How to make a plywood splitter for the Puma

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trublustu
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How to make a plywood splitter for the Puma

Post by trublustu » Mon Sep 10, 2018 10:57 pm

Hello all.

I have been developing a splitter for my track day Puma for a couple of years now
Ever since the very attractive, but unfortunately, not super strength fiberglass one was broken, going off track at Rockingham.
I think this one is the fifth incarnation. I`ll not bother explaining why each previous design got binned. but they did!

I have tried a few different shapes and materials and I think I`ve just about worked out the best way of doing this.
Here`s a `how to` I put together whilst making the most recent.

I won`t go over how to fit the splitter as this is covered here, in this "fitting a splitter to a standard bumper" thread. viewtopic.php?f=51&t=24938

You will need....
An open working area with flat bench big enough to sit the bumper on.
6ft x 2ft sheet of 12mm external plywood
tape measure.
2 small/medium clamps
carpenters pencil
6mm drill
Jigsaw
Orbital sander (medium and fine paper)
small pot of external varnish
small pot of automotive paint
White spirit (for thinning)
10 M5x25 stainless bolts + nylock nuts
20 M5 mudguard washers. (8 of which need grinding/filing to a `D` shape
2 x `L` shaped brackets (approx 3" x 1")
A nice warm day.

The very best material to use for a home made splitter is 12mm Marine Plywood.
This type used a special glue which stops the sheet swelling when it gets wet.
Great stuff, but It`s not exactly cheap!
So, the more cost effective material I am using is 12mm external hardwood plywood, sealed with paint (which I`ll come to)
You`ll need a sheet almost 6ft (180cm) x almost 2ft (60cm).
I bought apiece this size from Wickes diy store.

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The bumper (with holes and no skirt as described in the fitting thread) then needs sitting on top of the sheet with the rearmost parts of the bumper EXACTLY lined up with one edge of the sheet.
The clamps will be needed to stop it falling over.
Also a couple of datum marks will help put it back in the right place if it shifts..

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Marks can now be made through all the tab holes in the bumper.
The next bit is quite critical.
Using a carpenters pencil etc (avoid ink) roughly scribe a vertical line from the leading edge of the bumper.
This is the basic shape of the finished item, so don`t rush...
You only need to do this on ONE SIDE of the bumper.

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By going over and over lightly you will start to get a consistent line.

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If the splitter is going on a road car, the front edge shape is pretty much finished.
So you can carefully draw a heavy line to along your scribe lines.
The finished article will look like this (this is Hi-gloss fiberglass gelcoat)

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If you want to make something a bit more lairy, funky or for track, then this is where you can turn your ideas into reality.
There are no rules, and your imagination is the only limiting factor...
Mine is for track. It`s extended at the ends to maximise downforce and stop air folding under the splitter.
(the flat ends are there for a reason too, i`ll come to that too)

Be as smooth as you can, as this is the cutting line and any mistakes now could spoil the overall result.

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On the back side, I have found it best to have a cutout as deep to where the radiator sits and with the ends as wide as the arch liner.

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the last bit of marking out is to find the exact middle of the bumper..

This is a good time to get a cup of tea, and reflect on how long it`s just taken to draw a line!
Because it`s time to break out the jigsaw..

Going very VERY slowly, cut the front edge along your smooth line.
Any swerving about now will either give you a very amateurish finish or even leave you needing to go back to Wickes and start again!!!

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The offcut can now be flipped over and a line drawn to mark the second cut.
The advantage of doing it like this, is that the finished article will be perfectly symmetrical.
The rear edge can be cut out too, this doesnt need to be as precise as its totally hidden.
It`s also time to drill out the fitting holes with the 6mm drill (bolts are M5 but will all have washers)
Like the cutting, drill through slowly so the drill bit doesn`t break chunks out of the back side.

I didn`t get a pic at this point, but hey presto, it should look like a splitter!!!

Even if you were as smooth as silk when cutting the front edge, a jigsaw doesn`t give perfect results.
So, now onto finishing.
If you have access to a router, a nice radius chamfer can be cut around the leading edge.
I dont! So half an hour with a sanding block uning medium paper to shape and fine paper to smooth you can shape the front edge so it has a clean edge (that water runs off!)
Ensure all, cutting drilling is done before moving on to sealing.

The splitter is pretty much finished. Now is time for paint.

