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  1. #1
    Hi all

    i am not new to cnc, i have built a small version once before from mdf but scrap it

    i now need a requirement 8 x 4 cutting area actual size will 1500mm x 2500 with 450mm z axis for carving vac form plugs, prominently used for wood, ply, etc and for cutting alloy sheet to 12mm, where possible, plastics, foam etc basically an all rounder!

    i will be starting this build in march, most of the stuff is on order and awaiting delivery

    build consist of

    hiwin/equivalent rails all round
    4 nema 34 motors kit with breakout and stepper drivers 1600 oz
    rack and pinion, - near help hear please with mounting brackets and gear reduction ideas????
    2.2kw water cooled spindle er20 with vfd, but looking into a 3kw

    this is where i have dilemma, i am not sure what to build the y and x base from as i need as much rigidity as possible to cut alloy/metal sheet

    welded steel box for the base (x) ali on verticals

    all from 8020 extrusion ( x and Y)

    a hybrid of steel and 8020 and ali y/z verticals

    and optimal height of gantry from table? as i need to be able to carve plugs up to 125mm in height from router tip

    what grade/thickness of ali to use for the y/z gantry? and ali thickness

    and help hear would not be rejected!

    my main concern is frigidness of the gantry

    i am also looking for volunteer/pay to help with cnc parts to be cut, i can help with any related IT issues as i am an IT engineer/Admin, no charge?

    look forward to hearing from you all and all the suggestion and advice

    would be great if i could meet up, or skype, i don't mind travelling, i live in Newark Notts

    i will be posting design after i have got some advice

  2. #2
    forgot if any member got any spare parts to sell or swap let me know, if the fit my needs, i will buy/swap

  3. #3
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    this is what i had in mind for the gantry y axis after do some basic calcs and using the spread sheet on here

    the deflection for y and z had a tolerance of 0.054, this being 2 x 4 " ali u channel and 1 6 " channel with y axis = to 1500mm but this may get reduced to 1350mm this may be wrong

    my calcs may be wrong as i may have use the ss in the wrong way

    please put me right

    ric

  4. #4
    Good to see someone using the spreadsheet. You'll find that if you change to similar size box section the deflection due to bending will be similar, but the bending due to torsion will be substantially lower. That's because the torsional stiffness of a channel cross section is very poor. Also put the rails for the Z-axis on the plate that moves up and down, so swap them round. It's much stronger this way since the distance between the supporting bearings and the tool is minimised. The best thing you could do to that design is loose the tall gantry sides, as they're invariably weak compared to the machine frame.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  5. #5
    Quote Originally Posted by Jonathan View Post
    Good to see someone using the spreadsheet. You'll find that if you change to similar size box section the deflection due to bending will be similar, but the bending due to torsion will be substantially lower. That's because the torsional stiffness of a channel cross section is very poor. Also put the rails for the Z-axis on the plate that moves up and down, so swap them round. It's much stronger this way since the distance between the supporting bearings and the tool is minimised. The best thing you could do to that design is loose the tall gantry sides, as they're invariably weak compared to the machine frame.
    i take on board the board the issue of u channel and move over to box are recommending ali box on the y vertical as well

    the z axis is one i pick off the net to try the nema 34 motor to see where i could put the pinion drive? my version is similar but to take a nema 23 or 34

    the z axis i am building is using hiwin rails and a lead screw set up

    can you send me a photo the z axis u spoke about please or threads

    on the height, i need to clear 6 " 150mm from tip of router to base and some of what we intend to d, is carve forming plugs, ie engine cowls what do you suggest? as this cnc is going to be used got mixed materials,

    hope to speak soon


    ric
    Last edited by ciscoeuk; 29-01-2013 at 08:30 PM.

  6. #6
    hi all this is an update of build i am in the design process stage here's what i been up to!

    the cnc base (bed) is steel constructed from 75mm, 50, & 25mm steal box

    i would like your thoughts please and weather this is up to the task?

    if anyone wants anything welding in steel from Pm a line, not to bad at welding, new 200 amp Welder on its way

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    have a look

    all welcome to comment
    Last edited by ciscoeuk; 30-01-2013 at 02:24 PM.
    richard armstrong

    building 8x4 cnc all rounder, 2nd build.... major headache....LOL

  7. #7
    Not a bad start, but a few changes will make it a lot easier to construct and stronger. The most important factor is how do you intend to fix the box section for the bed (25mm) to the rest of the frame? It looks like it's just welded on at the moment, which makes the bed nice and strong, but the issue is with such a large Z-axis (450mm) you want to be able to adjust the height of the bed. The general idea is for sheet material you put the bed high up, so where it is in your drawing, then for the occasions where you need more Z-travel you drop it down. This is easy enough to do if you drill a series of holes in the 6 vertical pieces, support the cross pieces for the bed on two 8' long prices of box section, then attach them to the frame with M12 bolts. If that's not clear then look at my build log. You've got no chance of cutting 12mm aluminium and having 450mm Z-travel, without having an adjustable height bed.

