Gas station without pumps

2018 June 27

Three boxes this morning!

Filed under: Uncategorized — gasstationwithoutpumps @ 21:30
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I got three boxes this morning: two via FedEx and one via an unmarked van.

One of the FedEd boxes was from Digilent—I ordered the new Impedance Analyzer attachment for the Analog Discovery 2.  I plan to check it out later this week with some precision resistors.  The design looks a little strange to me (using latching relays with 100mΩ contact resistance rather than lower impedance FETs), and there is no mention of using precision resistors for the reference impedances, so I suspect that it is not quite as good as it should be.  I also ordered the Breadboard Breakout for the Analog Discovery 2, as the female headers on the flywires that it comes with are getting a little loose.  I’ll probably test that out in the next week or two also.

Another FedEx box was from eBay for a new toaster oven (the Breville BOV845SS).  Our old one still works, but the buttons on it are getting a bit unreliable, and I was unable to take the box apart to clean the contacts (one of the screws I needed to remove had its head stripped without my being able to get it out).  The new one does a better job of producing uniform toast, so I like it better already. (I had toast for lunch today, so that I could test the toaster oven.)

The third box was the most fun: a Monoprice Delta Mini 3D printer. I spent a chunk of the day trying to get it to work. The gcode file included on the micro SD card printed ok for about 20 minutes, then retracted the filament a long way and continued “printing” without laying down any more plastic. I tried it twice and it failed at about the same point each time, so I suspect a corrupted gcode file, but I don’t currently have any way to read the micro SD card to see. (I have an SD reader, but it is old enough that it doesn’t include a micro SD slot.)

I then downloaded Cura and Printrun-Mac-18Nov2017 to try driving the printer directly from my Macintosh. I downloaded the Make Magazine test files from Thingiverse and Cura profiles from https://www.mpminidelta.com/slicers/cura.  The profile files on that wiki only work with Cura 3.2 and 3.2.1, so I had to download version 3.2.1 of Cura also.

I had no problem getting Cura to load and slice the stl files, but I could not get my Mac to talk to the printer (it saw the USB device  as

Malyan 3D Printer:

Product ID: 0x0300
Vendor ID: 0x2e26
Version: 2.00
Speed: Up to 12 Mb/sec
Manufacturer: Malyan System

but did not create a serial port for it).

Several online sources also concluded that Mac OS X cannot talk to the printer via USB. This is generally believed to be a firmware bug in the printer.  The printer is running version 44.160.3 of the firmware, which seems to be a very recent version, so Malyan System has not fixed the USB bug yet.

I have one very low-speed HP laptop that runs Windows (which we refer to as the “Barbie” laptop, because of its bright color and toy-like capabilities), which was originally purchased (used @ $75) for testing PteroDAQ on Windows.

The Barbie laptop had no trouble talking with the printer using Printrun, and I tried printing the Make magazine 4_DimmensionalAccuracy.stl file (note: the double “m” in “dimension” is Make’s spelling error, not mine).  Cura estimated a 45-minute print time, but Printrun estimated 67 minutes, which was fairly accurate—there must be some speed setting in Cura that is wrong about what full speed is for the printer.

Make’s preview of 4_DimmensionalAccuracy (from their Thingiverse folder).

The MDM_4_DimmensionalAccuracy.gcode file printed ok, but I had trouble getting it off the build plate. A wrench to twist it off worked best (after putting a small gouge in the plate trying a technique with a screwdriver and mallet). The nominal 20mm dimension of the object turned out to be 19.35mm, which is rather smaller than desirable. The layers were 24.35 by 24.30mm, 19.35×19.35mm, 14.50×14.55mm, 9.70×9.75mm, which is fairly consistently 3% smaller than they are supposed to be.

Make’s 2_XY-test preview file, from their Thingiverse folder.

My second test was with Make’s 2_XY-test.stl file, which I sliced with 0.2mm layers, 10% infill, and a Cura-generated raft (“build plate adhesion” checkbox). The raft did seem to make popping the print off the build plate easy (though not having much area in contact with the plate probably helped also).  Removing the raft did delaminate a little of the bottom layer in one place.  The texture of the vertical walls changes rather abruptly each time there is a hole in one wall, probably due to a change in the way the head moves when a continuous circuit is possible and when it has to either reverse or skip the hole. (Sorry, no photos—it is now too dark out for natural-light photos, and I’ve never had much luck with flash on macrophotography.)

