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• circuit milling: 0.05 mm (2 mil) trace/space

  Paul McClay • 09/13/2024 at 05:10 • 0 comments

  Last year 0.2 mm trace pitch seemed pretty tight:
  

  "... just think of the precision required to take off the copper layer and only the copper layer, and leave traces down to 0.2 mm behind." -- HaD Prize 2023 finalist announcement

  ---

  Here's half that...
  

  ---

  Admittedly more tedious than $pendier option$ with a big friendly START button, but this little machine got the job done.

  • From counting pixels[1] and a little more math than expected[2], I figure the 0.1 mm center-to-center traces (the skinny ones) are 46% trace and 54% space. So 0.046 mm trace and 0.054 mm space. Not 0.050 but both round to 0.05 so I'll go ahead and plant that flag. In barleycorn units: 1.8 mil trace and 2.1 mil space out of 3.9 mil pitch, and again I'll conveniently round to 2 mil trace/space of 4 mil pitch.
  • I have to stop thinking about how to interpret the various irregularities -- maybe that will be another log entry later. For example, the horizontal segments at top-left (which are diagonal) are straight but the similar horizontal (diagonal) segments at top-right are wavy. Both were cut by moving in the same direction at the same rate. The segments on the right were the first in their loops where the bit plunged at their left (in that pic), moved not-so-straight to the right, then continued clockwise. The 2nd and 4th of those (down from top) were approached from about the same direction and have about the same kink. The same segments came out better when cut with ~30 μm (~1 mil) more backlash in Y (found and fixed before cutting the example shown). The "vertical" (diagonal) segments at the left look generally straight but a little more rough than the rest -- those came out worse when cut with a little more backlash in Y. It looks like the cut path deflects a few tenths (of a mil) to the left relative to travel. Etc.
  • But mostly: hey look at that! Not "just barely" but actually pretty decent. Another increment of exceeding already much exceeded expectations for this extremely low cost, extremely compact CNC design. !.

  ---

  did he say "tedious"?

  Yeah. It was a development exercise. Lessons learned may help make future work at this scale less tedious, but probably not not tedious.

  how

  You're already reading this project about how to build a little CNC mill. Elements of coaxing the built thing to carve tiny isolation lines through copper cladding include,

  • stable hands-free magnification
  • design to X/Y stepper full steps
  • repeat to refine
    • pointy v-bits
    • runout
    • density test cuts
  • repeat to refine
    • level
    • level test cuts
  • laps

  ---

  stable hands-free magnification

  This time I went straight for the stereo microscope because not needing one wasn't an objective. I've also used my phone on a little tripod for nearly no (incremental) cost, and a USB camera for le$$ than the microscope, either of which might have adequately supported this exercise.

  ---

  design to X/Y steppers' full steps

  The small steps in the least-stepped segments adjacent to straight segments match the 0.025 mm practical limit of horizontal positioning for the motor+screw units used here. (The little jog segment length is step×√2 for diagonals (pic at 45°).) That step-over distance corresponds to one full motor step. I'm running x8 microstepping for best acceleration & speed (another log entry "soon"...) but single microsteps are so uneven that there's no fraction of a 0.025 mm step cycle that's useful for positioning. Designing to a 0.025mm "snap grid" puts each feature at the same phase in the microstep cycle for each motor....

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• Newer Z is gooder

  Paul McClay • 07/03/2024 at 04:08 • 0 comments

  The first Z axis was ... good enough to not fuss with for a while while fussing with the X+Y axes. The second try (i.e. first attempt to improve) was meh. This one came out better.

  The moving part & clamp changed more than the fixed part. I'll have to decide whether to make the next one slimmer or make the base plate behind it wider.

  ---

  The most visible intent/reality gap with the first 3d printed (vs. 2d laser-cut) Z axis was the fiddly half-dozen M3 socket head screws in the tool clamp.

  The clamp screws ran into single-perimeter holes. That "worked" because pull-out strength can be ok. But it didn't really work for the idea in mind because the hole threads were vulnerable to torque-out and wear from frequently turning the loaded screw  ̶k̶n̶i̶v̶e̶s̶ threads (call it "slice-out"?). That required attention and a tool to torque up the screws carefully, and to carefully torque all of them instead of just half (one side) to ensure even (i.e. minimum) tension.

