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Delrin V-wheel Kit is sloppy?

Discussion in 'General Talk' started by Matthew Carson, Oct 7, 2015.

  1. Matthew Carson

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    I am building a large delta printer and designed the carriages around a V-rail and printed carriage with 3 (or 4) of these wheel kits.
    After thinking I had designed a weak carriage I finally realized the delrin wheels would wobble on a tightened assembly, every one!
    I understand that by design the precision 1 mm thick shim that goes inside is supposed to match the inside ridge of the wheel, but apparently that ridge is a hair short. This either isn't right, or I am trying for more precision than these are intended for. I can feel the play with my hands. It is not a lot but in the right design that slight amount translates to a lot of tilt. The wheel is not actually clamped onto anywhere, it is a 'precision' fit.
    Has anybody else encountered this?
    The only solution I can think of is to reduce the thickness of the shim until the play is gone, except I dont' have any tools to shave it down squarely. That would also throw off the wheel height from the mounting surface, although maybe not enough to matter for my application.
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    You might contact @Mark Carew on this one. Sound like a fabrication tolerance issue and he is in the best position to test the existing stock. There should be no play whatsoever in the completed assembly.
     
  3. Mark Carew

    Mark Carew OpenBuilds Team
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    Hello @Matthew Carson
    Rick is right as it does sound like a tolerance issue on the wheels. Please contact the OpenBuilds Part Store Team and they will ensure that you are taken care of.
    I will also let them know so they will reach out to you as well.
    The good news is that we have spent a lot of r&d recently to make sure these wheels are exact and that there is no movement, so this should not be an issue going forward.
    Thank you for your feedback as well as your patience Matthew
    Mark
     
  4. Matthew Carson

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    After grinding down the spacer until the outer rim of the bearings can clamp onto the inside of the delrin wheel, there was still visible and tactile play, albeit smaller.
    What I also observed, last night, is play in the bearings. In a dual track setup where a pair of overlapping v-rails has a set of wheels on each side, so that the plane of the wheels are lined up, the load is all axial, which means the inner and outer races of the bearing are being pushed in opposite directions.
    These types of bearings were not designed for that. In addition, if the load is unbalanced and causing a torque, then even a smidgen of play allows a lot of tilt because the v-rail track width is not very big and a small amount of wheel tilt/shift translates into a large amount of stage tilt This is a fundamental issue I am going to have to design around. I created some diagonally opposing configurations in Solidworks that put the wheels on the backside corners of the 20x20 extrusion I was mounting the v-rails onto. The designs are rather clunky and I am not sure they are good enough.
    Here is the original design. I am stuck with the 20mm extrusion and I kind of need the 80mm wide spacing for the rod-arms. The most stable solution is to clamp a pair of extrusions on each side of the center extrusion to get a wide stance, but then I get a very very wide stage and it will more prone to bowing under a load or tightening the wheel grips on the rails. The stage is printed in PLA and decent stiffness. The rod-end spacing is 80mm to (supposedly) increase stability because the bed is 350mm and I want the rod-spacing-to-length to preserve the same ratio as the mini Kossel I originally had.
    (I feel like this has already gone off subject, can I move it elsewhere?)
    [​IMG]
     
    #4 Matthew Carson, Oct 7, 2015
    Last edited: Oct 8, 2015
  5. Flash22

    Flash22 Veteran
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    I have had issues with the delrin wheels what I have since replaced for the polycarbonate items, as you say the bearings are not up to the loading in some scenarios, I had 2 fail within 2 hours of use with the outer bearing pulling away from the inner

    I have been looking at skf taper bearings or deep v groove bearings to aid with loading not exactly cheap tho
     
  6. Mark Carew

    Mark Carew OpenBuilds Team
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    Not sure what your working on but if your gantry plate is not stiff/strong enough for your application. You could use a wider V -Slot to gain a wider stance then the 20x20 your trying to use, you may also want to up the plate thickness to make up for any bow for the wider plate being used.
    @Flash22 Where these OpenBuilds bearings? We have been using these bearings on all our builds some using extreme test gantry load scenarios and we have never had a bearing fail, this would be highly unusual so we are curious what could have caused this. Thank you for your feedback
    Mark
     
