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TrueUp Kit Version

Discussion in '3D printers' started by Keith Davis, Mar 24, 2017.

  1. Elmo Clarity

    Elmo Clarity Journeyman
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    I think you are getting the terms "pitch" and "lead" mixed up. It is the "lead" that is important in the calculation. As the picture I posted shows, the number of starts will not change the pitch, but will change the lead.

    Bottom line is, your Z resolution is limited by this number. With the 2:1 ratio I have, I can use layer heights that are multiple of 0.02mm. Is that correct?
     
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  2. Elmo Clarity

    Elmo Clarity Journeyman
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    I have not found anything yet to decode the TR values. I have seen 4 start screws labeled as both TR8*2 and TR8*8. The important things to know is the pitch, starts, and lead. Lead is equal to PITCH * STARTS.

    With my setup using 40T on the screws, there is not much room between the pulley and the frame. So to get a better gearing ratio, you would need a smaller pulley on the motor. I did find some 10T ones that would give you a 4:1 ratio, or 0.01mm/step. I'm thinking the 0.02mm would be good enough, at least for my work.
     
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  3. Alessandro Parisi

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    So, after some calculations based on "Prusa calculator" webpage:

    - with a config of "1 Full Step" , 20T - 20T, Pitch 8mm -> I can have resolution of 0.04 (in the slicer I must put a layer height multiple of 0.04)
    - with a config of "1 Full Step" , 40T - 20T, Pitch 8mm -> I can have resolution of 0.02 (in the slicer I must put a layer height multiple of 0.02)
    - with a config of "1/4 Step" , 20T - 20T, Pitch 8mm -> I can have resolution of 0.04 / 4 from driver (in the slicer I must put a layer height multiple of 0.01)

    but the last configuration is in microstepping mode, so in not the correct mode for positioning the Z axis.. and maybe better have the 1st or 2nd configuration using the correct layer multiplier in slicer software

    Is that correct? :)
     
  4. Elmo Clarity

    Elmo Clarity Journeyman
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    I believe so. At least I will be using the second case of 0.02mm when I get my printer finished.
     
  5. loglow

    loglow New
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    See Keith's previous post. Microstepping on the Z axis doesn't matter (and is even preferable since it's smoother) as long as each layer still lands on a full step! So your calculations are important, but you still probably want to use 1/8 or 1/16 microstepping.
     
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  6. Alessandro Parisi

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    Yes, after read the previous post of Keith I think I'll use a 8mm pitch lead screw with 40T/20T pulleys to have 0.02mm/step on Z axis without microstepping.

    So my possible configurations in slicer will be multiple of 0.02 as: 0.04mm/ 0.1mm / 0.2mm / 0.3mm and so on...

    Or I'm considering to replace my trapezoidal lead screws with regular M8 lead screws with 1.25mm pitch and use 20T/16T for having 0.01mm/step as in the project (with full step)

    Now it's CLEAR :)
     
  7. Elmo Clarity

    Elmo Clarity Journeyman
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    Clear as mud? Right? :)

    Just to cloud things up, microstepping is fine if used to move from one full step to the next. Just don't end the movement on a non-full step.
     
  8. Keith Davis

    Keith Davis Veteran
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    You are correct Elmo. In regards to acme lead screws, the thing we are looking at is actually LEAD not PITCH. On a threaded rod there is only one start so lead and pitch are synonymous. But the LEAD on an acme screw is the actual travel per revolution. The Prusa Calculator is therefor confusing (and wrong) in having a field labeled "Leadscrew pitch", it should be "Leadscrew lead".

    Yes, OpenBuilds Tr8*8-2p leadscrew will travel 8mm per revolution or 0.04mm per step w/ a 200 step motor. So your layer resolution would need to be in 0.04 increments. A 0.3 layer height would be 7.5 steps, not an even step. But you could use a 400 step motor and have 0.02mm per step, an improvement.