  Not the quick, casual, routine operation I had in mind.  

  ---

  Reducing that mess to two thumb nuts:
  

  • better reflects the "very inexpensive" idea of making it easy to drop in a daily-driver rotary tool
  • improves durability by turning metal nuts on metal screws to secure/release the clamp while the screws in plastic can be driven once and left alone.

  ---

  A less evident fault with the first printed Z axis was sagging PLA around the warm motor.

  The motor mount screw holes yielded some but didn't fully fail. I don't know if that's because it stopped creeping after I turned down the motor current, if it relaxed to some equilibrium and stopped there, or if it was ten minutes from falling apart.

  In any case, it wasn't a big surprise that the PLA softened.

  For the first version I opted to just print it and see what happened before getting too wrapped up in trying to anticipate heat effects. It didn't take long to confirm that the pulley(s) couldn't be PLA. PETG is working fine there (white vs. blue in the second pic). The motor attachment to the base part wasn't so obviously bad. It looked fine for a while. Distortion around the screws became evident after a while but wasn't a big deal. The screws continued to hold. It was "ok" to use but definitely needed some help.

  I suppose it's possible that with two motors the motor current could be reduced enough to keep the motors cool enough for PLA. I haven't tested that. (A second motor/pulley/cord can be installed for cheap insurance against dropping the big angry part. That's more of a concern in the laser-cut version where the cord/s is/are hidden and run close by sharp edges.)

  ---

  In the second version I tried embedding hex nuts at the surface -- middle in the pic below. They didn't help pull-out strength which still relied on the screws holding in the plastic part and I doubt they got any less hot than before. The idea was to try spreading the radial load over a larger area of PLA. I think they actually helped more than what I had in mind: by fixing the screws perpendicular to the motor tabs they spread the radial loads much more by requiring the motor to drag the whole screws sideways through the PLA if it was going to go anywhere. They also protected the threads in the PLA hole from stripping by providing a hard stop to torque the screws into. It looks like they worked because there's no indication that they moved. Caveat I didn't run that version very long or in hot weather.

  While the nuts seem to have worked well as far as tested, that arrangement had a couple of drawbacks. If a nut were removed, I didn't have any great ideas for how to put it back in the right orientation to match the nut thread to the hole thread. And nuts would add a line to the BoM which I'm trying to keep short. 

  For this version I'm trying PETG plugs in the PLA part to hold the hot motor mount screws -- right side in the pic above. PETG (or whatever...

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• Meh. New Z is fail.

  Paul McClay • 05/03/2024 at 22:26 • 3 comments

  Pretty but not stiff. Time to learn me some FEA? Back to the drawing board.

  Thumb nuts > bunch of screws.

• Thicker Brass bis: Made a Thing

  Paul McClay • 02/20/2024 at 05:59 • 0 comments

  (2 Jul 2024 update: add 2nd pic)

  Made a thing from brass thicker than paper and that isn't just a flat cutout:

  ⸻	<update>
  	Tried again better paint (more correct color and less wrinkly) but still not right better milling
  ⸻	</update>

  It's a shanyrak[1], as stylized in the national emblem of Kazakhstan[2][3]. Because my wife is Kazakh.

  Yes, the paint wrinkled when I sprayed clear over it. A lesson in alkyd/acrylic/time issues. Call it a rough draft/proof-of-concept piece. Or maybe I should brag up my successfully executed wrinkle finish.

  In October last year (writing in Feb '24), in a press to maybe possibly get a competitive HaD Prize final entry together (failed but that's a different story), I tried cutting something more interesting than a backlash test pattern in a chunk of brass thicker than a thin sheet, which failed in a confidence-inspiring way.

  Months of other stuff happened.

  When opportunity to try again came around, I had the idea of (re)starting with a simple figure that my wife might like -- a shanyrak -- since she tolerates all this nonsense. And Valentine's day was imminent.

  That was supposed to be simple but turned into another scope creep fest... ...which could turn this into a dissertation that never gets finished so maybe I'll just add some notes to the [2] footnote in case I ever come back to write more about that.

  ---

  Process

  roughing + lowest flats

  I rough cut the face, outline, and the center pocket down to a level above any detail with a 1mm end mill. Then cut the deepest pockets to final shape & depth with a 0.38 mm (0.015 in) mill.

