1. #1
    Edward's Avatar
    Lives in London, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 0-1 years. Has a total post count of 95. Received thanks 2 times, giving thanks to others 0 times.
    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
    Edward's Avatar
    Lives in London, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 0-1 years. Has a total post count of 95. Received thanks 2 times, giving thanks to others 0 times.
    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
    Edward's Avatar
    Lives in London, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 0-1 years. Has a total post count of 95. Received thanks 2 times, giving thanks to others 0 times.
    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

  7. #7
    Edward's Avatar
    Lives in London, United Kingdom. Last Activity: 13 Hours Ago Has been a member for 0-1 years. Has a total post count of 95. Received thanks 2 times, giving thanks to others 0 times.
    Quote Originally Posted by routercnc View Post


    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.

    Thank you. I tend to read the forum posts from all over the place, using the search function for whatever interests me. I just read and keep it in my mind, I do often bookmark, but I have hundreds of bookmarks and trying to find the right one eludes me;)

    I think I intend to use the router for larger pieces, so they would tend to be centred on the bed, no area being predominant. For the smaller pieces I think I will tend to use my milling machine.

    Yes, I will seek to minimise the length of cabling to the control box. Initially I thought of placing it under the table, rather than fixed to the wall, but I have to think of the pros and cons about that one. One thing is certain, the VFD will be separate from the control box.

    Edward

  8. #8
    If your machine will end up in a static location where all round access might be a problem aim to locate electronics, drives and motors where not only will they not be subject to cutting debris but where they will be accessible for service and repair,

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

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