Advice for parting line in my first 2 piece mold

When I do a flange, I usually hot melt glue some timber brackets on, to save the plug surface the brackets land onto 3m green masking tape. Jeff.

 

I plan to do exactly what you just suggested thankyou everyone for the advice. It's definetly been a huge help

 

That will work. Test a piece of the plexiglass with the resin and solvents you are going to us to make sure it doesn't melt or deform.

What materials are you going to use on the mold?


I like the sawhorse thing.

 

I have used the plexiglass before with just wax and had no issues with it. The mold construction will be tooling gelcoat, tooling resin or ISO as my supplier calls it. I have chopper roving I will take a strand and separate it and lay it in the corner of the plug and flange followed by 3 layers or 1.5 chop mat 2 layers or 17oz Biax.

 

I would generally go real slow when making a mold. I'd let the gel coat cure plenty good, like overnight. Then one layer of 1 1/2 oz mat with the minimum catalyst needed and another good cure on that. Then another of mat, after a number of hours, another and then after another break maybe two etc. Stability was what I wanted, no heat, no distortion, no shrinkage. I used ISO on molds and parts too.

 

I have always read you need to build molds slow like you suggested. However in the past I've built several molds and always built them every layer at once with no waiting. The molds always were fine. Not saying it's the right way but I never understood the theory of building them slow. Is it to prevent shrinkage and distortion? Will I see a noticeable difference in the finish building it slow? The parts I make out of the molds are not high tolerance and are so thin the barely hold shape.

 

If there is shrinkage, big, flat, areas like your top and sides can have a tendency to distort and become dished. If it's in the mold, it will be in the parts. If it's not in the mold, it can still happen in the part if using a hot mix or a high shrinkage resin.

Mats' weight is stated per square foot while everything else is per square yard. So a layup of "3 layers or (of?) 1.5 chop mat 2 layers or (?) 17oz Biax." is a layup of 74.5 oz per sq yd. That seems like a fairly heavy layup (about 1/5") and the exothermic heat buildup may be enough to shrink or distort. I wouldn't do that much all at once on a mold, but maybe I was always too careful.

 

We'll how did I do? I wanted to thank everyone for tips and advice. It allowed me to build this mold without any doubts. I'm happy with how it turned out and hopefully someone else can use this thread to guide them thru as we'll. now that the mold is done I have a question regarding the parting line. Should I let this line alone and spray gel as I normally would or do I need to try to seal it with clay before spraying gel? Also I will be using frekote wolo instead of pva and wax to release these parts. I'm asuming I should release my flange before putting the mold togather?

 

I usually smear a bit of plasticine/modelling clay into the join & then just wax it till it's slightly "negative" in the surface, this leaves the molded part with a slightly positive line that will brush off with some fine wet & dry paper & then polish, don't know if your release system is compatible, shoot an extra pass of gelcoat over the join..... but don't over do it!
Jeff.

 

Looks real good! You might want to glass an external frame to the mold to help it keep it's shape and let you mount it so you can rotate it around for better positioning when laminating.

Those 'hoods' you're making, are they expendable, like able to get damaged and replaced often?

 

I plan to glass an external frame too it.yes the hoods are throw aways. Most hoods will make it a season without a major wreck the just look horrible at the end of year due to the rocks and mud and parts flying off cars. However if they take a bad wreck usually only thing left salvageable of the cars is the motor and steering box. I will post a pic of a complete car.