  I guess it doesn't take much metal to make a (relatively) big pile of glitter. 

  Here's an opportunistic illustration of the divided project architecture: 1) the CNC core, whether this project here or elder sibling #Minamil 2dc: a minimal CNC mill, and 2) a structure that can be something fancy like parallel work in progress at #"Desk Accessory" CNC Milling Machine but doesn't have to be.

  The CNC part doesn't care whether it's in a tidy little box or scattering chips to the winds. If you're here for the CNC you can build the CNC and carry on.

  This pic shows a concrete illustration of the realized practicality of having a "desktop" CNC on my desk. The mess stayed in the box and that little patch is trivial to suck up with a hand vac. So long as it's sitting on a flat surface, which I think is a reasonable expectation for a desk.

  (having written "vac" I probably should add "HEPA". and the opening in the box under the XY table is for an air filter that isn't there yet -- the double-stack fan (high static pressure) will pull air down and (filtered) out the back so fine dust doesn't float up out the open top of the enclosure. which it does. that arrangement worked pretty well in the previous frame build. that all could be replaced with a vacuum hose stuck in a hole in the same spot -- which could be interchangeable if the fan and vac hose were the same diameter. i'll have to write all this air/dust stuff in a log at some point and trade all these words for a link to that. after finishing the fan/filter box there.)

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  paint - and lost messages from the future

  Paint's not my thing. What I learned from this encounter is to do pretty much everything differently.

  I think I cleaned the surface adequately. It was freshly cut and cut dry so it should have been pretty clean after vacuuming out chiplets anyhow. 

  I used a rattle can, which meant masking around the workpiece and covering a fairly large area to manage overspray.

  Lesson: dust again after masking & draping.

  This was weird: That's probably too much paint for a first/single coat. I ended up spraying a load of paint...

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• Build? Start here.

  Paul McClay • 02/06/2024 at 05:39 • 0 comments

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  ---

  I've tried to make the CNC part of this (relatively) easy to reproduce from some 3d printed parts and a minimum of other stuff. It should go together by assembly with as near to zero fabrication as possible.

  Writing up how to actually get that done is a project in itself. What I have so far is pretty rough, but I think it conveys enough information to give you a fighting chance to build a working machine.  As of writing, I intend for this log entry to serve as a stable "start here" point with links to the latest work in progress as it evolves.

  Please let me know If you're thinking about actually building one of these. I've turned on "public chat" for this project (big orange button on the project page, or right here) and set up a Discord server. We'll see if either of those gets any traction.

  ---

  Here's what I've got so far...

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• Jolly Wrencher 2023

  Paul McClay • 01/01/2024 at 05:57 • 0 comments

  ---

  Cut but didn't publish this back in October, so I better hustle it up here before 2023 expires (in my timezone)...
  

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• Thicker Brass

  Paul McClay • 10/10/2023 at 00:26 • 0 comments

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  Brass. More than 5 mil thick.

  If you squint, you might see a Jolly Wrencher in there. It didn't come out like I wanted, but the fault was mine.

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• doors again: current and (maybe) future

  Paul McClay • 10/08/2023 at 05:20 • 0 comments

  In the previous log page I walked through the history of the enclosure part of "frame+enclosure". This entry describes the latest iteration. It's all kinda deep weeds and I don't know if anyone will ever actually read it. I wrote a lot about this because it's been one of the more convoluted parts of working out something that might work well enough to call "done" for this project.

  ---

  Many words and little proofreading follow, so I have no idea how this all differs from what I think I wrote...

  ---

  In all previous flavors of storage/working enclosure, the doors fold 180° to collapse for storage, then close rather conventionally like doors. Another possibility was to have each door fold 90 deg then each door closes around the two open sides, one over the other.  That would avoid having two edges meet at a corner -- which seemed like trouble before discovering that it worked quite well. Reasons I didn't do that in the first place included the hassle of making the hinges different between the two sides, and more significantly, with single-thickness door panels, that leaves no opportunity to attach anything to the inside of the outside door, I already wanted to avoid attaching anything to the outside.  So that was going to complicate closure.

  Then I looked for hinge options to get away from tape and decided to try these:

  They multiply the panel thickness. Folding them double also adds the width of the web between the two panels, so the fold would be that much more than twice as thick. Quite counter to my earlier obsession with minimizing footprint @@@link.

