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Thread: 3D printing strengths and weaknesses

  1. #1
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    Default 3D printing strengths and weaknesses

    It can be surprisingly strong, even in plastic.

    I messed up a print and, being who I am, I figured I'd bust up the mistake to see what it could take. I was impressed.

    PLA, can't remember the exact fill... maybe 15-20%, gyroid, very light. Started by pinching some protruding arms in a vice, just going after the weakest points. Very slow failure mode, after a surprising amount of force. Basically, the shell slowly delaminiated from the fill. After that, I tried to crush the body... vice couldn't do it (it was at the Electronics bench at the college where I work... not the greatest), so I went down to the Mech shop and used the press. Took a metric ton, slowly crushed, repeated a few times. Very nice slow crush, no snaps or surprises. I really like the way these 3D prints fail. No drama at all.

    The more I test my failures like this, the more comfortable I get using these prints in places that matter. Just cheap PLA but if you've got room to make something relatively thick it can have a crazy strength to weight ratio.

    But, can only be fast OR accurate?

    They've got a new way to deal with dimensional accuracy now.

    MIT just ran an article about a new printer someone there developed. It prints to very high tolerances (not specified) by scanning the part after each layer and then using AI to automatically adjust the next layer to account for shrinkage etc.. And, this printer is designed for production, not prototyping. "Inkbit’s current industrial printer has 16 print heads to create multimaterial parts and a print block big enough to produce hundreds of thousands of fist-sized products each year ..."

    http://news.mit.edu/2019/inkbit-3d-printer-0604


    Yeah, fast AND accurate. Not something that will wind up in my den next week. But, the idea of printing a layer, then looking at it to see where it's off, and then compensating with the next layer automatically... coming to a printer near you, probably a lot sooner than you think. Just like that gyroid fill, from the research paper to the slicer software faster than you can learn to spell it.

    Can only do small things?

    There's that pedestrian bridge too: https://mx3d.com/projects/bridge-2/
    They basically 3D printed it out of MIG welding wire using industrial welding robots. It's so new they can't use it... presumably because they can't get an engineer to sign off on it. I mean, do you know how a bridge made entirely out of welding bead will hold up in various failure modes? They're wiring it for sensors and plan on watching it... probably for a long time.

    But, how long before there's a home-shop CNC table rigged up with a MIG welder? What could you make with that? How long before they shrink the size of the bead down and use computer vision with AI learning to compensate and produce high-accuracy parts?

    Could you imaging the strength to weight ratio of a 3D printed metal structure using a gyroid fill?

    David...
    Last edited by fixerdave; 06-07-2019 at 07:59 PM.

  2. #2
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    Heat up PLA a tiny bit, leaving it in a hot car, it melts and deforms like cheese. Why I use PETG.

    Sent from my SM-G950U1 using Tapatalk

  3. #3
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    Quote Originally Posted by RB211 View Post
    Heat up PLA a tiny bit, leaving it in a hot car, it melts and deforms like cheese. Why I use PETG.

    Sent from my SM-G950U1 using Tapatalk
    How much better is PETG for temps? I intend on picking some up on the next filament order, but I've got so much that it might take a while.


    David...

  4. #4
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    Quote Originally Posted by fixerdave View Post
    Could you imaging the strength to weight ratio of a 3D printed metal structure using a gyroid fill?
    .
    An Engineer at work is currently doing his masters, poetically enough at McMaster U and gets to play with their new $2.5MM laser metal printer. Neat stuff. its a 2.5MM cool toy for academia now, and lasers remain expensive.....but it'll come down and we'll see more of it.

    I got a printer recently and it changes your outlook on design, or it did mine. Prior to, the starting point was the form factor of bar and sheet and it went from there. That is such a huge constraint on design it actually made design easier....narrow lines you had to colour within. 3D printing is like designing castings except you don't have to worry about how hard the pattern is to make. Its more difficult and an adjustment now that all of sudden the shape should be the most economical set of compound curves and fill that will get the job done.
    Last edited by Mcgyver; 06-07-2019 at 09:39 PM.
    .

  5. #5
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    Quote Originally Posted by RB211 View Post
    Heat up PLA a tiny bit, leaving it in a hot car, it melts and deforms like cheese. Why I use PETG.

    Sent from my SM-G950U1 using Tapatalk
    I remember when you first got your printer you were sold on ABS for the same reason. Now its PETG. I have not tried either yet but would like to hear more of your thoughts and why you now favor PETG over ABS.
    (I bought a roll of ABS to try a while back but its still unopened)

  6. #6
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    I have only used my 3d printer a little bit since I got it a couple years ago. Its one of those tools thats VERY underutilized. I need to force my self to consider using it for tasks more often.

    I recently 3d printed a automatic bullet feeder / collator for my progressive reloading press. Its open source on thingaverse. I just downloaded the files and printed them. The feeder works fantastic. The commercial equivalent costs around $800. It takes the bullets that are nose down and flips them so they are all nose up before going down the tube to the press.

    Here is a video of it being printed and used. (not mine, just a video I found) https://www.youtube.com/watch?v=HznohMfdH6M

  7. #7
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    Quote Originally Posted by RB211 View Post
    I use PETG.
    What brands/colors did you use, and which one do you prefer?

  8. #8
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    I like PETG too, ABS is tough but on large prints I find it warps off the bed (I need an enclosure).
    I really like this stuff https://filaments.ca/products/hdglas...t-clear-1-75mm
    I have used other brands too and it all seems pretty good.
    Cheers,
    Jon

  9. #9
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    I like the Amazon Basics PETG, printed both clear and black. ABS for small stuff works great but gives off toxic gases and requires very high temps. PETG offers 90% of the qualities of ABS with lower print temps and not toxic. Basically an easier to print substitute for ABS. PETG is a little more flexible than ABS as well.
    ABS doesn't do tiny details nearly as well as PLA.
    Prusa uses PETG for all of it's printed parts that are on his printers, except for the fan nozzle near the hotend which is ABS. My fan nozzle is PETG and has been doing fine. PETG also has the best layer adhesion, and sticks a little too well to the build plate.

    Sent from my SM-G950U1 using Tapatalk

  10. #10
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    Strengths and weaknesses... My friend Ray has the Prusia Mk3 and has done a LOT of printing, starting with testing and dialing in builds with all available materials. Things I learned from him are:

    You can build interesting designs, including nested pieces that move freely. Most of the time. He has about a 30% success rate with that. This is an example of a complex single print design that he had limited success with. https://eleccelerator.com/3d-printed...all-one-piece/

    You can duplicate broken parts pretty well. Like conventional machining, You have to guess at what parts of the design are functional and what are artifacts of the production process. A problem that often arises is that you have to guess at what properties of the material are important. Ray built a dozen or so dishwasher rack clips for me, trying to find one that could withstand the heat while under the stress of holding dinner plates on edge.

    Ray had a heck of a time making threads that were actually accurate. Fortunately, the plastics are forgiving because of a low yield strength. A metal screw will thread through a plastic nut that is way out of spec.

    Where 3D printing shined for Ray was the "rapid" prototyping of parts for his friend's fledgling guitar building endeavor. They were able to collaborate online and ray would bring the finished parts to work with him the next day.

    Dan
    At the end of the project, there is a profound difference between spare parts and extra parts.

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