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jamiemcshan · Newbie Joined: 09 Jan 2011 Posts: 10

Hi guys, still pretty new to all this.... Is it an option to have relief holes in your mold to allow suction to come up through the mold to get extra suction and provide more details? I am working on an 80% scaled Ghostbusters proton pack for my son. I have the mold all done for part of it, and pulled by first pull last night. It was ok, but the detail is lacking in some areas and I was wondering… if there are areas that are going to get cut out later anyway, if it was a good idea to put holes there that feed through to the bottom of the mold and allowed suction to the middle of the mold. Here is a photo of my first pull. I was thinking of adding holes where the 4 circles are on the top to help suck the plastic down into those circles and provide greater detail. Those areas get cut out later for lights. Thoughts?

RRK4 · Novice Joined: 17 May 2011 Posts: 58

I'm no expert but I think that is a very common thing to do.

spektr · Master Joined: 07 Jan 2008 Posts: 425

If you want to do that, heres a couple things to think about. Drill the holes near the radius of the area you are venting. Put it in the middle and the plastic will cover it when it pulls down. second, vacuum is flow sensitive, after you put in ports, counterbore them a lot larget than the hole is. I use a lot of #60 drills to port tools and come back and druill them up 3/16th or so. really helps.

jamiemcshan · Newbie Joined: 09 Jan 2011 Posts: 10

Thanks for the advice. I was just going to put them dead center, but you make perfect sense. They will just get covered up... Glad I posted. I think I will also see if I can add some holes around some of the other edges to see if it will pull them in a bit more too.

crashmann · Guru Joined: 27 Sep 2005 Posts: 501

One of my favorite things to do (because I am nerdy), is to examine plastic clamshell packaging and see where they put the vent holes. Many food containers are vacuum formed - Pringles single serving chips, clear plastic fruit containers, bulk hard drive packaging, tons of stuff.

By looking at these products, you can improve your design and vent your molds for vacuum forming.

Charlie

jegner · Posted: Sat Jun 11, 2011 1:24 pm Post subject:

Proton Pack? Cool!

jamiemcshan · Newbie Joined: 09 Jan 2011 Posts: 10

Yep, it's 80% scale for my son. But, now that I drilled relief holes, I got a great amount of details, but I couldn't get the mold out. I had to rip off the styrene to get it out. Not sure what to do. I was going to get some talcum powder tomorrow to see if that will help. Any other suggestions???

RRK4 · Novice Joined: 17 May 2011 Posts: 58

Did you try spraying some air up under the edge?

jamiemcshan · Newbie Joined: 09 Jan 2011 Posts: 10

Trust me... I tried everything. I blew air in the relief holes. I mounted a handle to the mold to pull with. It wouldn't budge.

I thought about trying to heat up the styrene with a heat gun. Anyone have any thoughts on that?

Jamie

RRK4 · Novice Joined: 17 May 2011 Posts: 58

I'm sure some of these guys will know how to handle it. It doesn't look like extreme undercuts to me.

I have seen talcum powder used in some videos but I think you don't want to suck it into your vacuum pump since its an abrasive.

jdougn · Posted: Sun Jun 12, 2011 3:09 pm Post subject:

Lots of good information being provided.
Something about the increased detail caused the plastic to lock to the mold. Look at the areas of increased detail and make sure there is at least 4-5% of relief or draft all all verticals and absolutely no undercuts.

I will not let talc powder get anywhere close to a regular vacuum pump. If you're using a shop vac it is probably okay. Talc destroyed my first vac pump and since talc is very fine grit I don't think most filters would catch it.

my .o2,
DougN
_________________
DougN - Just in case you're wondering, I got my "rating" legitimately... by posting aimless drivel, useless advice, and pointless questions.

RRK4 · Novice Joined: 17 May 2011 Posts: 58

... or maybe cut it off and put in a couple of strategically placed seems.

jamiemcshan · Newbie Joined: 09 Jan 2011 Posts: 10

Well, I got lucky. I finally got a good pull and was able to get it out. I put a bunch of talcum powder all over it. Then I started trying to get the mold out as soon as I stopped the vacuum. While the plastic was still warm. I'll post a photo of the finished prieces shortly. Thanks everyone for thier help.

Jamie

jamiemcshan · Newbie Joined: 09 Jan 2011 Posts: 10

I just read somewhere that they used PAM as a release agent. Has anyone used this with primmed MDF and if so, what does it do to the primer? Is this a one time deal?

Here is my completed molds.

And here is my completed pulls.

I think all in all, they turned out pretty good. This is a small homemade 12x24" table with a shop vac. I figure for a table that cost me like $10 to make, it does work pretty well.

Jamie

spektr · Master Joined: 07 Jan 2008 Posts: 425

We all do know why we remove the parts warm dont we???? Plastic shrinks as it cools and all those wonderful square looking blocks "tighten" on the tools. This is one of those tools that needs a bit of draft, or better yet, if made in any qantity at all, a female mold. An ideal candidate for a poured tool..... Try to use the plastic itself to help you when you can, and here, the plastic shrinkage would release a female part......