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  1. #11
    Ok - had some time and re-designed it with square rails :)

    For the X, I'm thinking of using: 40x80 Heavy Duty Aluminium Extrusion (http://www.aluminium-profile.co.uk/a..._ITM02604.html)
    8mm Slot Ix = 26,87cm4, Iy = 101,19cm4, Wx = 13,44cm3, Wy = 29,29cm3

    The Y's, similar, but the 40x120 - Those will then get bolted down onto a lovely solid flat surface :) [Later to be upgraded to solid Steel table]

    Question 1: For the X, the rails will be 80mm apart (bottom of rails), is this ok? Or should I rather go for the 120mm on the X - which means bigger side plates etc.

    Question 2: I've gone for 10mm Aluminium all round (6mm to hold the motor on the Y, and attach the Ball nut housing) - thoughts ?
    [ Most of the 'bend' will be in the lateral movement for the Y, and the square rails will 'support' the 10mm... so see no need to go more. ]

    All Steppers 3.1Nm with pulleys, 1:1, and 1.5:1 for Y [Powered by 60V stepper drivers]

    RM1605 for Z, and RM1610 for X & Y. (ends or F, extended from 15mm to 30mm)
    BTS Automation will open end of Feb after their Chinese new year... hoping to order soon :)


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  2. #12
    Which drives are you going for when you say 60V AM882 or EM806 about 68V would be better.

    If I am not mistaken 90 x 45 and 180 x 45 work better with the BK/BF bearing blocks. But Dean probably chime in with the correct size
    ..Clive
    The more you know, The better you know, How little you know

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  4. #13
    Quote Originally Posted by Clive S View Post
    Which drives are you going for when you say 60V AM882 or EM806 about 68V would be better.

    If I am not mistaken 90 x 45 and 180 x 45 work better with the BK/BF bearing blocks. But Dean probably chime in with the correct size
    Clives correct Bosch Rexroth 45 x 90 slot spacing matches the hole spacing in the BK/BF12 bearings. If using Item section then you'll need spacer plates.

    10mm Ali is too thin 15mm is the minimum I'd use. 20mm prefered.

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  6. #14
    Thanks - Will look at the difference in specs and price for the AM822 and EM806 - any recommendations ?

    I'll look at the 90x45 & 180x45 - thanks!

  7. #15
    When you say 10mm is too thin - I agree in some part, but let me try explain my thinking...


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    On the Y Side plates, most of the "force" will be stopping the X beam flexing, and moving in the Y direction, so on Y1.
    The forces on X1 (if the X is bolted down on the bottom plate properly) will be minor.

    On the Z axis gantry, the back plate - I agree - 15 or 20mm. It will flex, although the blocks should support it, apart from the 30mm gap between them, so only "bend" that will apply will be on the small 30mm bit inbetween the blocks... Whats bend like on 30mm of 10mm plate?

    On the front Z plate, the plate will be bolted to the square rail. Surely the 20mm rails will stiffen up the 10mm plate?

    I don't want to put extra weight on it if I don't need to - but you guys know what works and what doesn't....

    I like to match the spacing, so will change the design to 90x45 - The BF/BK blocks will be on spacers...so the bolt will go through the BF/BK, through spacer and into profile. :)

    I'll then swap out the 120x40 with a 180x45. This will also give me more cutting (working) space.

    Currently (according to my calcs and drawings) the Z has the ability to travel at least 120mm.

    Thanks!
    Jacques

  8. #16
    Quote Originally Posted by Jacques View Post
    Thanks - Will look at the difference in specs and price for the AM822 and EM806 - any recommendations ?
    The EM806 is upgraded AM882 but there's not a massive difference between them in performance terms. The AM882 can be bought much cheaper so I'd go with those.

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  10. #17
    Quote Originally Posted by Jacques View Post
    On the front Z plate, the plate will be bolted to the square rail. Surely the 20mm rails will stiffen up the 10mm plate?

    I don't want to put extra weight on it if I don't need to - but you guys know what works and what doesn't....
    Yes to some degree they do but that means they are also under bending forces and linear rails don't tolerate much error and will bind. The Z axis is THE MOST IMPORTANT piece of the machine so if you skimp here then you will regret it later guaranteed.

    The bearing plates you could probably get away with 10mm but why bother just buy one plate size for all key areas it will be cheaper or not much more money.

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  12. #18
    Will amend my design with the changes.

    Thanks JazzCNC

  13. #19
    Can anyone recommend a good supplier for 45x90 & 45x180 profiles ?

    Also cut to size Aluminium plates 15mm & 20mm ?

  14. #20
    I can't help with profile suppliers but you can cut those shapes with basic tools. Cut the aluminium on a bandsaw close to size and then finish the edge using a hand held router and carbide cutters. You need a template or straight edge to run the router edge along. Your shapes are main rectangles or triangles so should be OK.

    As for 10mm vs 20mm I know aluminium is expensive so you are trying be economical so here are my suggestions on the minimum areas to use 20mm on, and why.

    Z plate
    as Dean says. Don't use the rails to add the stiffness. No worries about weight either - the steppers will lift more than you think once they are driving a ballscrew.

    Y axis upper and lower bearing plates
    Several reasons:
    1. If you use 10mm plate you will have to use very small bolts into the side to mount them to the Y plate. So could probably only fit say 6mm bolts to connect them and this is just not good enough. They will bend and you can't get much torque into them to get a good clamping load

    2. The 10mm plate has a small footprint onto the Y plate so is much more likely to bend up and down at the joint.

    X axis bearing plates
    1. They hold the gantry and stop it rotating. The triangular plate on the sides transfers this load down the outside to the bearing plate, but the X bearings are in the middle of the plate. This means that the unsupported corners on the inside will bend. Therefore they should be 20mm.
    You could add another triangular plate on the insides as well but it is a bit awkward to attach back to the gantry front face.

    2. You will need to counterbore the bolts which hold the X bearings onto the X bearing plate so that the gantry can sit flush. I'm guessing these are around M6 so need ~6mm of counterbore depth. In 10mm plate this leaves just 4mm of metal holding the bearing to the plate. This is a bit thin in my view, whereas 20mm still leaves 14mm of metal.

    3. The triangular plates on the side will bolt onto the edges of the 10mm X-bearing plate and you will have to use fairly small bolts (~6mm) which is a bit small.

    Finally . . .
    X ballscrew drive plates
    The strips which drop down to mount the X ballnut to are quite thin. They will twist when the load is applied as it is offset. A thicker plate with a pocket for the ballnut would be better, or at least some support, but it sounds like you have limited tools so you could build it like this and use the machine to make some beefier parts.

    Another finally . . !
    I don't think you can assemble the Y axis and Z axis can you? I think you've done the classic 'lock-out'. Walk through the steps of bolting it together in your mind and make sure it is possible and there is a build sequence.
    As you are using packing pieces to mount the Z bearings to I think you will have to extend them (and the Y axis plate) say 15mm below the level of the lower Y axis bearing plates to be able to bolt from the back. The top is OK as it already extends above the level of the upper Y axis bearing plate so you can bolt through from the back.


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    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

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