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  1. #1
    Member kaldis12's Avatar
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    Default DIY VMC Opinions

    Hey guys,
    What are your thoughts about this build?

    The workspace is 300x250x250mm. I would use 20mm linear guide on all axes (how strong precompression?) and 20mm 5mm pitch (2005) ballscrews with antibacklash nuts on all axes. The plates would be rotary ground steel plates. The Y axis "holder" would be filled with epoxy granite mix. Planning to use ER20 watercooled spindle. The motors are nema 34 servos.
    Do you have a reccomended spindle or different collet type?
    What should I improve on the design?
    What controller should I use?
    I attached the pics.

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    Attached Thumbnails Attached Thumbnails DIY VMC Opinions-vmc-jpg   DIY VMC Opinions-vmc2-jpg  


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    Default Re: DIY VMC Opinions

    It desperately needs some diagonal bracing to prevent the uprights flexing under load.It also seems considerably overpowered with those NEMA 34's,they will just bend it further and faster than a more modest motor.There are some apps out there for Android phones that will calculate the force generated by any motor you specify with the thread you select.I suggest you run the figures and see what kind of force you need to accommodate.If the CAD package you use has a FEA capability,run it to find the weak points with that kind of force applied and then improve it.A couple of tubular steel braces will almost certainly cost less than five or six buckets of epoxy based filler and will take less time to have ready-once it becomes clear where they are needed.



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    Default Re: DIY VMC Opinions

    Google VMC frames and have a good look at them.

    Look at rail spacing, proportions etc.

    Nothing should be a flat plate.

    To be blunt, your design is going to be very weak. Start again.

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    Default Re: DIY VMC Opinions

    I made a second version, what do you think? It has a 400x300x400 work area. X axis would be about 80kg
    The X and Z axis looks waay better, but I'm not sure about the Y axis. Maybe I should made it into a Y shape or maybe I should reinforce the back of it too?



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    Default Re: DIY VMC Opinions

    I think it needs to be shown when you are ready for our comments and it isn't visible at present.



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    Default Re: DIY VMC Opinions

    sorry, for some reason it didn't upload it. Here ya go

    Attached Thumbnails Attached Thumbnails DIY VMC Opinions-vmc3-jpg  


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    Default Re: DIY VMC Opinions

    Don't build that.The upright part looks absolutely massive and yet has no lateral support and the height increases the leverage from lateral movement.The extreme length of the spindle mounting bracket gives a high torque loading to the base of the upright and the lower web of the motor mounting bracket may well foul the piece being worked on if you need to produce a deep feature on the side away from the column.It does look like some of the components are now of a size that will give some rigidity,now you need to go through the rest of the mechanism to bring it all up to that level.



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    Default Re: DIY VMC Opinions

    If I improve the Z axis, the upright part and the mounting bracket it would be okay? Do you have any good idea how to mount the spindle to the upright part? It is about a 210mm long section.



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    Default Re: DIY VMC Opinions

    My reaction is that if you are seeking the challenge of building a machine,you have made a start on the process.There will need to be several more iterations before the design is able to meet your expectations.Did you calculate the force that the leadscrews will generate for the motors you wish to use?I have doubts that the construction you are proposing will maintain is shape under even a quarter of that load.Additionally,high speed machining of aluminium is a specialised field-do you have experience of it?

    If the intention is to make components,rather than the intellectual challenge of machine building,I suggest you buy a benchtop mill and equip it with steppers as the machine will have the rigidity and will have been made fairly accurately.If you were to really go to town and add ballscrews,it could be a very useful thing to have.With the advantage that you could use the machine in manual mode to make the brackets and other parts you might need.



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    I did some calculations and I based most of the drawing on that.
    Its more of a challange to myself as I have access to other bigger mills. A conversion seems to easy for me
    Quote Originally Posted by routalot View Post
    My reaction is that if you are seeking the challenge of building a machine,you have made a start on the process.There will need to be several more iterations before the design is able to meet your expectations.Did you calculate the force that the leadscrews will generate for the motors you wish to use?I have doubts that the construction you are proposing will maintain is shape under even a quarter of that load.Additionally,high speed machining of aluminium is a specialised field-do you have experience of it?

    If the intention is to make components,rather than the intellectual challenge of machine building,I suggest you buy a benchtop mill and equip it with steppers as the machine will have the rigidity and will have been made fairly accurately.If you were to really go to town and add ballscrews,it could be a very useful thing to have.With the advantage that you could use the machine in manual mode to make the brackets and other parts you might need.




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