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Ex-Racer Spitfire Mk1 Rebuild


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Made the latch boxes today. I had put the gelcoat into the mould yesterday so set to go.

Plan is to use hand layup and vacuum bag for these and the front valance so this is a bit of a trial run to test the process on something relatively small/cheap.

For these I used four layers of 200g carbon cloth laminating epoxy resin which has a slightly thicker consistency than the infusion resin. I also went for the fast cure resin which is ready for coming out of the mould after six hours rather than 24 for the slow resins. But means that everything has to be cut and prepared before starting as the resin pot time is only 15-20 minutes.

The four layers of cloth give a finished thickness of approximately 1mm which is plenty thick enough

Layup one layer at a time, covered with peel ply and then a later of breather cloth which is there to soak up excess resin as the layup gets compressed under vacuum.

The whole lot then goes into a bag and gets a vacuum pulled. Only 20% for this rather than the 80 - 90% for the resin infusion.

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All went very well until after about 20 minutes the bag suddenly lost vacuum. Hunting around i found a couple of pinholes on the back of the bag where it had got stretched across some rougher bits on the back of the mould. Managed to mostly seal these up with a bit of tape and just had to keep an eye on things until it all cured.

Lessons learned for when I make the front valance.

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Pleased with the results. A bit rough and ready but that was expected, especially as I used PVA as the release agent and it is really difficult to keep that from pooling in corners. Not an issue as everything is hidden.

I still am surprised at how something so ridiculously light can be so rigid. The two twin moulding weighs 48g !

While I was doing that I was also getting the mould for the valance sorted. It's in two pieces so the part can be extracted but the smaller part has had a bit of a hard life and is cracked in the corner. So I decided the simplest thing was to make up a replacement mould section.

Starting with taking a 'negative' from the part mould.

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Edited by Escadrille Ecosse
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Nice.  Versatile stuff.

If I ever get my ITBs done I'm going to need an airbox with trumpets and I'm liking the idea of composites.  Strong suspect this would constitute running (fast) before I have learned to walk...... so it'll probably end up in metal......

Meanwhile, I watch and dream :smile:

 

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8 hours ago, PeteStupps said:

That is insane. Is that really correct?

Pete, my mistake. Can't read my own handwriting. Checked again and the two untrimmed parts are 78g not 48g.

So by the time they are trimmed they'll be about 30g or so each. For a 1mm plus thick part.

Strong enough to take my weight. I tried by standing on one of them :woot:

This stuff is bonkers.

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A quick tart up of the mould for the front valence and get that made... ha! Plans of mice and men.

I took the mould off a glassfibre panel that I had and was all that was available at the time. It was a bit rough and ready to say the least although I did a bit of fettling at the time while I was adding the air dam. Didn't really matter too much at the time as I was bolting it to the bottom of the bonnet of the race car rather than off the chassis. Bit more of a challenge now it needs to hang off the brackets as triumph intended.

I got the new end section made quite quickly and while I was at it I added a bit more of a flange to the other end to make the bag moulding a bit easier. The mould section still needs a bit of polishing to get rid of the sanding marks.

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Then stuck the thing on the bench to work out where the slots for the bonnet hinge brackets go.

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First off is the centreline. The short mark is roughly where the knuckle in the valence lies while the long mark is the geometric centreline based on the end to end of the valence, and how it fits on the car of course. Roughly 1/4" between the two although to be fair it's quite possible the original steel panel was like this.

However all started to get a bit more difficult when I tried to fit the mounting brackets. Basically they don't. The returns on the flanges that take the seal to the bonnet are in the way. Hmmm

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I suspect that the return was added  to give some strength to the mounting area when there is no internal bracing. But not much use when the it gets in the way of the mounting brackets and doesn't really help the rigidity of the panel either. The other thing is that the mounting tabs on the steel panel are set below the top of the valence to give more space for the brackets.

Considered modifying the mould to replicate the correct arrangement more accurately but aside from all getting way beyond this part of the project brief, having thought about it it would be a re-entrant on the mould and without another break flange somewhere it would be impossible to release the part after moulding. Probably another reason why the bunch that made the original panel didn't bother.

So after a bit of thinking I have a plan. I made up two plywood slip forms that will get lightly stuck into the mould and create the appropriate shape for the mounting areas. These will come out of the mould with the part and then I can remove them and trim everything to size afterwards.