    Another improvement, set the jumpers to run the driver a 1/2 steps with a 400 step motor and now you have 0.01mm per step/halfStep. Here's a secret, 1/2 steps are not microsteps, they are physical locations just like full steps are. Why? A half step is achieved by reverse polarity, trapping the rotor magnet between two full steps. That position is just as accurate as a full step. But your driver has to be jumpered to 1/2 stepping to get that effect. 1/2 stepping on a Z axis is pretty jerky and a bit noise since it runs at the same full current as a full step, but it works producing 0.01 increment resolution.

    I would suggest (since you have the 40T pulleys) you use a 400 step motor with your 20T pulley on the motor and your 40T pulley on the leadscrews. That will also give you 0.01mm per step - and work for most usable resolutions.
     
  9. Elmo Clarity

    Elmo Clarity Journeyman
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    I had forgotten about the 0.9 degree motors (400 steps). Will have to think about that. But is 0.02mm layer height going to be that much better than 0.01mm? I hate all the extra time it takes to print a 0.1mm layer height version 0.2mm. Not sure I would ever want to do anything less than 0.1mm. :)

    And I am using a Duet. Not sure how to change the microstepping on it. I'm pretty sure it can be done though.
     
  10. Keith Davis

    Keith Davis Veteran
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    In a nut shell, you've got it, exactly.

    That's why that "Optimal Layer height for your Z axis" section is on the prusaprinters.org/calculator, it's there to help you NOT use layer heights that do not stop on full steps. I instead used it to find screw ratios that let you land on full steps regardless of layer height. Prusa and I keep looking at the same things through opposite ends of the same telescope/microscope.
     
  11. Keith Davis

    Keith Davis Veteran
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    When I use 1/16 I have to turn the pots voltage way up ( 0.79) to get enough power. With 1/8 0.64 will do it.
     
  12. Keith Davis

    Keith Davis Veteran
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    I use the M8 threaded screw simply because M8 nylon nuts are easily available. Nylon nuts are cool. Since nylon is an elastic polymer, the nut swells, and if necessary deforms, to fit the threads tightly. If the nut is anchored solid in the glide body, this snug fit eliminates any backlash. Nylon acme nuts are not easily found. OpenBuilds Nut Block and Nut Plate are acme thread nylon nuts for the same anti-backlash advantage, but they do not fit the design.
     
  13. Elmo Clarity

    Elmo Clarity Journeyman
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    I printed my own ACME Nylon nuts (well, PLA) for my lead screws. :) Seems the nylon nuts I ordered have gotten lost between somewhere over there and here. That is why I switched to the lead screws. If I ever get those nuts, I still have the parts to switch back to them.
     
  14. Keith Davis

    Keith Davis Veteran
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    If I was going to print my own nuts, I'd use ABS or PETG. They are elastic polymers, whereas PLA is not. PLA will sheer to fit the threads whereas the other two will deform. That makes for an anti-backlash fit. Conversely for the same reason, I print all TrueUp parts with PLA because of the many threaded holes in the TrueUp design. Sheer strength threads will withstand more torque than elastic threads. Actually I use a filament called PLA Pro, which is far less brittle than regular PLA, but can withstand a lot more torque than ABS ot PETG.
     
  15. loglow

    loglow New
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    I've recently discovered (the hard way) that some PLA formulations don't tap nearly as well as others. There was one (with a matte finish) that just turned into a gooey mess and the screws slid right through, whereas others seem to tap fine. I've had more consistent success tapping PLA using larger threads (eg. M5 vs M3). For smaller/finer threaded holes, I've become a big fan of heat-set threaded inserts which are usually made of brass. Installation is much faster than tapping, the only tool needed is a soldering iron, and they're pretty cheap (about $0.05 each). Plus they look nice and are stronger, especially after several assembly/disassembly cycles.
     

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  16. Keith Davis

    Keith Davis Veteran
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    Never tried them. Do you have a link for M3?
     
