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  1. #141
    Quote Originally Posted by biketrialsdave View Post
    Perhaps I should design that in now...
    No perhaps about it Dave needs to be done. The Z axis is KEY area don't matter how well built rest of machine if Z is shite or weak.!!

  2. #142
    Quote Originally Posted by JAZZCNC View Post
    No perhaps about it Dave needs to be done. The Z axis is KEY area don't matter how well built rest of machine if Z is shite or weak.!!
    OK, I'll get onto that tomorrow! I assume 2 linear rails with the ballscrew in-between them sitting in a slot to reduce the overall depth? I'm using THK HSR15 carriages for the other axis, I assume these will be OK for the Z too?


    The drop brackets on the rear are 5mm steel at the moment. I can increase this and also add some kind of right angle bracket perhaps.
    Last edited by biketrialsdave; 19-11-2015 at 11:26 PM.

  3. #143
    Lee - How do I delete a reply I made ?
    Last edited by cropwell; 20-11-2015 at 08:23 AM. Reason: Replied to old post - deleted duplicate info

  4. #144
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 9 Hours Ago Has been a member for 4-5 years. Has a total post count of 914. Received thanks 147 times, giving thanks to others 5 times.
    Quote Originally Posted by biketrialsdave View Post
    OK, I'll get onto that tomorrow! I assume 2 linear rails with the ballscrew in-between them sitting in a slot to reduce the overall depth? I'm using THK HSR15 carriages for the other axis, I assume these will be OK for the Z too?
    Even if you don't really need them for strength, this is one place where "20" rails and carriages can be useful to give just a bit more clearance between Z plates for the ballscrew and nut. If you have to buy them and don't have something in stock already, this might be something to consider.

  5. #145
    Quote Originally Posted by biketrialsdave View Post
    OK, I'll get onto that tomorrow! I assume 2 linear rails with the ballscrew in-between them sitting in a slot to reduce the overall depth? I'm using THK HSR15 carriages for the other axis, I assume these will be OK for the Z too?
    Yes more than enough regards forces etc but has pointed out by neale 20mm can work better regards spacing etc. Personally I use 20mm on all axis for simplicity and hardly any difference in price.


    Quote Originally Posted by biketrialsdave View Post
    The drop brackets on the rear are 5mm steel at the moment. I can increase this and also add some kind of right angle bracket perhaps.
    Yes you need more bracing to stop deflection. 5mm steel isn't really upto to it without being braced.

  6. #146
    I have 15mm rails on Z and they work ok but they use M3 bolts on the rail and carriages which look very small compared to M5 on the 20mm rails on my Y axis. When cutting I can feel vibration across them especially the top ones and for this type of machine I would go with 20mm on Z.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  7. #147
    Thanks for all the feedback guys. I think I'll go with Hiwin 20mm for the Z axis. What would be the "minimum" recommended centre distance between the two rails? I want to keep this as small as possible to maximise the effective Y axis length but without compromising rigidity. At the moment my whole Z axis assembly is 130mm wide..

  8. #148
    Quote Originally Posted by biketrialsdave View Post
    Thanks for all the feedback guys. I think I'll go with Hiwin 20mm for the Z axis. What would be the "minimum" recommended centre distance between the two rails? I want to keep this as small as possible to maximise the effective Y axis length but without compromising rigidity. At the moment my whole Z axis assembly is 130mm wide..
    Well generally I always suggest 250mm minimum, obviously this harder to achieve on smaller machine with smaller z assembles...

    .Me
    .Me

  9. #149
    My Z axis plate is 147mm wide and the Z rail centres are only 115mm apart. I did this to maximise Y travel and placed my Y axis bearings pretty much back-to-back.

    This works fine for me, but it can give you more stability and less likely to rack if the Y bearings are spread further apart, but you are trading Y travel. If you do spread the Y axis bearings out further, closer to Lee's figure, then I don't think you need to follow suit with the Z rails and can keep them fairly compact.

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

  10. #150
    Your machine looks great, thanks for all the advice.

    I've increased the plate width to 170mm now. The z rail centres are 118mm apart at the moment. Do you think the carriages need to be separated more in the z axis? (They are 119mm centres) I'm trying to reduce this length as much as possible in order to reduce the total height of the z axis plate (if that makes sense.

    Also, is it worthwhile pocketing the carriages slightly like I've done elsewhere?

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    Last edited by biketrialsdave; 22-11-2015 at 12:47 PM.

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