  7. Flash22

    Flash22 Veteran
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    I can not possibly comment but as you said to me via PM its a open build and you have no control over parts supply - the ones from the openbuilds shop are a lot better quality

    main issue was with the Z axis what has now been sorted out

    Water under the bridge


    Regarding bearings as your aware there are many types, the loadings on the wrong type of bearing, coupled with a inferior quality causes premature failure - a standard shielded bearing is fine for rotation use but if you start loading on one edge or face it will increase wear

    As another interest I rebuild engines (Mainly J.A.P and Briggs) and radio controlled cars, bearings play a big part in both - sourcing bearings for 50-70 year old engines can be tricky at times with the RC stuff its finding high performance bearings - ceramic and even TiN/cobalt coated for high speed
     
    Mark Carew likes this.
  8. Val Cocora

    Val Cocora Veteran
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    I have the same problem this weekend with 20x80 v slot rail. The wheels wobble in the rail, even when the eccentrics are tightened. Not sure if the pictures attached can tell much, but at least you will get the idea. Perhaps it would help to mention the wheels are delrin double v shaped. Everything was purchased from openbuilds, except the rails.
    I must say I'm quite puzzled, as I never experienced this before.
     

    Attached Files:

  9. Ronald van Arkel

    Staff Member Resident Builder Builder

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    Might be the angle of the track-sides. Can you provide a picture of the wheel and the V-Slot how they touch each other, best taken from the end of the V-Slot with the wheel close to the end and no load is needed.

    -Ronald
     
  10. Val Cocora

    Val Cocora Veteran
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    I 'fixed' it by using 4 wheels instead of 6. It seems the middle wheels, especially the fixed top one, caused misalignment upon tightening. Also, using solid wheels seems to have helped a bit. But what I wonder is, should I tighten the wheels with the load on, or off?
     
  11. Steven Hook

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    Hello,

    Is there a solution to the "precision shim thickness"?

    I have the same problem. The C-Beam kit I bought last year around August time, has only now May 2016, got to be set up and tested. I am surprised to find that the mini wheels are very sloppy. I can hear an definite clunk if I give my spindle a good seeing to. This translates to 1mm movement at the tool tip. This isn't acceptable! It is because the washer is 1mm thick and the flange on the inside of the wheels is 0.8mm thick. If you do the math(s) it isn't ever going to work, the "precision shim" needs to be about 0.5mm - 0.7mm thick to take up the play in the bearing and grip the wheel rim. I suspect that the 1mm "precision shim" was chosen because it is really cheap, but, no thought has gone into the engineering aspect.

    Could someone please send me the proper parts.

    Thankyou!
     
  12. Val Cocora

    Val Cocora Veteran
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    Hi Steven,

    I believe you have to return the parts to the store, there is a link for that in parts store, if you have an account.
    For that, you will receive credit in store.
    Worked wonderfully for me, I encourage you to use it, Mark and the Openbuilds team are pros.
     
  13. Barry Danks

    Barry Danks Veteran
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    @Mark Carew
    During assembly I have noticed the same thing. The 1mm shim is thicker than the stop in the mini wheels, but the standard size wheels seems to be fine. I'm going to put the mini wheel on the granite table tomorrow and measure the exact width of the bearing stop.
     
  14. Mark Carew

    Mark Carew OpenBuilds Team
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    @Barry Danks
    Hey guys,
    First thank you for the feedback on these wheels.
    Too be honest on our end we are not experiencing this with any of the Builds we work on here so its tough to say what may be going on until we can have them in hand to check over.
    Val is right, if you could please contact the Part Store Team (Contact@OpenBuildsPartStore.com) so that we can arrange taking a look at these wheels to see if there may be a defect that could be corrected.
    They will be glad to work with you to make sure you are up and running as soon as possible.
    Thanks again for your help.
     
  15. Flash22

    Flash22 Veteran
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    since swapping the bearings out for ones supplied by mark I haven't had a issue - some of my precision shims where in fact just stamped washers what has now be rectified
     
    Josh Hulgan and Mark Carew like this.

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