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Yes, Another G0704 Cnc Conversion

Discussion in 'CNC IN THE HOME SHOP' started by benster, Dec 1, 2016.

  1. benster

    benster United States Iron Registered Member

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    Gents - adding another to the growing collection of conversions. I did not go the standard HOSS conversion or pre-made conversion route. I did however, buy my ballscrews with double nuts precut direct from Chai (linearmotionbearings2008), and bought all the controller components from Automation Technologies. After some hiccups getting the controller box laid out and wired to my liking I ran into some more issues with stepper timing. Apparently timing on the X/Y steppers needed to be divided by 5, I have no idea why this is. One thing to note is the 9082 stepper driver is substantially bigger than the 5056 and mounts had to be made to fit it in the enclosure.

    From a hardware standpoint, everything went as usual except the x-axis ballmount. In addition to cutting clearances on the x ballnut, I had to grind out the bottom of the table to clear. I am bringing it, as well as the saddle to a friends to have it machined properly this weekend. As it stands I did not grind it close enough to the ends and the x-axis bound up if panned over too far. I also plan on redoing my stepper mounts and angular contact bearing setups. On the advice of a coworker, I am going to back the bearings up to each other and preload them against each other, then capture the whole assembly.

    I also predrilled all the holes and cut the grooves necessary for a one shot oil system. I've been fiddling with some custom low profile banjo fittings but they've become more trouble than they're worth and I might go back to off the shelf fitings.

    Here are the current specs and some pictures. I would take some more pics of it completed but it's taken apart to be machined this weekend.

    X Axis: 570 oz-in Nema 23, 1605 ballscrew with double nuts, Keling 5056D 5.6A driver
    Y Axis: 570 oz-in Nema 23, 1605 ballscrew with double nuts, Keling 5056D 5.6A driver
    Z Axis: 906 oz-in Nema 34, 2005 ballscrew with double nuts, Keling 9082D 8.2A driver

    I'm using a 48V 12.5A Keling PSU and KL-DB25 breakout board. I built a desktop to run LinuxCNC.

    Side note, what's the best way to add videos? I have a couple of it running. Should I upload to YouTube?

    20161120_131820.jpg 20161117_180725.jpg 20161122_150839.jpg 20161121_163435.jpg
     
  2. benster

    benster United States Iron Registered Member

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    Took the table and saddle over to a friends and cut some more relief. Put it back together. Going to do some test cuts this evening. The X-Axis is still binding a couple inches away from the ends of the table, not sure if this is because of the alignment of the table ends. I plan on making new ends once its up and running well.

    IMG_20161203_130103.jpg IMG_20161203_130115.jpg IMG_20161203_140215.jpg IMG_20161203_140210.jpg
     
  3. benster

    benster United States Iron Registered Member

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    First useful thing I've made so far, a custom optical limit switch for the Z-axis. The Z-axis was first so I could home the z axis and not lose my tool heights every time I restart. X and Y are going to follow. Should be quick since I've refined the program and gotten tool heights down.. Still need to get the wiring together and the script in LinuxCNC.

    20161221_180110.jpg
     
  4. benster

    benster United States Iron Registered Member

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    I put belleville washers on the ballscrews in the x and y. I'm down to undetectable backlash in the y axis only when the table is centered. When its over to the right, and the vise is on the left, it goes up to .002". Is this just down to gib adjustment? The x axis is <.0005", but I plan on making new mounts that should allow the left bearings to float axially. I think right now its overconstrained which is adding a lot of resistance.

    Any ideas why the backlash changes in the table?
     
  5. TomS

    TomS Active User H-M Supporter-Premium

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    Sounds like the ballscrews are moving axially. If your ballscrews have axial movement using belleville washers it will only get worse when you take a cut and add cutting forces to the equation. You need to pre-load/shim the AC bearings in their housings to eliminate ballscrew axial movement. Or you need to use belleville washers that exert more pre-load. Does this make sense?

    Tom S.
     
  6. benster

    benster United States Iron Registered Member

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    That might be it. The AC bearings are preloaded against the mounts, part of my upgrade plan is to preload them against each other and then capture the assembly. I'll make the y axis mount first and see how it performs, since that's the axis with backlash currently.

    Sent from my Nexus 5X using Tapatalk
     
    TomS likes this.
  7. MontanaAardvark

    MontanaAardvark United States H-M Supporter - Premium Content H-M Supporter-Premium

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    I just noticed this thread; I've been documenting my efforts to do the Hoss conversion on mine and finally got it running.

    This picture is just small enough that I can't read the part number and try to reverse engineer it, so do you have any sketches, drawings, schematics or something?


    Thanks,
    Bob
     
  8. benster

    benster United States Iron Registered Member

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  9. MontanaAardvark

    MontanaAardvark United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Thanks for the quick link. Got the data sheet to read and visited the web page.


    Bob
     
  10. benster

    benster United States Iron Registered Member

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    Sorry for the delay getting you the models, I was busy with work. Here is the link to the housing in Fusion 360, if you don't use Fusion 360 let me know and I'll get some drawings made up.

    http://a360.co/2kM9dxF
     
  11. MontanaAardvark

    MontanaAardvark United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Thanks.

    I downloaded Fusion 360 and played with it a little, then had that computer barf on me before I got anywhere. I haven't installed it on the replacement computer. This will be a good excuse to re-download Fusion and do the tutorials.
     
  12. MontanaAardvark

    MontanaAardvark United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Hate to bug you, but I had originally considered microswitches for limit switches and read complaints about their accuracy. Do you have any data on what kind of position uncertainty there is with these? Do you just use it to keep from raising the z-axis too high, or what?


    Bob
     
  13. benster

    benster United States Iron Registered Member

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    This optical switch in the enclosure I made is repeatable to <.001", I don't have a tenths indicator to measure anything less. With the optical switch as a home I have soft limits set in LinuxCNC to prevent the head raising too high. I didn't use micro switches because of the same accuracy concerns.
     
  14. cut2cut

    cut2cut United States Active Member Active Member

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    Why would you preload both the bearings against each other. I could be wrong, but I think that removes all the preload applied to the ball svrew, which is the main point of using two AC bearings. May as well use one standard ball bearing and tighten it down on that one bearing instead.
     
  15. benster

    benster United States Iron Registered Member

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    It doesn't due to the shoulder on the ballscrew. Here's a shot of the old vs new setup. The bearings were modeled wrong so the red lines are their orientation. On the old mount the through bore wasn't bored out enough so I used shims to only contact the outer bearing race against the mount. The shims aren't modeled.
     

    Attached Files:

  16. cut2cut

    cut2cut United States Active Member Active Member

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    Well, its hard to know where you are putting the shims in your new new model but in any orientation/configuration, you must have a gap between the two inner races at all times. If not, you are defeating the purpose of using two opposing AC bearings. Hope this helps.
     
  17. benster

    benster United States Iron Registered Member

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    Yea I get what you're saying, the actual AC bearings inner/outer races are offset, the ones in the model are just a generic ball bearing of similar dimension and don't show the offset. I've been using the setup for a while now and never updated the post, but currently I have no detectable backlash in my Y-axis. I need to make a similar mount for my X-axis.
     

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