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www.TK560.com Vacuum Forming, Movie Prop, Sci-fi and GIjOE Forum
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harley guy Novice
Joined: 25 Nov 2005 Posts: 71
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Posted: Wed May 02, 2007 2:37 pm Post subject: whats the easiest way to remove your molds? |
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whats the easiest way to remove your mold? i was woundering if any one has some good ideas of removing a mold from 1/8 - 3/16 abs plastic. ok my mold is 18in. long x 7in. wide x 5in. tall., they are made out of wood, they are very simple like a big oval bowl shaped, no valleys or anything. i have machined the sides of the mold 1 degree angle so it will comes out easier, i have drilled air holes in the mold to allow air passage, so your mold doesnt act like a suction cup. i have machined a big pocket on the bottom of the mold for 2 hand grips to help pull the mold out. i use baby powder on the molds before pulls and this mold is a pain in the butt to get out. my more complex mold comes out 10 times easier, very weird. i remove my molds by smacking them onto a 4 x4 piece of wood till they come half way out of the plastic, then pull the mold the rest of the way with the hand grips. i usually pull the molds out right after i form it while it is still warm. should i wait til it is cooled down? i thought when it cools down it shrinks to the mold? any hints on what or how to get your mold out easier. |
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faithblinded Newbie
Joined: 28 Apr 2007 Posts: 14 Location: Cleveland, Ohio
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Posted: Wed May 02, 2007 3:13 pm Post subject: |
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I'd consider trying a negative mold. It's often recommended in cases where bucks get stuck. It's nice because when the plastic cools it will shrink away from the mold, not tightly around it. I'm suprprised not to see more negative molds in use here
I've heard of using a heat gun to coax them out, though of course you risk warping the piece.
Sounds to me like you did everything right. Although 1 degree of draught sounds negligible. If I recall, 2-4 degrees is usually recommended, with 3 degrees being mostly reliable. YMMV
From all you said, I think I'd be ready to try a negative mold. Worth a try.
good luck
Ken in cleveland |
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drcrash Guru
Joined: 04 Sep 2006 Posts: 705 Location: Austin, Texas
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Posted: Wed May 02, 2007 3:20 pm Post subject: |
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One way to do it is to blow air backwards through the vent holes and pop the plastic off the mold. A lot of big industrial vacuum formers do that---they suck the plastic down, let it cool below its thermoforming range but not much more, then blow air the other way through the vent holes.
It actually shouldn't be too hard to do that with a wooden mold, for something you making a lot of. You'd just need to rout some channels from wherever the vent holes come out the bottom, put some air tubes in them (or cover them up with a sturdy riser to make air channels) and countersink a quick-disconnect air fitting there. After you make the part, raise up the mold, attach a compressed air line and give it a burst of air. You'd probably want to use an orifice to limit the airflow, so that you don't blow a hole in the plastic or explode the mold, but I'd guess it wouldn't take much.
(I recently loosened a styrene part by blowing into the vent holes on the back of a mold with just my mouth. I think it helped, anyway... I'm not really sure.)
1 degree of draft isn't much. The usual recommendation I've seen for fairly easy demolding is 3 degrees or more. I think 1 degree should be doable, though.
Is your mold bare wood, or painted, or what?
You are right not to let the plastic cool completely before trying to take it off. The more it cools, the more it shrinks and tightens on the mold. _________________ Paul (a.k.a. Dr. Crash)
Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com
Last edited by drcrash on Sat May 05, 2007 7:57 am; edited 1 time in total |
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harley guy Novice
Joined: 25 Nov 2005 Posts: 71
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Posted: Wed May 02, 2007 6:57 pm Post subject: |
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its plain not stained or painted. the wierd thing is the other one that is similar but more complexed with 2 valleys little over 1-3/4 deep x 2 wide, comes out with 4 wacked real easy. the simple mold is a pain. i was going to change the degree angle, but i need a tight seal when i put the two casestogether. i just cant figure it out. i guess the small things in life are a pain to. drcrash i have thought about the blowing air in it to. that might be my next step or maybe i was thinking a pulley puller type rig. it will hold the plastic down and pull my fixture out. the rig wont be hard to make but will take room up. i pull about 50 - 100 pulls a week, some times more depending on orders. just trying to get some different ideas, to make life easier. |
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jegner Site Admin
Joined: 30 May 2003 Posts: 2144 Location: Texas, USA
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Posted: Wed May 02, 2007 9:12 pm Post subject: |
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Try removing the mold while the plastic is still warm. Not so hot as it would loose it's shape, but still soft.
Also, I tend to add risers with a 15-20 degree angle, this really helps my molds release.
JIm |
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crashmann Guru
Joined: 27 Sep 2005 Posts: 501
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Posted: Thu May 03, 2007 10:43 pm Post subject: |
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You might try using an air compressor to shoot air between the plastic and the mold. Lift up a corner, then point your air nozzle in and give it a quick blast. There's a biker scout armor maker who uses this technique on his pulls that have 1/2" undercut.
