If this note is still here, and you might consider making one of these things for youself, start here not here. Really. Click away while you can. We'll wait...

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You're still here? Ok.

For context: the previous log serves as a checkpoint where anyone interested in making and using one of these things for real can stop reading because this and foreseeable updates are going off into deep weeds for a while before getting back to anything actually useful.

My tension at this point is that I've been accumulating a backlog of project evolution to log, but the evolution is a bit sideways and not yet to a point of "here! build this!" or "hey! look at this!" and I rilly rilly really don't want anyone who's thinking "hmm, I might actually do that" to think "hmm, it looks like I should wait for this immanent update". Really. If you're thinking about making and using one of these things for real: there is nothing about to drop that's going to make you wish you'd waited.

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So what's this half-year (so far) of "sideways"?

tl;dr: another failure to change one thing at a time.

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Dear Reader: I don't know that writing this out will benefit anyone other than me trying to keep my own story straight, and to shift a partial load of backstory out of anticipated Log entries that might possibly reflect more forward progress.

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From the previous log: one fine day I discovered solid sliding contact between layers of the XY stack. It appeared to have been so for some time and through a few revisions without hindering normal operation. I could have just said "so it is" and let it be so. But trying to pass that off as a working mechanical design seemed like a slouch too far.

So here's a story that runs more-or-less linear through the part that could have been easy, then diverges.

The printed parts of this X+Y stack are all PLA -- the printable plastic that's stiffer than most (all?) alternatives that aren't exotic. When it's not too hot. And too hot isn't very hot. The X & Y steppers run hot enough to make compatibility with PLA a question from the start. That's why the motor+screw units live at the outboard edges of each layer and with open-ish ventilation around the motors. Empirical results so far indicate that the thicker middle part carries the Y motor without trouble, but the thinner top part softens enough to let the X motor droop.

The greater vulnerability of the top part/X motor is no surprise.

Working clearances reduce direct support for the motor to a long thin cantilever:

With the interior of the part body thinned out so much, support for the motor leans more on the stiffness of the perimeter. The motor+screw unit fits right along the front edge, which runs between the front corners which are supported by the left & right edges, which have greater section depth through their cantilever projections beyond the supporting rod ends:

The front face supports the front edge of the otherwise floppy font third of the top surface -- from which the motor hangs. It also has a big hole in it for airflow to cool the motor. Continuity of edges above & below the big hole help the face resisted bending, but the resulting parallelogram is weak in shear, which pops the 'stiffness of the perimeter' baloon. Reducing the vent area seems like the wrong answer to a heat problem.

So the X motor is held up by some long, thin, warm cantilevers. Clipping a couple of corners of the big hole might have helped. A little. Maybe. 

...And that all turns into a sliding interface with the part below, as highlighted in the first image above. Which works. For inaesthetic reasons.

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Hmm...

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How about shifting the motor+screw to the other end of the front edge?

aside:

I was already considering that shift as part of a deferred cable routing aspiration which I had "...convinced myself to stop thinking about ... But d[id]n't not consider it anymore." But the current round of failure to change one thing at a time has finally killed it off. By replacing it with a different cable routing aspiration which benefits from the same shift for a different reason.

I think the original and simplest idea that might have been most quickly implemented to solve the motivating problem was that moving the motor to the corner would permit (i.e. reduce inhibition inhibiting) restoring the integrity of the perimeter by moving the big hole from the front face to the top surface directly above the  ̶h̶e̶a̶t̶e̶r̶  motor.

I think that would have improved both mechanical support and also ventilation. Better ventilation would reduce heating and softening of the material.  All good. Except for the risk that wrapping a relatively thin wall close around the motor might introduce enough new bad to bury the good. Based on nothing, I think it would probably have worked.

I think but don't know because I didn't actually get a part printed before the next idea.

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Being closer to the corner, a brace under the motor (i.e. under the screw next to the motor) could tie into the extra-deep section of the left edge a little back from the corner. Then the dubiously thin & heated corner of the perimeter could go away and open up the corner completely around the motor.

The brace would tie into the left edge with a relatively short joggle. That still depends on the stiffness of the perpendicular segment, but it's a relatively short segment with at least a little more than minimum thickness in it. The part that needs to be stiff is still pretty close to the hot, but the hot is even more better ventilated.

