An infusion went wrong

Posted on October 13, 2014 by mark

So, I was finally ready to infuse the transmission tunnel top, after deciding on a compromise. The compromise was to not spray the part with clear gel-coat first, even though I had some scratches in the mould. [1]. I reasoned that the scratches will leave a positive on the part, and that can be flatted off with some wet-and-dry and a little polishing.

So, I laid up the part (one layer of 350 facing cloth, and one layer of 200 backing), found to my surprise that I got the bag to seal first time, and set about infusing the part.

DISASTER

This is the first time I’ve had a stuck infusion, and as I think about it, it was a culmination of a bunch of factors all adding up together to cause issues. The factors were:

I decided to infuse along the short side and go up the full length of the part, rather than infuse across the shortest distance (I’m running low on infusion spiral)
it was 10C in the shed when I was mixing the resin, and I thought “It’ll be OK – it means I can use quick catalyst and it won’t go off all that fast”. I ignored the gloopy sensations.
I was feeling impatient, and thought I could get away with quick resin, allowing 10 mins for degassing because it was cold
my oven is out of action: it’s in pieces while I make it bigger for the transmission tunnel. I thought I had enough kingspan for the job, and I was short by one roof baton length. This is now bought and sitting in the boot of my car. This again was an incentive to go for the quick catalyst
when I was mixing it, it felt more viscous than normal, which should have been a warning that stuff was about to go wrong.
when I infused it, it got stuck half way along the part and the resin went off in the pot.

So, I think the resin being too viscous meant it didn’t march along the part quick enough before it started to go off. If I’d used slow resin the infusion could have ran at the snails pace it was going at and it wouldn’t have been a problem. What’s more, I could have warmed the resin up (with the slow catalyst) and it still wouldn’t have been a problem. For the handbrake bracket, I actually had the resin at 40C to ensure it wetted the part out properly. So, this evening I will finish the oven, take the half-part out of the mould, salvage the cloth I can which I’ll keep for backing layers, and have another crack at it.

[1] My compressor has died, and the replacement part (£160 if I can wait for a machine-mart VAT free weekend)

Composite Fuel Tank #4 – trial part fitted

Posted on August 12, 2014 by mark

and I’m a happy bunny. The finish is a little rough, and I can do a little mould polishing to get that, but once the part is in, it will never be seen again, so I’m not going to get all artistic about it.

Prepare to swoon at the fitment …

Top Down – here it is, fitting nicely, stopping about 100mm from the gear lever. There’s a good 10mm clearance all round between the tank and the rest of the transmission tunnel.

Open Wide for the Doctor

This is the view right down the tank into the sump.

Bolt Recess

Here you can see the cut-away area of the part I made to allow me to get a socket in to first insert and then secondly tighten the 1/2″ bolt for the top of the diff cradle.

Tank and Chassis fail to meet

The tank nicely runs under the chassis rail. This is just shy of 10mm. The tank isn’t going anywhere once it’s in, so I’m not stressing this.

Diff Clearance

Again, loads of room here. The diff cradle is held in place with 1/2 inch bushes, so there’s no way can it ever touch. I’ll also be making prop-catchers, so I won’t worry about the prop hitting it. And the tank will be in aramid, so i’m not fussing that.

Topping Out

Here’s the tank the whole area behind it is where the old MG Midget tank used to sit. The black brackets are temporary. I’ll made something rigid out of CF that spans the top of the tank between the cross-members. The tank itself will have m6 male fasteners bonded on to it, so it can be fitted from below.

The last picture demonstrates just how far I’ll be able to move the mass of the tank. It’s forward by 300-400 mm, to the point where it’s now inside the axle line. The aramid tank will have better impact resistance properties than the steel one it replaced, and being in the new place it is in the chassis, will benefit from greater impact resistance. The area behind (at the top of the picture) where the old tank used to hang from will be replaced by a crumple-zone.

And … Attach

These are Big Head fasteners. You basically put a big dollop of the special 2-part epoxy glue no the part (after keying it), push the fastener through, let it set and trust it.

I don’t have a solution for the front of the tank yet – I think I may take a bracket off the prop-catcher I haven’t made yet, or make a top-hat shape, cut a hole in the tank and stick the top-hat to it, but inverted so the top hat makes a recess. Then I can stick a big-head to it (I have some female ones) and bolt through from the other side of the transmission tunnel. It’s going to be … specific.

Composite Fuel Tank #3 – prototype part pulled

Posted on August 12, 2014 by mark

Or – Transformers – Fuel Tanks in Disguise!

