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Plasticman Expert
Joined: 08 Jul 2006 Posts: 109
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Posted: Tue Apr 24, 2007 9:23 pm Post subject: Made first pull with ABS |
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I managed to find some "smooth both sides ABS", and made a first pull tonight. Some things I noticed.
1. ABS takes a long time to heat up. I let th oven pre heat for 15 minutes and once I put the ABS on it, it took 14 more minutes to get a 4 inch sag out of it.
2. it stinks really bad compared to Styrene, almost toxic, cough, cough. definately do it in a highly vented area.
3. Its way stronger than Styrene and can be man handled more to remove from the mold. Of course I went from 0.060 Styrene to the 0.093 ABS so...go figure.
4. Its more apt to getting deformaties in the finish. I have small bubbles and a cold spot on my pull, even after heating the oven all that time!
The good news, (I think) is that I probably can sand out the bubbles and the cold streak and nuvus it back to a high luster. I didnt pre dry the ABS, so that may be a problem. Gotta figure that one out.
All in all I'd say the first pull went well.
Questions:
Am I heating it too much? Do I need the sag like styrene does? Maybe it got too hot and that is what caused the bubbles? Should I preheat my molds? Is .125 Styrene as strong as this too?? |
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crashmann Guru
Joined: 27 Sep 2005 Posts: 501
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Posted: Tue Apr 24, 2007 10:23 pm Post subject: |
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Cool! And yes, that ABS is some nasty smelling stuff compared to HIPS. I have not found any conclusive evidence as to what causes the pitting. I suspect too much heating in the oven and moisture trapped in the plastic. It probably does not need as much sag as HIPS. However, if it's not sagging, then it's not as pliable - and there is the reason you need a high vac setup to make successful pulls with ABS.
This also demonstrates an advantage of the flip flop design versus over under. With an over under, you provide all the pressure pushing down on the plastic holding frame. A flip flop has a hinge, and you can press all of your weight on the opposite side. The hinge will assist you with sealing the plastic to the table (and there's no danger of burning off your eyebrows )
Try another pull, and heat it for a shorter time. You may need an assistant to encourage the plastic to seal around your molds.
Charlie
TI-386 |
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remarque Newbie
Joined: 06 Oct 2006 Posts: 22 Location: The Carolinas
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Posted: Wed Apr 25, 2007 8:26 am Post subject: |
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How well did the plastics take the detail of your mold? I've tried 0.060 haircell ABS when I first started vacuum forming, but by the time I got it out of the oven and onto former it had cooled and the mold only formed half way.Good job though. |
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Plasticman Expert
Joined: 08 Jul 2006 Posts: 109
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Posted: Wed Apr 25, 2007 10:16 pm Post subject: |
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It took on the shape really well. I have a robinair 15600, so vacuum is no problem. I was pulling 27 inches of vacuum for this pull. I have the flip flop design too. It seemed like it sealed better than the Styrene. I am going to try cutting down the heating time and preheat the oven for 25 minutes this next time. I agree with crashman that the ABS is getting too hot and too close to the coils. I was looking at the flash that I cut off and there is no pitting anywhere but near the center where it got closer to the coils. So next time less sag. |
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cod Master
Joined: 05 Nov 2006 Posts: 322 Location: San Francisco
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Posted: Thu Apr 26, 2007 2:41 pm Post subject: |
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Plasticman wrote: | I have the flip flop design too. ........ I agree with crashman that the ABS is getting too hot and too close to the coils. I was looking at the flash that I cut off and there is no pitting anywhere but near the center where it got closer to the coils. So next time less sag. |
Of course, you'd have the opposite 'problem' with an over/under (the center would be too far away from the coils. ) _________________ <.o'> |
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Stomper Master
Joined: 01 Oct 2005 Posts: 473 Location: Woodburn, Oregon USA
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Posted: Fri Apr 27, 2007 8:01 pm Post subject: |
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It seems to me that you have to look at this like you would cooking a thick-cut steak... lower heat for a longer amount of time so you don't burn the outside, while the inside gets cooked enough (I like mine medium rare, BTW) You may have to actually heat it longer at a lower heat level for the "whole sheet" to get pliable enough. Perhaps placing it slightly further above your heating elements so that "sag area" in the middle won't get bubbly and pitted while the outer edges get warm enough.... just a thought. _________________ Tony Krewson
FEAR... is not my god!! |
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drcrash Guru
Joined: 04 Sep 2006 Posts: 705 Location: Austin, Texas
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Posted: Sat Apr 28, 2007 8:47 pm Post subject: |
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Stomper wrote: | It seems to me that you have to look at this like you would cooking a thick-cut steak... |
Yeah... I have to wonder if people are just heating the plastic too fast and burning it on the outside before the heat soaks through.
In lieu of heat control, I've dealt with that a couple of ways.
One is to stand there flipping the heat on and off every 20 seconds or so. (Not so often at first, before the plastic has heated up much.)
That's pretty much how a lot of industrial vacuum formers work---they use a "proportional timer," where the fraction of time the elements are on controls the (average) heat level. And they often start out on a higher setting at first, then back off to a lower "soak" setting (to let the surface heat "soak in"), where the heat is off a bigger fraction of the time.
On my little bottom heater oven, I've also just flipped the plastic over now and then, so that it's getting half as much heat on one side, but heating both sides. That works surprisingly well, despite letting some of the hot air out, if you don't overdo it. (It'd be kinda awkward with a big flip frame, though.)
I'm thinking of making my little over-and-under taller, with a deeper oven, and setting it up as a hand-turned rotisserie kind of thing. _________________ Paul (a.k.a. Dr. Crash)
Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com |
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harley guy Novice
Joined: 25 Nov 2005 Posts: 71
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Posted: Wed May 02, 2007 2:21 pm Post subject: |
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i form 1/8 abs all day long. takes 3-1/2 minutes to heat a 24x36 sheet for forming. i have a flip flop design. you have to make a adjustable oven so you can change the heights. not all abs will heat up the same so you wil have to adjust the oven height. make the oven be able to rasie and lower. make the oven shroud adjustable to. so when you lower your oven, you can raise your shroud to meet with the plastic holder. if you need pics, search my flip flop design rig. |
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Plasticman Expert
Joined: 08 Jul 2006 Posts: 109
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Posted: Wed May 02, 2007 3:27 pm Post subject: |
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I will check that out.
Also just noticed that I had a broken coil on the outer ring for that pull. That might be it...... |
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cod Master
Joined: 05 Nov 2006 Posts: 322 Location: San Francisco
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Posted: Wed May 02, 2007 5:05 pm Post subject: |
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Plasticman wrote: | I will check that out.
Also just noticed that I had a broken coil on the outer ring for that pull. That might be it...... |
speaking of broken coil wire .... there ought to be a way to splice it together with some sort of nut/bolt combo. This would change the overall segment resistance, but maybe not that much? even then , maybe you could add another scrap of nichrome to get it back to the proper length/resistance. ? A little steel nut/bolt inline on the coil shouldn't change things that much.. in terms of heat distribution. _________________ <.o'> |
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Plasticman Expert
Joined: 08 Jul 2006 Posts: 109
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Posted: Wed May 02, 2007 9:44 pm Post subject: |
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I just twisted it back together. Ive broken the coils now a couple of times. they are very brittle after they have been heated up. i am glad I kept the extra wire. The resistance does change, but in my case thats good because I made the outer coil a little to long anyway. Now maybe it'll heat a little better. |
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