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  1. #1
    Fairly new here but I've finally got started on my design. The machine will be used for cutting ally, tool steels and other metals, it may do the odd bit of timber/MDF/plastics.

    I'm hoping to get a working area of around X1200 - Y700 - Z250 so obviously it'll need to be strong.

    The frame is 80 x 40 x 4 steel box section, I've not drawn the stand yet but it will be constructed of the same.

    The gantry sides are 800 x 300 x 25mm Ecocast. They will be better supported than currently drawn, some good old viagra bits to be added . The crossbars are currently drawn 100 x 50mm. I'm hoping I might get away with some ally extrusion to try and keep the weight down but not if it's going to compromise the strength too much.

    I'm hoping I can afford HIWIN RG Series linear guides @ 25mm for the Y and possibily 20mm for the XZ.

    I've thought about having 2 linear guides per side of the Y axis, top and bottom. Overkill do you think?


    Any thoughts on the design so far? I'm not the sensitive type so fire away.

    Cheers
    Ian
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  2. #2
    Quote Originally Posted by IanS1 View Post
    Fairly new here but I've finally got started on my design. The machine will be used for cutting ally, tool steels and other metals, it may do the odd bit of timber/MDF/plastics.
    This design won't cut Tool Steel or Mild Steel it's absolutely no where near strong enough. It will only just about handle Aluminium.

    If you want to cut Tool steel or any Steel then I'd suggest converting a Milling machine or at the very least build a Moving table machine and massively beef up the frame.
    A moving gantry machine is not the right choice and the Gantry and frame would need to be 5X stronger than what you have designed and then require the correct spindle.

    The twin rails while adding some extra support in one area actually weaken the machine in another has the rails they sit on can no longer be supported and thr frame work between them would need to be made very strong with lots of triangulation braces. You could gain just has much support and save money while increasing machine strength with just one set of rails/bearings by making the bearing spacing much wider. Obviously this would require the machine to slightly longer to achieve the same cutting area but would be far better.

    Honestly scrap this design or heavily redesign and beef up if you want to cut any Steels other than Alu.!!

  3. #3
    Perhaps I'd better kurb my enthusiasm for cutting tool steel then Jazz, to be honest I'd be happy cutting ally.

    Right, so the 2 linear guides either side wouldn't be of any real benefit. That's good, that'll save me a few quid and hopefully make the overall design easier.

    What about the linear guide width, 25mm OK? Bearing distance, there's about 105mm between the ends at the moment. Would you recommend at least doubling that?

    Thanks for your input.

  4. #4
    Would skinning the frame around the table with some 5mm thick sheet steel beef it up enough or would I need some angular trusses in between the uprights and base cross bars too? I was going to skin the inside around the table with some sheet steel anyway to help contain the chips.

  5. #5
    Quote Originally Posted by IanS1 View Post
    What about the linear guide width, 25mm OK? Bearing distance, there's about 105mm between the ends at the moment. Would you recommend at least doubling that?
    when you say 25mm I suppose you mean Rail not carriage width.? If so then yes that will be fine if your using supported round rail but massive overkill if using profiled rails like Hi-wins. 20mm will be fine for profiled, even 15mm will handle far more load than you'll throw at them but 20mm carriages workout easier to use has they larger and suit better.

    To be honest the Min/MAX distance for separation on Y axis( Which I call Z axis) will depend on several factors like number and location of ball-screws and rail used. 300mm total bearing plate width will be fine in most cases and less if using profiled rail and twin screws close to the bearings. 200mm will even work if the gantrys strong.

    Regards the gantry then you need to seriously beef up this area with bracing. I'd also use wider stronger Cross beams between gantry sides.

    Skinning is ok for containing chips and looks etc but wouldn't rely on it for strength and the down side being it's very resonant and you want to avoid resonance if possible.
    Stronger base frame work is the best way then skin for cosmetic reason if you feel the need.!

  6. #6
    D.C.'s Avatar
    Lives in Birmingham, United Kingdom. Last Activity: 05-01-2016 Has been a member for 4-5 years. Has a total post count of 326. Received thanks 30 times, giving thanks to others 24 times.
    Quote Originally Posted by IanS1 View Post
    The gantry sides are 800 x 300 x 25mm Ecocast. I'm hoping I might get away with some ally extrusion to try and keep the weight down but not if it's going to compromise the strength too much.
    Can I ask why you went with ecocast?

    I don't think ecocast is structurally any stronger than 6082, (Jazz can probably confirmor refute this) it is just precision ground which is useful for mounting rails on but not required for the gantry sides. With the dimensions you provided, 6082 from aluminium warehouse would cost 90 +vat each as opposed to 125 +vat each for ecocast.

    Edit to add, don't worry too much about the weight of the gantry, there is a really good spreadsheet here that allows you to play with figures and a few extra kgs has very little effect.

    http://www.mycncuk.com/forums/faqs-p...do-i-need.html

  7. #7
    Quote Originally Posted by D.C. View Post
    I don't think ecocast is structurally any stronger than 6082, (Jazz can probably confirmor refute this) it is just precision ground which is useful for mounting rails on but not required for the gantry sides.
    Yes and no really it's not structurally stronger but it is more stable has it's cast not rolled, and yes it's precision ground. That said your still correct it's a waste for things like gantry sides etc where ground plate isn't required.!!. . . . Use it for bearing plates and Z axis mostly the rest will be fine with normal plate.

  8. #8
    Quote Originally Posted by JAZZCNC View Post
    when you say 25mm I suppose you mean Rail not carriage width.? If so then yes that will be fine if your using supported round rail but massive overkill if using profiled rails like Hi-wins. 20mm will be fine for profiled, even 15mm will handle far more load than you'll throw at them but 20mm carriages workout easier to use has they larger and suit better.

    To be honest the Min/MAX distance for separation on Y axis( Which I call Z axis) will depend on several factors like number and location of ball-screws and rail used. 300mm total bearing plate width will be fine in most cases and less if using profiled rail and twin screws close to the bearings. 200mm will even work if the gantrys strong.

    Regards the gantry then you need to seriously beef up this area with bracing. I'd also use wider stronger Cross beams between gantry sides.

    Skinning is ok for containing chips and looks etc but wouldn't rely on it for strength and the down side being it's very resonant and you want to avoid resonance if possible.
    Stronger base frame work is the best way then skin for cosmetic reason if you feel the need.!
    Yes, 25mm profiled rail. I'll look at 20mm instead. When you say twin screws, do you mean one either side? If yes, that is my intention, driven by a single motor using pulleys and belts.

    Yes, the gantry need some serious beefing up and is in no way finished in the drawing. I'll do some more work on it and post again.

    With regards to the resonance, I know some folks have used kiln dried sand to fill the box section but has anyone used sound deading materials stuck to the back of the skinning to help with resonance control? I have some sheets of a bitumen based damping mats which work very well for killing resonance. More info here: Bitumen Based Damping Mats [01] - 0.00 : SoundProofing Services, Sound Insulation, Acoustic Insulation, Acoustic Foam, Acoustic Panels

  9. #9
    No particular reason for the Ecocast, 6082 it is. Thanks for the motor sizing link D.C., be useful that.

  10. #10
    Being fairly new myself I tend not to be to much help when it comes to machine design but why don't you look at buying a proper mill & possibly converting it to cnc if you want to cut mainly aluminium & other metals. Would seem like a far better investment for what you want a machine to do.

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