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  1. #1
    Hi All,

    I have been reading this forum with interest and busily designing my CNC machine.

    It will comprise of a steel frame, steel gantry and aluminium Z axis.

    I want it to be as accurate as possible and will be cutting acrylic, plastic, wood and hopefully light aluminium.

    Over all the machine size will be 2600mm x 1500mm (8' x 5') with a cutting area of 2200mm x 1150mm (7.5' x 4').

    I have already purchased 2500mm linear rails for the X axis and will mate them to dual HGH20 linear blocks on each side.

    The Y axis will use linear rails with HGH20 blocks also.

    I have read with interest the threads that use bolted top rails for the X axis and I am thinking of using epoxy to level the top of the rail between the linear rail and the top rail.

    I will have a rack and pinion system on either side of the X axis mated to NEMA34 stepper motors. I am going to use the R&P drive systems from CNCRouterParts.com

    Here is the frame design as it stands at the moment:





    The Gantry will be made from a 250mm x 150mm RHS steel beam and I am going to add a flat plate inside the bean to strengthen it.

    I am working out whether to use a ballscrew on the gantry or to use a R&P system here as well.

    Here it is:





    I would like to hear peoples opinions on the frame as this is what I will weld up first.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
    Hi,
    IMO:
    - Dont add plate inside, add it at the back and bottom if you feel that its necessary
    - Use ball screws as much as possible if budget permits it. So maybe even rotating ball nuts for both sides of the gantry.
    - Add some more short supports left and right, 3 each side is too low for such long rails

    Good luck with the build!
    project 1 , 2, Dust Shoe ...

  3. #3
    Ok, here is my updated table design with the extra supports in place.

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  4. #4
    Hi,
    when i said above for the plates i meant the gantry.

    What would be the square steel box profile size? I calculated it many times and for steel machine/this size especially/ is best to use bigger profile 100x100x3 or 4mm and simplify the structure. I say always 100x100 as it is the max that could be handled and cut at home using dry saw or small band saw.
    The benefits are:
    -simpler
    -easy to cut at home
    -easier to solder
    -stronger
    -less metal for the same strength so cheaper

    You could read more here and see changing the table design leads to substantial savings http://www.mycncuk.com/threads/5302-...highlight=tony

    In fact if you have the means the bigger is better here.
    project 1 , 2, Dust Shoe ...

  5. #5
    Quote Originally Posted by BrentonSpear View Post
    Ok, here is my updated table design with the extra supports in place.
    I personally would not put a rail all around the bottom and I would add triangulation in.

    I would have it sitting on say six legs, that way it would be a lot easier to set up on an uneven floor. Also make it out of 4mm or 5mm box section then you will have enough thread depth for fixings.
    .
    It might be worth thinking about having heavier cross rails and ditching the centre supports to be able to use the underneath to store sheet materials. ..Clive

  6. #6
    Hi Guys,

    I was looking at using 50mm x 50mm x 4mm SHS steel tubing for the frame.

    Silyavski, that is an interesting thought. I suppose I could do it in 100x100x4mm SHS. I will have to do the price calculations. I am planning to get all the pieces cut to the required lengths at the place I buy the steel so the size of the SHS is not really an issue.

    Clive S, I had always planned to add feet to the frame.

    Here is the updated design with the feet in place.



    For the gantry I am going to look at how I get a ball screw between the rails of the Y axis.

    I think I will put an I beam inside the RHS beam and then remove material to make a void. I have seen other person do this and it looks doable.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. #7
    What sort of span will I get with a 100x100x4mm beam? Could I get the full 2500mm?

  8. #8
    I have had a rethink on the steel size and now modelled it on 75x75x4mm SHS.

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  9. #9
    Add some more inner pieces for the worktop area and you have it nice and clean
    project 1 , 2, Dust Shoe ...

  10. #10
    Quote Originally Posted by BrentonSpear View Post
    I have had a rethink on the steel size and now modelled it on 75x75x4mm SHS.
    That is much better now with the triangulation bits put in and heavier steel section. Good luck with the build. ..Clive

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