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• images: assembly from ready parts vs. fabrication

  Paul McClay • 10/27/2021 at 06:57 • 0 comments

  (This is mostly a place to stash photos for reference from other text)

  Certainly many people have made very low cost CNC machines from scavenged parts, scrap materials, an equipped shop, and a fair idea of what they were aiming for.

  This project presents a design based on two main assemblies – the X+Y axes, and the Z axis+tool clamp – built from a few specified hardware parts and some laser cut flat pieces following detailed illustrated assembly instructions.

   The frame that holds the Z axis over the X+Y axes does call for ad hoc construction from available material, but that can be made to eyeball precision from practically any rigid flat-ish material and would not benefit from over-specification.

• Minimally milling fine-pitch circuit board features

  Paul McClay • 10/23/2021 at 07:26 • 0 comments

  (copypasted from mainline project: #Minamil: a minimal CNC mill. And friends. )

  Responding to a comment on an earlier log, I wrote:

  I haven't written much yet about the blue Wen dremeloid used for most of this project so far to keep it cheap. The main trick [...blah blah...] acceptable runout. I don't think it was ever going to cut the SSOP footprint tho.

  Since then, I got some renewed motivation to try again...

  ...and made it happen. A perfect spindle would be nice, but in the spirit of pushing down the hardware requirement and frustration with the "better" tool, I went back for another round of tweaking away runout. I'm finding more tricks but don't really have that down to a method for a good how-to yet.

  The overall process for milling this example went something like:

  • use stable magnification
    • I've used a phone (camera) held in a phone claw on a tripod...
    • ...until gaining unfair advantage coincident with this iteration
  • tweak the v-bit to small runout (...see? just type the words and its done...)
  • adjust spindle speed to minimize resonant vibration at v-bit tip
    • I've read of doing this by sound and/or feel, but I had to actually watch the tip of the bit under magnification while adjusting speed
    • assuming speed control either onboard or external to the rotary tool 
  • peck a hole just through the copperplate
    • 1 oz. copper is nominally 0.035 mm or 1.4 mil thick
  • measure the breadth of the hole - I did it like this:
    • using magnification...
    • turn the v-bit sideways to view the tip edgewise as a fine point
    • set jog step to 0.025 mm = one whole step (20 steps/rev, 2 revs/mm)
    • position the bit over the hole just a step above the surface
    • jog a few steps to one side
    • step the bit point back toward the hole and stop at the first edge
    • continuing in the same direction, count steps across to the other edge
    • hole diameter = steps * 0.025 mm
      • ideally 4 steps for a narrow-angle 0.1 mm v-vbit
      • more likely 5 for a "perfect" setup, and 6 or 7 will be pretty good
  • use measured peck diameter as tool diameter for generating gcode

  Tool changes for drilling and milling won't be so carefully precise. Notice in the video below:

  • pilot drilled the through-holes with the v-bit in an attempt to help the center the less carefully chucked drill bit
  • maybe might have helped with precision of through-hole locations maybe
  • didn't prevent the swinging drill from carving an oversize hole in the top surface
  • drill did self-center and exit holes are not oversize
  • narrowing of through-holes with depth somewhat visible in vid thumbnail below

  Sub-2-minute video for eye-candy:

• Non-selected bid for "Challenge 3: Reimagine Supportive Tech"

  Paul McClay • 08/23/2021 at 01:10 • 0 comments

  This was my shot at "Challenge 3: Reimagine Supportive Tech"...

  It was a little Procrustean. Others hit closer to the mark. Leaving this here for the history.

  ---

  1. Discuss the challenge the project addresses.

  This entry addresses Challenge 3: Reimagine Supportive Tech

  Create technology that acts as ... more inclusive ... beginner-friendly tech for aspiring engineers!

  Many projects across the maker community begin life as the solution to a problem. How can we fill a gap in hardware? ... How can we bring more people into the fold through more accessible and entry-level projects? ...
  Your solution should make it easier for others to build electronics or make electronics devices more accessible; modular, hackable, or affordable.

