Non-Boat fiberglass question...

I have a fiberglass mold question that's not boat related, but it seems that all of the good fiberglass forums are geared towards boat building or repair.

Is it ok to ask here, or is there a more general fiberglass forum out there?

thanks in advance.

Doug

 

Throw it out into the ether and see what comes back. Some good glass guys on here.

 

Odds are, it might help someone doing a boat, so feel free to drop the question. No charge

 

I will second the above comments by ComFisherman and RWatson - there was a thread on here fairly recently by a gentleman asking about fibreglass construction techniques - we initially thought that this was in reference to a boat, but no, it was in relation to a fibreglass spoiler that he was building for a car.

So go ahead and ask as many questions as you like - and if you can post some photos as well of what you are concerned about, then even better.

 

Thanks for the welcome.

I trying to make this plastic van grill into a plug, so that I reproduce it in fiberglass.

It seems fairly straight forward except for the louvers. From the front view, they look just like any louvers you'd see on a pair of wooden plantation shutters etc.
But from the backside you can tell they're hollow and only have the front face. If I'm explaining myself correctly.

on the plug, I'd start with a piece of MDF about 3" bigger than the grill on all sides for the base. I'd kerf the bottom side of it and and bend it to match the arch of the grill.

then mount the grill face up and use body filler to smooth any irregularities in the fitment etc.etc. The louvers seem to be the sticking point for me. They will touch on only one side. Should I fill the in the louvers so that they touch on each edge. i.e. their cross section would look similar to this |\ vs. just this \

 

That injection-molded plastic automotive grill, as designed, would be a tough part to reproduce in fiberglass cloth and resin.
Are they no longer available as NOS or salvaged?

 

very expensive and fragile...

I had planned on kind of "dumbing down" a lot to the injection molded features......think of the end product as a type of a shell/cap. Kind of like those rigid dash board caps or covers that go over a worn dash pad. Only this wouldn't have anything under it. That might not be the best analogy....

is there a way to build the louvers with an "A" cross section (to make it easier to cast) then somehow trim the unwanted part away afterwards? In short, are there techniques or things i can add to the design to make that trimming easier (than free hand trimming each one)?


thanks.

 

Is the main issue with plug design; not to have anything that "under cuts" back in.....which would trap the piece in the mold?

 

An injection mold would have moving pieces to mold the tricky bits and retract out of the way to de-mold. Plus the injection mold is built to wrap all the way around the intended part, with a plug you'd need a way to drape cloth and resin and would have difficulty in the corners, etc.

 

The basic outer shell isn't hugely difficult but the various clips and brackets may be quite challenging.You really need to fill the gaps between the slats and it would be a good move to extend the headlight and badge recesses inwards a bit and then create a flat surface.It doesn't have to be a marvel of precision engineering as the function of the extra material is to stabilise the shape.Some sort of flange projecting from the periphery would be very useful for locating the hardware that attaches the panel to the vehicle.

 

I would make a plaster mold/plug off of existing face.
Plaster is cheap and the easiest to chip off of the original.
Once the plaster cast is removable in one piece then additional plaster can be used to fill in the gaps. Dry plaster can also be sanded into shape.

 

Hi Doug, for a small production run, or to make a mold and or plug, I'd be tempted to stabilise the flimsy plastic grille on a steel frame, or even on a vehicle, and paint release agent, then several litres of latex - liquid rubber, liberally, with thickness everywhere, some reinforcement, and with a stiff framework backing glued in to keep it in shape when removed, and placed on a flat base. You can be messy with the latex, then when cured you slice away the un needed excess rubber as required to remove the mold from the grille, and also to allow access and easy removal of future FG parts. Use this rubber mold as is for a one off part, or to first make a mostly solid rigid FG plug, copy of the grille shape, which you smooth, trim, shape, and modify however you like, to then make a useful working FG mold of your new reproduction grille, again with a stiff framework backing to keep it in shape. Make the more tricky clip on shapes prior, out of separate small molds, which you trim and finish off, and then put in place inserted and located in your production mold, to be glassed in when laying up your final product, every time. You may need to make removable pegs, pins, and shapes to reproduce some surfaces, slots and holes. Parts may need to be removed before completely hard, to make removal easier. There will always be some extra trimming, smoothing, hole drilling, etc. The original plastic's mold of steel is made to thousandths of an inch tolerances or less, to avoid re-working parts, like removing flash from between mold halves; your parts will need to be manually trimmed every time.
If your production mold becomes damaged, make a new one from your plug. Or start again from your original rubber molding. Rubber deteriorates relatively quickly, so don't count on it lasting for years. If there is a profitable and large market, it may be worthwhile, but otherwise it is a lot of work for a simple car part.

 

A couple of points to add to the previous posts;a plaster mould will work in some circumstances but has a couple of attributes that need to be worked around because while it is cheap,it is also heavy and brittle.Which means that the plastic component will need quite a lot of support in order to retain it's shape and it may need temporary flanges added to prevent the plaster from sagging too much.Which points to the advice from seasquirt as being extremely sound as some form of temporary bracing will be a big help.He is also quite correct about each part needing to be trimmed to finished size as it is near impossible to lay up a component with the required laminate thickness extending to the final extent with out the presence of some surplus material to support it.

The compatibility of tooling gel and the plastic used for the old part may be an issue and there are numerous ways to overcome this.One of the most certain is to cover the plastic part with self adhesive PTFE film or even flash tape as this will cover any residue of silicone that may have been applied when the vehicle has been polished.A careful cleaning and coating with PVA might suffice and a cured PVA film can be waxed over for additional insurance.

Back in the 90's a friend who was and is a good laminator asked me to help prepare some car parts for him to manufacture a mould from.The fad for fitting body kits to cars was in full swing and he wanted to put carbon panels on the car in place of the original plastic to make it look "cool".I was happy enough to help him and while the items were much smaller than that being considered here,the principles apply.I used hot melt glue to attach bracing to the back face of the originals and used this as an attachment point for some battens that supported the flanges that needed to be in place to hold the peripheral shape.The flange also served to support the brackets he used to locate the fixing points on the non-visible side of the component.I handed the pieces over and left him to make the mould and the component,he made the parts and found a way to attach the mounting hardware and I heard no more about the project.

 

Seems like structural foam would be a way to do it. But it needs to be a split mold somehow.

 

You could certainly use structural foam to brace the existing part.I may not have spotted the reason for splitting the mould,might we be enlightened?