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I will make up the internal brackets separately and glue them in later to stop the thing flopping about on the car.

And then depending on how I'm feeling I might make up a new mould, split horizontally so I can make replacement valances if this one gets trashed*. Bit of extra work but I put off doing it with my (good) original fibreglass bonnet until it was broken beyond salvage.

*this happened to my mate the other day. Parking at his flat has these automatic bollards. Three of them at the entrance. Unfortunately the middle one, which he couldn't see didn't go down all the way and took the spoiler off his Porsche 911 as he tried to drive in. Expensive.

 

 

 

Edited by Escadrille Ecosse
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  • 2 weeks later...

While I was at the mould I laid out a straight edge for the bottom of the air dam and laid on a piece of tape to mark it on the finished piece. Bit of a faff. I used a plastic tape with a silicone adhesive resistant to resin for the job, not the masking tape in the pic.

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Because of the rather vulnerable location of the valence and because carbon fibre is a bit brittle I decided to include some Kevlar in the layup to improve the toughness of the part. However, Kevlar is a right swine to cut so I also acquire some very nice titanium nitride shears designed for just this job. £23 on Amazon so not cheap but what a difference.

This is an example of cutting some fine Kevlar cloth with a pair of brand new ordinary scissors compared to the shears. Not just a neater job but the mess on the right took about five times as long.

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To make life a bit simpler I am actually using a twill cloth that is 50/50 carbon and Kevlar.

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As this is a vacuum bagged hand layup everything has to be cut out beforehand because it all gets a bit time critical. A layer of carbon cloth, two layers of carbon/Kevlar, an extra reinforcement layer around the cutouts for the bonnet hinges the peel ply, breather cloth and the enormous vacuum bag (4' x 5' ) to put it all in.

Applied the gelcoat and once it was cured I started the layup. Which is where things went a bit awry. I got the resin and first layer of carbon on and was just starting on the next layer when I noticed that the brush I was using was getting a bit stiff and tacky. Next thing and the pot of resin went off all in a rush. Very hot and smoking. Bugger.

So I peeled off the layers I had already put on and wiped off as much of the resin as possible before leaving the whole lot to cure. The irony of it all being that stuff too almost exactly the requisite 6 hours to harden.

I suspect that there was enough mechanical energy added by working the brush to set off the resin on that which then set off the rest of the stuff in the pot.

For the second attempt I used a mix of fast and slow hardeners for the resin and only mixed up half the amount needed at the start. Even so it was still a bit of a scramble to get everything on and by the time I was getting near the end of the first batch of resin the brush did a repeat trick. So new brush and new mix and everything assembled and into the bag.

No photos of this bit as it was all a bit manic - and sticky. The worst thing is that because the part is so complicated a lot of the cutting and trimming of the cloth has to be done as you go.

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And pull vacuum and get everything settled and compacted.

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I was very careful this time to make sure that both sides of the mould were completely covered with the breather cloth which is like a fluffy blanket so that there were no sharp points to cut the bag. Also careful not to work the bag with my fingernails too. This time it pulled vacuum no problem, although given the size of the bag it took quite while but all holding fine. Should be cured tomorrow.

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Cured overnight so went to get the thing out of the mould this afternoon after turbo trainer session and then cutting the hedge :blink:

Out of the bag and still wrapped in breather cloth which has soaked up the excess resin from the laminate.

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Then the easy-ish bit getting off the breather cloth that is largely resin free.

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Then it's onto the workout. Pulling off the combined peelply and resin soaked breather cloth is a right swine of a job.

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Once you can get a bit off it gets a little easier. As does taking it off in strips. The houndstooth pattern is quite cool.

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All off and not to get the thing out of the mould.

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That also proved hard work. Although in the end it came out mostly ok. There were a couple os spots where I must have lifted pinholes in the gelcoat when pulling off the first failed attempt at laminating. As a result it stuck to the mould a little and pulled off some more gel. Nothing major though. Looks OK. The mounting plates worked out fine.

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Front view

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With the Kevlar/carbon mix the thing is both very flexible and yet stiff at the same time although I still need to make up and glue in the mounting brackets.

And the all important weigh in....

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On 9/15/2021 at 9:22 PM, Escadrille Ecosse said:

Next thing and the pot of resin went off all in a rush. Very hot and smoking. Bugger.

I'm following this thread with much interest having produced epoxy/carbon components for my boat in the past (and some heat shields for the GT6). After experiencing exothermic reaction in a pot I found that using a shallow container gave a bit more working time. Keep up the good work.

