Fender Plugs for BMW ALPINA 2002 racecar

General Composites Discussions Composites Talk
#1

I am really excited to have found this forum - I wish I had found it before I started work on the fender/plugs for this car because I know I could have saved myself a whole bunch of time and money. I’ll make a long story short, I aquired this car about 7 years ago and at that time didn’t that it was a famous ALPINA 2002 race car that raced in various DRM (Deutsch Renn Meisterschaft) races as well as ETCC (European Touring Car Championship) races in 1974/75. In 2007 I discovered the true history of the car and had the ALPINA works confirm as well. The car was essentially intact and unmolested except for the body work. ALPINA had constructed one-off fiberglass fenders (front) fender extensions (rear) and front spoiler for the car. The molds were disposed of many years ago so no help there. ALPINA sold the car in 1976 to an Italian who disposed of what existing body work was on the car in whatever condition it may have been in. Where I am now is that I have the front right pretty nearly done - just needs some tuning up on the front. The left side is another matter. It needs a whole bunch of re-work that I am in the process of so that it becomes the mirror image (or close enough at least that no one will be able to tell) of the right side - I’ll spare everyone the details of how I managed to get this one so far off of the other. Based on the other threads I have read here, it sounds like when I am done/done (really done) with both, the way to go is to have the parts shot in Duratec primer, then sand and polish from there. I have read a fair amount on the subject as far as the mold making goes, however I just dont have the equipment to spray on the tooling gel coat for the mold or the gel coat for the part. I am also working in my garage which does not have heat. I am located in Northern California (Bay Area) so temperature isn’t a huge deal (most of the time), but I am thinking that it may be better to find someone that can help me with that portion of the work, so any leads of folks locally that might be willing to look at it would be appreciated. Rather than post up a slew of photo’s go to:

www.picturetrail.com

Member Name: 74fuely

All of the albums on the car are there (alot to look at), and the one of interest would be “Front Fender Fabrication”

Any additional advice always appreciated.

#2

welcome to the forum. I am always happy to help, feel free to ask questions. Good luck on your project!

#3

Assuming folks have seen the plug molds that I am constructing for my race car I have a few questions.

  1. It dosen’t appear to me that I have any negative angles that would require split lines or making the molds into two pieces (confirm please)?
  2. I am now pretty close on the rough shape of the left side plug, just the never ending sanding, finishing etc., I had originally planned on using rattle can spray paint to put the finish on the exterior, following what I have read in terms of getting the right number of coats of paint on, the sanding from 400-1200 and then polishing etc., I have read a number of places that Duratec primer is the only way to go. Since I don’t have my own spray gun I would have to pay someone to shoot the Duratec on my plugs. So the question is can I get the quality I want out of rattle can spray paint in the finish versus Duratec?
  3. If Duratec is the only way to go- can you spary Duratec out of say a Preval sprayer?
  4. Skipping forward to completing of they plug, although I am not planning any sort of production for parts I planned on using Tooling Gelcoat, just in case I do want to possibly make some parts to recoup some dollars. I understand tooling gelcoat is a bit harder than standard gelcoat and better suited for more production. Not that much more expensive than regular gelcoat so what the heck.
  5. Can you get an adequate finish “brushing” on Gelcoat on to the plug. I am guessing that you probably need to have it shot on to get both the coverage and thickness. Again since I don’t have a gelcoat spray gun I would need to have someone shoot the gelcoat. At the end of the day If I need to have someone shoot the gelcoat I am going to need to find someone to make the mold and the part for me…and maybe this is just adviseable.

To the greatest extent possible I am trying to do as much myself and would really like to be able to make the mold and part myself. It may not be practicle to do however in a non temperature controlled (or dust controlled) garage here in Northern California. If anyone has any ideas (ballpark of course) on what it would cost to make the mold off of my plug and then one part that would be great too. Thanks again.

#4

Duratec primer and high gloss black are best combination for plugs in my opinion. you can buy a cheap $25 dollar gravity feed spray gun with a 2.5 tip from local stores as long as you have a compressor. you can brush on tooling gelcoat but you are best to spray it using a pressure pot.

#5

brushing polyester gelcoat may lead to alligatoring, due to the variance in thickness where the brush leaves a thin line of gelcoat. i’ve been always brushing gelcoat on my molds, but its a risk… the alternative would be to use epoxy tooling gelcoat, which is always brushed cause its thick like grease, but theres no danger of alligatoring , and the strength of it is a lot more than polyester. That would force you to use epoxy resin and woven fiberglass to make the mold, and the cost skyrockets.

also, i would recommend you buy a compressor , its always handy to have one, and since i’ve been burnt more than once with painted surfaces and waxing, i would recommend using pva as a release agent. if you learn to spray it properly, or even brush it, it leaves a glossy surface, and makes demolding a breeze.

#6

Based on a limited amount of research it seems that the epoxy would be pretty expensive. I currently don’t have a compressor although I could probably get one for a few hundred dollars, the only problem is that it will sit idle for the most part when this project is done. I could probably rent one as well.