  This could look like:
  ...
  * Creating beginner-friendly projects or jumping off points into STEM education

  Within a focus on electronics

  A trend toward making new ICs available only in fine pitch SMD packages increasingly defeats many low-cost circuit assembly techniques apart from making custom PCBs to a level of precision that challenges homebrew etching. This makes new electronics components increasingly more exclusive, less beginner-friendly, less affordable, and less accessible to beginners and STEM students. While several services now provide high quality PCBs in small quantities at low prices, the "low" cost includes weeks of waiting for delivery to most locations. Such long cycle times quash fearless iteration for beginners and students.

  Beyond electronics

  3-axis CNC milling, the traditional "CAM" of CAD/CAM, resists commoditization and remains a complex and often difficult art. Learning generally requires perseverance and access to costly equipment. Pandemic lockdowns keep students away from institutional teaching facilities. Even at the low end of "hobby" mills, costs in hundreds of USD and dedicated space requirements exclude many potential beginners or home-study students.

  ---

  2. Discuss how the project will alleviate or solve the problem that the project addresses.

  This project presents a 3-axis CNC mill of novel design that can mill very fine PCB features, and provide entrée to real 3-axis milling, at much lower cost than any other ready-to-assemble option that I have found to date. 

  Specifically in regard to electronics, this project significantly drops the cost of milling PCBs for immediate use and with precision suitable for very fine SMD pin pitches required for access to increasingly many new electronics components available only in fine pitch packages.
  

  Generally in regard to CNC machining, this project significantly drops the cost of entry to learn full 3d CAM by building and using a real machine to make real parts from usefully strong materials.

  The mill presented in this project features:

  • extremely low cost
    • much lower than any other option I've found without relying on "lucky" scavenging and/or part fabrication from stock
    • detailed <$50 BoM
  • ready-to-assemble parts
    • vs. plans for fabrication
  • extremely compact
    • store on a shelf and use in a small space on busy desk 
  • specific bill of materials
    • vs. "scavenger hunt" parts list

  ---

  3. Publish at least one (1) image illustrating how the project might be used. This may be a sketch, schematic, flow chart, rendering, or other type of image.

  Above, log entries, and Gallery

  ---

  4. Link to any repositories (e.g., Github).

  Instructables

  primary: Low(est?) Cost Reproducible 3-axis CNC Mill

  refers to: A Cheap Compact Linear Motion Slide

  Onshape (CAD)

  primary: Minamil - a minimal CNC mill

  imports from: pmc's cheap linear slide

  Vimeo

  videos

  ---

  5. Document all open-source licenses and permissions as well as any applicable third-party licenses/restrictions.

  CC BY-NC-SA

  ---

  6. Submit the project to the 2021 Hackaday Prize using the “Submit project to...” option found on the published Project Profile.

  Submitted 30 July 2021

  ---

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  Is this a unique solution...

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• Compared to... what?

  Paul McClay • 08/20/2021 at 19:54 • 0 comments

  tl;dr: Minimal appears able to produce finer PCB features than common low-end generics.

  ---

  To what existing baseline can we compare Minamil's PCB milling capability?
  

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  The "cheapest" CNC

  As of August 2021, it looks like the dominant “cheapest” CNC machines for PCB routing[note 1] and other (very) light hobby use are variations of “3018” - a generic design with 30cm x 18cm work area, and typically 4-5cm Z travel. Other “xxyy” designations indicate similar machines with larger or smaller work area. Various sellers offer machines of very similar design built to various levels of cost & robustness. Current examples listed by Amazon include: basic <$150, “pro” ~$200, and “max” ~$300.

  Smaller machines of similar kind include essentially all the same parts and do not cost very much less.  Construction from shorter lengths of similar linear rods & extrusions may give smaller units greater stiffness.
  

  I have not yet found where this design comes from, or when. My current best guess is that “CNC 3018” was already generic before English speakers wrote much about them on Teh Internetz. Please comment if you know.

  Not having one myself, I don’t really know what they can do. After a bit of searching I’ve found several mentions of milling/routing PCBs on these machines, but little indication of use for very fine pitch components or high density of small features.