  That was a reason to reconsider wrapping the doors around the corner instead of folding double. Joining thin panels with thick hinges also relieved the problem being unable to attach anything to the inside of the outer door or outside of inner door (i.e. only to inside of inner door). So, giving that a try...

  Those hinges fit between panels. Their thickness sets a "free" thickness for hinges at the frame. After looking at a lot of unsuitable hinges, I figured out that was enough to space for bespoke hinges.

  The dark material in that pic is just tacked on to show where the solid side would end if it were cut for the thicker panels. The outside door edge should bear directly against the solid side panel.

  "bespoke hinge" really means three different hinges -- just for that side.

  On this side the hinges carry the inner door while the edge of the outer door should bear directly against the inside face of the solid side panel. For the inner door, the hinges also back up against the solid side panel, and clearance between the fixed half and the edge of the door goes to zero with the door closed. When pushed in from the corner, the inner door should bear directly against the fixed parts of the hinges which bear against the solid side panels. A few small plastic parts will be more squishable than the whole door edge meeting the side panel, but the hinge in the inner door will buckle and/or compress before sending much load into that door panel anyhow.

  Then there are more different hinges on the other side to keep the hinges behind the plane of the outer panel.

  Again for the hinged panel the clearance between the moving panel and fixed half of the hinge goes to zero with the door closed, to bear whatever load they get which will be moderated by the hinge between door panels on that side.

  In that corner, the inner door panel bears against the thicker fixed parts of the hinges, which again bear against the frame side panel.

  (This pic also shows how the enclosure panels extend below the hard box to the level of the bumper feet to sweep the work surface. That helps to contain the mess. And I think flat-ish smooth-ish surface is a reasonable requirement for what to have under this thing.)

  That all adds a lot of bulk, especially where the folding hinges double up at the...

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• feature creep vol. {n+=1}: doors

  Paul McClay • 10/07/2023 at 05:34 • 0 comments

  Another log mostly about already-dead stuff that I took pictures of before breaking it down to make it different again.

  ---

  I tried to make this vulnerable corner at least not super fragile. It turned out to be super not fragile.

  
  

  It will take a much harder hit without damage. But the under-developed closure is just a short peg that sort of gets close enough to a small magnet to be weakly encouraged to not wander away, and hitting it much harder was bouncing the doors open, and that would confound the point of this visual demonstration. So just a tap for show.

  I think I'm going to miss that clean, durable arrangement. The problem is that it was hinged with packing tape and that's not a long-term solution. I've been noodling ideas for making hinges that should age better with least loss of compactness or acute durability.

  I've had another go at it, and maybe found a thing to try next. But first, a little about how we got here.

  ---

  ---

  Starting with some history from the preceding laser-cut designs up to what I liked about the last iteration before breaking it.

  Before beginning

  Way back in pre-history, a piece of paper on each side of the frame did the job.

  CDROM discards are a perilous gateway drug.

  ---

  One thing lead to another and I got started into the laser-cut precursor to this project, retronamed "Minamil 2dc".

  ---

  Zeroth: zero

  A couple of 2-axis test ⋅ cuts with just the first XY table encouraged me to:

  1. keep going with the idea
  2. rig up some sort of debris containment ...

  First: pepakura

  ... so before cutting anything, the first 3-axis frame had a 3+-sided paper shroud.

  The "wings" projecting forward from the sides kept debris pretty well corralled to the tabletop. That actually got a little bit elaborate where it folded around and projected beyond the frame, and passed moving wires through without opening a big hole. (cable management has been a thing from the get go)

  Aside: in this project I emphasize the distinction between the CNC mechanics and the fancy enclosure that you don't need to make the CNC part work. Here illustrated. You don't even need a road atlas if you don't mind a little mess.

  Made from garbage-grade wood scraps, used uncut as found.

  Second: win

  This actually works really well.

  Four-sided enclosure. That really helped to make table-top work more simply practical. Taking advantage of how the horizontal axes collapse to a footprint smaller than needed in operation, the walls of the debris corral fold in to make a smaller box that doesn't have to occupy a bunch of space that it's not using.

  Having the front panels cut before I had any idea what to use for hinges, I just taped the panels together to visualize the basic idea while I figured out what to do for hinges. That worked well enough to become the answer for hinges.

