I broke my YM-14 (and how I fixed it)

Discussion in 'Community Support' started by Dave Hylands, Sep 17, 2014.

  1. Michael Reed

    Michael Reed Staff Member

    We've been having a few problems with YM-14 - it is scheduled for re-design in mk 1.1. Unfortunately I needlessly attempted to make things more compact. The newer model will have a much less constricting access hole for the Y-MAX switch and plenty more 'meat' in the bottom section to increase the strength that is lost by the t-bolt cut out.

    Solid effort repairing it so easily though! If you need a replacement part Dave, just let us know & we'll be happy to oblige.
  2. Michael Reed

    Michael Reed Staff Member

    I'm also considering creating a wiki structure of reported problems & what version they are classed as resolved - it will be segmented by the assembly range designator (YM, TO etc.) and then I'll set up a syntax for referencing the particular part (eg. YM-14) and then have a description and images field.

    Do you have any suggestions or desires for how I set this out?
  3. I think that the wiki page sounds reasonable. Anything searchable will be useful.

    One of the first questions will be "How do I figure out what version I have?"

    And since I didn't discover about the swapped swithes until after all of my belts were tensioned, I wound up using a regular allen wrench and removing the screw holding YM-10. Then with that bolt removed I could move the piece enough to allow the limit switch to be freed. It was a little tedious to unscrew/rescrew YM-10 since I could only get about 1/6 turn before having to remove and reposition the allen wrench, but I figured that was easier than untensioning the belts.

    I also broke IS-22. I replaced it with a scrap cut out approx the same size and drilled holes in the right places. Having the extra square holes considerably weakens that part. I didn't think I was using excessive force, although I broke it when tightening it up a second time (I originally mounted the IS-22/IS-23 on the wrong side (so the bolts weren't accessible from the top - Doh).
  4. Michael Reed

    Michael Reed Staff Member

    We've had one other person have problems with IS-22 as well - looks like I'll have to come up with something clever to change that too.

    In terms of determining your version number - luckily this will always be etched into the back panel. We figured that the curse/beauty of laser cutting the design would be rapid changes & updates so we wanted to make that one easy to find.

    PS I know your pain with the Allen wrench - that's why we so desperately wanted to include the driver kit. Sorry it still managed to get you :p
  5. I think that using a different material for the pieces that clamp the belts might be appropriate.
    The black acrylic is quite brittle. Perhaps using a thicker version of the clear plastic material (which seems to not be as brittle).
    I was tempted to make small metal piece but decided it would be overkill. UHMW or one of the variants is quite strong, and also not brittle, and is probably laser cuttable. I have 1/16" sheets that I use (but I don't yet have a laser cutter). It's a real pain to machine (using a milling machine) since it has a tendency to melt, but my table saw does a wonderful job.
  6. Michael Reed

    Michael Reed Staff Member

    We've been strongly considering swapping out a few critical parts like that for ductile materials, the two choices I'm currently tossing up between are:
    - Acetal (delrin): looks nice, cuts well, quite strong, ductile (not brittle) but is very expensive. This might still be practical for only some small parts though.
    - plywood: doesn't look as nice, cuts well, reasonably strong, ductile, cheap as chips.

    Out of interest Dave, what would be your thoughts on having most of the other internal parts of the printer made from wood (ply most likely). You wouldn't see them once assembled but would mean you're less likely to break parts during assembly.

    PS the clear material is also acrylic - batches of the sheets will often have mildly varying properties including ductility. More importantly though, the chemicals required for black make it more brittle than clear and the frosted pieces are actually quite ductile. But on the flip side the frosted acrylic is very difficult to cut consistently as it warps a lot while cutting.
  7. The issue with plywood will be dimensional changes due to humidity, especially due to seasonal changes. I think making parts that don't need the dimensional stability out of plywood would be fine.

    This page suggests about 0.1% dimensional change for a humidity change from 40% to 80% (0.050 change per 4 feet is about 0.1%)

    So for the longest belt, it's about 30 cm from pulley to pulley. So 0.1% of 300mm is 0.3mm, which I think could break things if you made the belts tight when the wood was small and then it expanded.

    But for parts like IS-22 - making it out of plywood would be fine.

    I love delrin for milling, but yeah it's expensive.
  8. Michael Reed

    Michael Reed Staff Member

    I actually had a discussion with a local engineering plastics importer this morning and I'm going in to inspect his stock of Delrin sheets and discuss prices tomorrow morning - so maybe Delrin for some of the parts is an open possibility.

    I also agree with the humidity issue in the plywood - I'm honestly quite surprised that machines like the Ultimaker operate so well in extremely high humidity conditions (ie. here in Brisbane). But like you mentioned the parts that would be made from it would be very small relative to the acrylic frame so expansion would hopefully be a non-issue.

    Additionally we have made quite a few models from MDF over the months while developing the design and we never seemed to have any dimensional fluctuation problems with them. Whatever we decide - we'll make sure to make some test models before we ship the design out.
  9. My understanding is that MDF is much more dimensionally stable than plywood (MDF has no grain, and a large component of the filler is some type of epoxy resin). MDF and plywood that's finished on all surfaces is more stable than material that it unfinished.

    I know when you purchase hardwood flooring you're supposed to let the boards stabilize for about a week to allow the boards to reach similar humidity to where they're being installed.

    The absolute humidity isn't really an issue, it's changes in humidity than can cause problems. Outside, our humidity goes as low as 10% in the winter and up to 80% in the summer. Inside, it fluctuates less (I have a whole-house humidifier).

    Of course it also depends on the design of the unit. If you make the entire chassis out of the same material, then everything should expand and contract in unison. It's the steel rods and belts that expand/contract at a different rate. So it depends on how well the design deals with that.

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