So, before I make the part out of lovely aramid and carbon I thought I’d do the sensible thing and crack a part out of chopped strand mat first. I wanted to do this for three reasons:

check the part for fit in the car – if the mould needed a tweak or two, now is the time.
check the part for fit for the ATL fuel sender – I’d gone to a huge amount of effort to site this so that it reaches to the bottom of the tank.
fill it full of water to see what the capacity is

Here we have the entire set of parts pulled and trimmed from the mould. As I went along, my trimming got a lot better a lot quicker. I realised it was far easier to scribe the part in the mould for where the trim-line should be, and then to pop it out and trim it. As such, I have a few gaps which have been sorted with how I’m bonding it together (30mm strips of glass, wet laid on).

Now the part is pulled and bonded together, hopefully you get a sense of the size and shape of it.

I managed to bond the whole of the top tank (the top bar of the T shape) internally, but the lower part needs to be bonded externally. I did a reasonable job, but it’s not watertight. It was good practice for when I do the aramid/carbon part.

The entire part weighs just over 2kg, which gives me a saving of 3.7kg over the standard midget tank. It’s a great weight saving, before I even take into account moving the mass about.

Carbon fibre Fuel tank moulds complete

Posted on August 3, 2014 by mark

Footwell Fettling for Friend’s feet, Part 3 – Finished

Posted on July 21, 2014 by mark

footwell part 11

Right, so, you’ve seen the video about laying up, and here is the final layup ready for the vacuum bagging stack. It also shows extra corner bracing and there are similar reinforced corners underneath in aramid.

The stack I have gone for is as follows:

6 layers of mould release wax to ensure a good barrier and a shiny finish
one layer of GC50 clear gel-coat to give it a good shiny finish and UV protection (which it won’t need under the bonnet)
three layers of chemical release agent
2x 350gsm CF, for the initial outer facing layers
1x 250gsm Aramid for intrusion protection
1x 200gsm e-glass for a little bit of flexibility in the part
1x 3mm soric for the core
400g of infusion epoxy mixed with 120g of catalyst (slow)

footwell part 12 Rather than go for a standard side-to-side infusion I went for a circular infusion down to the centre. This stuck me as better because going edge to edge would require the resin to also climb back up the vertical slope and could spend time infusing into the corners. The vacuum will drag it up eventually, but it could be a pain. Furthermore, if there is a long wait as it gets into the final corner, you end up with the situation where resin is going into the catch-pot and the part isn’t yet fully infused (which is money down the drain). At least this way the infusion is relatively uniform, and gravity is acting on my side.

Once infused, I baked it at 50C for 12 hours in the oven, and then pulled the infusion stack off. Following is the video of me using the air-line lazy method for getting the first part of the stack off (the vacuum bag). I also used a new kind of peel-ply (knitted rather than the standard spikey flat stuff). It’s great for this kind of infusion because it will pull under vacuum into all the difficult corners. However, it remains a little stretchy after infusion, so it requires more effort to tug/haul/swear out.

Once the entire infusion consumable stack is removed, the part is left in the mould and the second stack is laid upon it in reverse order (without the GC50). The mould performed well and managed to split without too much trouble and about 50-75g wasted resin. I know Warren (who manufactures parts at volume) has a much more refined process for managing resin amounts – he writes the amount a part needs on the back of the mould. My parts are one-offs, so there’s no need to stress about that.

footwell part 14 Once I had split the mould, and got the first half off, the second gave up the ghost really easily and I had a part! This was a hell of a moment because it’s the first time I’ve gone from idea to composite part in 3 dimensions. On the part you can see the extra shiny side, which was incredibly easy to get to. I washed the chemical release agent off with warm soapy water (didn’t seem to make much of a difference, to be honest) and then I put a little Farcela 300 Polishing compound on to a cloth and gave it a bit of a rub – no real application of elbow grease required and this is the result.

The part has been partially trimmed (dremmel with a steel slitting disk, P3 safety mask) and offered up and it’s a great fit. You can just see the deliberate fitting gap between part and chassis, which should be between 1 and 2mm for the adhesive to work well.

footwell part 17 This time the view is slightly different in order to show the clearance a little more between the part and the chassis. I had deliberately left a min of 5mm to allow for some absorption in a side-ways impact. I could have taken the footwell deeper if I hadn’t welded in the extra strengthing bar you see there to complete the cradle around the engine.

footwell part 18 Sorry about the crap qualitty of the photo, but this is where you shove your feet. It has been sized to take size 11 trainers so most normal feet will fit fine. For final fitting, I’ll trim that remaining lip off, and bond the part of the contacting edges only. If I decide to go belt-and-braces, I will make some 90 degree angle and bond that onto the chassis and wrap it around on to the part.

