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  1. #1
    Hi,

    I am in the process of designing the bed for my CNC machine and would appreciate any guidance regarding frame dimensions and material choice.

    My plan is to weld a steel frame together with 10mm * 50mm plate welded to the sides of the upper rails, which will then be milled by a local machine company in readiness to accept the linear guide rails. They have quoted 800 to mill the side rails and drill all of the holes.

    Their machine is super accurate and will ensure that the rails are 100% parallel and level to each other, resulting in super accuracy. Whilst 800 is expensive it will save me the headache of getting the rails aligned

    My plan is to base it on the axyz 4000 series machine as shown below.

    Click image for larger version. 

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  2. #2
    First can I ask the main intended use.?

  3. #3
    Quote Originally Posted by JAZZCNC View Post
    First can I ask the main intended use.?
    The main use will be for machining timber panels for furniture and timber for boat making. I would, however, like to have the flexibility to be able to machine alloys as well, so having an accurate machine would be ideal.

    I don't want to use aluminium profile section as I think those machines have poor resale if you ever decide to build another one.

    Do you have any suggestions that might be of help ?

    Thanks

  4. #4
    Quote Originally Posted by flanagaj View Post
    The main use will be for machining timber panels for furniture and timber for boat making. I would, however, like to have the flexibility to be able to machine alloys as well, so having an accurate machine would be ideal.
    If it's mainly for wood then that sort of accuracy is not going to make an appreciable difference. 800 sounds a lot ... invest it in profile rails etc. How can you be sure that after the frame has been machined when you fix it to the floor it does not distort.

    Getting the rails parallel is not a problem - once you have the gantry mounted and put a couple of bolts in one rail the other will self align. Either that or you can use a DTI to align them by affixing it to one carrage with the needle against the other rail.

    Another way to get them parallel in the vertical plane is to mount them on (the right type of) epoxy. Pour the epoxy on the rail mounting surfaces with a channel (or several channels) in between and gravity will level it 'automatically' with very high accuracy.

  5. #5
    Quote Originally Posted by Jonathan View Post
    How can you be sure that after the frame has been machined when you fix it to the floor it does not distort.
    I too did think about this and came to the conclusion that as the machine is to be made from pretty substantial material it will not be able to distort. Do the large professional cnc machines get aligned up on site when they are delivered ?

    Quote Originally Posted by Jonathan View Post
    Another way to get them parallel in the vertical plane is to mount them on (the right type of) epoxy. Pour the epoxy on the rail mounting surfaces with a channel (or several channels) in between and gravity will level it 'automatically' with very high accuracy.
    I have read about this, but never did find out where the "right type of epoxy" can be sourced.

    I don't want the machine bolted to the floor, I just want it to sit on the levelled feet.

    Do you think that once a frame is constructed from 80mm * 80mm * 6mm box section and then machined it will still be able to distort ?

  6. #6
    80 x 80 x 6 box section can still distort. The size of the machine you are building will be rather heavy, 80 x 80 x 6 box section aint light. Unless you level it very well it will still move. If you decide to bolt it down then make sure it is perfectly level on its feet or you will pull it out of alignment with the bolts.

    Ian

  7. We would certainly be interested in hearing the personal experiences of anyone who's used epoxy et al to level the top rails of a larger frame. Our Mark-3 machine will be for 8' x 4' sheets. (That said, we're still assembling the bits for MK-2).

    Karl

  8. #8
    Quote Originally Posted by Web Goblin View Post
    80 x 80 x 6 box section can still distort. The size of the machine you are building will be rather heavy, 80 x 80 x 6 box section aint light. Unless you level it very well it will still move. If you decide to bolt it down then make sure it is perfectly level on its feet or you will pull it out of alignment with the bolts.

    Ian
    Do you think that is over sized ?

  9. #9
    Quote Originally Posted by Web Goblin View Post
    80 x 80 x 6 box section can still distort.
    Yep, anything will distort. It's a matter of how much and the effect it has.

    Heavy frame = good, as long as you don't have to move it!

    For a machine purely for woods it does seem a bit excessive, however you seem to want to use it for milling aluminium too in which case it pays to make it as strong as you can.

    What sort of tolerances do you require as that it what determines if machining the rail surfaces perfectly parallel is necessary? You can compensate for it perfectly well in software.

  10. #10
    Quote Originally Posted by Jonathan View Post
    Yep, anything will distort. It's a matter of how much and the effect it has.

    Heavy frame = good, as long as you don't have to move it!

    For a machine purely for woods it does seem a bit excessive, however you seem to want to use it for milling aluminium too in which case it pays to make it as strong as you can.

    What sort of tolerances do you require as that it what determines if machining the rail surfaces perfectly parallel is necessary? You can compensate for it perfectly well in software.
    Ideally, I would like to have an accuracy of at least 0.05mm. Worst case scenario I could stretch to 0.1mm, but no worse

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