  Aside: the side panels were cut tall enough to be taller than the raised Z axis (sans tool) and protect it for mindless storage. Then the Z axis got longer and broke that feature. The counterweight and its mast and beam fit inside[a] the closed box for storage -- until the counterweight got killed off.

  [a] Sub-aside: that vid emphasized need to have a vacuum handy. That was self-inflicted by opening the doors outward then getting clingy debris up to my elbows after reaching in there. Later I got the clue that pushing the doors in, like the one on the left in the right half of the pic above, allows reaching in and doing stuff with much less hassle.

  Made from less crappy wood, HDF, and acrylic scraps, cut on a table saw.

  A relevant feature of this version is that the attached doors fold back flat against the side panels.

  That proved really helpful when flipping the box around to do stuff with the doors open, and when handling a removed side panel without either removing then re-taping the door panels, or dealing with an awkward big thing that's either awkwardly floppy or awkwardly levering...

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• about runout

  Paul McClay • 10/02/2023 at 08:18 • 0 comments

  tl;dr: if you can see it you can tweak it

  Some examples of work from this little CNC and its precursor demonstrate pretty small runout from a generic faux-Dremel rotary tool. Repeating that will be part of replicating this project for anyone so inclined. It also seems like it could be useful to anyone trying to do fine work with a not-so-fine tool.

  The point, when I get to it, will be anticlimactic. It's pretty simple. But I haven't seen it elsewhere in my limited scope of reading. So: sharing. Akshully I've written this before but that was buried in another topic and without illustration. So: sharing with pictures this time.

  ---

  ---

  To reduce runout when using a cheap generic rotary tool and maybe some other small-cutter tools:
  

  • See the current runout using stable magnification that you're not trying to hold still in your hand
  • Tweak the bit toward center
  • Repeat until runout sufficiently reduced

  That's all <yawn/>.

  ---

  More verbosely, and with pictures...

  ---

  See

  The gif above shows a view through a microscope on a stand that can look sideways. But that's cheating. Here's a method more in line with the "low cost" theme here:

  That's my daily driver phone in a little pocket tripod (which I've cropped :/ but you've seen a tripod before).

  • that phone is not new but not too old to have a camera that can focus close enough to do this
  • manual focus in "pro" mode helps; otherwise you'll probably need to put something right behind the bit to appease the autofocus
  • the viewfinder grid provides a fixed reference to help perceive small deviations at the tool tip; otherwise put something with a vertical edge close behind the tool (which might also appease the autofocus if you're stuck with that)

   That looks like this:

  While less crisp than the gif above, you can see that you can visually resolve a small fraction of the bit diameter (0.5 mm in this case), which is the practical scale for runout.

  ---

  ---

  Tweak

  Established Brand general purpose rotary tool collets aren't fantasticly precise. Generic clone rotary tool collets are really poor (typically, in 2023Q4). They are basically poorly made ball joints. The good part of that is you can point the bit any direction you want.

  I'm using very small cutters here, which don't generate very large radial forces. So firmly finger tight on the collet is tight enough. A very tight collet makes it hard to make small tweaks. If the collet is not tight enough, the bit will "walk" out and drive down into the workpiece. So there's an element of "just right", but for small cutters that seems to be a pretty wide range and easy to hit.

  Very small cutters break easily at the tip, so take care to apply tweaking to the shank and not the thin end.

  I think you should probably not do this: I started out tweaking by hand -- with a finger around the bit and thumb against the collet for good leverage. That sometimes meant pulling pretty far down the narrowing neck of a short bit and perilously close to the skinny end. Nothing bad happened, but that just seemed way too close to blood to expect that it would never go badly. So I printed a tool:

  I've been using that, but It's just a first whack at the idea and not a great example. So I hope you'll make a better one.

  Applying tweak without slashing a finger. In the photo my finger is behind the bit for contrast, which makes this a poor example of applying tweak without slashing a finger, but you can see the idea.

  ---

  ---

  Repeat

  While you probably won't get as close as you want on the first try, this method seems to converge much faster than "open loop" fiddling for that once-in-many low-runout chuck-up that teases you with knowledge that it's possible but only happens when you're not trying to make it happen rant rant.

  ---

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  And if you're still reading...

  Rolling a stiff cylinder around the collet nut to make a slip-on anti-pointy guard has saved some bits and probably some blood. Especially useful...

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