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  1. #31
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    May 2003
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    Perth WA
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    Hi Phil,
    I worry about the canterlever effect of your design. Those three staggered uprights can only get fixed together with a couple of T nuts so the joining elements and overhang create problems in my mind.

    Have you thought about the front two being carried to the top and then a piece at right angles at the top carying back to pick up the Y axis? Either that or cutting your losses and do away with the offset by dropping the third vetical member all together.

    Your Y axis design has already pulled it tighter together and with some extra work on the Z axis - screw and rails at the rear of Y beam and a box surrounding the gantry beam to mount the spindle on you might jag it.

    Also do you need the gantry to be as high as it is? Less height means much more rigid design.

    Just something to ponder about.
    Cheers,
    Rod

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  3. #32
    Join Date
    Dec 2005
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    Brisbane
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    286

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    Good, thanks for that, I just sent the order out to AME System but switched to the full length gantry sides following your recommendations.

    and with some extra work on the Z axis - screw and rails at the rear of Y beam and a box surrounding the gantry beam to mount the spindle on you might jag it.
    I don't ever remember seeing Z axis rails behind the gantry, do yo have any links to something like that?

    Would it make more sense to order 12mm rails and ballscrew for the Z then the 16mm ones?

  4. #33
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    May 2003
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    Perth WA
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    Hi Phil,
    I need to say I am not an engineer so I can't recommend anything - I just make suggestions to get your mind thinking. I would hate to stuff up your machine for you and it's your job to pull it all together in the end.

    The good thing about a forum is if an unworkable suggestion is made then somebody else chimes in and corrects it quick smart.

    No haven't seen anything on rear mounted rails and screw but that doesn't mean it can't be done. If you are committed to mounting those components on the front (which is fine) then yes 12mm supported rails and screw will be adequate and also help keep it tighter to the gantry beam.
    Cheers,
    Rod

  5. #34
    Join Date
    Dec 2005
    Location
    Brisbane
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    I get confused with Chai's BK/BF thingies, will those things easily bolt to the unserside of my extrusions?

    Will the BK/BF thing accept Nema 23 motors? (i.e. does the motor bolt directly to the part?

    How dp I calculate how much ballscrew length I need bearing in mind these BK/BF things s they bolt at each end of my alu table?

  6. #35
    Join Date
    May 2003
    Location
    Perth WA
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    The bearing mounts can be mounted on their face or the base. Have a look at the drawings and you can see both mounting points. These are only bearing mounts and not motor mounts so you will have to make you own motor mount. You can either direct couple with a helical or other type of coupling or you can go pulleys and belt.
    A motor mount is easy - four posts (standoffs) and a plate with a hole in it and then you can make the micky duck version when your machine is running.

    The length of the screw will be determined by the travel you want. No point getting a screw with less travel than your bearings will deliver. Then add the machining of both ends to it. I make ny own mounts so can't help you with dimensions of the end machining. Chai should be able to give you those details. You can also get the length of the nut from his ebay listings to work out how long you need the ballscrew thread for the travel on your machine.
    Cheers,
    Rod

  7. #36
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    Ok, I'll have to check this out some more

    One more question, Can I roll the bearings out of the rails I got from Chai or is there heaps of ball bearings that are going to fly away if I do that? Is it safe to take them off the rails?

  8. #37
    Join Date
    May 2003
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    Perth WA
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    Yes you can take the trucks off the round rails as the bearing are retained by the assembly.
    As a general guide square rails and ballscrews leave them in place or be prepared to repack the ball bearings back in the assemblies. Not an easy task and assumes you can find them all when they spill out.
    Cheers,
    Rod

  9. #38
    Join Date
    Dec 2007
    Location
    Melbourne
    Posts
    105

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    Phil,

    Re the machining of the ball screws, this is what I provided to Chai and had no problems:

    1. At the BF end I need the ball screw machined to fit the internal diameter of the bearing and the groove for the retaining clip.

    2. At the BK end I need the ball screw machined to fit the internal diammeter of the bearing, the thread cut for the lock nut (for a distance of 12 mm) and a 8 mm diameter / 16 mm long shoulder for the coupling.

    I also sent Chai a diagram which I have hopefully also attached here!

    The lock nuts (at the BK end) are about 8.75mm wide.

    I also went for the cheaper Air Mail option (rather than EMS) and it took about 3 days (the week before Christmas).

    Hope this helps - let me know if you require an additional information.


    [IMG]file:///C:/Users/ASW/AppData/Local/Temp/moz-screenshot.png[/IMG]

  10. #39
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    I received my order of extrusions from AME System yesterday.



    Of course, I couldn't help but to spend a few hours today bolting up all my parts. This is what the CNC looks like at the moment. I'm really surprised at how fast it all came together. I ordered my ballscrews and Z rails from Chai a few days ago. Looks like I'll have to wait until these get here before I can go on with the build. I've got a feeling that machine will be done in no time.



  11. #40
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    Feb 2008
    Location
    Australia
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    Looking good but I think you might have an issue with twisting if your ground is not dead flat.

  12. #41
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    of the table or gantry? or both?

    At this point it's all temporarilly bolted together. I've got a feeling once I attach the ballscrews and do the Z axis, I might have to adjust a lot of parts to true the CNC. Right now its just been assembled the down and dirty way It 'looks' fairly flat but that doesn't mean much until I put some straightedges to it.

  13. #42
    Join Date
    Dec 2007
    Location
    Melbourne
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    Quote Originally Posted by Phil Mailloux View Post
    I received my order of extrusions from AME System yesterday.



    Of course, I couldn't help but to spend a few hours today bolting up all my parts. This is what the CNC looks like at the moment. I'm really surprised at how fast it all came together. I ordered my ballscrews and Z rails from Chai a few days ago. Looks like I'll have to wait until these get here before I can go on with the build. I've got a feeling that machine will be done in no time.

    Phil,

    Are the side bearers 30 x 60 profile and the cross members 30 x 30 profile? I am about to get the Al for my build (AME starts back on Thu) and my bed is about the same size as yours. I was planning on strengthing the X axis with some 100 x 6 mm flat Al - have you noticed any flex in your X axis?

  14. #43
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    Feb 2008
    Location
    Australia
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    Quote Originally Posted by Phil Mailloux View Post
    of the table or gantry? or both?

    At this point it's all temporarilly bolted together. I've got a feeling once I attach the ballscrews and do the Z axis, I might have to adjust a lot of parts to true the CNC. Right now its just been assembled the down and dirty way It 'looks' fairly flat but that doesn't mean much until I put some straightedges to it.

    It's more of just imagine if the ground is not level, the weight on the table will it cause the frame to twist. It is not a major issue because if there is any twisting you can beef up the support.

    When I was working on my Aluminium build I could notice twisting in the frame and mine was made of 80x80 heavy with 6mm steel plate. Once the weight is on the machine it will conform to the concrete floor, and after renting a factory with polished floors which look flat they were far from it (Then again I am very picky)

    Then again this wont be a problem if the ground is level, but if you move the machine you will have to level it again.


    I should probably shut up now and let someone else answer who has build more machines than myself.

  15. #44
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    Sep 2008
    Location
    sydney
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    2,370

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    just caught this one Phil,
    good on you for making the step to cnc.

    look sweet

    im going to have to get you to cut some fanned boards for me

  16. #45
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    Dec 2005
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    Brisbane
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    286

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    I don't need a CNC for that Did you see my fanned fret slotting jig?

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