Stronger than steel, far better shape, and I’ve not yet made a weight for weight comparison with the steel I cut out. I’m proper thrilled.

Footwell fettling for friends feet – part 2

Posted on July 18, 2014 by mark

So, it’s time I completed the write-up of the carbon-fibre footwell, lest alliteration break out o’er the land.

In Footwell Fettling Part 1, I go through how I make the part, and you can find the other footwell posts which are tagged with the footwell tag. I didn’t ever say I was original.

Following on from the sharp-edged part, I then rounded off all the edges using quadrant beading and prepped it for spraying. The process for cutting back and adding the quadrant beading has been gone into at some length in the composite fuel tank section, so I won’t labour it here again.

Here is the part, flatted back, polished and waxed. I waxed it because the wax serves two purposes: performs as a release agent, and gives a shiny surface, filling in all the tiny micro-scratches that come from polishing.

What I’m learning is that you need to add shine on every part of the process in order to get a reasonable shine out of it without major effort at the end.

Here is the part offered up to the fluted sign-board flange. I’ve tried all sorts of methods to get a good straight cut and have settled on a tile shape transferring thingy, and a steady hand with a fresh Stanley knife blade. I’ve tried cutting along steel rules with the Stanley knife, and have found that I get better results with just simply cutting by hand and eye. You can see the green breaker-tape sealing the flanges to each other; resins can’t stick to the tape, so you get a simple seal and don’t have to worry about release agents. Similarly, you can see the moulding wax filling the gaps between the parts and the sign board.

A word of note here – sign-board is far too flimsy on its own to be a flange material, so it needs to be backed up with some form of stiffer board (I use 6mm ply), glued together with hot-glue. Similarly, the ply needs to be glued to the base and part using triangular gussets. Here you can see the whole thing set back at a distance, and get an appreciation of context.

It puts the gel-coat on its skin or it gets the hose again. What you don’t see is me spraying the whole affair with a couple of coats of PVA release agent first. Again,that’s been covered against the footwell tag.

Three layers of 450g CSM backed up and set in poly-resin. You can see how I’ve taped the thermocouple to the part in the oven to avoid over-heating. The part can easily exotherm to 40,50C and if the oven doesn’t sense that, it can add more heat than is needed and the part will over-heat and be trashed. This is also both halves of the mound made together and going in for the final bake.

I’ve split the moulds and you can see a few things. Firstly, the finish looks matte, and this is due to me also adding a chemical release agent on top of the wax to be super sure it was going to come out. From a seasoned mould, this isn’t a problem, but for a green mould that’s a one-off, belt-and-braces is what you need. The arrowed part is where the mould took some of the body-filler from the part with it, so even with all this extra releasing, I still had a mild sticker.

Here are the two mould-halves re-attached to each other. The flanges have been drilled and cross-bolted (M8, because they were handy). The shiny side has been polished by hand quite quickly with Farcela compound, just to demonstrate the difference between the ‘out of the part’ finish, and the final polish before a part gets pulled.

Here is the whole mould backed in breather cloth. Because I’ve split and then reattached the splits, it won’t be easy to get a vacuum tight seal for a pleated bag, so I’ve got to go for an envelope bag. Breather fabric is just a soft, cheap, disposable cloth designed to absorb resin. The red circle shows a part of a corner I didn’t notice wasn’t properly wrapped and this caused a punctured bag. Click here to see a close-up and to see how easy it is to puncture a bag.

I’ve already made the post about laying up the cloth in this youtube video, and next will be the removal and fitting to the car. Believe, me, it’s f’excellent.

Footwell fettling for friends feet – part 1

Posted on June 3, 2014 by mark

So, bugger the old passenger footwell. It displeased me because it was at 90 degrees to the floor, making it super uncomfortable for anyone over 4 ft tall.

This displeasure became one impulsive moment with the air-chisel and flap disk and it was out. Of course, the solution is composite.

The specification for the new footwell is to :

have it angled for comfort,
gain 75mm travel for feet
add some kind of surface ridges for strength and grip
accommodate size 11 trainers
be lighter than the steel that came out
be stronger than the steel that came out
have superior impact resistance in case of the clutch letting go
double up as a foot-brace for passengers

ancle cracker

The Original Footwell – here it is, and obviously at 90 degrees to any sane sense of comfort. Furthermore, the Fury footwell is quite short and anyone over 5’8 is going to struggle to be comfortable. You can also see the rust on the left and the carbon/aramid trial floor panel I made.