    It'll be a lot easier to make if you use 50mm box section, or something bigger than 25mm, for the bed and use less of it. Also add in some diagonal pieces to the main frame since without them it will skew relatively easily.

    Since you want to use this for cutting aluminium, if only occasionally, I wouldn't use rack and pinion since the resolution and rigidity will be worse than with ballscres. You can easily use a ballscrew and 3Nm nema 24 motor on the 1500mm axis, however to use ballscrews on the 2500mm axis requires a large ballscrew and big motors, or rotating nuts.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  8. #8
    Quote Originally Posted by Jonathan View Post
    Not a bad start, but a few changes will make it a lot easier to construct and stronger. The most important factor is how do you intend to fix the box section for the bed (25mm) to the rest of the frame? It looks like it's just welded on at the moment, which makes the bed nice and strong, but the issue is with such a large Z-axis (450mm) you want to be able to adjust the height of the bed. The general idea is for sheet material you put the bed high up, so where it is in your drawing, then for the occasions where you need more Z-travel you drop it down. This is easy enough to do if you drill a series of holes in the 6 vertical pieces, support the cross pieces for the bed on two 8' long prices of box section, then attach them to the frame with M12 bolts. If that's not clear then look at my build log. You've got no chance of cutting 12mm aluminium and having 450mm Z-travel, without having an adjustable height bed.

    It'll be a lot easier to make if you use 50mm box section, or something bigger than 25mm, for the bed and use less of it. Also add in some diagonal pieces to the main frame since without them it will skew relatively easily.

    Since you want to use this for cutting aluminium, if only occasionally, I wouldn't use rack and pinion since the resolution and rigidity will be worse than with ballscres. You can easily use a ballscrew and 3Nm nema 24 motor on the 1500mm axis, however to use ballscrews on the 2500mm axis requires a large ballscrew and big motors, or rotating nuts.
    JONATHAN
    thanks for the advice and taken on board,

    i have decided to cut the z axis height down to 400mm ballscrew as the y gantry is 2x8 ali box

    decided this after i found out the you can mill sections at a time and glue together to for a fibreglass/vac form plug i think mach 3 has that ability or was it artcam????

    at a later date build a cnc router for carving vac form plugs,the later cnc 800 x 800 from ali extrusion and plate this does not have to so stiff and rigid as it only carving foam/plastics and MDF and pine

    since i posted i have modified the frame to be very rigid, see pics


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    i know that using 50mm box would be better and save some pennis but i decied to stick to the 25mm as a way of spreading the weight and of course it looks nicer but this may change

    as for the x axis and using rack or ballscrews the jury is out on that at the mo , thanks for the spanner by the way LOL

    i will post my idea for using rack and pion and a lock plate,

    i will have that idea up soon

    speak later, buy the way i am on skype if u want to face to face pm me

    ATB

    ric
    richard armstrong

    building 8x4 cnc all rounder, 2nd build.... major headache....LOL

  9. #9
    PART TWO

    Y GANTRY IDEAS

    IDEA 1

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    hiwin rails, nema 34 x 2, rack and pinion, aluminium plate not to sure what thickness to use or use box section and mill a lap joint, bolted and ali welded


    Idea 2
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    hiwin rails x 2, nema 34 on spring drive plate, ali box section, rack and pin, use box section and mill a lap joint, bolted and ali welded

    Ideal 4

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    Idea 5
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ID:	8096ball screw & tread moved to bottom 2 X NEMA 34 use box section and mill a lap joint, bolted and ali welded

    this might be over engineered???????

    let me know what you think

    advice please

    ric
    Last edited by ciscoeuk; 30-01-2013 at 10:39 PM.
    richard armstrong

    building 8x4 cnc all rounder, 2nd build.... major headache....LOL

  10. #10
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    oooooops i missed

    idea 3

    as idea 1 but using 2 or 3 stacked bearing and holder boc ali and direct drive nema34

    ric
    richard armstrong

    building 8x4 cnc all rounder, 2nd build.... major headache....LOL

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