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Old 28-09-2015, 16:19   #16
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Re: Having a little trouble removing part from male molds

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Originally Posted by HankOnthewater View Post
Hard-rock-candy is right. Air pressure will relieve the vacuum post curing.
Drill a hole ( ie 3-5 mm) in the mould, glass a tube on it, strongly.

A shrader valve? Why not? Although I have not seen that done.

When preparing the mould, fill the drilled hole with a smear of wax, then PVA before the first (gel) coat. After curing put the hose or nozzle on the tube, and it will pop.
For a big mould you may need to drill and prepare more holes/tubes
the above is good altho I would use water. water does not compress so when it releases it won't have the potential to go flying and hurt someone. Regular water pressure from the city water is around 6 to 10 psi which is more than enough.
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Old 28-09-2015, 16:41   #17
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Re: Having a little trouble removing part from male molds

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Originally Posted by tinkrman69 View Post
...Regular water pressure from the city water is around 6 to 10 psi which is more than enough.
Pretty sure it is 10 X that much. On yacht shore water hookups, we regulate it down to less than 50 lbs.
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Old 28-09-2015, 17:34   #18
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Re: Having a little trouble removing part from male molds

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Originally Posted by Krilleonnova View Post
normal polyester shrinks that's why you have problems
use polyester made for building molds it has a foaming agent in it so it swells when it hardens. Meaning the part gets bigger than the male mold or plug.

But then you have a part made from mold making resin.
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Old 28-09-2015, 17:38   #19
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Re: Having a little trouble removing part from male molds

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Originally Posted by Lokiyawl View Post
The mold shown in the link you provided appears to have plenty of relief so I have to wonder if despite the PVA and wax that you might still have some sticking issues. I have had some luck with building up the wax on a new mold, spraying on a thin coat of PVA/allowing it to dry fully and then applying a thin coat of wax over top of the PVA without wiping it off. It seems that the first several pull off of a new mold are always the hardest and once broken in the parts start coming off on their own as the shrinking occurs during curing. You can hear the little pops as the bond between the mold and the part separate as the polyester shrinks. The suggestions to vent, use air or water pressure can work but I am actually surprised that you are having any release problems with the the part shown in the link. Maybe try a different wax, PVA should not even be needed, especially after the mold is broken in. I have always used the Mequiars Mirror Glaze #8 wax myself. Good luck. James

Wax + PVA is a no no, it's one or the other; wax if you need a finish. PVA softens wax, and it will bead like water when sprayed on a waxed surface. Use a dedicated release wax, not just any old wax. I recommend Partall Paste #2 for rough molds. Never had a part stick with even a single coat of Partall.
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Old 28-09-2015, 20:11   #20
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Re: Having a little trouble removing part from male molds

Thanks for all the tips.

I think what I'm going to do is, on the next part, add a tube or valve to blow air into the mold, as several of you suggested. OR mabye I'll glass in a garden hose fitting to screw on a hose (ah, maybe that's overkill).

For example, I have a female mold that will produce a part that is about 36" long with a diameter of about 4" and has outward flanges. This is a combination part that will be a hull stiffener and cable raceway.

https://picasaweb.google.com/1112749...13478/Release#


I created this female mold from a male pattern constructed out of that blue styrofoam board from Lowes. I had the same problem removing this mold from the pattern as I did with the foot pump cavity part/mold. I ended up dissolving/chipping the foam away, then scraped away the drywall mud. Al that was left was the thin later of Duratec primer, which wasn't difficult to remove once I lifted the edge with my fingernail and sprayed water under; it just peeled away easily.

So on this mold (the red one), I'll drill a couple of holes and maybe glass in some schrader valves.

I did try beating the crap out of it and wedging plastic, then wood around the dges of the foot pump cavity part, but that didn't do anything but damage the mold and part of the finished flange (no biggie, that damage will be concealed behind the cabinet).

Regarding the wax vs pva. I did notice some pva beading on some portions of the foot pump cavity pattern. I wiped it all down with alcohol and just used PVA. No realease issues. on the previous three parts I made about 2 months ago, I used wax (mcquires carnauba) and pva with no beading and no release issues (except for vacuum issues). On this recent foot pump cavity, I used mother's carnauba, then pva and had some beading. I alcohol-wiped it clean and just used PVA. I'm kinda reluctant to not use pva. I guess i'll try a test spot on some scrap, waxed and test releasing it.

It's really gratifying being able to make these parts, but it is a real disappointment to destroy a pattern ( or male mold) just to get the part off, even though I only intended to make a single part.

From what I gather and have experienced, the only issue I have right now is the vacuum effect. Once I break the vacuum, there is no release issue.