First Fit of the Footwell. So this is the initial first fit of the footwell. It’s been deliberately designed to have a gap between the chassis members on both sides in case of an impact. As well as this there’s a gap of 1 mm between all aspects of the footwell and the chassis members again to allow for epoxy adhesive. It’s been made from sheets of 3*450 gsm chopped strand mat.

Here it is looking down from the top. You can see how it gets close to the chassis members to give the most leg room and foot room possible. It also has to get close to the starter motor and avoid the bell-housing but has to give enough room to get a spanner in there as well.

Initial Bonding. I used ISOPON P 40 chopped strand matt body filler compound used to give the initial bonding. It’s very strong and very quick to set; generally it will set in under 20 minutes, rock hard. This is much better than hot-melt glue which leaves a residue that you can’t sand.

Reinforcement. once the ISOPON had set I have then reinforced the joints with expanding foam. This adds nothing to structural integrity but later I will need to cut into the joints in order to put the quadrant beading in place. The expanding foam gives me something to rest the quadrant beading on. In this case I will use body filler to stick the beading to the foam, and what survives of the P40.

And so to bed. he is the part ready for final finishing. You can see lots of gaps which will need to be filled with body filler. I also need to cut all of the 90° corners out and replace them with quadrant beading. I use quadrant beading to give a large radius because carbon fibre does not like going round sharp corners. If you leave it with sharp corners then there’s a good chance there will be bridging and associated voids and weaknesses.

split mould, making progress

Posted on April 17, 2014 by mark

So, I’ve laid up two of the four quarters of my composite fuel tank mould. It’s a simple layup of gel-coat, and then three layers of 450gsm chopped strand mat, set in polyester resin. Nowt flash.

Since I’ve done the first half and the second half mated to it, I’ve learned a couple of lessons:

cut a lot of cloth to templates to fit the major areas – handy that I had the spare flanges from the first mould-part to size the cloth – this wasn’t an option when the first flange went in.
run at 1% to 1.5% catalyst – The gel-coat needs to form a chemical bond to the resin in the backing layers, and that is done with the exothermic reaction when the resin goes off. In the first mould-part I found the exotherm was kicking in before the final layer went down. This meant that the fibres were setting whilst sticking up and making lumps. lumps mean bubbles, gaps and bridging. With the second mould-part, I used the bare minimum of catalyst and the exotherm only really kicked in as I was putting the last piece on. This is perfect and gives the gel a good baking. Each mould-part needed about 2.2kg of resin.
don’t leave any spiky bits after a layer is finished – it just makes it worse the next layer. See above. Roller them carefully flat.
Apply only one layer of gel-coat. Again, mixed with minimum catalyst in order to get it on once without gelling. I have other jobs to get done so I wasn’t watching the gel-coat go off. Experts spray this on and bank on about 0.4mm of gel-coat. Painting this on means 1-3 mm. However, that gives me plenty to polish into.
Don’t try and paint gel-coat on if it starts to gel in the pot. scrap and mix more. my previous attempt with gel-coat did go a little lumpy, making the lumps and bumps worse – see 3 above

Here are the ‘bad one, then good one’ pictures:

Finally, here is the part with both flanges in place.

More composite fuel tank updates

Posted on December 21, 2013 by mark

This post is really about some of the manufacturing detail I’m going into as I make the part. As I’m sure you know, the sensible route to getting a composite component is:

Make the part you want out of any old stuff so you have to get the right mock-up shape. I’m using kingspan and covering it in glass. I also like kingspan because it sands really well with an orbital sander, and till take bog (body filler) nicely both as a glue and as something to put on the surface when building complicated shapes.
Cover the part in glass so that it is rigid and all the foam is separated away because of course you can’t take a mould straight from foam – they will become one and we all know what happens when two become one.
Where I can, I’m cladding the part in pre-made sheets of 450g chopped strand matt glass which I made on a pane of glass. The reasons are that firstly the sheet made from glass has a reasonable surface finish and secondly it’s a lot less faff to clag this on than wrap the whole thing in glass, set in resin and then flat and polish, flat and polish FOR EVERRRR until I have a sensible surface. Thirdly these sheets, being quite flat, mean I can trust the angles I have them in at so I can reduce the chances of mechanical lock.
Where I can’t clag, I’m putting body filler in, which is great for filling the gaps, but must be recessed slightly back from the overall profile. The filler will then be coated in resin. This is because you can’t go body-filler straight to mould surface – when you pull the part from the mould you will leave the filler behind. So, for the want of a little deft work with an artist’s brush and some resin, I can avoid this.

