Vacuum bagging – joy of joys

There’s a great joy in doing a vacuum test on a bag and seeing that it’s held vacuum, before you infuse. That’s what I did last night. Admittedly it dropped somewhat over night, but not enough to cause me issues, especially since I was planning to pop the part in the oven with the pump on anyway.

So, I made a mistake though. When I’d bagged up, I hadn’t actually fitted the tube to the inlet, when I was testing the vacuum, which meant cutting the bag (in the approved manner) to push the tube through and seal it against the silicon connector.

However, fitting the connector and reestablishing vacuum gives me quite a strong leak – either my connector seal isn’t good (unlikely), or the tiny hole I had has been made worse by slacking and reestablishing vacuum – far more likely.

So, I’ll check the seal because that’s quick, otherwise it’s another scrap bag and time to try again. I don’t want to chance infusing over it because there’s already the first half (infusion up to the core) in there and mullering the second half will scrap all that good work already done.


How many layers of carbon fibre = 1mm?

“Hmmm” – I hear you say. “I hadn’t thought of that”, and “Why on earth do you need to know that?”, you follow up. I sense you ponder, as you pour yourself a nice New Zealand Sauvignon Blanc, what with you, dear reader, being the carbon fibre sophisticate I know you are.

Well, the reason is, I’m making some brackets to hold my new handbrake actuator in place, which weighs 2.4kg. In the world of normal steel stuff, I’d get by with 1.5mm brackets and that would hold. So, bearing in mind that cabon is stronger and lighter than steel weight for weight, I shouldn’t go much thicker.

so, what’s the answer? Well, my research (for resin infusion only) is that for every 200gsm, you get 0.2mm worth of thickness.

Also, I’m using 3mm Lantor Soric as a core for all of this, which separates the layers and adds stiffness for little extra weight, but more volume consumed. What’s more, the soric also works for compressive hard-points.

This bracket pair (post to follow) follows Warren’s Rule (every composite part must do at least two different jobs). The brackets hold the handbrake actuator, they couple the bottom of the transmission tunnel side to side, making it a box for part of it’s length (adding rigidity) and it’s a flat piece of carbon, improving underfloor aero.

Video of footwell layup pt1, 20x speed

Well, I finally laid a youtube egg.

The video below shows the template making and layup of the composite footwell, covering

  • getting the core material the right shape
  • cutting templates of the cloth
  • layup testing
  • spraying gelcoat
  • realising i need more practice at spraying gel-coat
  • painting the gel-coat
  • being unhappy with that and ripping it out

Comments are especially welcome.

How to set up a Sestos D1S PID controller

sestosSo, I and many others it seems, have been struggling to set up their Sestos D1S controller. It was a great buy, about £35 from ebay with a solid state relay and thermocouple. I can’t complain about that. It was also relatively easy to wire into the oven I’d made. I put this together with a load of kingspan and the internals of a domestic fan oven I’d wombed up (again from ebay) for £10. Add a project case and some other bits and wire and we’re off.   It went together and in theory powered up properly. The light on the front came on, the relay activated and the element came on. From that though, it never really settled on to a value; it would just overshoot in an unnerving way. What you’re meant to do is let it auto-tune itself (which can take a few hours) and then it should be super-lovely. What actually happens is:

  • you read the manufactures instructions and realise that the single sheet of A4 isn’t going to help. You scratch your head, you have a go at fiddling with it, and it makes no sense. So you stop.
  • Then what happens is you go googling and find a whole bunch of people who’d had issues with this (weirdly brewers and gourmets from America) and I found this far more excellent page from a chap I think is called Claes Junk. It gives great instructions about how to set up the controller, but doesn’t help with the auto tune I’m struggling with.
  • You throw your hands in the air and buy a PID from a different spot – I ebay’d PID controllers, and went looking for distance nearest first from my house. I found Simon at Harrogate Automation Controls who has a massive amount of PIDs and other magnificent bits of gear. He knows his stuff and had things like cabinets and contractors to PIDs and compressors. We spent a happy hour chatting and I came away with a new controller for an outstanding price
  • Feeling like your oven is getting a new start, you ring Warren and tell him what you’ve done, and he also reminds you that he has the same PID and his works. So, I got Warren to give me his config and I fed it in
  • Now it kind of works, but it overshoots by 10 degrees. It doesn’t overshoot and then nicely hold the new temperature, but wavers around +- 10 degrees.
  • Yo go back to Claes’ instructions and rerun the autoconfig.
  • forget you’d left it on and leave it running overnight
  • Bugger me – it works. rather than finding fire, I found a nicely working oven which was holding the temperature within 0.2 degrees.

So, for those of you wanting to configure your Sestos, do what I did and lift my config values (below) and then run the auto-config.  The ones that matter are:


Parameter Definition Value
df Hysteresis 0.3
CTRL Control output (3 = PID) 3
m50 Integral 100
P Differential 300
t Hysteresis time 160
CTL Control Period 10

Thus endeth the lesson

PID controller woes

I’ve been having trouble with my composites oven. I think it lies in two areas:

  1. it’s a little leaky – can be fixed with a bit of expanding foam and a more careful cut of the kingspan i’ve used to make it. I could build a wooden frame for it as well, but that seems a lot of faff
  2. The sestos PID controller I have is a bit hard to use – it’s well understood the chinglish instructions are abominable.

So, how to fettle this myself?

I’ve found this great page at which gives a great description of what the variables mean and how to set up a PID. Now at least I am armed with the info I need to fix this.

I’m actually thinking of making my own and the plan is:

  • keep the triad switch for the oven, fan, etc.
  • write a C++ application to do the PID control from a PC
  • configure multiple ramping profiles that are saved and can be selected at will
  • the application can have multiple learning points, so the PID can be most efficient at each ramping step
  • use a pair of xbees to provide wireless sensing and control of the oven
  • have 3 temperature sensors – two in the oven and one for ambient temperature
  • have a set of fans in the oven as well as the initial fan so that hot-spots can be eliminated
  • logging so you can see what the temp was doing

Saying that, there’s also this quite sophisticated controller which does most of the above and has a serial interface and instructions in English. So, I could write the application to control the PID and just use it for logging – but I wouldn’t get the wireless control of the oven (mine is in the shed).

Your thoughts?

Choices, choices.

Footwell fettling for friends feet – part 1

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

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.


IMG_0099Here 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.