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  1. #1
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    Jul 2007
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    36

    Exclamation Momus rebuild

    Hi folks I asked this sort of question on the Momus pages some years ago but no answers so now I have reworded it and hope someone can help.
    Want to convert to ball screw for X and Y.
    The x and Y axis are 700mm x 650mm Z is already a ballscrew.
    I have TWO Keeling Stepper motors which are currently driving timing belts for these two axis . These are model KL23H-284-35-4B.
    I can use these TWO for two ball screws on X and get another stepper altogether for Y. What would people suggest.
    My current thoughts on ballscrew choice would be 16mm with 5mm pitch or 10mm pitch. Which is recommended??
    I have a GECKO controller to drive TWO outputs to Y steppers on the upgrade I understand that is possibly ok but total current for both is limited to 3 amp. Again any comments . I am not sure if the standard Gecko off hand has a 4th driver which would solve the problem as I have no interest right now in any other 4th output.
    Any comments appreciated. Work is primarily thin ply MDF acrylics, occasional thin aluminium.
    Direct drive or timing belt drives to ball screws. Again what is preferred.
    Hope someone can help .
    regards
    Rayna

  2. #2
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    Jul 2018
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    3038

    Re: Momus rebuild

    Hi Rayna- working thru your Q's
    1) the current steppers are fine unless you want to draw more than 3A through the Gecko
    2) You could use 12mm as these screws are quite short. 5mm pitch will give you large forces but will be slower and 10mm will give you good speed but less force. Generally for a router 10mm is a good compromise
    3) By "Gecko" do you mean the Gecko 540? If you require a 4th axis into the future this means the G540 has to be replaced or there are ways to add this on I believe
    4) Direct drive is usually sufficient, This makes the assembly long and the motors usually overhang the machine. If room is tight then use a belt and reflex the motor above or to the side of the screw. If the design is OK for this (please show us a piccy) you can use belts to drive both sides from one motor then you only use 3 axes allowing the 4th to be free. This has compromises but maybe could work for you...

    What do you hope to achieve with the screw drive vs the belt drive? Peter

  3. #3
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    36

    Re: Momus rebuild

    Quote Originally Posted by peteeng View Post
    Hi Rayna- working thru your Q's
    1) the current steppers are fine unless you want to draw more than 3A through the Gecko
    2) You could use 12mm as these screws are quite short. 5mm pitch will give you large forces but will be slower and 10mm will give you good speed but less force. Generally for a router 10mm is a good compromise
    3) By "Gecko" do you mean the Gecko 540? If you require a 4th axis into the future this means the G540 has to be replaced or there are ways to add this on I believe
    4) Direct drive is usually sufficient, This makes the assembly long and the motors usually overhang the machine. If room is tight then use a belt and reflex the motor above or to the side of the screw. If the design is OK for this (please show us a piccy) you can use belts to drive both sides from one motor then you only use 3 axes allowing the 4th to be free. This has compromises but maybe could work for you...

    What do you hope to achieve with the screw drive vs the belt drive? Peter
    Thanks Peter,
    12 mm / 10 mm pitch sounds good.
    Yes Gecko 540
    Can easily use single motor to drive the two X shafts so no new stepper needed. Presume can use timing belt and pulleys for that .
    I have not had personal experience of running the machine myself as at the time I was too busy with other things and had lent it to a woodworking friend to use.
    Reason for considering is that he suspected it may be loosing steps in some way with timing belt drive.
    The last job my friend was running was making small wooden crosses about 10mm thick ~70 high and maybe 45mm wide with body widths of ~12mm. What was happening occasionally not with every one was that the long vertical leg below the cross arm was loosing width by about 4-5mm on one side. We are not tech savvy enough to identify the problem as it did not occur continuously with every cross but irregularly through a run that was cutting about 48 per sheet of material.
    So after that he bought a chinese cnc unit and I stored the Momus at back of my shed till now when retired I feel I should do something with it .
    I would be very interested in comments but on the computer side I am pretty useless. I enjoyed very much the challenge of the mechanical build in the first place.
    regards
    Rayna

  4. #4
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    Jul 2018
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    Re: Momus rebuild

    Hi Rayna- The belts are not the cause for loosing steps if correctly adjusted. I'd check everything mechanical in the machine before considering a change to screws. One thing I have had happen is that the grub screw onto the motor shaft flat comes slightly loose so it moves slightly when it changes direction. I don't use grub screws anymore I locktite the pulley to the shaft, never had trouble since... If I were to upgrade a Momus it would be to get proper rails either round or square... Peter

  5. #5
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    36

    Re: Momus rebuild

    Hi Peter. I am sure you are correct and firstly I should check out all the mechanicals before moving on.
    I spoke to my friend again and it is a few years back that all this happened so his memory of it is not as good as would help but contrary to what I said his memory of it was that while it cut numbers of the crosses without a problem, on occasions it would just not progress through the program but did random stuff. He tried all sorts of tweeks but did not seem to get on top of things so he went for the chinese machine which he has been very happy with. He feels there were too many areas where errors could compound with the home built Momus.
    So in a way I am not a lot further ahead and with my limited skills in the computer electronics area I might be hard pressed to have any confidence in doing anything correctly.
    In actual fact I might be better getting something that works from day one. I feel that with the Gecko 540 controller, its power supply and the Kelling steppers I have good items that could be reused. To go to a rebuild replacing both guide rails and maybe ballscrews would cost but that is not a worry for me now with funds in hand.
    When I look at what one can buy off the shelf one is totally confused with claims counterclaims and actual machine capabilities. The one key thing that everyone seems to be selling is machines for engraving in which I have no interest. Cutting plywood mdf acrylics itc up to maybe max 5mm is more my target.
    Once again any further comments appreciated.
    regards and thanks
    Rayna

  6. #6
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    Jul 2018
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    3038

    Re: Momus rebuild

    Hi Rayna- Don't spend anything pull the momus right down to nuts and bolts and rebuild. Will be fun and the machine will work once put together as best that it can be Plus you will learn about the electrons on the way... Peter

  7. #7
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    36

    Re: Momus rebuild

    Thanks Peter probably a good approach to take. Will get it out andtake a closer look and maybe move on from there.
    Many thanks for your help and comments.
    Rayna

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