As ever, this is easiest explained with pictures:

Here is the joint between two panels. Both panels have been cut and bogged down and while the bog is soft a bit of a push allows the bog to squeeze out into the gap, Add deft work with a lolly stick and the gap is scraped out.

You can also see a big gap between the panel and the part. This will be radiused back so I don’t have any right-angles into which I can’t get cloth.

Rivets are handy to stop the panel sliding down the part on the bog. whilst it’s claggy stuff, it still has a propensity to flow. I suppose this is another odd reason why kingspan is so useful – you can stick rivets into it.

Here is the bottom of the tank with the three panels attached. What you can’t easily see is the slight angle the tank tanks to follow the fury transmission tunnel, which is angled.

More on the fuel tank

Posted on December 17, 2013 by mark

So, work on the tank progresses. I’ve got the top part mostly clad in sheet CSM, but now am focusing on the lower part – I need to do this in order to be sure the top tank mates well to the lower tank – they’re going to be made as two tanks then bonded. I can’t make them as two totally separate but connected tanks because the fuel level sensor wasn’t bought to work like that.

Here is the tank on the bench – you can see where I’ve started to clad it in sheet chopped-strand-mat (CSM).

Here is how it looks with some of the sheet clad into place. Note that I’m not stepping it as the cut kingspan in above shows. If I were to try and follow that, there would be two consequences: Firstly, less capacity. Secondly getting cloth to follow tight right-angles won’t work and will lead to bridging and a weaker part. I will take the orbital sander to all the edges where the places meet to smooth them out. They’ll then be filled with bog and coated with resin so I can make a mould from it. Needless to say, I will have to be sure the bog is slightly recessed so after being painted with resin (to seal it) I don’t create an unwanted positive profile that gives me mechanical lock in the mould. Even half a millimeter may make it so hard to get the part out without destroying the mould. I’m not intending to reuse the mould but it would be a massive shame to destroy it in case I ever need to modify the part.

Here we have the trial holder for the ATL Fuel Sender Probe. The housing is a cut down mixing cup and it’s set at an angle to point the sender down into the tank. Once the angle is right and it sits just where I want it in the lower tank I will glass over this so it becomes part of the main tank (that is, part of the part of the main tank that becomes the mould.

Here is the tank screwed into place on temporary brackets using self tapping screws. I know the fuel-sender will sit a little proud of the old boot floor, but that doesn’t bother me. I’d sooner make a demountable hat of some description for it rather than have the tank lower and lose capacity. I had to screw the tank in early to be sure I had reliable datum points when locating and attaching the lower tank.

Here you can see the tank avoiding the diff-attaching plate and the diagonal uprights that are part of the diff-carrier. The angle isn’t great but it I have at least an 25mm between the tank and all uprights. On reflection, the clearance is a little too great and I may be losing a little capacity. However, if I’m in a sideways shunt I have a lot of room for things to deform. The layup will also be very tough – aramid and e-glass. This will have massive impact resistance, and using layers of e-glass rather than carbon will add a little flexibility. This is not load-bearing or structural.

I had to build in two recesses, one on either side – the assembly order is specific here. The tank goes in first and the diff carrier second. This means I need to leave enough room around the tank to get a bolt in to secure the diff carrier. And I did – I’m quite pleased with myself.

Here’s the top view of the top tank. Note the massive void behind it, which is where the old tank sat, well high and well outside of the axle line. You appreciate how bad this is for polar moment of inertia, right? I was tempted to add some extra bulges on the back of the tank under the roll-bar, but this will be putting mass outside/behind the axle line. What’s the point of taking such a purist view if I then compromise? If I find myself really struggling for range I can always add a tank in this void where the old tank was. If it’s empty it will only add a kilo or two. My future plan is to remove the tank-mounting frame at the back and replace it all with a single CF crush-cell. This follow’s Warren’s law of composites. The new part will be lighter, and stronger than the rotting steel it replaces.

Here’s the lower part of the tank in place. The wooden bits show there the original guestimate cuts of kingspan need extending out to in order to maximise volume available. This angle doesn’t show it well, but there’s an inch minimum between the tank bottom and the prop. Again, it’s an IRS so the prop isn’t moving anywhere unless it lets go. The tank also swells out at the sides at the back (where the two sticks cross). There’s about half a litre or so to be gained by swelling out the sides like this.

All these little additions to capacity may not seem a lot, but if every half-litre can be baked in then I make serious gains in capacity. Bearing in mind the old tank weighed 6KG and carried 18L of fuel in the wrong place, I feel this will be a step forward.

furyrebuild

Rebuilding my Fisher Fury, from start to finish

Category Archives: Aramid