924Board.org

[leadfoot]

This is a basic how to for making custom parts from scratch using some simple tools and proceedures, there's plenty of how to's on youtube on making parts. This one deals with making a fan shroud as there have been a few posts recently on changing fans out.

To start there are some supplies you'll need;
polyester resin and MEK catalyst, about 1 litre should do you, I used 750ml on this part. you can get kits that contain both the resin and catalyst you need.
some fiberglass mat or chopped strand mat. in 195gsm and 400gsm
you need the thinner stuff for getting the contours right first and then lay up the thicker stuff for reinforcement.
paintbrush, container
scales that measure to 1 kg in increments of 50gms
2.5ml measuring spoon
laminated wood and cardboard
plasticine
release wax
rubber/vinyl gloves, filter mask

I first cutout a piece of carboard in the size of the radiator and measured in about 2cm from the edges for the mounting points. This will serve as the flange for mounting.
I then laid my fans out on a piece of laminated wood in the size I required and drew an outline on the board, this was trimmed up to size. The board thickness you choose will act as the standoff height from the radiator.
I then centered the board on the carboard.



Next thing was to apply plasticine to the edges around the board and form a bevel or contour for the air to move across. Remember this will be in reverse so creating a concave imprint in the plasticine will give you a convex shape on the part. I trimed mine off at around 75 degress on the sides and left it slightly concave on the top and bottom edges. You could also use silicon or clay if you wanted to, the silicon would have to dry first though.
A couple of applications of wax were made to the carboard and the laminated board. The lamination is very good at releasing the part and doesn't require to much work.







After I was happy with the shaping of the mould I then got everything ready I needed for fiberglassing.
You'll probably want some vinyl gloves on now too.
First cut up or rip up the fiberglass into manageable pieces, and some different sizes so far as strips, angles and squares. This will help shape around the corners and so you don't have to cut it later and get you scissors full of resin.
most resins are a 2% mix. they generally state no less that 1% and no more than 3%. The more resin you have and the more catalyst the less time you will have.
So with those measurements, in 250ml of resin you mix 5ml of catalyst, or 1ml catalyst per 50ml of resin to get your 2% mix. Hence the 2.5ml spoon.
Now I wouldn't generally mix up more than 350ml of resin in either a cup or if you are inexperienced. Speed is of the essence and your mix will heat up and melt shit and then go rock solid in about 30 seconds.
If you want to mix up more get a 4 litre ice cream tub and mix no more than 500ml, your still going to have to get alot of it out of the tub pretty quickly though.
pour 250ml into your 500ml measuring cup.
measure 2.5ml add , then another 2.5ml and add
stir with the paintbrush quickly. Most resins are blue and will start going through to a tint of yellow very shortly after the catalyst is added.

Brush a layer quickly onto the board, don't worry about being too neat.
The next step is to get the 195gsm mat down onto the board and apply more resin to saturate the fiberglass.
Work quickly and stipple the resin into the mat to first get it wetted out and then keep applying until the mat is saturated out and you cannot see the white strands of the glass fibre. more resin than less at this stage. keep stippling the mat so that it becomes plyable and contours to the mould. work around overlaying the mat until you have two / three layers of 195gsm down and then start on getting two / three layers of the 400 down. you will mix up two more batches of resin when you run out.
Make sure you go past the edges as these will be trimmed back later.
If you think the part may be too thin for your liking when you take it off mix up some more resin and apply more glass fibre within 24hours and it will bind to the previous layers no worries.



More to come...

Ok you have two options now after laying up the mould,
let it be for about 24hrs and hack into it with a cutting disc on an angle grinder wearing a respirator and a plastic jacket or disposable suit
or
wait for the resin to go off and pick the consistency that will be firm enough to lift off yet soft enough to trim up with some scissors.

I chose the latter in this case and have pictures of the results below.
I used scissors for the edges and a stanley/extendable blade to trim the fan cutouts from the front and back.
This will get you most of the way cleaning up the part and a final sand once the part is cured completely will be all you need for the shaping.









As you can see the part is around 5mm thick and a bit rough around some surfaces. This will happen if you seperate the part too early which was the case here, the sun wasn't really out today and it probably should have left it an hour or so longer... just have to time it well...
Also because I'm not using a gel coat for the part this will will save you money and time. For casting body parts I use a gel coat, which is essentially another layer of resin that acts as a base for getting a perfect coloured and hard surface and allows a stable surface for good adhesion of a paint layer.

Next you can either sand and paint over for simplicity or build up using a body filler and sand this back for a smooth finish and then paint.
A cheap body filler can be made using talcum powder added to your resin mix, enough to stiffen up the mix. Be warned it will not sand as well as commercial body filler as it tends to ball up more on the sandpaper.

here's a pic of the filler stage, essentially just a skim coat yo help level off the surface. I didn't go too crazy with it. Add a coat, sand back and add another coat to get all the dimples out. I just did the one coat on this part.



and then a spray of primer



spray some paint



and back



drill some hole, mount some fans, connect some wiring



and the back



have fun and don't stick you hands together
Stu
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Joes924Racer]

Nice work, have to ask a question though. You dont think having a shroud like that will restrict air flow and cause the thermo time switch to kick on sooner and run all the time?
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[leadfoot]

Joe, the shroud improves efficiency and forces the air to be sucked through the radiator, otherwise your just relying on high to low pressure draw. Given that i have two intercoolers infront of the rad and minmal direct exposure it is even more important...
Cooling efficency of a rad is considered in three ways; surface area of the core as a heat exchanger, coolant flow speed through the core and air flow through the core. I'm dealing with essentially no 1&3 by having air travel past a greater surface area...not just where the fans are located and by sucking air though the whole core at speed.
Settin up air dams to force the air through the rad is another benefit to look at too. This traps the air in front of the core and forces it to go through instead of around.
Stu
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Cedric]

[MikeJinCO]

A little translation for those of us who don't speak metric very well. Go to the drugstore and buy some paper(not wax covered or plastic) 3 fluid oz. bathroom cups. Put in catalyst at a ratio of 10 drops per fluid ounce. With polyester resin close counts, but go short on catalyst rather than extra. Only use extra catalyst if it is quite cold- like freezing. I originally used it repairing race car bodies(back about 1970) and in the middle of the summer at 90F even using 10 drops per ounce can really cook off in a hurry. If using epoxy you must be much more precise in your mixing.
_________________
Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)