3 ms·

> A better option is to build a case from parts you cut out of a sheet of plastic (anywhere from 1mm on up) that you then glue together. Not a bad way to go,

> A better option is to build a case from parts you cut out of a sheet of plastic (anywhere from 1mm on up) that you then glue together. Not a bad way to go, but I found that for hand assembly, I had a really hard time with the glue out of control; I probably needed a better applicator than the default tube of epoxy. Instead, I would go with VHB (Very High Bond) tape. Also weird to use, if you are using the thin 1mm width, but I can position the tape more carefully before I press it into place.

kragen 5y ago
I don't know anything about this stuff, but from YouTube I'd think other options would include: - machine a form out of wax or delrin (or clay), pour a silicone mold, and then pour liquid plastic into the mold, either a not-yet-polymerized resin such as a thin epoxy, or a molten thermoplastic; - similarly, but use plaster instead of silicone and burn out the form in a kiln before pouring (not applicable for clay); - 3-D print the case, and if you don't like the layer lines, smooth them out with either a coat of paint or by smoothing an ABS print with acetone vapor; - 3-D print a form for molding. Even for injection molding, you might start with an aluminum mold, which won't last as long as hardened steel but will cost a lot less. But I don't know anything about this stuff so maybe it's not applicable to this case?
- webmaven 5y ago
  > molten thermoplastic Unless there are products I'm not aware of, mostly thermo plastics require high pressure injection that isn't feasible for a hobbyist setup. > a not-yet-polymerized resin There are lots of products like this (a bewildering variety, really), but in general they aren't particularly convenient to use, and you'll have a lot of failures. Factors that can mess you up include temperature, humidity, air bubbles (so many air bubbles!), mixing ratios, over mixing, under mixing, contaminates on the mold surfaces or your mixing containers, pour holes too small, not enough exit holes, entry/exit holes in the wrong places, molds held together too loosely leading to leaks, too tightly leading to distortions, etc. Except for the possible exception of relatively simple shapes and small items (like dice), just about everything you can imagine going wrong will, and you'll end up with a lot of waste before you get something you can use, and disposing of the failed attempts responsibly is another challenge. There is a caveat though: if you're trying to make a soft part (whether in a hard or soft mold), the materials are generally a lot more forgiving of errors, but that's tangential to the challenge of making a case.
  - kragen 5y ago
    Thanks! I think I've mostly watched resin casting demonstrations by very experienced people, so I may have unreasonably positive expectations of what is possible, but I think it's fairly common for art students to get some successful resin casts in a single-semester sculpture course? Which I think implies a cost of first success well under US$10000? As I said, I haven't tried it myself. Michal Zalewski makes it sound pretty achievable. As far as thermoplastic molding goes, aside from the vacuum forming that someone else suggested, there seem to be a lot of experimental options. There is a YouTuber who has built a couple of DIY injection molding machines (http://www.youtube.com/user/AndysMachines http://www.youtube.com/user/AndysMachines), and Star Simpson did successfully mold recycled HDPE plasticized with vegetable oil in an open-top mold (https://www.instructables.com/HomemadePlastic/ https://www.instructables.com/HomemadePlastic/), but the results are not super smooth. My recollection from melting plastic cups in the oven as a kid (probably polypropylene) is that you end up with a puddle with a pretty flat and smooth surface except for whatever lettering or imagery was on the outside of the cups, so I feel like you might be able to get a smooth top out of an open-top mold, but I don't know which plastic that was, and melt degradation might be an issue. https://youtu.be/KA1UELu33FI https://youtu.be/KA1UELu33FI shows some apparently successful open-top molding with powder made from recycled polypropylene (skip to the last minute of the video) but doesn't test it for strength. https://www.youtube.com/watch?v=2OYbyzgErvo https://www.youtube.com/watch?v=2OYbyzgErvo recycled polypropylene into a two-piece water-cooled mold improvised out of aluminum baking tins, but seems to have suffered major melt degradation possibly due to overheating it in a can on an open fire. https://youtu.be/Ae8_OWju8RM https://youtu.be/Ae8_OWju8RM recycled (probably heavily filled) HDPE into a billet in an aluminum can in a thermostat-controlled electric oven at 180 degrees and had a lot of porosity due to high melt viscosity, then turned the billet down on a lathe; the outside of the billet seems to have suffered enough melt degradation to make it machine much more cleanly than the center, which produces the kind of long stringy chips you'd expect from HDPE. https://youtu.be/blSvUqfuiuo https://youtu.be/blSvUqfuiuo makes an HDPE sort of gingerbread man in an open-top silicone oven mold, the kind you'd use to make gingerbread-man-shaped muffins, suffering melt degradation severe enough in parts to turn the HDPE brown, warping, and significant porosity due to high melt viscosity. https://youtu.be/-igxhoGEQFU https://youtu.be/-igxhoGEQFU shows really nice marbled results melting HDPE in a panini press with a silicone mold release, then pressing it into a billet in a particleboard mold with a bench vise, but still suffering some problems with porosity. By turning it on a wood lathe they are immune to problems of warping etc. Polycaprolactone deserves a mention because above its glass transition you can mold the thermoplastic with your bare hands, but pouring it into a mold is out of the question because of its high viscosity, and as a result of that low Tg you tend to get a lot of creep, and parts become unusably weak in a warm room. So I think you've convinced me that thermoplastic casting without injection molding equipment is not a practical option for making low-volume parts. Thank you for sharing your experience!
webmaven 5y ago
> Not a bad way to go, but I found that for hand assembly, I had a really hard time with the glue out of control; I probably needed a better applicator than the default tube of epoxy. There are a couple of things you can try: Squeeze the glue (of whatever sort) onto a disposable surface (a scrap of foil generally works for me) and use a wire or whisker of some sort to pick up and apply small amounts in a controlled fashion. Tack the parts together with minimal dots of cyanoacrylate, and use gobs of the real adhesive to put it a fillet on the inside corner. You can also use a jig of some sort to position the parts you're gluing. Solvents instead of an adhesive are a bit more forgiving of accidental over application (you just spill it off and wait a moment for the excess to dry). > Instead, I would go with VHB (Very High Bond) tape. Also weird to use, if you are using the thin 1mm width, but I can position the tape more carefully before I press it into place. An interesting suggestion, and not one I've tried. Thanks, I'll keep it in mind.