  • At the beginning of this year, Electronics Weekly blogger Steve Bush wrote one of the better overviews of this category that I’ve found so far. That post was the second of a two-part series. In the first part he wrote “However, like so many people before, I am tempted to have a go at modify[ing] the little cnc to [...] have, maybe, 0.2mm accuracy with softer stuff [than aluminum]”. He recommends a youtuber’s videos, one of which details how to mill a PCB “preceisely” on a 3018. That video, from Sep. 2019, shows fairly coarse through-hole features:

    That gives data points at "0.2mm accuracy" and coarse through-hole (0.1") scale PCB features. 
    

  • YouTuber bitluni’s video “The Cheapest CNC Milling Machine” from April 2020 shows a failed attempt to cut SO (0.05”) pitch features, and then a usable result with 0.1" through-hole and sparsely placed 0603 discrete surface-mount parts:

  • YouTuber HomoFaciens, specialist in building high function from extremely low tech/cost inputs, posted a video “Isolation milling a PCB with the CNC 3018Pro from Mostics” in Feb. 2021. It shows his spindle running with obvious significant runout and he produces a board with coarse through-hole features:

  • Teaching Tech’s Oct. 2020 video “Homemade custom PCB guide using free KiCAD software” discusses design compensation for wide milling tracks and shows a board with coarse through-hole features and thinned tracks:

  • For a non-graphical example, guidance at Hackerspace Nijmegen (currently displaced due to COVID-19) advises minimum 0.5mm separation with between traces: "Milling PCB's with 3018 Chinese Desktop CNC"
  • DIY TECH BROS on YouTube have the cleanest example that I've found so far. Their  “CNC PCB - high quality with the budget 3018 CNC” shows, with dramatic flair (a la WEGSTR CNC?), a clean SO-pitch breakout board. From the photo, I think it looks like their isolation path width is about 0.2-0.22ish mm.

  • In a very extensive tutorial series + discussion "Milling PCBs with cheap Chinese "desktop" CNC-router" spanning Aug 2018 to Sep 2020, author esaj reports "I've made boards with 0.3-0.4mm traces". Although he doesn't focus on fine-pitch parts, his sample photos show some very finely cut traces. If I've figured right, this photo crop below shows isolation grooves cut as small as ~0.18mm:

    He reports generally configuring...

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• "useful" T/SSOP-8 breakout ... almost

  Paul McClay • 08/15/2021 at 08:11 • 0 comments

  update: add photo at end
  

  Earlier I milled a simple T/SSOP-8 breakout board to validate milling for 0.65mm pin pitch.

  While doing that I checked what I might have in SSOP-8 to put on it and found some MAX4326 op amps on an old laptop mobo. The datasheet recommends two bypass capacitors ",,,as close as possible to the device supply voltage input [and] the ground end of these capacitors near the ground plane...", which is likely serviceable for nearly any 8-pin dual op amp, and also for many other 8-pin packages. [note 1]

  Hmm. Only single-side copper-clad board on hand, so no ground plane. Can I do something with a single copper plane? Doodle doodle...

  Yes, there's a loop in the ground trace -- it's really small. I haven't tried to figure at what frequency it would start to matter but I'm pretty sure it's a disregardably large number of 10ᵐᵃⁿʸ Hz for anything in DIP-8.

  ---

  Actually this project is supposed to be more about milling than PCB design so... The adjacent traces are 16mil (0.4mm) center-center. The traces and grooves look pretty close to the same width, or about 8mil (0.2mm) each. Each groove cut in two passes about 3mil (0.07mm) apart. That suggests it's cutting about a 5mil (0.13mm) groove. The paths around these little islands where the two outlines diverge a little are not far from 5/8 the width of the rest of the grooves, so that seems to be about right. 
  

  Cut with a 0.1mm 20° V-bit. That's pretty small runout - which is mostly about the nice spindle - which doesn't really fit the "cheap"/accessibility theme unless you already have one. However the generality of the separate rotary tool allows amortizing its cost, whatever that may be, over many other uses. The point being that the little mill can make good use of a good spindle. Given a nominal tool diameter smaller than the trace separation, FlatCAM generated toolpaths with a little separation between the adjacent trace outlines, which made room for an additional small loop to fully clear the space between the capacitor lands. The space between the capacitor and the chip supply pin was too wide to clear with two outlines but not wide enough to fit another full loop (fit four outlines) so a little island remains.

