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8mm spindle clamped when I fasten delrin nut

Discussion in 'OpenBuilds Forum Help' started by Schwipp, Apr 29, 2019.

  1. Schwipp

    Schwipp New
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    Hi everybody,
    I am from Germany and bought an openbuilds 1010 lead .. kit. When I had mounted the gantry set plate, image 1, and inserted for a test the 8 mm spindle, it was awfully strong clamped in the anti backlash nutblock, even when I had inserted it only into the first half of the nutblock. I found out that this clamping decreased when I loosened the two scews, with which the nut block was attached to the gantry plate.
    With other words: the anti backlash double nut is seriously bent / deformed when the two screws attaching it to the gantry plate are tightened.
    Of course, this clamping effect is noticable also because the anti-backlash nut, which I got, posesses very little dimensional tolerances.
    I discussed the situation, mostly with myself :D, and thought: this cannot be... I found a solution in which this clamping effect is absent.
    I show you a small sketch made with autocad and a photograph of the realy assembled hardware, it works perfect and there is no clamping effect on the spindle even when the nutblock is fixed very strongly to the gantry plate.

    First the autocad view, above, white, a 4 mm thick "polycarbonate double shim", one piece with two holes 5 mm, instead of the two 3 mm long alu spacer and the two 10 x5 x1 shims.
    In the middle the delrin double nut block
    Below a piece of 6 mm thick aluminium with two M5 threads for the m5 screws, now app 25 mm long.
    You can see a foto of the assembled new arrangemant,
    it fits into the C mount with enough space (app. 2 mm space below the aluminium plate)
    and it works perfect, does not change the clamping pressure on the 8 mm spindle
    ciao Schwipp

    Note added later: By the way, why is the thread bore in the nut blocks for the 8 mm spindle of such catastrophic quality concerning the dimensional tolerances? Are they drilled in China by hand?
    In some of the blocks the spindles are guided more or less soft but rigid in oblique direction, see photgraph, I can not use it at all and return it to my official openbuilds dealer in Europe. In other nut blocks the spindle are completely loose with lots of backlash and I can alter its direction easily and a lot. And the one I show you in the image had 3,8 mm diameter bores instead of 5 mm for the M5 screws, as if somebody in China took the wrong drill.
    3 images + 1 added later:
     

    Attached Files:

    #1 Schwipp, Apr 29, 2019
    Last edited: Apr 30, 2019
  2. GrayUK

    GrayUK Openbuilds Team Elder
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    If I am reading your post correctly, you have replaced the original "Backlash Nut" with a square piece of plastic with a hole drilled through it? If that is the case, then you no longer have a Backlash Nut, and therefore will be susceptible to backlash in the future. The principle of the Backlash nut is to allow you to feed the threaded bar through both elements of the nut with the grub screw loosened and not applying any pressure, then, by adjusting the grub screw, apply pressure to both sides of the thread at the same time, and thereby remove any play there may have been or may develop. Your premise seems to be to eliminate this pressure. It is common for the threaded nut to be extremely tight, to begin with, and it is sometimes recommended you attach a drill to one end and run it through the nut several times just to make it a little easier. I have not heard that the Backlash Nut deforms when tightened to the back plate before, and if this was the case, you only need to contact the supplier to get a replacement.
    I may have completely misread your post, and apologise in advance if I have.
    Gray
     
  3. Alex Chambers

    Alex Chambers Openbuilds Team
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    I'm not sure he has done that @GrayUK - the anti-backlash nut is also the means by which the leadscrew transmits movement. Otherwise I completely agree - I don't know how they create the thread in the delrin, but new nuts are usually very stiff because the thread is not completely formed and needs to have the leadscrew driven through it several times.
    Having said that the bore in the nut should be parallel to the surface clamped to the gantry plate.
    Alex.
     
    #3 Alex Chambers, Apr 30, 2019
    Last edited: Apr 30, 2019
    GrayUK likes this.
  4. Schwipp

    Schwipp New
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    @GrayUK:
    you wrote: "you have replaced the original "Backlash Nut" with a square piece of plastic with a hole drilled through it"
    No, the " comparetively soft" anti-backlash nutblock I got from my dealer now is in the center of the "sandwhich"
    (compare my autocad sketch above, second colorful image, and please also read the alternative text when you move your mouse on its title text)
    and is no longer deformed by the compressive force, even if I fasten the 2 screws very very strong - it is the large area which helps to reduce the pressure (= force/area).

