linderpat

not loving it - it is to reminiscent of a 944 spoiler. I prefer the "duck" style for our cars.

Jerry Feather

Hi Hans. Great to have you chime in. Actually I was kind of wondering how the final product made inside a female mold would be expanding and at what point that would take place. I am also wondering how the mold itself, being made on the outside of the plug, will be expanding and at what point.

I have alway intended to make the mold off of the outside of this buck; I just haven't even yet figured out just how I am going to do that. I have consulted with one of my good friends in the aviation industry who does some of this kind of fabrication and have studied his process and his mold for making nose caps for the front of his wing tanks. I don't recall any issue with expansion in his process.

I plan to make the female mold in three pieces that will then be clampled together for the molding process. One of the parts of the mold will be the base which will essentially be the same shape of the part of the hatch where this spoiler mounts, and it will have an opening in it all along nearly the full length of the spoiler through which I will be laying the fiberglass and resin. The other two pieces will be the front/inner surface and the rear/outer surfaces, which will join at just about the apex of the top edge.

I'll first make the base mold and then finish it to the bottom front and rear edges and beef it up for rigidity, then I'll make one of the other molds off of the base mold so it mates at the bottom to the base and then up to the top edge, then the final mold will be made to mate to the first two. I'm just not sure yet how the intitial layup will take place for the base and then the open edge of the second one. The third will be simple since it will form to the first two.

I think the process will come together about the time I get to it.

hans14914

If you make the mold as you propose, then the finished parts will be nominally smaller than the original plug. The epoxy tends to shrink, not grow.

Make sure that you use tooling resin for your mold. It has better release properties and also shrinks less. It is formulated to withstand the heatcycles from parts you plan on curing in the mold. If you use normal resin, it will only last a few parts before you have to start making repairs.

The Fixer

To make a female mold would suggest you plan to fill that mold with what?

I thought you were doing a one off fiberglass spoiler.

I didn't realize you were gearing up for a production process.

If you plan to make a fiberglass spoiler, it would be hand laid over the buck and grow in every direction.

Then the excess trimmed (that part is ugly, I didn't show it) sanded and gel coated.

Now that Landseer and Ed mention it, it does make the car look like a 944.

I would tweak it to not.

Jerry Feather

Everyone seems to be missing the point of this thread. I had hoped to be showing you HOW TO make something like a Bikini Spoiler for your car, so this is intended to be more about the process than about the design. Sure, the design is part of the process, but when you get to the point of following my suggestions about the process, you can come up with whatever design or style of spoiler you desire. I'll be anxious to see your results.

I don't think I will be "in production" with this spoiler, and given the lack of interest in either having one at all or in having something that doesn't look like the one I am making suggests that I would be ill advised to count on anyone ever wanting one. Nevertheless, I didn't want to find myself in Matt's spot with all the interest in his design and him having the need to "pull a mold off of it" at some point.

I may not even put one of these on any of my 928s, at least for the long haul, since, as I mentioned before, I really prefer the naked butt of the 928 as was intened in the original desiugn. However, I can envision putting one on any of my cars from which I have removed the wing, and maybe even the S spoiler, but before I am in a positon to fill the holes and paint the hatch or the entire car.

I haven't paid any attention to the 944 spoiler, but it occurs to me that maybe it is just that great minds seem to work alike. After all, I suppose the 944 spoiler was designed by Porsche; and Matt even suggested that mine looks real "Porsche," didn't he?

Jerry Feather

It also occurs to me that filling the mold with concrete might even shift the weight distribution very well in favor of the rear end, much more like the 911s which are so popular, and would certainly add to the "down force" that we seem to be striving for. Other than that, Matt, I wonder why you would ask what I intend to fill the mold with.

Of course, since I have stated that I intend to make the resulting spoiler out of fiberglass and resin, it seems logical that since you now realize that I am not going to cover the buck with the finish material, except to make the mold, that I will be lining, not filllng, the mold with fiberglass and resin.

Jerry Feather

Thanks, Hans, for that pointer. I actually learned something about that from my aviation buddy. In fact, I have acquired a large can of what I think is the correct resin for the mold purpose. I'll verify that, since I got it for another project I was working on, and be sure that I follow your suggestion. Thanks again. Your are one creative guy.

The Fixer

I like the Ducktail on the 928 because even with it, it retains it's OB looks!

I'm sorry Jerry,

I thought you may have changed your plan on a final material to something similar to the S spoiler. (with all the female mold talk)
I have a BS in Industrial Design so i went in another direction.

My apologies.-Matt

Jerry Feather

I guess no one has ever posted a picture of this supposed "duck" rear end on a 928. I wonder what you are all talking about.

Jerry Feather

And, no need to apologize, Matt. I perceive this as all amongst like-minded 928 enthusiasts. I understand now why you suggested that my finish product woud be about 1/8 inch bigger all around.

The Fixer

Thanks Jerry, but you put a lot of effort in and I know what that means.

What do you think about building it up and making it look like the factory 'S' Spoiler but a bit larger (and more aggressive) and keeping the wiper delete obviously.

When (If) you reference the real 928 item (S Spoiler) in shape, it will be a winner product.

I hope you consider this. You have serious skills.

All you need to do is build it up (laminate)

Jerry Feather

Matt, it seems to me that what you are describing is something akin to the spoiler that Mark A. has posted earlier in this thread with the red exagerated S spoiler he shows. I am not too interested in going there with this project. What I had/have in mind is more of a refinement on the spoiler you have developed for the RS project.

I don't think mine is much more than what yours amounts to in terms of size and agressiveness. I don't see any need for much more than that for this project.

I am still interested in seeing what you and Ed have in mind for the ducktail version of this spoiler. If mine is not a ducktail, I wonder what is. Too, I would think that if mine is not a ducktail, a ducktail would be somewhat less than mine in terms of its size and shape.

The Fixer

Imo, your's would not be considered a Porsche 'Ducktail' spoiler.

Your spoiler is something different. Porsche ducktails are characterized by the extreme angle, and are dished out. They have a curved large radius finish at the top. Mine IS a ducktail spoiler but a little shorter because the rear end of a 928 is not as low as a 911.

A ducktail spoiler must look like what is found on a Porsche Carrera RS or RSR from the '70s. If you go and refine it, it is no longer a ducktail.

"A ducktail spoiler divided, can not stand"

Jerry Feather

Oh! I guess I was thinking of something that would be more like an actual duck's tail, something more like Porsche put on the 904.

Then I googled "ducktail spoiler" and guess what I came up with--a whole raft of images of spoilers that look almost exactly like mine, in respect to its shape, but in various sizes or heights.

Jerry Feather

Then I just Googled "Porsche 911 ducktail spoiler" and guess what? The images shown are almost exactly what I think I have created with the Bikini Spoiler in this thread, except, as you point out, since the 928 rear is a little higher than the 911, mine (and yours) are not quite so tall.

I cannot see how you can envision your spoiler as akin to those 911 ducktail spoilers. In fact the ones shown even incorporate something very similar to the two foreward extensions that mine has, which are to both cover up and to utilize the S4 wing mounting points, in the 928 case. I'm not sure why the 911 spoilers have them but they all seem to have something much like them.

None of the 911 spoilers are standing up so goal post straight as yours seems to and they all have such a nice curvature on the top/foreward surface, as mine does, to help make the ducktail-like shape.

Too, none of them have the ridges and such that you suggest are required to be called ducktail. They are all just as smooth and flowing as I am trying to make mine.