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  1. #11
    PAULRO's Avatar
    Lives in LIMERICK, Ireland. Last Activity: 3 Weeks Ago Has been a member for 4-5 years. Has a total post count of 178. Received thanks 2 times, giving thanks to others 198 times.
    I could go with a heavier extrusion if that would aid the machining of plastics and aluminum (light gauge) from time to time. i have a choice of extrusion for the gantry ( length 1610 mm ) either 100 x 50 , 4.18 kg/m, 120 x 40 , 4.35 kg /m or 120 x 40 , 6.8 kg /m. i don't know if that would make for a better or worse situation.

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    the images above show the gantry attached. i have yet to spec motors so haven't any motors mounts designed. i'm currently getting through Irvings tutorial on motor specs. what a great read!! i'm hoping nema 23s 3nm will do the job , by the way if i do go with these motors should i go for the heaviest i can get? any thoughts on this and the gantry extrusion choice would be appreciated.
    Last edited by PAULRO; 05-08-2014 at 10:12 PM. Reason: MISSING IMAGE !!!

  2. #12
    PAULRO's Avatar
    Lives in LIMERICK, Ireland. Last Activity: 3 Weeks Ago Has been a member for 4-5 years. Has a total post count of 178. Received thanks 2 times, giving thanks to others 198 times.
    by the way i'm going to use timing belts to connect to the ballscrews

    Paulro

  3. #13
    100x50 will be fine but if possible get the HD version.

    3Nm motors will work ok with 16mm screws but with 20mm you'll need to slow things down due to extra inertia so you'll get lower rapid feeds.
    You'll want 10mm pitch which will be more suited to wood and plastics. Now if you use 20mm pitch screws and gear 2:1 ratio then you will still get same feed rates as 10mm pitch with 3Nm motors but with a couple of nice advantages.?
    The ratio halfs the speed 20mm pitch gives but this gives same feed and resolution as 10mm so we get same speed but with half the screw speed but at same time doubles the motor torque. Lower screw speed means less chance of whip on long screws so it's win win.!



    You'll need to run the motors around 70Vdc on decent drives to get best from them.

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  5. #14
    These are the motors I used, they perform well.
    http://www.cnc4you.co.uk/index.php?r...product_id=367
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

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  7. #15
    PAULRO's Avatar
    Lives in LIMERICK, Ireland. Last Activity: 3 Weeks Ago Has been a member for 4-5 years. Has a total post count of 178. Received thanks 2 times, giving thanks to others 198 times.
    i'm going to put this m/c in my garage and that has a 6 ^2 twin and earth supplying the fuse board. it has ELCB. protection and an MCB for lights and MCB for sockets which supply a freezer, washing m/c and dryer in a separate room at the back. am i exceeding the supply with a m/c spec of this size? would anyone know the amperage required for a build of this spec.?

    crisis averted, i 'm told 6mm2 is good for 35 amps. should be fine, i hope!!!
    Last edited by PAULRO; 06-08-2014 at 04:45 PM.

  8. #16
    My shed is supplied by 6mm^2 armoured cable, I have a machine with 4HP motors and a powerfull dehumidifier, plus other smaller machinery. This works because there's only me in there so there are only 2 things at most operating at the same time.
    I keep meaning to measure the current taken but as yet I've not found my clamp meter.
    Last edited by EddyCurrent; 07-08-2014 at 10:28 AM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

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  10. #17
    PAULRO's Avatar
    Lives in LIMERICK, Ireland. Last Activity: 3 Weeks Ago Has been a member for 4-5 years. Has a total post count of 178. Received thanks 2 times, giving thanks to others 198 times.
    originally i designed around 16 mm x 10 mm ballscrews for X (1440 long) and y ( 1395 long) and 16mm x 5mm for z . i know from reading your previous posts that the length is critical or rather going over a certain length will almost certainly introduce whip at high speeds. i would like at some stage to tackle a Mayan calender and so i'm curious about resolution if i go with a 20 mm pitch. I'm not sure also about the amount of clearance i should leave between ballnut and bearing blocks either end. is there a standard clearance that i should factor in ? i have left 15mm either end but i'm not sure if this is enough.

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    i could also use nema 23 4Nm motors instead of 3Nm. (courtesy of Eddycurrent ) would the same psu ,motor drivers , smooth stepper, break out board etc. do for both? just trying to get a handle on the cost of everything required is a job in inself!!!!
    Last edited by PAULRO; 07-08-2014 at 12:05 PM.

  11. #18
    At this length then go with 16mm you'll be ok, 16mm will allow slightly faster acceleration due to less inertia. Resolution with 20mm isn't a problem because the ratio effectively makes it same as 10mm and even with 1:1 ratio 20mm res you'd still have enough to cut the mayan calender.

    There's very little between the 3Nm and 4Nm motors in terms of performance so you wouldn't really see much differance. Either will work fine with what your planning to use. Just run them around 70Vdc and you'll be fine.

    With bearing blocks/ballnut then all you need is to leave a enough clearance in case you over run limits. In which case the limits should stop the machine so you need enough clearence for the over run. That said your better fitting hard stops in case of over run and have the bearing blocks just past these.
    To be honest I wouldn't sweat over it you can control this with adjusting limits and they take a fair old bang to damage anyway so worst you'll do is knock something out of alianment.

    Let me just say if your at the point of planning in cad to this level of detail then your wasting time that could be better put to use building the machine because in reality you'll more than likely to see a better place to put them on the actual machine.!! . . . . . Time to put the pencils down and pick up the tools.

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  13. #19
    PAULRO's Avatar
    Lives in LIMERICK, Ireland. Last Activity: 3 Weeks Ago Has been a member for 4-5 years. Has a total post count of 178. Received thanks 2 times, giving thanks to others 198 times.
    it's time to put the overalls on o.k i should have steel middle of next week so i'll be fighting iron the following weekend. i'm just gathering the most info before i start into the build. i will be missing in action in the near future for a couple of weeks so i'd rather take time at this stage and plan it out . having said that i have enough info to get me up and running.
    Last edited by PAULRO; 07-08-2014 at 02:20 PM.

  14. #20
    Just for the crack, keep a spreadsheet of everything you buy and the cost, maybe categorise as 'mechanical', 'electrical', 'sundries'
    Last edited by EddyCurrent; 07-08-2014 at 07:55 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

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