I think there's fair odds it would have worked.

I think but don't know because I didn't actually get a part printed before the next idea.

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Consider:

In the status quo, the wall at the motor end of the pocket that locates the motor+screw unit is thin. It was kept thin to maximize the free air volume around the motor.

(How much did a thinner vs. thicker wall really improve ventilation & cooling? I don't know. Categorically, there are lots of guesstimated details where I haven't done any A/B testing or otherwise tried to determine which details really matter, which don't matter, or which really matter and are wrong. STEM projects, anyone?)

For a first try at relocating the motor, I just shifted the same pocket and thin wall over toward the corner.

For all the same rationalization as tying the under-brace to the left edge, that end wall now looks like it could serve as a cantilever of deeper section. But it's thin. But now the reason it was thin (if it ever mattered) is ventilated away.

So it could be thicker. And internally detailed to print solid. That, plausibly coupled to the left edge, would make a much more stout cantilever. Maybe stout enough to do the job without any janky under-brace.

Being shifted left, that thickened part of deeper cantilever section also aligns with less clearance cutaway (where bearing clearance doesn't have to also clear the bearing tie).  So reinforcement of the more substantial cantilever can more substantially extend back into the top surface and over to the left edge.

I think there's fair odds it would have worked.

I think but don't know because I didn't actually get a part printed before the next idea.

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If I correctly recall how this went, the obstacle to just printing that was a need for some decisions about details of (not shown here) how to preserve the option of attaching a workholding slab on top of the stack. That kept me in the mode of thinking about what could get pushed around where and where could the thing that was there go and constraint solving generally...

...and that left edge looked so much like it wanted to be straight.

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So...

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So... why not push the motor a little more left?

Because that would break the "box" -- the (130 mm)² hard footprint of the XY stack.

So...?ᵃ There's already cable and cable ties out there.

But the internal routing aspiration hasn't died yet.

So...?ᵇ What's the big deal about the small square?

The minimal footprint aspiration hasn't died yet.

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And that's all a bunch of stuff where my overwrought side quest for fancy packaging distracts from this relatively straightforward, repeatable, potentially useful project.

An aside above mentions internal motor cable routing. Like the limit switch wiring which is already internal. Early in the project, after a load of fussing with the internal limit switch wiring, I deferred fussing with motor cable wiring. A little further into the project, I convinced myself of a good reason to forget about internal motor cable routing. A little more further into the project I saw a way around said good reason to forget about it, which involved the same shift of the X motor that looks like a way out of the currently motivating heat sag problem. And yet still managed to stay out of that rabbit hole.

And the whole box shrink thing. That's really super not this project. I've burned a lot of stare/ponder/sketch time on that. For reasons that aren't part of this project. And yet had managed to avoid doing anything about it.

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Until...

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...while one teensy detail shy of just printing parts that seemed likely enough to solve the motivating not-really-a-problem...

...the background noise of staring/pondering/sketching bounced out of the familiar entropic well and tumbled into a constellation of ideas that threatened to disturb >two years of peace over in the fancy box project.

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Here ends the linear narrative.

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As much of the divergent part as I ever get around to writing about, and some results that aren't "sideways", will appear over in the fancy box project.

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In scope of this project, the 3d printed XY table had developed to it's latest form...

...as a recognizable evolution of the first idea that looked like it might work:

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Now, not so much:

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That's a lot of change. Hopefully it's as good as "sideways" and not backwards. At least it hasn't sagged yet.

I'm not pushing to publish the new thing yet because the pictured example still required some handcrufting to make it work. (Those aren't the shims you're looking for.)

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Map out of the Log backlog

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At the moment, I expect the next thing will be a Log entry over in the fancy box project. That's moved considerably more "forward", in that context, than the "sideways" leap described here.

Then maybe back here to describe what happened to the XY table. Either for real with well-sorted parts to build from, or "prospectively" anticipating that I'll eventually get this version well-sorted for repeatable reproduction.

I still don't foresee this XY revision going anywhere so exciting that it will be worth waiting for if you want to build your own little mill now.