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I 3d-printed a key. enter image description here enter image description here When I put it in the lock the pins move but, when I go to turn it the key rips and the lock doesn't turn. I compared it to the real key and it's identical. Is there something I can do to make it work and not rip? Is there some filament that I can print it out of? I used ABS.

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    $\begingroup$ There's a reason nobody sells plastic keys to go in metal locks... it's just not a good combo. perhaps a more exotic filament can provide more rigidity, but I'm certainly not knowledgeable enough of this to tell you. I'd start by taking a look at the material specs for some of taulmans offerings, if they're available. $\endgroup$
    – James T
    Oct 6 '16 at 7:11
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    $\begingroup$ With you printed key in slip a small flat blade screw driver or a small knife blade in along side the key and see if you can turn the locking mechanism. This will let you know the key actually does move the pins properly. Are you polishing your finished print with acetone after your done. This will tighten up the fibers a slight bit. $\endgroup$ Oct 6 '16 at 21:19
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I must admit, I've never printed a key...but I think I can help anyway:

Print method: Consider printing on side, solid concentric infill. Or, if you can't manipulate your infill pattern, just increase the perimeter so you get the same effect, several continuous perimeter layers around the outline of the key.

Print material:

  • Elongation before break is important here in addition to tensile strength...you need it to be stiff enough, but not brittle.
  • ABS, PLA, or HIPS: Not likely to be successful...but maybe.
  • PETG and PETG based filaments like T-Glase, N-Vent, nGen, INOVA-1800: A little better, but still likely to deform and/or break.
    • Polycarbonate: Great for this, but is a fairly advanced material which tends to require pre-drying, enclosures, and PVA for hold down as well as a hot end that can handle at least 290C.
    • Nylons: Good, but most Nylons may be more "bendy" than you want for this.
    • Taulman's Alloy 910: Bingo. This should work nicely if you'd rather not struggle with printing polycarbonate. Alloy 910 prints near ABS settings, sticks well on a PVA-treated heated bed. (I use 85C for bed)
    • I would not suggest a CF filled filament for this because they tend to be brittle. Matter Hacker's NylonX with CF is a possible exception since it's nylon based, but I haven't tested it...yet.
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That is correct! Take your raw ABS plastic and try to bend and break it. Do it again with a few lengths. Pretty easy to break it right?

You issue is the material is not up to par with your goal. Your heavy duty lock takes too much force to turn.

Your solutions are to

  1. Find a stronger material. These are considered stronger than PLA / ABS

    • PVA
    • PET
    • Polycarbonate
    • PETT (SHATTERS!)
    • POM, Acetal
  2. Use the PLA to make a lossless cast of the key and use metal

  3. Find a easier lock and or invest in oil for the lock.

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Which direction are the layers being printed? If the layers are printing top to bottom (in relation to your picture) there isn't a lot of sheer force required to break the key when turning. If you make the layers print from left to right you might have better luck.

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    $\begingroup$ I don't think it was printed like that. If it were printed like that there would be a lot of overhangs, which wouldn't have come out as well as we see in the picture. In the second picture, it doesn't look like it snapped between two layers, but instead the entire thing deformed. $\endgroup$ Oct 6 '16 at 5:46
  • $\begingroup$ I agree that layers, shells and infill needs set to optimize the print. Plastic keys do work (at least one time). AAA has provided it clients with a spare key cut into a credit card for backup use in case main keys are lost or locked inside. And there is the soda bottle key which in hard to turn locks the addition of a "tension wrench" is needed. $\endgroup$ Oct 7 '16 at 15:49
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"You're going to need a bigger boat^H^H^H^H filament" . Perhaps one of the carbon-fiber-loaded filaments will hold up, or perhaps a bunch of silicone spray dumped into the lock cylinder is needed.

If you want to get really fancy, start with a thin metal key blank and deposit the filament around that. This might give you enough structural strength. I don't know exactly how you'd print on three sides, as typical RepRaps and their ilk aren't set up to work around an object. Possibly printing with the key vertical and zero infil would allow you to insert a metal stiffener after printing.

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  • $\begingroup$ What is the purpose of the comment about boats? Your comment about deposition the filament around a metal blank is not achievable with any standard printer so I'm not sure how that helps. $\endgroup$ Oct 7 '16 at 9:15
  • $\begingroup$ @TomvanderZanden You dang youngsters! See "Jaws," a 1975 movie. $\endgroup$ Oct 7 '16 at 11:58
  • $\begingroup$ @TomvanderZanden I think the "^H" is supposed to mean he's pressing "backspace", like the end result is "You're going to need a bigger filament". -- I've seen weird hacks where you can print a hollow area (without infill) to insert a captive nut on reprap printers, it's definitely not trivial though. (Which is lame because that needs to be more of a thing!) -- I bet with some work, someone could use a similar approach with a key blank. $\endgroup$ Oct 8 '16 at 6:29
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First step is to optimize the print, layers, shells and infill. While ABS should hold up, if optimized, for at least one use. It may not be the best filament. PLA actually tests higher PLA vs ABS.
As I had posted in a comment, finishing ABS adds strength to the filament bundle. An acetone dip, vapor or hand wash of the part helps bond the outside edges. Parts that I make out of ABS for use on my car and motorcycle I vapor finish then polish with a soaked rag for a much more durable part.

Comparison tests of filaments are out there for the searching SUCH AS THIS ONE which compares strength of common filaments in use as a caribiner. But finding one that does a true comparison like the ABS vs PLA that I linked I have not seen.

If you do look at other filaments I would avoid ones like iron, stainless, brass, carbon fiber, etc. as these actually are shown to be reduced in strength as the particles suspended lower the filament bonding.

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  • $\begingroup$ I misread "while". $\endgroup$ Oct 8 '16 at 15:38
  • $\begingroup$ You can print this 100% solid and will still likely fail in my option. Only solution is stronger plastics. $\endgroup$
    – StarWind0
    Oct 10 '16 at 15:52
  • $\begingroup$ It is possible in some cases. KEY PRINTING $\endgroup$ Oct 13 '16 at 0:37

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