Building a Sea Chest

[mbmcdermott18]

Dave thanks for the advice.

I was going to wax it with partall #2 before applying the pva do you think this would seal it up ok or should I paint it?

I have read about people making the mold smaller on the top. How much smaller should it be? Is it pretty much a guarantee that the part is not going to come off w/o tearing up the mold? If so thats ok but I would like to be able to keep it.

I was thinking I would drill several small holes in the sides of the mold and then fill them with wax then when I get the part ready to take off I will drill a tapered hole into the bottom of the mold that I can put my blow gun in and use a little air pressure to break it free.

[77SceptreOB]

Originally Posted by Blue_Heron

Your mold doesn't have any taper. You will have to destroy the mold to free it from your part. Male molds that are intended to be re-used always taper from the opening to the inside. In other words, the closed end is smaller than the open end so it will slide out easily once you break the bond with the new part. I'm not saying it won't work, just that you need to think about how you're going to get the mold out without damaging your part.

Listen to Dave on this one. I made the same mistake on my first big fiberglass project. In the end I spent 3 hours hammer & chiseling the part out of the mold, while destroying the mold in the process while being EXTRA careful to protect my part....Taper is a must! My final part worked out okay, but my mold was trashed. Getting that "plug" out was a total P.I.T.A.!! I would say a 1/2" taper on 6" would be the minimum I would use. Say about a 1" setback for every 12" of vertical wall. Dave "Blue Heron" has more experience on that and may weigh in with his thoughts on minimum taper.

[hermco]

2 degrees is standard minimum draft angle. A small part like that might blow off. I found Honey Wax works well on that material. I did some tests and PVA was the least effective on MDF. Since it is already made I would give it a try what the hell. Stuff is easy to bust out, just add water! Just do your layup then drill a hole in the top to accept your air blower tip. Be sure to only drill thru the glass and not the plug. Then tap with a rubber mallet.

[mbmcdermott18]

Well I decided to put a couple coats of polyeurethane to try and seal it up. We will see how it goes. Ringleader over on classic mako seems to have good success just waxing the mdf.

I am interested in removing these parts. How much force is usually required to separate the mold from the part?

After thinking about it I believe my plan of attack will be to drill a hole in the bottom of the mold through the mdf that will allow the air to get into the mold which will have holes drilled in it to allow the air to get in between the outside of the mold and the part.

Then I am going to thread a quick connect into the hole and hook up an air hose into it. Starting at 75 psi I will work the wedge around the flange and see how it goes. If she doesn't pop at 75 I will increase @ 25 psi increments.

If it becomes obvious that the part won't pop I will just unscrew the sheet of mdf from the mold and take it apart from the inside.

Thanks to everyone who has offered their opinions and advice.

Hope everyone has a Merry Christmas

Mike

[strick]

I would not worry too much about saving that male one off mdf mold as it will likely warp or break before you ever use it again (mdf loves to absorb water)...plus it is not tapered like Dave already mentioned. They are cheap and easy to make anyways..... If you want a super smooth surface then you should coat it something before you wax....the wax alone will leave some streaks in your part...I dont know that it really matters anyways....how smooth your surface is....I was thinking it may have been easier to make a female one off mold but then your smooth surface would be on the out side. It would have been easier to free the part....be careful with compressed air and molds! If you did not seal/join the area where the base connects to the box it may leak air....then start a hacking away!

strick

[mbmcdermott18]

Mold has 4 coats of partal #2 and three coats of #10 going to begin laying glass this morning we will see how it goes

[77SceptreOB]

Good luck, keep us posted...

[SBD]

If you plan on spraying gelcoat, I would thin it at least a little. It will spray a LOT better regardless of the gun. I have tried a variety of guns and have settled on an old school siphon style from Home Cheapo.

[mbmcdermott18]

Popped the part at about 430 this morning had to break up the mdf wasn't too much trouble. Final laminate was 1.5oz mat/1708/1708/708/1708/1.5oz mat. Part came out pretty good. Most of the flange will be trimmed back.

[Blue_Heron]

Originally Posted by mbmcdermott18

Final laminate was 1.5oz mat/1708/1708/708/1708/1.5oz mat. Part came out pretty good.

Congratulations. Looks good. And with 4 layers of 1708, I don't think you need to worry about strength.

Dave