Question for those with GRP moulding experience

I'm preparing (my first) mould to make a door panel and I'm undecided on how to prepare the inside corners of the return flanges (that become the outer edges on the part) before starting to lay up.

Do I leave them sharp, or make a 4 mm fillet with plastacine?

Considerations -

If I leave them sharp:
The gel coat sharp edges on the part will be liable to chip. - I would give them a say 2 mm radius by sanding? Hopefully not breaking through the gel coat.
Difficult to get mat into the corners when laying up.
3 mm panel gaps will look better with sharper panel edges?

With 4 mm radius fillet:
Takes time to make the fillet
Easier to lay-up
4 mm will become say 5 mm once sanded smooth if necessary to even the edge out?

So which is better/easier? The parts will be painted - eventually.

Cheers

Fred W B
 

Russ Noble

GT40s Supporter
Lifetime Supporter
Ideally Fred you don't want to be playing around with plasticine because of the lack of finish.

Make your plug the exact shape that you want the moulds and subsequent parts to be. If everything is properly waxed and there is no mechanical bind (ie conflicting tapers) square edges should come out OK. Make sure after you lay up your first layer of glass, and after it hardens, that you go over it and grind out/repair any airbubbles before adding further layers.

From a production point of view slightly rounded edges are always better than sharp crisp lines but no need to go for anything as large a 2mm radius.

All the above IMHO! I am just an amatuer. Some one like Bill Hough might see this and give you the advantage of his professional opinion.
 
Hi Fred
I am brand new to this forum and one of ther GT guys(Ian Anderson)over here in the UK has asked me if I can help you out with your moulding question.
I am a self employed Fibreglass repairman of some 30yrs so should be able to help you out :drunk:
If it was me doing this I would make a 4mm radius out of plasticine as you have already said.
Use a 4mm drill bit and cove in the edges making sure that the plasticine goes right into the corners.
You could get away with a 3mm radius and then profile sand once the panel is released.
You must make sure that you use a good release wax and coat the mould at least 6 times,polishing it up between each coat to get a good high gloss.
This will help the panel release once it is all cured.
You should leave the layed up panel in the mould for at least a week before you release as this will allow for curing and shrinkage to occur in the mould and also to keep the panel in shape.
If you would like to send me a pm I can lead you to a link on a forum that I belong to here and you can see ,step by step how I have constructed a front splitter with just basic laminating skills and a few simple tools.
Kind regards
Paul R
 

Ian Anderson

Lifetime Supporter
Paul

Many thanks for that - your fiberglassing experience would be appreciated by a few on this forum

Cheers
Ian
 

Russ Noble

GT40s Supporter
Lifetime Supporter
Dead right Ian.

I've already PMed him for the link to his splitter posts. Perhaps Paul should show the link here for all to see.....
 
Hi Fred,

They are available as a leather covered pocketed unit from RF or as a bare do it yourself GRP shell as you are proposing I believe. At $100+gst/pr for the shells you'd have to add up materials and your time to see if you can save a dallor.

cheers PB
 

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