I’m now convinced that I can get the printer to work, so I need to pick a tool for building models in STL format and pick some project(s) to work on.  My son thinks that I should use OpenSCAD, which is a “programmer’s CAD tool”, providing easy ways to create shapes using programming language and view the results, but not edit them interactively.  Given how very frustrating I found the SolidWorks GUI last fall, I think he may be right—I’ll look into OpenSCAD.

One of the first things I’ll print, though, is a design by someone else—extension legs to raise the printer and improve the air flow underneath.  Lengthening the legs by just 1cm will greatly reduce the noise the printer makes.

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5 Comments »

  1. I hope you enjoy playing with the 3D printer. I’ve had so much fun playing with my first 3D printer (a prusa-style gantry printer) that I more recently bought a corexy cube printer that I’m rebuilding almost completely from scratch, and I’m far enough down the rabbit hole that I’m now designing and milling my own parts for my new build.¹ (“Journey to the center of the earth‽” ☺)

    I strongly recommend printing from the card, not the computer. Most new µSD cards come with an SD adapter.

    I use OpenSCAD a lot. I started from the OpenSCAD cheat sheet.² The language it uses is C family but a bit persnickety. I’d also suggest that you consider starting with OpenJSCAD which uses javascript, or perhaps ImplicitCAD. I’ve tried using FreeCAD. It’s clearly powerful, and it’s good for fillets and chamfers, but I have found it hard to learn and prone to crashing, and sometimes the UI just refuses to do things that I can do by typing python into the embedded python console. (If you were unhappy with SolidWorks, I’d be surprised if you were happy with FreeCAD.) In OpenSCAD, do pay attention to the modifiers (!, #, *, and %) — they don’t have working syntax highlighting in the code editor, but they are important to quick iterative model development, and it is good to know that you can leave them in final code because they affect the quick render only, not the final render. Also, the quick render sometimes is just wrong, and it’s very bad when presented with coincident surfaces. I often add tiny overlaps to my geometric operations to avoid coincident surfaces to make the fast rendering clearer. Quick render is also very dependent on 3D graphics performance. Full render can be expensive, especially with complex curves on shapes. I often end up using minkowski sums, and I work creatively to use them on the smallest and simplest elements I can, sometimes making the model code more complex in order to render 10 or 100 or 1000 times faster. (Check your model code into git early and often while building your model and you will thank yourself a thousand times; that’s the “good lab notebook” of OpenSCAD model work.)

    Do more research on build plate adhesion. Rafts are a pain to clean off parts. Don’t print straight on the plate. Glass sheet (or mirror) sprayed with AquaNet hairspray is one effective option for PLA filament — it sticks very well until the bed cools, at which point prints pop off easily. Blue painters’ tape applied evenly across the whole surface can work. PEI costs more but has wider applicability. However, make sure your bed is very flat before investing in PEI. I’m in the process of starting over with ATP-6 milled aluminum tool plate for heated bed in my larger 3d printer and putting a sheet of PEI on top, because the rolled aluminum sheet bed it came with was not flat and warped more when heated. But in general, wait for your print to cool down before removing it — you want it both to harden and shrink slightly. (Count that cooling time as part of the print time not as an annoying delay after printing?)

    I would stick with PLA for filament until you are used to it; it is the most forgiving filament to work with generally. You do want to keep it dry though; if water vapor gets into it, you will get bubbles of steam inside the hot end and it’s not great for your prints. After that, PETG is probably next easiest (with its own challenges).

    What kind of lead screws does the monoprice printer use? If it doesn’t use trapezoidal threads, expect it to have poor layer definition.

    ¹ https://plus.google.com/+MichaelKJohnson/posts/jCYcEu7SHiD
    ² http://www.openscad.org/cheatsheet/

    Comment by Michael Johnson — 2018 June 28 @ 13:53 | Reply

    • The Mooprice Delta is supposedly very fussy about what micro SD cards it accepts, only liking older, smaller ones, so I had not considered buying a new microSD card just to get an adapter to talk with my mac. I don’t mind dedicating the Barbie laptop to running the printer, as I don’t use it for anything else, and Printrun does provide estimates of the remaining print time, which is not available with the SD card. A lot of people recommend getting a Raspberry Pi and Octoprint for printing on the Monoprice Delta, but I’ve already got the laptop working, so see no need to get another machine for the printer.