Firstly, especially if your using simple external plywood, you will need to seal and prime the wood for it`s final paint.
To do this, some external varnish should be thinned with approximately 10% white spirit. (colour unimportant)

Once it`s had a coat and dried, give the upper face of the splitter a sanding, This helps give a better final finish.
Repeat this process at least once, sanding between coats.
Pay particular attention to the drilled holes, It `all helps keep moisture out of the plywood core.

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Once the plywood is sealed it`s time for the final paint finish.
I have used carplan black auto paint, any brush on car paint will do.
Once again, give it a couple of coats, sanding in between.

Like me, you`ll probably get giddy and clamp the splitter to the car to see how it looks.

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The last coat of paint is the one everyone will see, there is no reason that you couldn`t use a rattle can, giving a very professional gloss finish.
Mine has been left with just the brush paint (track car, so it`s about go, not show lol)

The splitter can be permanently fitted to the bumper now.
Have the bolt heads below and nuts above, hidden inside the bumper, also use mudguard washers below and D shaped washers on the top.
I have fitted canards to the ends and splitter to create a vortex of high pressure air down the side of the car and stays where the downforce is at its greatest.

So after a day of carpentry you should have something looking a bit like this.

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It`s as simple as that.
The wood cost me £20 and the paint/varnish another tenner.
The fasteners were about a fiver and the splitter stays were ebay specials at about a fiver
Total cost of well under Fifty quid.
I have made them out of scrounged materials before costing next to nothing. But they didn`t last. This one should...

If you have any questions, feel free to get in touch. I`ll try to fill in the gaps...

Stu Morris..

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Last edited by trublustu on Fri Sep 14, 2018 12:09 pm, edited 2 times in total.
3 x
Dedicated Track Car Progress Thread
http://www.projectpuma.com/viewtopic.php?t=26160" onclick="window.open(this.href);return false;
YouTube track sessions and `incidents`
https://www.youtube.com/channel/UCC5QLi ... 4GCrMVmmlQ" onclick="window.open(this.href);return false;
Trackheads facebook group
https://www.facebook.com/groups/517158591786800/" onclick="window.open(this.href);return false;

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How to make a plywood splitter for the Puma

Post by red » Mon Sep 10, 2018 11:58 pm

8-) Nice write up, thanks!
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How to make a plywood splitter for the Puma

Post by trublustu » Tue Sep 11, 2018 12:25 am

No probs Red.
I hope it`s helpful..
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Dedicated Track Car Progress Thread
http://www.projectpuma.com/viewtopic.php?t=26160" onclick="window.open(this.href);return false;
YouTube track sessions and `incidents`
https://www.youtube.com/channel/UCC5QLi ... 4GCrMVmmlQ" onclick="window.open(this.href);return false;
Trackheads facebook group
https://www.facebook.com/groups/517158591786800/" onclick="window.open(this.href);return false;

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How to make a plywood splitter for the Puma

Post by stuart1275 » Wed Oct 10, 2018 7:21 am

Looks good nice work :-)
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How to make a plywood splitter for the Puma

Post by wilko33 » Thu Nov 08, 2018 8:59 pm

Out of curiosity, why don’t you take the splitter all the the way under the engine?
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How to make a plywood splitter for the Puma

Post by trublustu » Sun Dec 30, 2018 1:55 pm

Hello Wilko.
I did try a D shaped splitter which fills in all the space right up to the engine.
It made no difference to how the splitter affected the handling.
More significantly, I couldn't get to the oil filter without removing either the splitter or whole bumper.
Or access the front of the engine at all. Even getting to the belts became a chore.
Life's too short, so the C shape won out...
2 x
Dedicated Track Car Progress Thread
http://www.projectpuma.com/viewtopic.php?t=26160" onclick="window.open(this.href);return false;
YouTube track sessions and `incidents`
https://www.youtube.com/channel/UCC5QLi ... 4GCrMVmmlQ" onclick="window.open(this.href);return false;
Trackheads facebook group
https://www.facebook.com/groups/517158591786800/" onclick="window.open(this.href);return false;

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How to make a plywood splitter for the Puma

Post by wilko33 » Tue Jan 15, 2019 1:48 am

I spanner a time attack car and it is a pain removing the splitter to get to anything, but the driver has tried a lot of different set ups and says the difference is really really noticeable with a full one.

I’m just starting to build a track puma and splitter/diffuser are on my experiment list!
1 x

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