Ian

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13 minutes ago, Gt64fun said:

After experiencing exothermic reaction in a pot I found that using a shallow container gave a bit more working time. Keep up the good work.

Ian

Good point Ian.

I'll usually make up a part mix or divide up a larger mix into two or three portions - I tend to use paper cups a lot - to slow things down a bit. It also helps that the unused mix isn't being heated by being held in your hand.

I use the small plastic trays that your carry-out curry gets delivered in for applying the gelcoat with a small roller and now you mention it, it does seem to slow down the curing rate.

I've had big mixes of polyester resin go off, 250 - 500g sort of quantities and they get too hot to hold and best put outside. The odd thing with the epoxy though was that it seemed to start on the brush. But boy did the mix get hot and we're only talking about 1/2" or so in the bottom of a paper cup - which is a rate of reaction I've not seen with polyester with that sort of small volume of mix.

 

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Started making patterns for the four reinforcing / mounting brackets.

Cardboard first then aluminium. Thought about just leaving it at this but decided that it's just a corrosion issue so I will probably use these to make carbon /kevlar ones and glue them on with polyurethane.

Although stainless steel is also a possible solution I guess.

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Worked on the brackets this week.

Made the moulds

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Laid up the parts, gelcoat then four layers of carbon/Kevlar cloth. Made a pair at a time to minimise the time pressure with the resin cure so two vac bags. Tee'd together to the vac pump.

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All went fine with this

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Trimming down was a bit of a swine. Almost wore out a nearly new tungsten carbide cutting disc in the Dremel on the Kevlar. Has a tendency to make lots of fluff and the quality of the cut is sensitive to the depth and direction of cut too.

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I had been going to start trimming the rest of the valance but will need some new discs so I glued the brackets on. Two part methyl methacrylate adhesive. Comes in a twin tube which fits in a gun applicator with special mixer nozzles. Impressive stuff. Appalling smell though :blink:

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All done....

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I tidied up the cut edges with a Perma-Grit sanding block and some 600 grit paper. Got rid of most of the fluffy edges but they will need a touch of resin painted on to seal them properly before painting. Will do all the cut edges once I've trimmed the rest of the valance which is marked out ready.

So there we are. The first of the new panels fixed together. A bit of a milestone, even if a very small one. 

 

Edited by Escadrille Ecosse
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Got out the PPE, the Dremel and the footswitch today to trim the valance to size. Yesterday I marked out all the cut lines including the holes for the bonnet hing mounts. That was a bit of a performance given that the surface is angled in two planes. And yes I noticed the slight Escher problem as soon as I looked at the photo!

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Took a while to cut that out. The Kevlar is a right pain. In the end I found that a thin blade intended for ceramics would do the job and the cleanest cut was achieved by cutting as quickly as possible. Which is all slightly scary in itself as the very thin blade is also very flexy and wants to wander with the 'grain' of the Kevlar. Filing and then sanding got rid of most of the fluff but still left a little that I will harden by painting on a little epoxy before sanding again. I think if I was using Kevlar again I would try and keep it away from the cut edges and have just carbon at the edges.

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Got that done and decided to carry on with the boot lock mount panel. That's all carbon and much easier to work although it produces a lot of what behaves very much like graphite powder and sticks to everything. After an initial vacuuming, tak rags made the best job of cleaning up.

Then I dug out the bootlid and trimmed that to size and glued on the lock panel with the MMA.

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That all felt quite exciting. At long last I am getting to something that will actually go on the car.

Only slight issue is that whilst the valance fits the chassis perfectly the shape is miles off the steel bonnet I have :blink:

I just used the mould that I used to make the original valance which matched the old GRP bonnet. And I don't remember having to fettle the shape. The steel bonnet has been well rebuilt so opportunity for that to be wrong as it is not the best of fits on the rest of the car either so I am putting the issue to one side for now. Worry about that bridge when I get to it.

Did some weighing in. The trimmed valance is now 618g

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The completed bootlid - without the steel frame is 2170g

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I don't know how that compares with a steel one but my uber light and floppy as a blanket GRP lid which has no frame or lock panel (or lock) is 1900g. That one is so structurally inadequate I was always worried about opening it when It was windy just in case it twisted so far it would split or break off at the hinges.

Edited by Escadrille Ecosse
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