Does that seem about right? To put a couple of holes/valves in the mold to break the vacuum. It'd be really discouraging to have to destroy this beautiful female mold to get the part off.

I'll grab some of that partall #2 paste and test that.

Thanks again for the help.
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Old 28-09-2015, 21:22   #21
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Re: Having a little trouble removing part from male molds

What draft angle did you use?
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Old 29-09-2015, 19:25   #22
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Re: Having a little trouble removing part from male molds

The draft angles vary between 5 degrees and about 10 degrees on the sides of the white foot pump part.
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Old 29-09-2015, 22:31   #23
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Re: Having a little trouble removing part from male molds

Quote:
Originally Posted by scherzoja View Post
Thanks for all the tips.

I think what I'm going to do is, on the next part, add a tube or valve to blow air into the mold, as several of you suggested. OR mabye I'll glass in a garden hose fitting to screw on a hose (ah, maybe that's overkill).

For example, I have a female mold that will produce a part that is about 36" long with a diameter of about 4" and has outward flanges. This is a combination part that will be a hull stiffener and cable raceway.

https://picasaweb.google.com/1112749...13478/Release#


I created this female mold from a male pattern constructed out of that blue styrofoam board from Lowes. I had the same problem removing this mold from the pattern as I did with the foot pump cavity part/mold. I ended up dissolving/chipping the foam away, then scraped away the drywall mud. Al that was left was the thin later of Duratec primer, which wasn't difficult to remove once I lifted the edge with my fingernail and sprayed water under; it just peeled away easily.

So on this mold (the red one), I'll drill a couple of holes and maybe glass in some schrader valves.

I did try beating the crap out of it and wedging plastic, then wood around the dges of the foot pump cavity part, but that didn't do anything but damage the mold and part of the finished flange (no biggie, that damage will be concealed behind the cabinet).

Regarding the wax vs pva. I did notice some pva beading on some portions of the foot pump cavity pattern. I wiped it all down with alcohol and just used PVA. No realease issues. on the previous three parts I made about 2 months ago, I used wax (mcquires carnauba) and pva with no beading and no release issues (except for vacuum issues). On this recent foot pump cavity, I used mother's carnauba, then pva and had some beading. I alcohol-wiped it clean and just used PVA. I'm kinda reluctant to not use pva. I guess i'll try a test spot on some scrap, waxed and test releasing it.

It's really gratifying being able to make these parts, but it is a real disappointment to destroy a pattern ( or male mold) just to get the part off, even though I only intended to make a single part.

From what I gather and have experienced, the only issue I have right now is the vacuum effect. Once I break the vacuum, there is no release issue.

Does that seem about right? To put a couple of holes/valves in the mold to break the vacuum. It'd be really discouraging to have to destroy this beautiful female mold to get the part off.

I'll grab some of that partall #2 paste and test that.

Thanks again for the help.

Easy on the Partall or you'll have prerelease problems instead!


http://www.amazon.com/Meguiars-Maxim.../dp/B002J854E8

Easy to get and works great for regular molded parts. There's all sorts of high temp and other specialty waxes, but this is an old standby for highly finished parts. At least four coats on a new mold and even then it won't be "cured" until it's popped a few parts and been waxed again each time.


Partall is awesome for a quick release agent, two to three coats max, just to be sure. It doesn't buff out like other waxes. But it will for sure release! If you don't need a finish, just try Partall without an air fitting, or you may blast your part across the shop! Best for quick one off parts which will be faired and painted anyhow.
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Old 02-10-2015, 09:33   #24
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Re: Having a little trouble removing part from male molds

If you are making just a few parts out of a mold, make your mold flanges a few inches wider than you have been, and when you are through laying up your part, lay 2-3 layers of mat off each of the corners, out into the wide open spaces of the wider flange. That makes a pull tab you can yank upward and slide in a wedge. When you are dressing the part, a metal cut off wheel zips it off, quickly and a touch with a grinder on the back of the part flushes it up.

If you lay a few pieces of uni directional along the flange, or pull a few tows out of some scrap biax and lay them along the flange of the mold before it is done being laid up, with a few tows twisting up onto the side of the part your mold flanges can take the abuse of a fair bit of hammering, or a truck driving over them without much extra material.

I normally make the flanges a third thicker than the rest of the mold. 1/4 inch mold, make the flanges 3/8ths... Just tear the mat up into the corners onto the surface so there isn't a hard edge line when the extra thickness material shrinks while curing out you don't see it in the part. That is less of a problem if you are using tooling resin...

For another quart or so of resin every 4 feet or so, you end up with a mold that you can't damage by hand held means... Makes parts a lot easier to pop out, so long as the mold can be held down firmly to the work bench.

Cheers,

Zach
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