Whoops! The tape didn’t hold.

Posted on April 5, 2015 by mark

First attempt at filleting with plasticine

Posted on April 3, 2015 by mark

Here is the first attempt at a fillet. I appreciate that it doesn’t look much from this distance (so there’s a close-up to follow). I’ve been using a 1″ ball and liquid wax dissolved in styrene as a lubricant. It helps if the plasticine is nice and warm and soft before one rolls it into a sausage and shoves it in.

However, I’ve got to stop now for a couple of reasons:

the wooden frame supporting the polypropylene has come away from the chassis – the adhesive holding it together came away today. This is a bit frustrating. What it means is that the base isn’t as accurate as it should be, and isn’t as supported as it should be, meaning things may shift under the plasticine.
I realised there’s still a little sanding to be done on the tunnel part to make it fit perfectly to the chassis. This is going to throw a load of dust about which will settle into the plasticine and contaminate the finish.

This is the filleted edge up close and again, it’s not easy to judge the finish. However, this is at the bottom of the tub and most of it will be covered by seat, so whilst I want the best finish I can make, I’m not going to get het up on making it perfect. I can always do a little post-finishing on the mould or even the part if the urge gets me.

Down the drivers site of the tub

Posted on March 28, 2015 by mark

Fairly pleased with this, ready for the back to go on (not sure how yet 🙂 )

Posted on March 8, 2015 by mark

Here’s the new transmission tunnel part – sides are mdc, and curved surfaces are body-filler. There’s an entire wooden frame in there keeping it all in shape.

I’m using some ultra sticky double sided tape to hold the side panels of the tub in place. You can see the stuff here. It’s incredible.

Here is the polypropylene plastic sheet forming the side of the tub mould. The tape gives me 0.7mm clearance between the sheet and the side, which is a good gap when I apply the epoxy adhesive to put the final tub in place. The adhesive has a maximum structural fill gap distance of 2mm so precision is called for.

Shiny transmission tunnel mould

Posted on September 1, 2014 by mark

Fixing a Dodgy Mould

So, I cut a corner and had someone do some finishing on my mould because I was pushed for time. It was a mistake – the mould had a lot of resin dripped on it, and the surface gel-coat was very orange-peely.

It was a perfectly servicable mould, but the transmission tunnel is something everyone will see when they look into the car, so I want it to be facing quality.

In order to sort the mould, I tried 600 grit on a sanding block, and it was making an impact, but not flatting it out as fast as I wanted (i.e. in one lifetime). Then I remembered that I had bought some 400 grit disks from East Coast Fibreglass’s clearance page. Add the disk to the heavy duty polisher I have, and off we go. They really chew through the gel-coat. I finished that with a 1000 disk and polish. After polishing, I saw that I had some fine scratches, so I flatted it by hand (600 and then 122 grit), and polished it back. Again, some scratches. I don’t know if they were being introduced by the polishing sponge, but I don’t have the will to keep trying.

What I have got is a mirror finish on the surface now, with some minor scratches which you can just see at the bottom. I’m hoping that a few layers of release wax will help fill the scratches, and I’m going to use a clear gel-coat before I infuse, which will then end up with some slight positives where the scratches are. These will be easy to flat and polish by hand.

I don’t want to flat back again in case I end up going through the black gel-coat.

I’m not sure if I’ve contaminated my polishing sponge or not here – more experimentation is required I think.

compound curves

Posted on March 10, 2014 by mark

Here is the join between the two bits of the tank – it’s taken quite a bit of time and bog to get this right, as well as using a flap disk on a drill to get the radius right. lots of polishing and filling as well. I managed to get some of the profiles right by taking a plastic bog-spreader and cutting a radiuses edge into it. I also found that a wooden tongue depressor also had a very useful profile for putting curves into things.

Fuel tank – ready for high-build

Posted on March 6, 2014 by mark

So, we’re moving further along with the fuel tank. The last post I did on this was more or less finished, but then I’ve done a little more.

Firstly I decided that the recess for the fuel-senser was a little tight (potentially tight) so i modified it, thus:

It’s a nice shaped curve, feels organic and now there’s loads, loads of room (I tells ya) to get the sensor in there.

The black disk is cut from a piece of carbon sheet I had made and then changed direction. It was lying around.

If the bits of bog on there leave me with a surface that’s not flat enough to work with a rubber gasket (which I doubt) then I can also cut another disk and bond it on – the epoxy glue can go on as thick as I need and it’ll leave me with a good sealing surface. Similarly if the angle on the black disk isn’t quite right and the sensor doesn’t go where I need it I can adjust it a little with adhesive. I’ve spent a lot of time trying to get that disk in the right place, so here’s hoping.

Here’s the final tank.

So, the last things that have been done have been to paint a little resin over the wood to lift the grain. This is necessary so I don’t end up with the grain lifting when I spray it. Once the resin has set, the grain is lifted and a quick once-over with 120 paper on a sanding block did it.

Lessons Learned

Paint the resin on carefully with an artists brush. I used a small paint-brush (it was late and I wanted the job done). I ended up with the odd run. I’ve sanded back what I can, but if I’d used an artists brush and taken my time, I’d have had less runs.
When you’re mixing resin, get the quantities right. The last time I was mixing this stuff, I was mixing it one to two litres at a time. I had a little measuring jug from lakeland for cooking. This time I mixed 100g of resin, and added 20g of catalyst. It should have been 2g. It bubbles and boils and then weirdly doesn’t go off for ages. It ends up looking like cinder toffee. Of course, it also has zero structural integrity.
Forming compound curves is difficult.

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.

Proud father of a … transmission tunnel buck

Posted on November 11, 2013 by mark

So, I managed to get the wet-lay done last night. It took a couple of hours and about 4 litres of resin. The stuff I was using was simple non Lloyds approved resin from Leeds Fibreglass Supplies which worked well. I mixed it at 2% catalyst and in 2L batches. It only started to gel-off right at the end of the tub, which was a success. Also, the resin was pink not blue, and turned gray as the catalyst started to activate.

The part came out of the mould in about 90 minutes which was a fair fight. I’m really glad I used PVA again because it’s water soluble. You just get a thin wedge in (I used a plastic bog-spreader) and spray some water down. It slowly starts the separation and all is well. Keeping forth the birth metaphor, you can see the birthing remains stuck to the part. PVA is like a skin (rather than EasyLease which is a chemical barrier).

Here’s a nice shot down the top of the tunnel, or chute, or birth canal, if it were. What you can’t see is the quality of the surface finish. It’s actually quite shiny but there’s little sunlight to reflect off it (cloudy overcast day).

It’s not all perfect though – no matter how much resin I poured on and how manic I got with the bubble-buster (i.e. special wet-lay roller) I just couldn’t sort some of the white patches and it’s come through the mould. There’s the odd bubble between the layers (which I will live with – this is the master buck, not the part) but there’s also some dry patches of glass on the face.

Next steps are to dress the surface issues and then seal for a part … can’t wait.