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  1. #1
    I am considering using a single motor, probably servo and two ballscrews/pulleys on the X (longer) axis. Before I go ahead, it has been mentioned on another thread that there is a preference for putting the pulleys at the back.

    Apologies if this has been discussed before, but assuming the pulleys and belt are covered from swarf, what other advantages are there in choosing front or rear placement?

    Also, how good and smooth is joint belt, (length to bespoke measure), I've only used closed ready-made lengths. So I guess it's a question of designing the positioning of pulleys and tensioning parameters around a given ready-made length that's close enough to your ideal, and then tension as necessary? Thanks

    Edward
    Last edited by Edward; 12-09-2017 at 10:09 PM.

  2. #2
    I am considering using a single motor, probably servo and two ballscrews/pulleys on the X (longer) axis. Before I go ahead, it has been mentioned on another thread that there is a preference for putting the pulleys at the back.
    I suppose it depends what you call the front or the back as you could operate the machine from the side. I don't see any difference where you mount the motor. Depending on the layout it could be mounted underneath the machine.
    ..Clive
    The more you know, The better you know, How little you know

  3. #3
    Quote Originally Posted by Clive S View Post
    I suppose it depends what you call the front or the back as you could operate the machine from the side. I don't see any difference where you mount the motor. Depending on the layout it could be mounted underneath the machine.
    Hi Clive,
    Quite true. You would also have to define which side, as there are 4 sides to a rectangle:) By the "rear" I mean the side behind the gantry (behind the spindle), although that could also be misinterpreted, if you want to be precise.

    Ok, semantics apart, by placing the pulleys at the rear and having the front clear, the front plate, if suitably designed, could occasionally be used to clamp a long piece when you needed to drill for side tapping, as an example. Provided the spindle reaches (overhangs) that far.

    On the other hand, with pulleys at the back, access for tensioning may be more difficult, depending on how you place you router, for instance, if the back is against the wall.

    Other than these considerations, I can't think of anything else.

    Edward
    Last edited by Edward; 13-09-2017 at 09:19 AM.

  4. #4
    Other than these considerations, I can't think of anything else.
    I think you have answered your own question The belt tensioning is not something that is done often, having the spindle to be able to come over the front end, could be good.
    ..Clive
    The more you know, The better you know, How little you know

  5. #5
    Thanks, Clive. I think I'll go for rear pulleys, all being considered. I think the tensioning will be done by just sliding the motor downwards a little, when necessary.

    Drilling to the side of a long plate can be awkward, often requiring fixtures. Normally I use a little mill where the head can be swivelled 90 degrees, but it's still a bit of a hassle.

    Edward

  6. #6
    Quote Originally Posted by Edward View Post
    Thanks, Clive. I think I'll go for rear pulleys, all being considered. I think the tensioning will be done by just sliding the motor downwards a little, when necessary.

    Drilling to the side of a long plate can be awkward, often requiring fixtures. Normally I use a little mill where the head can be swivelled 90 degrees, but it's still a bit of a hassle.

    Edward
    Do you have a link to the thread where you saw it being discussed?

    Other things to think about are:
    Position of motors and length of cables back to control box (shorter could be preferable)

    If you tend to cut in one location on the machine for most jobs, or at least in one half of the machine, then a pulley mounted at the same end will reduce the amount of twist in the ballscrew on rapid changes of direction. This in turn gives a minor positioning error but I would guess this is very small and could be ignored on DIY machines.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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