3D printing questions

To all youse folks doin' tree dee printing- I have been thinking about this technology recently and was wondering about different materials printed on the same part. More specifically,
printing the plastics over metals and woods. The differential expansion and shrinking, and bonding. So, for example, suppose the plastic was printed surrounding a metal or wood part. Would the plastic crack as it cooled? And will it bond to the metal or wood? I suppose the wood could be heated before the plastic is applied but how long would it stay warm? I have seen machines with heated platens so maybe the wood or metal object could be heated by the platen. But most of the metal objects I have been thinking about surrounding with the printed plastic are fasteners or stiffeners. They wouldn't be sitting on the platen. So nuts held captive by the plastic are a good example. And does the plastic need to bond to the metal for my application? I don't know, but lets say it does. Is there some type of glue that could be used that would make the hot plastic bond to the metal? For lightness wood can be a very good material to combine with plastic to make a strong part. I can envision a part that is plastic on the outside to achieve a particular shape, like a handle, but with a wood core for strength. And what about using a variety of plastics to make an even better part? Say a luggage handle that is wood core surrounded by a hard plastic contoured to fit the fingers with soft plastic in the finger grooves. Can this be done with the materials available to the average experimenter with a limited budget? I know there are a lot of questions above and I appreciate any answers from folks who know about this stuff. I want to experiment with 3D printing and have some ideas but I have not been able to find much info about the above questions from people who actually have experience trying to do what I want to do. Thanks, Eric
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On Fri, 21 Feb 2014 18:26:31 -0800, snipped-for-privacy@whidbey.com wrote:

Interesting idea, Eric. I'm sure it's possible but have no idea how to go about it with a 3DP.
Have you tried asking on some of the 3D printing blogs or forums? You'd find extremely active experimenters there with all sorts of printers and software types.
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On Fri, 21 Feb 2014 18:26:31 -0800 in rec.crafts.metalworking, snipped-for-privacy@whidbey.com wrote,

The hot plastic certainly does shrink as it cools. If it didn't, it might be permanently bonded to the print bed. One of the tricks to master is getting it to stick enough to stay there until the print is complete, in spite of shrinkage, but still be able to remove it without damage.

Cracking, not so likely. Warping, more likely.

Captive nuts are easy. They don't even have to stick, just be trapped in a matching cavity so they can't rotate. Put a Pause in your G-code at the top of the cavity so you can place the nut before it's filled over.

Typical construction is plastic deposited solidly at the surface of the part, with the inside filled with a network of threads to achieve a specified percentage of infill to give the needed combination of lightness and strength. But you could certainly use a wood insert in some cases if you designed for it.

Soft plastic is not common yet, but I saw some from adafruit. You would probably have to make the parts separately and assemble them.
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On 02/22/2014 11:32 AM, David Harmon wrote:

The local electronics parts store has one of the open frame Velleman units on display, and it's always making one thing or another. From looking at the thing, it's basically got a nozzle like a hot glue gun, except it's fed with monofilament that is unwound from a spool as it is needed. The nozzle apparatus is moved about with stepper motors in an x-y fashion, bumping up a notch in z when one layer is done.
The deposition is too fine to see it being built, except for the head moving about, but given enough time it certainly does make something. They've also got a 3-D scanner that can scan an object to be printed, but I don't know how well it could see into cavities.
Jon
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On 22/02/14 02:26, snipped-for-privacy@whidbey.com wrote:

Can't help with the subject but an impressive 3D printing project of a full sized Aston Martin http://www.independent.co.uk/life-style/gadgets-and-tech/news/would-you-download-a-car-man-3d-prints-lifesize-aston-martin-db4-8744159.html?origin=internalSearch
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On 2/21/2014 6:26 PM, snipped-for-privacy@whidbey.com wrote:

Your metal part has to be the same temperature as the plastic. You need to have some experience cleaning injection molding nozzles!
All molded plastic shrinks as it cools. This is how you are able to remove plastic objects from a mold. Where plastic must be molded to produce a hole, the hole must be tapered so the mold can be removed in spite of the shrinking.
Wood would probably smoke at the temperature of molten plastic.
Paul
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On 2/21/2014 6:26 PM, snipped-for-privacy@whidbey.com wrote:

Your metal part has to be the same temperature as the plastic. You need to have some experience cleaning injection molding nozzles!
All molded plastic shrinks as it cools. This is how you are able to remove plastic objects from a mold. Where plastic must be molded to produce a hole, the hole must be tapered so the mold can be removed in spite of the shrinking.
Wood would probably smoke at the temperature of molten plastic.
Paul
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On 2/21/2014 6:26 PM, snipped-for-privacy@whidbey.com wrote:

Your metal part has to be the same temperature as the plastic. You need to have some experience cleaning injection molding nozzles!
All molded plastic shrinks as it cools. This is how you are able to remove plastic objects from a mold. Where plastic must be molded to produce a hole, the hole must be tapered so the mold can be removed in spite of the shrinking.
Wood would probably smoke at the temperature of molten plastic.
Paul
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