPM hope fully this sheet will help.

    I have the 500W supply up and working have programmed the Arduino board driving the 4.2A stepper controller, made an opto rev counter thing from half an Olham coupling.

    Will post an updated picture up here http://www.mycncuk.com/forums/blog.php/2916-Bodgecurrently only one there at the moment.

  9. #8
    Concept is correct will make a rough drawing ... had not thought of feeding via the collect due to the motor shaft being in the way. http://www.mycncuk.com/forums/blog.php/2916-Bodge

    Think I will just take another picture and upload it..


    Quote Originally Posted by John S View Post
    Might have this concept wrong so bear with me.
    What about scrapping the chuck, fit a collet chuck and just nip it on the work.
    Push the work thru the collet with a pneumatic cylinder or even lever feed, stop on the LH outboard end so you feed the same every time.
    Drill in a block on the cross slide.
    Part off tool in another bock.
    Write a program to start spindle, position drill and drill, retract, move to part off, feed new length, wash and rinse.

    Basically you have re-invented the sliding head lathe.

  10. #9
    Sorry got the wrong end of the stick.
    I read where you were using a Sieg lathe.
    My post was based on modifying said lathe.
    John S -

  11. #10
    No worries The material diameter prohibits automating the first two or three sizes of SIEG Lathes as the maximum feed through diameter on them is around 10mm.

    Slight delay in proceedings this wee and weekend as I will be at the FABLAB Manchester's 2nd Birthday event demonstrating my Huxley Seedling 3D printers.

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