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  1. #21
    Looks good but i have a general dislike of motors mounted on long tubes - not too stable and prone to loosening.

  2. #22
    Y axis motor is attached to the gantry end plate (which is now 15mm thick, 10mm just look to flimsy!) with 4 50mm long spacers.
    Have you thought about how you are going to tension the belt?
    ..Clive
    The more you know, The better you know, How little you know

  3. #23
    Quote Originally Posted by Clive S View Post
    Have you thought about how you are going to tension the belt?
    I was planning on slotting the holes in the gantry end plates so I could just slide the whole motor up and down.

  4. #24
    My first ever machine had 4 posts like that and it took a while to get them all the same length. I didn't have a lathe back then. If they are out a bit the motor will be skewed and the belt won't run straight on the pulleys.

    The other more popular option is to put the motor behind what is in your drawing the small orange box section, and run the belt horizontally out the back of the gantry, between the upper and lower beams. You just need a big L bracket to mount to and it is a bit more tucked out of the way.

    For your other question - there are lots of pulley engagement formulae around but you can tell by looking that you are OK there with ~180 degree contact.

    Make sure you have pulley / belt clearance should you ever want to do 1:2 instead of 1:1 to get more speed, and have adjustment in the motor plate to accommodate.


    On the overall design it will work fine, but do think through if the underslung ballscrews will be easy to set up and align. Imagine that the base frame cross members (which the ballscrew blocks mount to) is not perfect, and end up on a different plane to the rails. It will tend to bind the ballscrew at some point and you will have to shim something in the system.
    If you go the more traditional route with the ballscrews mounted down the side, driving the side members of the gantry directly (no underslung part), I think all the connections can be made with the appropriate 'slip plane' to get it aligned. This will quicker, cheaper and simpler to build and would be my preference.

    Up to you but just make sure you can visualise the adjustment process for any scenario if it is not perfectly built.

    If you are going underslung just to stiffen the gantry I'd put the efforts in on the gantry itself, e.g. plating across the back etc. (Not saying it needs further stiffening mind).
    Last edited by routercnc; 31-01-2018 at 09:51 PM.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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  6. #25
    I have a Clark mini lathe so getting them the same length should be easy.
    I did consider putting the motor behind the gantry... can't remember why I chose not to. I'm sure there was a reason. I'm gona look at this again cos it would be a nicer design.
    Thanks for the pulley info, I will take a look at the design formulas for reference anyway. They might come in useful one day.
    Last edited by diycnc; 31-01-2018 at 09:53 PM.

  7. #26
    The motor location is a no-brainer to me. Machine the gantry side to accept motor with a slot for adjustment and lengthen ball screw so goes thru side then put the belt on outside of gantry out the way from chips etc and put a cover over. Simple and neat.

    Pulley size is little small but nothing to do with teeth but because you won't have enough Boss left after machining for grub screws. This will then mean putting grub screws thru the teeth which isn't ideal.
    I find 20 teeth gives good balance leaving enough boss for M5 grub screws. Certainly no less than 18T.
    Last edited by JAZZCNC; 31-01-2018 at 11:25 PM.

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  9. #27
    That's a brilliant idea! Can't believe I missed that.
    Any suggestions how I could cut a pocket in the aluminium end plate? I currently only have hand tools, a pillar drill, small lathe, trim router, circular and jig saw, no cnc or mill.
    I guess I could just cut out a big slot in the aluminium end plate, big enough to fit the motor through. Bolt the motor to a thinner aluminium or steel plate, which is then bolted onto the end plate. No need to cut any pockets.

    Or I could just pay someone to cut them to me, but where's the fun it that!

    I didn't know the boss dimensions changed when pulley size changed. Will take a closer look at this later today.
    I would prefer to use taper lock pulleys on the motors but I can't find any that will fit my 8mm motor shafts.
    Last edited by diycnc; 01-02-2018 at 01:22 PM.

  10. #28
    Any suggestions how I could cut a pocket in the aluminium end plate? I currently only have hand tools, a pillar drill, small lathe, trim router, circular and jig saw, no cnc or mill.
    Have a look through Joes vids his machine is completely build with a few tools and a hand held router

    https://www.youtube.com/watch?v=22cC...-dWEjqhAPJw0Bz
    ..Clive
    The more you know, The better you know, How little you know

  11. #29
    Quote Originally Posted by diycnc View Post
    I would prefer to use taper lock pulleys on the motors but I can't find any that will fit my 8mm motor shafts.
    You won't find taper lock that go that small on teeth size. 32-34 is about smallest you'll find. Plus they are heavy so have lots of inertia which can live without on small motor.

    Like Clive says get the router out if want some pockets. It's easy done just go at it steady.

  12. #30
    Quote Originally Posted by routercnc View Post
    On the overall design it will work fine, but do think through if the underslung ballscrews will be easy to set up and align. Imagine that the base frame cross members (which the ballscrew blocks mount to) is not perfect, and end up on a different plane to the rails. It will tend to bind the ballscrew at some point and you will have to shim something in the system.
    If you go the more traditional route with the ballscrews mounted down the side, driving the side members of the gantry directly (no underslung part), I think all the connections can be made with the appropriate 'slip plane' to get it aligned. This will quicker, cheaper and simpler to build and would be my preference.

    Up to you but just make sure you can visualise the adjustment process for any scenario if it is not perfectly built.

    If you are going underslung just to stiffen the gantry I'd put the efforts in on the gantry itself, e.g. plating across the back etc. (Not saying it needs further stiffening mind).
    Thanks for the advice. The way i imagine it is the screws first need to be on the same plane as the gantry travel. With the current design this can be achieved just with shims. Then the screws need aligning to the axis. Hopefully there will be enough play in the holes in the BK supports to allow enough adjustment. If not i can simply drill over sized holes in the underside of the frame, and use either nuts inside the tube, or if i cant get a spanner in there make a small plate with 4 threaded hole. This will give me plenty of adjustment to compensate for the inevitable poorly assembled frame!

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