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harley guy · Novice Joined: 25 Nov 2005 Posts: 71

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.

faithblinded · Posted: Wed May 02, 2007 3:13 pm Post subject:

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

drcrash · Posted: Wed May 02, 2007 3:20 pm Post subject:

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.
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harley guy · Novice Joined: 25 Nov 2005 Posts: 71

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.

jegner · Posted: Wed May 02, 2007 9:12 pm Post subject:

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

crashmann · Guru Joined: 27 Sep 2005 Posts: 501

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

drcrash · Posted: Fri May 04, 2007 10:31 am Post subject:

ANH trooper · Master Joined: 20 Oct 2005 Posts: 305 Location: UK

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.

crashmann · Guru Joined: 27 Sep 2005 Posts: 501

drcrash · Posted: Sat May 05, 2007 9:17 am Post subject:

harley guy · Novice Joined: 25 Nov 2005 Posts: 71

drcrash · Posted: Sun May 06, 2007 7:21 am Post subject:

crashmann · Guru Joined: 27 Sep 2005 Posts: 501

TK 109 · Guru Joined: 11 May 2007 Posts: 712 Location: Galena, Ohio

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!) Laughing

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-Alex

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