With a smooth mold, there is no air to fill the gap when you are lifting the plastic. Blasting a little air helps encourage the release.
Click here for the posting on Omega Wing
Charlie
TI-386 |
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drcrash Guru
Joined: 04 Sep 2006 Posts: 705 Location: Austin, Texas
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Posted: Fri May 04, 2007 10:31 am Post subject: |
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harley guy wrote: | its plain not stained or painted. the wierd thing is the other one that is similar but more complexed with 2 valleys little over 1-3/4 deep x 2 wide, comes out with 4 wacked real easy. the simple mold is a pain. i was going to change the degree angle, but i need a tight seal when i put the two casestogether. |
Are you using the same oven, same amount of sag, and the same side of the plastic against the mold?
Just checking... I've had some funny experiences with overheating one side of the plastic. If the too-hot-and-liquidy side is against the mold, it can be way harder to get off of a difficult mold than if the not-quite-so-hot side is against the mold.
(I had an entertaining experience recently with PVC going right through the windowscreen over my platen, and making zillions of little mushroom-shaped barbs that would not pull back out. Oops... but I was glad it didn't make barbs into platen holes and possibly wreck a nice many-hole platen. I managed to get it off the mold, though, after cutting away the excess and heating the mold & plastic in my kitchen oven at 225 for three minutes.) _________________ 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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ANH trooper Master
Joined: 20 Oct 2005 Posts: 305 Location: UK
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Posted: Sat May 05, 2007 3:20 am Post subject: |
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I find warming up the plastic again with a heat gun really helps a lot. You will also find that handles or something to grip inside the mould will help pull it out too after you have reheated the plastic forming. I never use any mould release or baby powder on any of my stormtrooper moulds which have some pretty bad shapes. |
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crashmann Guru
Joined: 27 Sep 2005 Posts: 501
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Posted: Sat May 05, 2007 8:35 am Post subject: |
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ANH trooper wrote: | ... I never use any mould release or baby powder on any of my stormtrooper moulds which have some pretty bad shapes. |
Pretty bad shapes?!?
Your stormtrooper molds have the best shapes I have ever seen!
Charlie
TI-386 |
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drcrash Guru
Joined: 04 Sep 2006 Posts: 705 Location: Austin, Texas
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Posted: Sat May 05, 2007 9:17 am Post subject: |
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That's some nice work! I'm going to have to try the lighter-fluid-and-Scotchbrite clay-smoothing thing.
By the way, what's up with the RPF? I was unable to successfully register a few months ago, and now it says that "registration has been disabled." _________________ 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: Sat May 05, 2007 11:55 pm Post subject: |
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drcrash wrote: | harley guy wrote: | its plain not stained or painted. the wierd thing is the other one that is similar but more complexed with 2 valleys little over 1-3/4 deep x 2 wide, comes out with 4 wacked real easy. the simple mold is a pain. i was going to change the degree angle, but i need a tight seal when i put the two casestogether. |
Are you using the same oven, same amount of sag, and the same side of the plastic against the mold?
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same heat, time, side, plastic. |
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drcrash Guru
Joined: 04 Sep 2006 Posts: 705 Location: Austin, Texas
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Posted: Sun May 06, 2007 7:21 am Post subject: |
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harley guy wrote: | same heat, time, side, plastic. |
OK, just checking.
Can you post pictures of your bucks?
I have found that 180-degree bowl-like shapes can be pretty hard to demold. In particular, if you lifecast sombody's face and go too far back (over the forehead, under the chin to the throad, around the sides to the ears) it can be difficult.
If you cut away the top part, say, above the hairline, it gets lots easier to remove---you can flex the sides out, then bring the top part away first, pivoting at the chin, and pull it off downward over the chin.
Is your final part the full bowl, or is there a piece that will be cut away later? _________________ 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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crashmann Guru
Joined: 27 Sep 2005 Posts: 501
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Posted: Sun May 06, 2007 8:56 pm Post subject: |
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Quote: | whats the easiest way to remove your mold? |
Have you tried making a 3/4" MDF riser with the sides tapered to 20 degrees? Once you've made the pull, pry the riser out, and that will leave 3/4" to drop out the original mold when you whack it on your 4x4s.
Quote: | By the way, what's up with the RPF? I was unable to successfully register a few months ago, and now it says that "registration has been disabled." |
They recently went through a board upgrade, and many of the accounts were partially locked out. I was unable to login, and the "I forgot my password" link used an old e-mail address that no longer exists. Contact the administrators and tell them your username is locked out. It took 4 days for me to get a reply, so be patient... http://www.therpf.com/sendmessage.php
Charlie
TI-386 |
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TK 109 Guru
Joined: 11 May 2007 Posts: 712 Location: Galena, Ohio
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Posted: Mon May 14, 2007 4:17 pm Post subject: |
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I use a flathead screwdriver, or a chisel to remove my molds. (of corse, sometimes my pull tears, but then this tells me that the mold wasn't coming out!) _________________ -Alex
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