Hello all, I'm back again with yet another question concerning how to mold object X to object Y. This time, it pertains to something with materials which would be easier to work with but probably flex a lot more.

I have a 1990 Miata with a front lip bolted to the bottom of the bumper. I also have some foglight bezels installed. I believe the lip to be polypropelene, and the front bumper is urethane.

I was wondering if it was possible to mold the bezels and front lip into the bumper for a seamless look?

For reference, this is another user's Miata which he has installed the foglight bezels and same front lip as I have (to be clear this isn't my car, just an example).




I'm worried yet again about cracking, flexing, and all that stuff. It won't break my heart if it's not possible so let me know what you all think. Thanks again!

Nope, plastics like that do not play well together at all. Again, look at factory stuff. Dissimilar materials are generally destined to fail. Now the most successful application of this type of thing is to go ahead, hack everything together, take a mold of the whole new grafted item, then strike a new complete fiberglas piece out of your new mold. It's a lot of work but not impossible for the hobbyist. Ricer guys around me try to fiberglas and epoxy a lot of this stuff together. I see them picking up their parts as they fall off around town and at car shows..... Sorry, but that is a true story.....

Ah. Duly noted - yet again.

I really wish I could make a fiberglass mold too, but that is out of the question unfortunately.

Well, at least think about this.... Have you ever heard of "lost foam" style molding? I've done it before and it really isn't that hard and can be done for a "one off" style piece. You can buy sheet foam (yeah, yellow, blue, pink stuff at the hardware stores). Take the nose pieces, bumper supports, etc., off the car. You can then bend the foam around the nose and glue more blocks of foam up on top of that. Once you've achieved some thickness you start carving, filing, and sanding up your shape. You open up holes to recess your lights, air ducts, etc. Once you've got your overall shape you simply fiberglas OVER this entire foam shape. You then take the entire piece off and you can melt all of the foam out with acetone from the back side. Your new nose can now be finished off with filler, high build primer, etc. Attachment points can be bonded to the backside of the nose to your original mounting points, lights can mounted, and you've got a brand new part.
It does take some time and creativity but it's cheap and effective.

Thanks again. It really would be something I'd love to do, just later in life. I could even make molds and profit from it. But as of today, I'm a lowly college student living at student housing. Although I'm sure of my abilities, I'm not sure the administration would be okay with a project like this.

Yeah, I get it. I was a music eduction major in college but minored in welding/engineering. I was lucky, I could take off the tux & tales, put on my overalls and head down to the welding lab where we do all kinds of crazy stuff....