I read somewhere that you can spray Gelcoat from a Preval sprayer? Any comments on that? I was thinking I could mix up say two of them and probably have enough to cover my plug - just a thought.

It may be that I am better off taking the plugs to someone and at least having them make the molds. I would be interested to hear if someone that has experience making molds/parts would have a guess as to how much time/dollars would be in to making both molds and one each (right/left fender). The fender (part) wants to be light weight, I was figuring on white gelcoat, then three layers of .75 oz matt, also need to color the resin “black” as that is what ALPINA did. Input appreciated. Thanks.

#7

Gel coats are way too thick to be spray with a preval.

Are the plugs full done and ready to make the molds from them?

#8

The direct answer is “NO” regarding completeness of the plugs (unfortunately). Been a little tied up lately trying to make money keeping myself and family afloate. That being said, the right side is for all intents and purposes right there. I had to mark it up with a sharpie for all the dimensions to re-do the left side. So what is left for me to do is to apply more paint, do the wet sanding and polishing - it is very (very close). The left side is all redone dimensionally and is as close as it needs to be. This side has been rough sanded in 80 and I am now going back over it with more filler to take care of the little stuff, then 180, 220 and on from there. I would say I conservatively have probably 4 hours (given the way I work) in the right side and 4-5 days total on the left before I could turn them over.

#9

One of the guys that has done a bunch of fabrication on my car has used him to make various fiberglass parts and pieces. Based on simple description of my parts he suggested somewhere around $2500 to make the molds (two total) and two total parts (one fender each side), included in that the cost of using epoxy to make both the molds and the parts. He suggested that quite often polyester resin/gel will shrink as much as .50" creating significant fit up problems with parts like mine. My plugs are pretty much right on the money as far as tire clearance and what not I really didn’t figure on significant shrinkage of any sort. Based on the work I have seen him produce I am certain he would do the job I want (need), unfortunately not in my budget currently. So my question is about epoxy (or epoxy gel coat). Is there such a thing or is it epoxy resin that has been tinted and thickened somehow. I really wasn’t too afraid to try to make the molds and parts myself with polyester, but no zero about epoxy resins. Can an at home do-it-yourselfer pull it off using the epoxy as a gel coat for making the mold and likewise making the part? Here are a couple of pics of the finished fender. I am in the process of shooting the fenders with white enamel rattle can paint. My process so far is to put a couple of coats on, wet sand with 400, then add a few more (trying to get a good solid 5-6 coats of paint on) wet sand with 400, 800, 1200 and polish out.

#10

Shrinkage of a part is discussed as a percentage, I would expect a shrinkage of half an inch to be applicable to a small boat!

Sure, Epoxy makes for top quality moulds, but there are other cheaper resins and systems which are specifically made for the job called ‘tooling resins’ and ‘tooling gelcoats’, these have very low shrinkage rates. Take a search for Duratec also.
I use tooling resins from Scott Bader and Nord, it depends on how many you plan on making too…

Make sure the paint you are using doesn’t react with whatever you are going to make the mould from. Use a different coloured paint (black) to spray on as a ‘guide coat’, when you flat it down any high and low spots will show through against your white undercoat.

#11

Since I am restoring the car, I am only looking to make the mold and then one part from each molds. Not looking to go “commercial” or anything like that. Ultimately if I ever sell the car I would sell the car with the moulds so that the new owner/owners could make replacements.

#12

theres no way resin shrinkage would mess with your fitment, the shrinkage is very minor.

anyway, about epoxy molds, they are actually easier to do,because theres no chance of gelcoat alligatoring or ??? like that, and most epoxy tooling gelcoats are very easy to apply. even for small production runs, you can use regular epoxy gelcoat (not tooling). the only downside is the cost. Epoxy resins cost 5 times as much as polyester, and same goes for the gelcoat. Also, you have to use woven fiberglass only, cause csm and veil do not work with epoxy. i make all my big molds out of epoxy now, cause of the smell mostly, but generally, they are much better, both to work with , and reliable as molds.

#13

Plus, you can’t spray epoxy resins.

#14

You can. :wink:

#15

Not kidding here…the fumes are deadly!

#16

Sounds good, I learned a lot (the hard way) making the plugs and I really would like to take a shot at making the molds and the parts. Other than making a test panel with the paint I am currently using (SEM Gloss White Enamel), they are pretty much ready to go. So my question(s) are, what brand Epoxy Gel Coat would you suggest for the mold and the part(s). Since you apparently cant use CSM, I need some sort of cloth that will go in multi directions (?). You can tell by the pictures of the plugs that they have alot of curves and what not. Any additional helpful advice is really appreciated - Thanks.

#17

in which continent are you? :stuck_out_tongue: if you re in europe, i buy my stuff from r-g.de

as for fabric, you can do the first layer with a 150gr/m twill, and continue with 300gr, and go even bigger later on. if the last ply doesnt want to stay down, put another layer of 150gr on the end, to hold everything down and keep fg needles from pricking you when it dries.

#18

I am in the United States (California)

#19

They are, the isocyanite fumes from 2k paint are too, but people spray them day in day out. The answer is not to avoid doing it, but go with the correct equipment - an air fed respirator.