Best way to prep mdf mold for making female mold

[konalure]

Hi, looking for tips on how to prep a MDF plug mold in order to pull a female mold in fiberglass off the MDF plug, I realise MDF is kinda a lousy material to try to pull a mold off of but for cost reasons I'd thought I'd give it a shot.. would a few coats of automotive primer sprayed onto the mdf mold after sanding and then sanded smooth and waxed well afterwards work, .. would a thin layer of epoxy be better and maybee seal the MDF better? last time I attempted to get a good plug out of MDF I made the mistake of trying some polyurethane spray on the mold first to seal it and it seemed to make areas of the mold swell.. any tips would be appreiciated..

thanks for reading, Del

[mc_n_g]

MDF plug mold in order to pull a female mold in fiberglass off the MDF plug?

Not quite sure I follow what you are trying to do. MDF plug?

[keebler303]

I have always used duratec gray surfacing primer. Its a bit pricey but its worth it. Spray one coat, sand, spray, repeat until you have a nice looking surface, then you can wet sand with progressively finer paper up to around 2000 grit. Then you can buff it to a shine. Pretty much a mirror finish. Then put on about 4-6 coats of car wax. Let the wax dry and buff it between coats. Then you are ready to go. Spray it with gel coat, let it tack up, then start putting on your glass.

I'll post up some pictures if I can find any on my computer.

You can buy the stuff here: duratec
don't forget you need the catalyst too! (MEKP)

Cheers
Matt

[keebler303]

Here is a top half and bottom half mold I did a while back. I CNC'ed the patterns from MDF, used the duratec as I explained above, then pulled female molds off the patterns.

Picture of the molds kind of sucks due to the orange tooling gel, but you get the idea.

Matt

[dsharp]

I don't know the shape of your mold but, if it's flat you can use 1/32" formica

[konalure]

thanks for the reply, i'll have to get some of that duratec primer.. another question I been pondering is possibly it would be a better stratedgy to just machine the female mold with my CNC itself out of mdf instead of even making a plug and then molding.. I may need to try several different molds anyways and it would cut down steps.. To give an idea of what im trying to do is setup a female mold for carbon fiber vacuum bagging.. I was worrying about the mdf leaking the pressure out but maybee if coated well with the primer it would work well enough.. anyways heres a few pictures of what im trying to mold.. the first one is what the female mold needs to look like.. the second is what the finished unit will be.( or the plug for the female mold..)
thanks again for the help

Aloha,

Del

[keebler303]

There can be advantages either way. If you make the mold directly and you mess it up (break it, part hooks up to it, etc.), you have to start over. With a core, you still have the pattern and can quickly make another mold. This is also an advantage if you ever scale up and want more than one of the same mold. Thats easy with a core. I'm not sure what changes you are looking to make but you can have a "master" core and then make a mold from that. If you make a part from fiberglass using the mold, then you can modify that part and then use that as the new core. If the changes are subtle, that would probably be the quickest way.

The MDF definitely leaks a lot of air under vacuum. Also remember that the duratec is not structural and will have a tendency to crack and chip unless it has a fiberglass backer. You will see some cracks and chips in my pattern. Not a big deal for a pattern, but for a mold, it would get worse and worse every time you ran it. If you're only doing a couple, it might work out, but it wouldn't hold up in a production environment.

Matt