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  1. #41
    Just easier to draw it hanging out the front so you can see where it is

  2. #42
    I may have misread this but the two rails under the bed seem to give total support to the outside edges and none in the centre? As most of the cutting will actually tend towards the centre do you think this is a good idea?
    I have never quite figured out the optimum separation but there must be one

  3. #43
    Quote Originally Posted by Robin Hewitt View Post
    I may have misread this but the two rails under the bed seem to give total support to the outside edges and none in the centre? As most of the cutting will actually tend towards the centre do you think this is a good idea?
    I have never quite figured out the optimum separation but there must be one

    Mmm as pictured the bed would be made of 100x100 square hollow section so shouldn't flex too much. However liear rail is cheap so wouldn't hurt to add one in the middle.


    Just doing the numbers, using 100x100x5 shs @ 14.7kg per meter. The traveling 0 shape fixed but moving gantry design reqires 4.2m of tube per 100mm width. So for a 200mm wide traveling 0 it would weigh 120kg, heavy but just managable .


    The very tall normal machine of the same size would need 15m of tube which would weigh 220kg.

  4. #44
    Flex is not the real issue, right now the name of the game is minimising the overhangs -smileyface

  5. #45
    Had another idea and amazingly I found a CAD program I actually like, it's a miracle! It's not for everyone in fact it's probably some people' worst nightmare but it's right up my ally. Instead of using your mouse to click where you want something you type it out in a sort of programming language.
    http://www.openscad.org/


    This design is sort of in between a fixed and moving gantry. As a result the bed is lighter than a moving gantry design and the gantry is lighter than a fixed gantry design. What do you think?
    Click image for larger version. 

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    If your interested in this cad program you can recreate my drawing with this code
    Code:
    color("Azure") cube([900,1500,100]);//bed
    translate([38.5,0,100])color("grey") cube([22,1500,23]);//left bed rail
    translate([838.5,0,100])color("grey") cube([22,1500,23]);//right bed rail
    //
    translate([30,310,105.5])color("green") cube([40,80,34.5]);//left front Ccarrige
    translate([830,310,105.5])color("green") cube([40,80,34.5]);//right front Ccarrige
    translate([30,710,105.5])color("green") cube([40,80,34.5]);//left rear Ccarrige
    translate([830,710,105.5])color("green") cube([40,80,34.5]);//right rear Ccarrige
    //
    translate([0,300,140])color("WhiteSmoke") cube([100,100,1000]);//left front upright
    translate([800,300,140])color("WhiteSmoke") cube([100,100,1000]);//right front upright
    translate([0,700,140])color("WhiteSmoke") cube([100,100,1000]);//left rear upright
    translate([800,700,140])color("WhiteSmoke") cube([100,100,1000]);//right rear upright
    translate([0,400,140])color("WhiteSmoke") cube([100,300,100]);//bottom left front-back join
    translate([800,400,140])color("WhiteSmoke") cube([100,300,100]);//bottom right fb join
    translate([0,400,1040])color("WhiteSmoke") cube([100,300,100]);//top left fb join
    translate([800,400,1040])color("WhiteSmoke") cube([100,300,100]);//top right f join
    translate([100,300,1040])color("WhiteSmoke") cube([700,100,100]);//front left-right join
    translate([100,700,1040])color("WhiteSmoke") cube([700,100,100]);//back left-right join
    //
    translate([38.5,278,140])color("grey") cube([22,23,1000]);//front left Cgantry rail
    translate([838.5,278,140])color("grey") cube([22,23,1000]);//front right Cgantry rail
    //
    translate([30,260,410])color("green") cube([40,34.5,80]);//left front gantry carrige
    translate([830,260,410])color("green") cube([40,34.5,80]);//right front gantry carrige
    //
    translate([38.5,800,140])color("grey") cube([22,23,1000]);//rear left Cgantry rail
    translate([838.5,800,140])color("grey") cube([22,23,1000]);//rear right Cgantry rail
    //
    translate([30,805.5,410])color("green") cube([40,34.5,80]);//left rear  carrige
    translate([830,805.5,410])color("green") cube([40,34.5,80]);//right rear carrige
    //
    translate([000,160,400])color("Seashell") cube([900,100,100]);//front gantry
    translate([000,840,400])color("Seashell") cube([900,100,100]);//rear gantry
    //
    translate([0,198.5,500])color("grey") cube([900,22,23]);//front gantry rail
    translate([0,878.5,500])color("grey") cube([900,22,23]);//rear gantry rail
    //
    translate([310,190,505.5])color("green") cube([80,40,34.5]);//left front Ccarrige
    translate([610,190,505.5])color("green") cube([80,40,34.5]);//right front Ccarrige
    translate([310,870,505.5])color("green") cube([80,40,34.5]);//left rear Ccarrige
    translate([610,870,505.5])color("green") cube([80,40,34.5]);//right rear Ccarrige
    //
    translate([300,160,540])color("Honeydew") cube([400,100,100]);//front spindle
    translate([300,840,540])color("Honeydew") cube([400,100,100]);//rear spindle
    translate([300,260,540])color("Honeydew") cube([100,600,100]);//left spindle
    translate([600,260,540])color("Honeydew") cube([100,600,100]);//right spindle
    Last edited by Rufe0; 10-01-2016 at 02:16 AM.

  6. #46
    Had another idea and amazingly I found a CAD program I actually like, it's a miracle! It's not for everyone in fact it's probably some people' worst nightmare but it's right up my ally. Instead of using your mouse to click where you want something you type it out in a sort of programming language.
    http://www.openscad.org/
    I used to use openscad a few years ago for 3D printing I think then it only produced stl files also it wouldn't import much into it or output dxf etc.
    ..Clive
    The more you know, The better you know, How little you know

  7. #47
    Hello everyone
    Wonder if I can get your opinions on this?

    I think making this out of 100x100x5 tube would be too weak. It would weigh 100kg so making it thicker isn't really an option. I think 150x100x3 would flop around and generally not be very rigid. So that pretty much leaves me with the option of making it in two halfs and bolting it together. Something like this

    Click image for larger version. 

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    This drawing is of 100x100x10 with 20mm connecting bits, or 25mm. Each half would weigh 77kg without connecting bits, near 100kg with them.

    I'm thinking bolting it together like this, red circles are bolts.

    Click image for larger version. 

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    Each connector would be welded at one end to C shapes and bolted at the other. Then they would be bolted to each other.

    I don't think it would be solidly connected enough though. I think the 0.1mm better deflection gained from using the 10mm wall tube instead of 5mm would be lost in the less than solid connection between the two.

    I think it would probably be fine if the cutting force is straight front to back or side to side but if it's at all diagonal then there would be all sorts of twisting and skewing forces that would ruin accuracy and rigidity.

    I'm just struggling to find a way to make the thing really rigid enough and still light enough for two people to carry when disassembled.

    Any ideas or thoughts? Thanks

  8. #48
    Just realized how todo it much better than this using solid flat plate bolted together to make a custom box section, kinda like a cardboard box, don't know why I didn't think of it earlier, I've not been sleeping right....will do some drawings soon.

  9. #49
    I have always thought that the best way to make one of these beasties would be to start with a sheet of 3 mm steel and rent some time on a 2kW laser. I'd go for 3 mm because it has a bit more flex in it so you can key in a few good bends to make it super rigid

  10. #50
    I'm going down the rabbit hole a little bit, Alumina Porcelain has a specific modulus, stiffness to weight ratio of between 4.8 and 16(imperial units). Steel is about 4.1 and aluminium isn't much better. So Alumina Porcelain is potentially 4 times as stiff per kilogram....

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