  LESSON: designing a PCB for isolation milling with simple offset outlines requires more attention to tool path widths - and overlaps. Kinda like designing features as multiples of shell thickness in 3d-printing, but for even multiples of tool size if using simple outlines. Or smarter software that can pick up uncut slivers between offset outlines... which is not trivial... for small pass overlaps.

  SO MAYBE: Geometrically, I think limiting "pass overlap" (stepover) to a tick over (under) 50% might solve a lot of that. (Or a more clever approach like #PCB Isolation Routing Software.)

  To be clear, this isn't all about stuffing a fancy $pindle in the cheapest mill. An old garage-sale Dremel® cut lines of two passes that look like less than half of 20mil (0.5mm) center-center in the prior example:

   ...so it should be able to cut traces on 16mil centers too. That earlier example was set up for a bit diameter closer to the designed clearance between traces, so the two outlines in each groove were practically on top of each other with very little separation, which gives 3mil back to the Dremel.

  ---

  Cutting this bypassed breakout took more tries (time) than really needed if I had a better idea of how to use the tool.

  This picture shows the first (left) and last (right) attempts to cut the little breakout:

  On the first try (left) I got a clean outline, then forgot to load new gcode after changing bits to bore the through-holes. In hindsight, I think that looks like I could have finished it and been done - because the bigger bit only went between a pair of capacitor lands and...

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• So why go vertical when horizontal was such a win before?

  Paul McClay • 08/15/2021 at 00:21 • 0 comments

  [this log entry copied from #Minamil where it was created 9 Aug 2021]

  ---

  When HaD editors gave #CDCNC , the one-off precursor to this project, its 15 minutes of fame, they commended the Z-horizontal layout which avoided lifting the heavy tool with a tiny motor & gave chip clearance for free. So why abandon those advantages?

  It wasn’t the plan. The new axes were going to be about the same size as in CDCNC, so I was just going to swap new parts into the old frame. What could go wrong?

  This design uses 0.5mm pitch screws, instead of 3mm or longer pitch used in optical sleds, to get more linear force from the same little 15mm motors that just barely make CDCNC go. The finer pitch screws are also self-locking, not backdrivable, so the machine will keep position without constant power to the motors -- another benefit, right?

  The ‘what’ that could go wrong is that self-locking leadscrews with little rotational inertia will chatter hard when loaded with force in the direction of motion[1]. So while these screws can drive a fair load upward, opposed by gravity, they’re helpless to let even an empty slide come back down, assisted by gravity, with any useful speed. Counterintuitive, if you didn’t already know this. I don’t recall any mention of it in the tiny slice of CNC lore I’ve read.

  So axes of this design won't be moving anything vertically without adding stuff to neutralize gravity. In which case it makes sense to turn the heavy, slow, and more often stationary axis back up to vertical.

  That adds complexity and brings back the chip-clearing problem. But in trade we get a much smaller footprint.

  ---

  Log entry
  

  Log entry

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  [1] from Dr. Orang Vahid Araghi's thesis, page 187 first paragraph:

  The first condition states that the lead screw must be self-locking. The second condition requires that the force applied to the nut be in same direction as the nut translation. The third condition defines a [...] limiting value for the mass of the translating part (depending on the lead screw inertia, coefficient of friction, and geometry of lead screw), below which instability does not occur.

• Parts Prices

  Paul McClay • 08/15/2021 at 00:12 • 0 comments

  [this log entry copied from #Minamil where it was updated 26 Oct 2021]

  
  

  ---

  Started tracking part prices because they've been a bit volatile and small changes to small prices can be significant. Still tracking because still changing -- some changes not small.

