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  1. #1
    If i wanted a cnc with a cutting area of 4' x2' what length rails and ball screws would i require for all axis. I like the look of the low gantry designs, i.e Jonathan's etc. I have decided to go with a frame made from steel box section. But that is as far as my knowledge goes. So plenty of help required and desired

  2. #2
    Hi Dean, What your asking is very hard to answer accurately without knowing the design and will change with different design.!
    That said I'm soon going to be building for someone a steel framed machine with very nearly the same dimensions.! . . . .So to give you an idea i've just quickly changed the Cad model to give the length you want, width was the same or slightly more anyway.

    With a design like the one in the pics below the X axis screw would be Approx 1400mm and the Y axis 825mm. The rail lengths would be approx 1475 and 850mm.
    The model is just at a very rough concept stage so nothing is aligned or setup and things like gantry sides will change shape, position etc with more work on the frame and more trimmings will be added like covers for screws and igus chain etc but it should give you an idea of how it would look.

    Every thing is 1/1 scale so motors, spindle etc are all correct and all materials can be got or cut from products that are available of the shelf, IE gantry sides (as can most of the gantry and Z axis) be got out of 200x20mm plate from Aluminium warehouse, 80x40x3mm Box section from local steel merchant etc. The adjustable bed is steel frame with KJN's 90x45 profile but could easily be replaced with MDF to save money.

    Hope this helps and just ask if you want to know anything.
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    Last edited by JAZZCNC; 03-01-2012 at 04:31 PM.

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  4. #3
    Thanks for that Jazz, that design is what i was thinking of. The Aluminium warehouse is also 1/2 hours drive away. How would i work out the cut lengths for the steel etc

    feel stupid now, the lengths would be the same as the rails

  5. #4
    Some good advice is get a decent cad program and start designing the machine before you start cutting anything.!
    It really does help with checking fit etc and finding dimensions etc.
    The time invested designing will be repayed as the build progress's because It helps keep the build on track and has time goes by having an accurate reference to look back upon really does pay back. . . . It's also a good motivator because you can visually see what your going to have at the end.:dance: (Amazing how several days or weeks of grinding,drilling etc can De-motivate.)
    Not only will it save you time but it will save you money because you'll not waste material making parts that don't fit or work how you thought they would.
    You can also work out accurately easily if several compnents can be got from a single length or stock or if you'll need an extra length.! . . . . Nothing worse than buying Stock you don't require when your on a budget.!!. . Equallly nothing worse than running short by 3mm because you "thought" it would fit.!! . . .If you use the suck it and see method Sod's law nearly always bites you when you don't need it.!!

  6. #5
    Am i right in thinking that 300mm rails and 300mm screw would be ok for the z

  7. #6
    Quote Originally Posted by deannos View Post
    Am i right in thinking that 300mm rails and 300mm screw would be ok for the z
    Draw it and you'll find out.

    It depends what travel you require, but it's probably fine. Ballscrew isn't necessarily the same lengths as the rails.

  8. #7
    Quote Originally Posted by Jonathan View Post
    Draw it and you'll find out.
    Fair enough, what is best to use, i.e free etc

    apart from pen and paper

  9. Not free but a very good CAD program for the money is ViaCAD 2D/3D V8 as it not only let's you design it but you can then extract 2D drawings from the model. I used it on my model and it really helped make designing and the build much much easier. Also I knew what materials where needed. Still ended up with a few tweaks here and there but that is better then major OS moment. Good luck.

    Michael

  10. #9
    Lots of people use google sketchup.

  11. #10
    Quote Originally Posted by deannos View Post
    Fair enough, what is best to use, i.e free etc

    apart from pen and paper
    Pen & paper is just as good if thats all you have, you don't need to be Norman Foster just have the abilty to draw lines and arc's to scale. Also think you'll actually find if you don't have any experience with Cad then it will probably be quicker.!! . . . . Thou you are going to have to learn Cad at some point because without it a CNC machine is pritty useless.:rofl:

    If you draw it 1:1 scale then you can use the drawings as templates for cutting and drilling.

    Can't stress how much easier it makes things having a good drawing, it doesn't need to be drawn to the very last detail but with key parts like Z axis then it really does help. . . . If you have plenty of money and can afford the "Cut it & see" route then go for it, other wise get drawing to save money.

    Ask if your not sure and need guideance but nobodys going to say you need exactly this length rail or this length screw because unless your copying there design exactly then really it's not possible.!

    At the very least you will have to give some idea of your want's and needs. IE Desired cutting area, Z travel, rail type, screw type etc.

    I'm more than willing to help you come to the final design for a machine, even help with cutting parts etc and I'm sure there will be others like Jonathan willing to make usefull helpfull suggestions but ultimately it's down to you and you that needs come too and understand the final design and components needed because your building it.! . . . . Nobodys likely going to do it ALL for you fully without plenty of beer tokens changing hands. (Unless your have 5'8" blonde nympo sister that likes fat bald yorkshire puddings.?? . . .In that case I'll be down shortly with the machine. .:rofl:)

    Get drawing then asking and don't buy or cut a thing untill your sure.!!

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