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  1. #1
    I have used a little mini lathe under my gantry router to good effect for vertical mill turning. If I wanted to make it into a 4th axis driven by a spare Nema 34 Could anyone suggest the toothed belt ratios to use please. It seems 50:1 or 100:1 are popular? Any experienced Knowledge gratefully sought.
    A source of the t/belt pulleys would be welcomed also please.

  2. #2
    Depends on exactly what are you going to do and the resolution you will like to achieve. Also if you would use it for indexing 4th axis, slow turning 4rth axis for milling or on top of that use it for lathe 4rth axis altogether.

    I keep a mini lathe for exactly the same purpose. What i intend to do is use 750W servo motor with brake so i have more possibilities.

    For example if you would use it with stepper motor without feedback, i would say then use it well geared. Do you intend to use it on place of the lathe motor and use the lathe gears or not?


    The Inturn mill lathe 4rth axis was geared originally 1:7 if i remember correctly and uses additional 150mm or bigger mountain bike hydraulic brake when indexing, at least before he further developed it. here is some info from the mega duty PDF:

    5C collet in spindle nose (draw tube included)
    1.25” Spindle thru hole
    5mm pitch GT curvilinear tooth belt drive
    12:1 ‘back gear’ ratio
    4:1 direct drive ratio
    Speed range change by quick simple belt move.
    Rotating parts balanced for 4,000 RPM operation
    7075 aluminum plate frame construction
    Reduces mass and draws heat off bearings
    Pneumatic internal spindle lock with 100ft-lbs @90psi
    Accommodates up to 3HP servo motors NEMA, DIN or OEM


    So according to me 750w braked servo motor on the place of the original one and using the lathe gears will fit well my intended purpose for small parts of plastic and aluminum, indexing or lathe jobs. If that does not work and have to direct drive it then 1:10 or what ratio pulley fits reasonably and forget about using it as lathe.


    By the way i can generate you any size HTD 5 pulley if you need to machine one. Just drop me aline.
    Last edited by Boyan Silyavski; 18-08-2017 at 03:14 PM.
    project 1 , 2, Dust Shoe ...

  3. #3
    If I wanted to make it into a 4th axis driven by a spare Nema 34 Could anyone suggest the toothed belt ratios to use please. It seems 50:1 or 100:1 are popular?
    With a single belt, you'll have trouble getting more than a 4:1 ratio, due to the size difference between pulleys. To get to 50:1, you'd need a worm gear, or harmonc or planetary gearbox.
    Gerry
    ______________________________________________
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  4. #4
    Boyan - the lathe does not have a gearbox, just a six position belt drive. I anticipate replacing the belt drive with a 20mm timing belt setup. Currently I am thinking 22T driver to 112T driven.
    Will only be used for wood plastic and maybe aluminium. Thanks for your information. I have no knowledge of servo`s. Just trying to use what I have at this time.

  5. #5
    You could use the belt calculator web for finding the right belt https://www.bbman.com/belt-length-calculator/ , i asume you know of it, but anyway here is the link.

    it seems that 17-18T is better choice as it has 6 teeth in mesh, versus 7 teeth for 20t, so you lose almost nothing. 6 teeth is the minimum recommended for HTD 5 belts, so you are ok there.


    so 17x7=119t, which is better as its a whole number of ratio . Its not bad 1:7 ratio . Its 180mm diameter puley, the big one

    I can generate you the pulley profile if you need. Thingverse also there is a pulley generator.
    project 1 , 2, Dust Shoe ...

  6. #6
    Boyan - Have you printed pulleys? I had not considered that option until you mentioned Thingverse. - Could print a 180mm dia. quite nicely in ABS. Got to be a cheap option if it would be serviceable? Thank you for the idea.

  7. #7
    You can increase the number of "Teeth in Contact" to at least 50% of the count on the driving pulley by using idler pulleys to generate a serpentine belt path as is done in the automotive industry,

    - Nick
    You think that's too expensive? You're not a Model Engineer are you? :D

  8. #8
    Nick - Yes adding a flat side idler would be quite simple. Thanks.

    Boyan - Ref. Thingiverse. Did you reference "Customizable Gear4"?

  9. #9
    Would you recommend any particular tooth form or pitch please?

  10. #10
    Sorry missed that on your reply Boyan. HT5.

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