    @Alex,
    thanks for your comment, I agree.
    Most of the single thread nutblocks I got in my set have a very loose contact to the spindle.
    When a nut is on the spindle and I tip it with a finger to it rotates easily several revolutions.
    The backlash in angular direction is about 2 degrees, that's too much I think.
    5 nuts have a weight of 8.5 gr each, one is 8.6 gr, ... one is 9.7gr, oops.
    What is the correct weight, if it would be really an openbuilds product?
    ciao Schwipp
     
    #4 Schwipp, Apr 30, 2019
    Last edited: Apr 30, 2019
  5. Alex Chambers

    Alex Chambers Openbuilds Team
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    I suspect the anti-backlash nuts are moulded around a length of leadscrew - hence the tight thread. The ones I got with my machine were very tight to start with (and we get a lot of posts querying how tight they are), but running the leadscrew through them several times with a portable drill eased them considerably. Tight when new is good, loose not necessarily unuseable but suggests shorter service life. At an angle useless. Where did you get your machine from - a genuine openbuilds source should sort the problem out for you promptly.
    Alex.:thumbsup:
     
    Peter Van Der Walt likes this.
  6. Christian James

    Christian James Journeyman
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    As Alex said, new nut blocks are usually quite tight until they are "conditioned". When fitting them though, they need to maintain alignment with the L/S when tightening the clamp screws - this needs some careful attention because tightening a screw tends to "turn" or "twist" the nut bock slightly thus biting into the shaft because its not now parallel. My remedy is to gradually nip up the screws and tap the screws with a small hammer (lightly of course) as I tighten them. This will bring the nut block into alignment.
     
  7. Schwipp

    Schwipp New
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    @Christian:
    you wrote "they need to maintain alignment with the L/S when tightening the clamp screws" what is L/S, I am from Germany, not a native speaker?

    From your comments I can extract, that there is indeed an effect on the clamping force to the spindle when tightening the screws. That was the reason why I started this thread, because the effect - for my opinion - was drastic (may be it was so shocking to me because it was the first time I use such contructive elements, earlier in my work life I only used metalic components).
    And I found out - as I described at the beginning above - that there is nearly not any effect on the spindle when I use my "sandwhich mounting" which is:
    4 mm Macrolon polyamid washer (instead of the 3 mm long aluminium washer + 1 mm precision shim) & nutblock & 6 mm thick alu plate with M5 threads, which I sketched above.

    And I think it is not the best construction to transfer all the tightening force trough a 10 mm diameter shim to the nutblock, which has a 9 mm bore at the position of the shim, and this bore even widens at the beginnig, thus there is only a ring shaped contact area between shim and nutblock with a width of 0.25 to 0.3 mm width, corresponding to roughly max. 10 mm┬▓ contact area. The 9 mm bore is nonsense, and/or a shim with only 10 mm diameter on this bore is nonsense as well, why isn't the shim some mm larger in outer diameter (at nearly no cost) ?
    Whose specialists idea was this construction :ROFL: ???
     
    #7 Schwipp, May 1, 2019
    Last edited: May 1, 2019
  8. Christian James

    Christian James Journeyman
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    Guten Morgen Schwipp. (That's about as much German as I remember from school!)

    L/S is LeadScrew.
    I agree with you about the 9mm bore in the back of the nut block - it is just ridiculous! I believe its an overhang from some years past when a 5mm screw was sunk into it to clamp to something but no one has bothered to change it since. If you look at my my build log you will see I had the same problem and a similar solution.

    Build log:
    Workbee "style" 1010 cnc
     
  9. Schwipp

    Schwipp New
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    Hello Christian,
    it is nice to correspond to some on the opposite site this planet; also late this day I could reply to a email from you one day earlier than you send your email, - answering before asking :) , in local time of course. I experienced this already.

    I like your thoughts corncerning constructing the cnc, my thinking and plans were equivalent. I made a long thread on this in German in a wood cnc forum,
    and mainly abused a wood cnc because the mdf-doors in our house in summer expand 1- 2 mm and in winter shrink and than again work well, this is not what I like for a cnc to happen.
    If you like to train your German....here
    Ciao Schwipp
     
  10. Christian James

    Christian James Journeyman
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    Lieber freund, Ciao. You speak Italian also!
    Think I might need a little help on CNC -aus-holz haha
    Anyway, time for bed here..:sleepy:
     
  11. Schwipp

    Schwipp New
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    only 5 words: tropo caro (the only italian very useful words which my parents were tought by a friend before they went to Italy many decades ago, = too expensive) and "non capito" = I don't understand
    Ciao!

    later: I will drill the threads myself with this from Great Britain
     
    #11 Schwipp, May 1, 2019
    Last edited: May 2, 2019

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