  ---

  Example BoM cost

  Sep 2021

  • $30.10 - 3x motors (Aug: up again. >2x from -1yr)
  • $5.83 - 12x bearings (3 extra)
  • $11.06 - 2x 600mm rods (100mm-kerfs & 200mm-kerfs extra)
  • $1.79 - 100x screws
  • <$1.00 - ~9"x30" 1/8" hardboard (cut from panel; keep remainder for more laser cutting stock)

  Total <$49.78 (+tax) 

  +21% from March 2021; now up to ~$17/axis; +51% from Jan 2020 start with this configuration at $33 :-/

  ---

  Getting parts faster in the continental US

  A lot faster for a little more $:

  • motors from Bangood buy 3 (cost from AliExpress sellers up --> penalty for buying from US stock down)
    • (26 Oct 21: Bg currently shipping from China, tho promised a little faster than via AliExpress; Bg has dropped & restored US stock before so maybe it will be back...) 
  • bearings from Amazon 1x10pcs (assuming Prime or total order over $25 for free shipping)

  A lot faster for  ̶a̶ ̶l̶i̶t̶t̶l̶e̶  more $:

  • rods from Amazon buy 3x6mmx401mm (longer stock to cut yourself; this & bearings will break $25 for free shipping if not Prime)

  Screws from Grainger or Ace Hardware if you live near a store -- maybe not in stock but will ship free to a store.

  Hardboard I've bought in 4x8 sheets (or 2x4) from Home Depot -- or check other building supply/lumber sources that have a panel saw for cutting big sheets down on request. Such places usually post a low limit on free cuts, like 1, but the person running the saw will often (IME always) do more if you ask respectfully and have your measurements ready. Check the max material size for the laser cutter you will use and think about how to divide the large sheet into pieces of that size with the fewest cuts. For example: the laser cutter I use most often takes material up to 32" x 18". Two cuts at 32" divide a 48"x96" sheet into three 48"x32" pieces. A third cut at 18" across the three together gives me three 32"x18" pieces ready to use and three 32"x30" pieces I can transport easily and cut down later. That's a lot of material for nearly free compared to acrylic, Baltic ply, etc. that you can use to iterate a design before cutting the expensive stuff. Or find that hardboard works well enough for a project -- like a little CNC mill or something.

  ---

  Part cost details

  For orders from US

  • CH-SM1545 -- motor + leadscrew
    • No cost changes for listed motor sources from Aug to 26 Oct 2021 -- stabilizing?
    • 26 Oct 21: no Aliexpress sellers remain other than ChiHai Motor outlets; and Banggood now ships from China (tho promised somewhat faster than via Aliexpress) -- which looks like consolidation to a single source at 2.1-2.3x cost when found this part :-/ )
    • Aliexpress "Shenzhen Chihai Motor Store" 6 Aug 21
      • link
      • spend: 3x $7.05 + $8.95 = $30.10
      • unit cost: $30.10 / 3 = $10.03
    • Aliexpress "CHIHAI Factory Store" 6 Aug 21
      • spend: 3x $7.05 + $9.35 = $30.50
      • unit cost: $30.50 / 3 = $10.17
    • Aliexpress "CHIHAIMOTOR Store" 6 Aug 21
      • spend: 3x $7.05 + $11.61 = $32.76
      • unit cost: $32.76 / 3 = $10.92
    • Banggood 10 Aug 21
      • link
      • spend: 3x $10.99 = $32.97
      • unit cost: $10.99
    • Aliexpress "TO-HO store" 21 Sep 21 (26 Oct 21: ceased selling some time since 21 Sep)
      • was $4.78 shipped Jan-Aug '20 and some time before that, which made a stronger argument for designing around this part!
      • spend: 3x $11.53 + $4.00 = $38.59
      • unit cost: $38.59 / 3 = $12.86 (+169% up from prior low)

  • LM6UU -- 6mm linear bearing
    • about buying bearings:
      • IME the common generic bearings all seem to come from the same or indistinguishable sources with stochastic quality
      • buying a dozen allows for selecting the best 9 with up to three rejects, which will probably be ok
      • while "real" bearings...

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• milling T/SSOP breakout - 0.65mm pitch

  Paul McClay • 08/15/2021 at 00:04 • 0 comments

  [this log entry copied from #Minamil where it was created 30 July 2021]
  

  ---

  Been a little quiet [t]here lately. Here's some pictures while I go find some words to go with them.

  Words about runout & {autoleveling <- homing <- limit switches} vs {mechanical bed leveling <- Z probing non-conductive surface} & um, what else? (update: nix limit switches; I was wrong about why I thought autoleveling required homing requiring limit switches)

  Previously about PCB milling:

  • second & third tries
  • first try didn't get a log entry

  Next:

  • +onboard bypass, with denser traces

View all 8 project logs