kragen 5y ago

I don't know anything about this stuff, but from YouTube I'd think other options would include: - machine a form out of wax or delrin (or clay), pour a silicone mold, and then pour liquid plastic into the mold, either a not-yet-polymerized resin such as a thin epoxy, or a molten thermoplastic; - similarly, but use plaster instead of silicone and burn out the form in a kiln before pouring (not applicable for clay); - 3-D print the case, and if you don't like the layer lines, smooth them out with either a coat of paint or by smoothing an ABS print with acetone vapor; - 3-D print a form for molding. Even for injection molding, you might start with an aluminum mold, which won't last as long as hardened steel but will cost a lot less. But I don't know anything about this stuff so maybe it's not applicable to this case?

webmaven 5y ago
> molten thermoplastic Unless there are products I'm not aware of, mostly thermo plastics require high pressure injection that isn't feasible for a hobbyist setup. > a not-yet-polymerized resin There are lots of products like this (a bewildering variety, really), but in general they aren't particularly convenient to use, and you'll have a lot of failures. Factors that can mess you up include temperature, humidity, air bubbles (so many air bubbles!), mixing ratios, over mixing, under mixing, contaminates on the mold surfaces or your mixing containers, pour holes too small, not enough exit holes, entry/exit holes in the wrong places, molds held together too loosely leading to leaks, too tightly leading to distortions, etc. Except for the possible exception of relatively simple shapes and small items (like dice), just about everything you can imagine going wrong will, and you'll end up with a lot of waste before you get something you can use, and disposing of the failed attempts responsibly is another challenge. There is a caveat though: if you're trying to make a soft part (whether in a hard or soft mold), the materials are generally a lot more forgiving of errors, but that's tangential to the challenge of making a case.
- kragen 5y ago
  Thanks! I think I've mostly watched resin casting demonstrations by very experienced people, so I may have unreasonably positive expectations of what is possible, but I think it's fairly common for art students to get some successful resin casts in a single-semester sculpture course? Which I think implies a cost of first success well under US$10000? As I said, I haven't tried it myself. Michal Zalewski makes it sound pretty achievable. As far as thermoplastic molding goes, aside from the vacuum forming that someone else suggested, there seem to be a lot of experimental options. There is a YouTuber who has built a couple of DIY injection molding machines (http://www.youtube.com/user/AndysMachines http://www.youtube.com/user/AndysMachines), and Star Simpson did successfully mold recycled HDPE plasticized with vegetable oil in an open-top mold (https://www.instructables.com/HomemadePlastic/ https://www.instructables.com/HomemadePlastic/), but the results are not super smooth. My recollection from melting plastic cups in the oven as a kid (probably polypropylene) is that you end up with a puddle with a pretty flat and smooth surface except for whatever lettering or imagery was on the outside of the cups, so I feel like you might be able to get a smooth top out of an open-top mold, but I don't know which plastic that was, and melt degradation might be an issue. https://youtu.be/KA1UELu33FI https://youtu.be/KA1UELu33FI shows some apparently successful open-top molding with powder made from recycled polypropylene (skip to the last minute of the video) but doesn't test it for strength. https://www.youtube.com/watch?v=2OYbyzgErvo https://www.youtube.com/watch?v=2OYbyzgErvo recycled polypropylene into a two-piece water-cooled mold improvised out of aluminum baking tins, but seems to have suffered major melt degradation possibly due to overheating it in a can on an open fire. https://youtu.be/Ae8_OWju8RM https://youtu.be/Ae8_OWju8RM recycled (probably heavily filled) HDPE into a billet in an aluminum can in a thermostat-controlled electric oven at 180 degrees and had a lot of porosity due to high melt viscosity, then turned the billet down on a lathe; the outside of the billet seems to have suffered enough melt degradation to make it machine much more cleanly than the center, which produces the kind of long stringy chips you'd expect from HDPE. https://youtu.be/blSvUqfuiuo https://youtu.be/blSvUqfuiuo makes an HDPE sort of gingerbread man in an open-top silicone oven mold, the kind you'd use to make gingerbread-man-shaped muffins, suffering melt degradation severe enough in parts to turn the HDPE brown, warping, and significant porosity due to high melt viscosity. https://youtu.be/-igxhoGEQFU https://youtu.be/-igxhoGEQFU shows really nice marbled results melting HDPE in a panini press with a silicone mold release, then pressing it into a billet in a particleboard mold with a bench vise, but still suffering some problems with porosity. By turning it on a wood lathe they are immune to problems of warping etc. Polycaprolactone deserves a mention because above its glass transition you can mold the thermoplastic with your bare hands, but pouring it into a mold is out of the question because of its high viscosity, and as a result of that low Tg you tend to get a lot of creep, and parts become unusably weak in a warm room. So I think you've convinced me that thermoplastic casting without injection molding equipment is not a practical option for making low-volume parts. Thank you for sharing your experience!

webmaven 5y ago

> Not a bad way to go, but I found that for hand assembly, I had a really hard time with the glue out of control; I probably needed a better applicator than the default tube of epoxy. There are a couple of things you can try: Squeeze the glue (of whatever sort) onto a disposable surface (a scrap of foil generally works for me) and use a wire or whisker of some sort to pick up and apply small amounts in a controlled fashion. Tack the parts together with minimal dots of cyanoacrylate, and use gobs of the real adhesive to put it a fillet on the inside corner. You can also use a jig of some sort to position the parts you're gluing. Solvents instead of an adhesive are a bit more forgiving of accidental over application (you just spill it off and wait a moment for the excess to dry). > Instead, I would go with VHB (Very High Bond) tape. Also weird to use, if you are using the thin 1mm width, but I can position the tape more carefully before I press it into place. An interesting suggestion, and not one I've tried. Thanks, I'll keep it in mind.