      I looked into various bed adhesion techniques before getting the printer, and I’ll experiment with some of them this summer. Blue tape was on my list of things to try, and a glass bed is a possibility also, though the triangular shape of the delta printer may require custom cutting of the glass.

      I do plan to stick with PLA for a while, if for no other reason than the toxic fumes of ABS. Also the Monoprice Delta Mini printer is not capable of heating the bed above 50C while keeping the hot-end hot (or so people report), so I may be restricted to PLA anyway. I don’t think the printer is capable of the 250C hotend and 100C bed recommended for PETG.

      OpenSCAD sounds more promising than OpenJSCAD (JavaScript has always struck me as a bad language—almost as bad as PERL). I’ve been using C for 40 years or a little more (I think I started before the Kernighan and Ritchie book was published, but I may be misremembering) and am fairly comfortable with it.

      The Monoprice Delta does not have lead screws. It uses toothed belts to convert the rotary motion of motors into the linear motion of the 3 arms.

      Comment by gasstationwithoutpumps — 2018 June 28 @ 15:25 | Reply

  2. Oh, no high capacity card support. I wonder whether that dependency on MMC is a hardware problem or a “use a new version of Marlin firmware” problem… Maybe they just didn’t connect “unnecessary” pins. Oh, well.

    I almost share your C familiarity (not quite 30 years now) and I was one of the early Linux hackers. The OpenSCAD language is C family in the same way that JavaScript is C family; it uses parentheses, curly braces, and semicolons. I meant that the details are idiosyncratic and non-transferable. But it’s widely used. ImplicitCAD’s language is basically the same syntax but has some interesting additional functionality.

    JavaScript: The Good Parts (famously a thin book) points out that hiding under JavaScript is Scheme; I’m partial to scheme and don’t really care about the details of Lots of Irrelevant Silly Parentheses vs. C-influenced syntax. Modern JavaScript is much more different from the original javascript than modern C is different from K&R C.

    PETG definitely doesn’t need 100⁰C bed. I print it with 70⁰C bed typically, and wouldn’t be afraid to try it at 50⁰C especially on glass. You can usually get higher bed temperatures with judicious insulation. You won’t use flexible filaments with a bowden drive as in that printer, because the filament will jam in the feed tube. That’s one of the reasons that I’m keeping around a direct-drive printer. ABS stinks and deals very poorly with drafts.

    Most people with deltas use circular (not triangular) glass (or mirrors) and really inexpensive pre-cut glass/mirrors have typically been available. Even borosilicate glass beds aren’t horribly expensive for your printer and are certainly available.¹ I would pretty strongly suggest using that with AquaNet hairspray as the best next step. I’m moving to PEI on my larger printer, but that will be mounted on flat tool plate that I’ve checked against my grade b reference plate for flatness. Leave extra time for the glass to come up to temperature on the surface because glass has so much lower thermal conductivity than aluminum, of course, but then you can remove it from the printer to cool faster, and the borosilicate glass is very very unlikely to break. (I’ve been successfully using plain window glass for years; the only plate that broke had nothing to do with printing! I even take mine hot off the printer and put them in the freezer for a quick release and they’ve never broken under even that extreme thermal stress.)

    A custom build² I particularly admire and am learning details from was done with timing belt for the Z axis; that’s a better choice than bad threaded rod! I’ve replaced the threaded rod on both the printers I purchased with better options. I’m glad they aren’t wasting your money on M5 threaded rod.

    ¹ https://www.amazon.com/120mm-Borosilicate-Glass-printer-Surface/dp/B075B1R9YZ $13
    ² https://drmrehorst.blogspot.com/2017/07/ultra-megamax-dominator-3d-printer.html — I’m using his bed mounting technique as inspiration for my current rebuild.

    Comment by Michael Johnson — 2018 June 28 @ 16:11 | Reply

  3. […] created from the new Monoprice Delta Mini 3D printer that I bought earlier this week (see Three boxes this morning!) are small plates to attach rubber feet to the bottom of the printer, to raise it off the table and […]

    Pingback by Adding feet to the Monoprice Delta Mini 3D printer | Gas station without pumps — 2018 July 1 @ 09:22 | Reply


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