  17. Elmo Clarity

    Elmo Clarity Journeyman
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    I used eSun PLA+ (sometimes called PLA Pro) and it was only for the two nuts on the screw for setting the 30mm length for mounting. Everything else in done in PETG.
     
  18. Alessandro Parisi

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    A question about X and Y microstepping, what configuration should I use with a 20T pulley?
     
  19. Keith Davis

    Keith Davis Veteran
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    1/16th

    I use 16T pulley for a 10micron resolution. A 20T pulley gives 12.5 resolution.
     
  20. loglow

    loglow New
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    I think all of them are manufactured by Penn Engineering:

    D.B. Roberts sells four varieties for 5-7 cents each with a minimum of $5 (roughly 100 pieces) per line item:
    McMaster-Carr sells two varieties of them in packs of 100 for a bit more (12-15 cents each):
    The IUB ones have slimmer profiles than the IUBB ones so they can fit in tighter spaces.

    The docs recommend tapered holes, but they're not strictly necessary. A regular hole that's a press-fit for the very bottom rim of the insert works beautifully. If the hole is too small then melted plastic can obstruct the end of the insert, which is really annoying (if it's supposed to be a through-hole). This isn't an issue if the holes are the correct size though (not too small) and the bottom rim can be pushed in by hand.
     

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  21. Keith Davis

    Keith Davis Veteran
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    Thanks a bunch loglow! Ordered from DB Roberts. Shipping doubled the price. If I like maybe ordering by the 1000 will fix that somewhat.
     
  22. Elmo Clarity

    Elmo Clarity Journeyman
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    For the Z Glide Bushings (the part the nylon rod goes into), you mention there being a taper to them. Is it just the bushing part with the taper or both the bushing and the Glide that is tapered? Mine is falling right through so something didn't print right. I am seeing about a 1mm difference between the top and bottom of the bushing.
     
  23. loglow

    loglow New
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    The insides of the glide bodies are also tapered.
     
  24. Keith Davis

    Keith Davis Veteran
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    The taper was added recently. You may have printed earlier files. Download the STL or SKP files again and compare. The batch with the taper have a notch in the bottom of the insert that is not present in the older ones. Also, be sure that you print glides and inserts the same direction so that Y or X is the width of the cavity and width of the insert. Mixing those directions up will create pieces that inherit whatever discrepancy you may have between X and Y accuracy.
     
  25. Elmo Clarity

    Elmo Clarity Journeyman
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    I was able to scale up the insert so they fit tight. I'll try re-orientating them as you describe and see what happens. Even with the tight fit, I am seeing some wobble on the X axis when changing directions and can see the glides rotating.
     
  26. Alessandro Parisi

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    So you configure 1/16 microstepping for X and Y, but the question is: between 10micron and 12.5micron something would be visible in a printed part??

    Thanks for your help Keith
     
  27. Keith Davis

    Keith Davis Veteran
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    To theoretically hit 12.5 would require microstepping. Microstepping is a phantom, you'll likely land on 13 on most layers, not 12.5. On a box shape you will not notice anything on the walls without magnification. On a frog, it would just add character :cool:
     
  28. Elmo Clarity

    Elmo Clarity Journeyman
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    Going to reprint the glides and inserts. I used the same layout you have in the STL file and it looks like this...

    upload_2017-4-29_9-12-6.png

    Is this what you were meaning? Note that these glides are for an ACME lead screw.
     
  29. Keith Davis

    Keith Davis Veteran
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    Yeah. The Y axis sets the width of the inserts AND the width of the cavities they set in.

    Since you had to remake the glide bodies for the 20x40, are you certain that you tapered the cavity top-to-bottom the same as the originals?
     
  30. Elmo Clarity

    Elmo Clarity Journeyman
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    I used OpenSCAD to cut and paste the original part so there are no changes to the part other than the width in that area.
     

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