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Eccentric Spacer Problems

Discussion in 'General Talk' started by JonHollander, May 29, 2014.

  1. JonHollander

    JonHollander Well-Known
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    I've been trying to build a belt and pinion carriage as shown in the example build video ( http://openbuilds.com/builds/v-slot-belt-pinion-example-build.97/ ), but I'm having problems getting enough pre-load of the wheels against the rails. Even with the eccentric spacers turned all the way in, the carriage is still loose against the rail.

    I've attached some pictures and video showing my build. Perhaps I'm missing something?

    2014-05-29 14.50.57.jpg 2014-05-29 14.51.14.jpg 2014-05-21 17.08.58.jpg

    I also took some measurements with calipers and noticed my 60mm rail measures only 59.75 (+-~.05). Is my rail out of spec?

    (I measured the hole center-to-center distance on the carriage plate as 80.68mm, which seems to match the drawings.)

    Has anyone else experienced this issue? Any ideas about what might be wrong or suggested solutions would be appreciated.
     

    Attached Files:

  2. Mark Carew

    Mark Carew OpenBuilds Team
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    Hi Jon,
    Well thats no good :)
    Looking into what could be causing this so we are building one one with new parts to test out. We'll see where there is a mistake made on one of the parts. I have not see this happen in the past so we will dig in and find whats happening and let you know what we come up with.
    Thanks for the heads up
    Mark
     
  3. Mark Carew

    Mark Carew OpenBuilds Team
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    After some experimentation we have found the hole spacing on some of Build plates as well as the V-Slot gantry plates to be culprit. This is mainly due to older drawings being used at the same time while trying a new manufacturing process. The good news is we are pulling the plates and updating the tooling for these new plates :) We will be touch though email with progress updates.
    Thanks for being patience as we work to get this corrected and thank you for bringing this to our attention.
    Mark
     
  4. mike125

    mike125 Well-Known
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    I am having the same issue with my V-Slot gantry plates. I just received them today, and quickly assembled a mock up slide, just to see how the mechanism worked. I did use some hillman group m5 screws from Lowes in my assembly because of the screw shortage in the part store. I don't know if the screws are contributing to the problem or not. Just like Jon, I have the eccentrics turned completely in and there is still play in the slide. I am trying to get a bolt together cnc router built similar to the routy so that I can start cutting plates for my Cheetah V-slot router.
     
  5. Mark Carew

    Mark Carew OpenBuilds Team
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    Hi Mike,
    Yes unfortunately there were many plates from this batch that went out and for this we apologize, we are working very hard to get this corrected as soon as possible so they there is not to much of a delay in your builds. The samples plates are being worked up now so we can approve them and start the production run soon.
    Thanks again for your patience
    Mark
     
  6. Robert J Rissell

    Robert J Rissell Well-Known
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    Mark,

    What about an idea of building in (or assuming builders are willing to ream out larger holes in the plates) and offering
    a larger size eccentric bushing? This would have the advantage of offering a larger offset at the cost of a larger hole.

    Using the same inner hole diameter would allow for the use of standard mount/axle hardware AND allow for the use of a
    greater range of diameter wheels/gears. I wouldn't see any stability problems, just more material weight and cost.

    Robyn
     
  7. Mark Carew

    Mark Carew OpenBuilds Team
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    This would work and its a good idea, but to be honest there is more then plenty of room to tighten the current eccentrics in place had the holes be en in the right place. I have been testing out the new beta plates and they are very tight at less then half the rotation at this point. I also see what your saying about the standard axle hardware and I like that idea, but for the different wheel diameters its really just a matter of proper hole placements on the plates.This is an idea to look into for future designs but for now with out having to go though and rework the eccentrics and the plate hole sizes for now we are good to go. I have made a few more changes from the latest version so I am reworking the test plates and we should be ready soon.
    Thanks for sharing these ideas Robyn, sometimes we spend so much time up close on a potential problem, that we cannot see some of the better solutions with out a fresh pair of eyes.
    Mark
     
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  8. DANIEL ELLIFF

    DANIEL ELLIFF Well-Known
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    Yes I have the same problem with the first order from the OpenBuilds parts store, so it really concerned me, seeing that I ordered a small sampling of parts to test fit and design from. I had assembled the mini v plate with the mini v wheel kits, additionally once I had the wheel kit just tight enough to eliminate perpendicular movement the rotation of the bearings were rough in two out of the 4 wheel kits.
     
  9. mike125

    mike125 Well-Known
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    Did you put a 1mm shim (washer) between the bearings? Sounds like that might be the problem because I did the same thing when I assembled mine.
     
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  10. DANIEL ELLIFF

    DANIEL ELLIFF Well-Known
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    Hey Mike thanks for the reply. And yes, I did put the shim in as directed by Mark's video instruction. Are you saying I shouldn't have, or just placed it incorrectly? I'm a novice with this CNC endeavor, so it may be trivial. Just wondering if the added friction will soon be a bearing failure.
    Thanks for your willingness to help.
     
  11. mike125

    mike125 Well-Known
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    The shim should be there. I didn't put one there and it had some rough movement of the bearings like you describe. So, I guess that is not the reason. I am still waiting for the corrected gantry plates to be back in stock in the store so that I can continue my build.
     
  12. JonHollander

    JonHollander Well-Known
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    While waiting for corrected gantry plates (any ETA Mark?), I hacked up a work-around that may be of interest.

    The stock gantry plate has large holes on one side of the rail to accept eccentric spacers and small holes on the other side for M5 bolts and regular spacers. However, if you enlarge a pair of smaller holes on the gantry plate, then you can put eccentric spacers on both sides of the rail. This gives you double the adjustment range and is enough to clamp the gantry tightly to the rail.

    If you have a drill press, there's an easy way to enlarge the small holes on the gantry plate while keeping the holes centered. First, attach a 5mm bit to the drill press. With the drill press off, lower the bit through the hole on the gantry plate that you want to enlarge. This centers the hole with the drill bit. Clamp the plate to the press table here, then raise the drill press, switch to a 9/32" (7.14mm) bit, and drill out the hole. The eccentric spacers should fit the new holes perfectly.
     
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  13. Steve B

    Steve B Veteran
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    This seems like an old problem, but I just assembled a gantry plate that appears to have the issue. I set it up for 60mm v-slot, the eccentric spacers are completely in and still there is play.
     
  14. Steve B

    Steve B Veteran
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    Took a second look at the plate design. I think the culprit in my case is that I'm using the spacer blocks to build the linear actuators similar to in the build section, but with 20x60 instead of 20x80 slot. Looking at the drawing of the universal gantry plate, you can see that the set of holes that's used to mount the spacer blocks are not on center with the holes you'd use for wheels if you were mounting wheels directly to the plates, they are set out just slightly.
     
  15. Mark Carew

    Mark Carew OpenBuilds Team
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    The new plates have resolved these issues
     
  16. Clearly

    Clearly New
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    BUMP

    Having this exact issue right now with mini vwheels and mini v gantry on genuine 20mm rail, even using openbuilds hardware. Can't snug wheels to v-slot even with eccentrics all the way in.
     
  17. Mark Carew

    Mark Carew OpenBuilds Team
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    Hello @Clearly
    Sorry to hear you are seeing this problem if you have not done so already please contact the Part Store Team - Contact@OpenBuildsPartStore.com and they will be more then happy to help resolve this for you.
     
  18. Clearly

    Clearly New
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    Yeah I tried that, not to swift with answering emails :p
     
  19. Mark Carew

    Mark Carew OpenBuilds Team
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    I do know that volume is high with the holidays but I am sure they will get back to you soon as possible.
     

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