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Type: Posts; User: drcrash

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  1. Thanks very much for the info. Is there a...

    Thanks very much for the info.

    Is there a suitable urethane primer that's easily available in a spray can, or do I need to deal with spraying 2-part stuff?

    Where would I find polyurethane...
  2. Thread: Dome

    by drcrash
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    1,212

    That would be difficult to do by sheet...

    That would be difficult to do by sheet thermoforming (vacuum or pressure forming).

    Tall shapes with steep sides are difficult. The plastic solidifies where it touches the mold first, and the...
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    I'm not sure what the length has to do with...

    I'm not sure what the length has to do with over-and-underness, unless you're just saying that it's big enough you want the compactness of an over-and-under arrangement. A side-by-side arrangement...
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    Yes. It doesn't seem that anybody who's built a...

    Yes. It doesn't seem that anybody who's built a TJ (Thurston James design) oven has measured it well, or if anybody has, I haven't seen the numbers posted.

    From what I've seen said, I'd guess TJ...
  5. Thanks for the tips. I did a preliminary...

    Thanks for the tips.

    I did a preliminary experiment with regular (Bondo brand) fiberglassing resin and glass cloth, and a 50/50 mix of plain resin and Bondo body filler.

    The resin/filler mix...
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    By that I assume you mean a 28 x 28 center part...

    By that I assume you mean a 28 x 28 center part and two 28 x 14 end parts ganged together...? (just checking...)

    I'm not sure what the alternatives there mean. I think the total wattage for the...
  7. Replies
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    The Imperial Armor oven calculator is actually an...

    The Imperial Armor oven calculator is actually an interface to a spreadsheet, and you can change the voltage, wattage, and/or number of nichrome segments. (Just type new numbers in the boxes at the...
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    I get it on that page (vacuum_pumps.htm) but not...

    I get it on that page (vacuum_pumps.htm) but not the other one, too.

    I am using Firefox 2.0.0.7 on a Mac iBook.

    I've noticed that problem on some page on Doug's site before (maybe just that...
  9. (priming and) reinforcing plastics with fiberglass

    (Sorry if you saw this question on the vacuum forming forum... didn't get an answer there, so I'm trying here.)

    I'm looking for advice on priming plastics and reinforcing them with fiberglass. ...
  10. Replies
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    Thanks very much for this tip. I was guessing...

    Thanks very much for this tip. I was guessing that I could just try it, and sand off the paint w/Armor All on it if I didn't like it, and that would be okay. I guess not.
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    I assume you're talking about one for an...

    I assume you're talking about one for an on/half/full heat control for an oven, or part of an oven...

    Here's a thread about that over at the tk560 vacuum forming forum:
    ...
  12. Replies
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    3,102

    rubbery thermoplastics?

    Hmm, I've been thinking that some "rubbers" (rubbery plastics) are thermoformable. I've been meaning to look into which ones... but maybe there aren't any

    You can vacuum form EVA foam, which is a...
  13. DC, I'd be interested in hearing more about the...

    DC, I'd be interested in hearing more about the multi-piece molds and stuff you made with them.

    Also more about forming around structural members, and leaving them in.

    That's the kind of thing...
  14. Replies
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    I'm using very inexpensive homebuilt gear. The...

    I'm using very inexpensive homebuilt gear. The pumps are very cheap and small, and there's no air eject. The "high vacuum" (from some sort of cheap vacuum pump & tank) fades quickly, losing about...
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    Yes, that's what I meant. My only experience...

    Yes, that's what I meant.

    My only experience with polycarbonate---maybe---is with some 1/8" "mystery plastic" scrap that I assumed was acrylic but now think is Lexan. The results were not good. ...
  16. Reinforcing vacuum-formed parts with fiberglass?

    Does anybody reinforce vacuum-formed parts with fiberglass on the back side? (Maybe just in the thinnest places, or at places where it's attached to something else?)

    I've been under the...
  17. Replies
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    I expect you're right. Melamine on top with PVA...

    I expect you're right. Melamine on top with PVA on the bottom seems like the best safe option so far.

    That would work for me, but I'm trying to come up with free plans I can put up on my site,...
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    heating and cooling PE & PP

    I'd be interested in general comments on how to pick between LD and HD and polyethylene and polypropylene.

    My understanding is that PE generally stays hot for a long time, and people often have to...
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    I thought that polycarbonate cooled quickly...

    I thought that polycarbonate cooled quickly (sometimes annoyingly quickly), but required a high temperature to form.

    I'd guess that either that means that polycarbonate has a high thermoforming...
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    Interesting. I've used silicone spray to soften...

    Interesting. I've used silicone spray to soften rubber seals, but didn't know that Armor All was mostly the same thing.

    Even so, it might work to seal the pores in paint reasonably well. Even a...
  21. Replies
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    interchangeable gaskets on tape-down sheets, sealing

    The polyester and epoxy work okay for the bottom of the platen, but your PVA solution is probably less trouble.

    I started with epoxy and polyester so that I could get two different effects---an...
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    Thanks for the suggestions. Doug (kayaker43)...

    Thanks for the suggestions.

    Doug (kayaker43) has already suggested the countertop stuff to me privately, but ideally I'm looking for something dirt cheap. (MDF plus PVA is good in that respect.)...
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    I'm familiar with PVA glues... just more going on...

    I'm familiar with PVA glues... just more going on than I made clear. I should probably have made it clearer that I'm trying to solve several different problems, ideally with one solution.


    ...
  24. Replies
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    Sorry, I didn't mean to make it sound like that...

    Sorry, I didn't mean to make it sound like that wasn't a fine solution. (In fact I've passed it along on another forum.)

    One of the things that's going on is that I'm also looking for things you...
  25. Replies
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    Hmmm... now I'm wondering if something like Armor...

    Hmmm... now I'm wondering if something like Armor All would do the trick. It's supposed to seal & protect plastics from oxidation (as well as UV). Paint is basically porous plastic that needs...
  26. Replies
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    That sounds familiar, now that you mention it. I...

    That sounds familiar, now that you mention it. I read up on paints a few years ago, and I probably knew that.

    I wonder if auto paints are the same way? I could imagine not, on the assumption...
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    Yeah, I got to thinking about that. (That's why...

    Yeah, I got to thinking about that. (That's why my posting about paint that hot plastic won't stick to had a preference for smooth, maybe gloss.)



    Yes... I suspect they dry porous so that...
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    Thanks all for the suggestions and useful info. ...

    Thanks all for the suggestions and useful info.

    I've got a half-made new platen, and when I get around to finishing it, I may get a chance to do an experiment.

    I'm thinking of testing it...
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    best paint that hot plastic won't stick to?

    I'm looking for paint that I can use on a platen surface, for some small platens that won't see heavy use. (Or I'd cover them with metal.)

    I'd like something smooth and durable that can take the...
  30. big vacuum forming tools from little CNC pieces?

    Does anybody out there use small cheap CNC machines to make large vacuum forming tools in pieces, maybe from MDF, and then fit the pieces together to make the tools?

    This seems to be a good way to...
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