So, I now have 5 different tins of chemicals that I use for composites, and some aluminium racking on which they sit. Needless to say, it’s a minor faff getting to the tin at the back when there’s plenty of other stuff on the shelf. To fix this, I bought some drawer runners, some 150mm wide MDF and set about making a custom shelf (I 3d printed the mounting brackets and the tin holders). I had printed some tin holders so the tins won’t wobble over – everyone deserves a chance to be a Weeble.
However, I was bonding them in and I nudged one and I didn’t notice. It’s slightly wonky.
I don’t know about you, but I can’t leave it like that. There’s a new part coming off the printer now (5 hours print) so I can replace the wonky one and square it off.
The questionable moral about this sorry tale? I’ve seen a few race-cars up on the ramp at my friend’s garage, and they look great from above. It’s when you get underneath them do you see if someone really cares. Are things routed neatly, is that a nice weld, or a bird-shit ‘good enough’ weld because no-one will see it. (before you ask, bird-shit welding is never good enough. Some people think it is). Have people taken the difficult but ultimately better route, or just clagged it in?
It’s even worse for kit cars – it needs to be neat – I’d never be a passenger in a car that looked lashed up.
And for the detail obsessed among us, they are soft-close drawer runners. Of course they are. Sheesh, what kind of animal do you take me for?
So, the first engine mount is now nearly a mould. I thought I’d share the prep process I’ve been going through in taking a 3D printed part to a CF part.
There are elements of the printing process I’ve had to compensate for – mainly that a part is many thin layers of plastic. For a non cosmetic part, this doesn’t matter on the the top of the part, but it does on the side. The gel-coat will go into the very fine layer lines there and lock the part. Also I made the part in a few sections and they had a visible seam where they bonded together. I had made it in sections for a couple of reasons – firstly because I only have a bed of a certain size. Secondly making it in a modular fashion means I can correct a small part of it, rather than waiting 10+ hours for a full print. Saying that, what you gain in flexibility you lose in post-prep time.
The post-prep phase is summarised as fill, flat, and flange.
So, I used some Dolphin-Glaze liquid filler to take care of the most obvious demands (such as the seams):
Once I’d got the filler in, I did some rough flatting. I also made a mistake here that can just be seen on the red piece on the side. I made the parts with a biscuit cut on each mating surface, and used printed biscuits to help lock it in whilst I bonded it with 2-part fast setting epoxy. On the red part at the mating surface it curled up a little. This wouldn’t have happened if I’d clamped it to the bench when the glue was setting. No biggie – when I flanged it later, I clamped it and bonded some carbon to the back to stiffen it and hold it in place.
After this I sprayed it with high-build primer and briefly flatted it. I used a rattle can rather than mixing up some two-part just because it’s a pain to spray. I have the correct mask and so on, but it’s just a lot easier for a small part to use a rattle can, even if it’s not the cheapest.
So – one flatted 3D printed complex part to make an engine mount.
Well, it’s been a decent enough holiday – I’ve finished 3d printing the front engine mount, and if the bonnet fits properly (I’ll know on Friday), I’ll flat it, crack a mould off it and make a carbon fibre engine mount – a first for me, and I think I’m blazing a trail a little there.
I’ve also been through the worst man-flu in the history of all mankind, but I still managed to have a good time, relax, read a few books and I’m currently getting through the ‘travellers’ box set on netflix.
Finally, the boxen1 of shame have been put out for recycling and don’t look too bad. Both full, but not priapic.
1 – The pleural of ox is oxen, therefore the pleural of box is boxen. Obviously.
So, this went wrong – clusterfuckingly wrong. There’s a video to show you just how wrong it went.
I was lifting my shiny new engine and shiny new gearbox into the chassis to start work on the engine mounts and I had a catastrophe. Normally when I lift it in, I take it in from the side and pivot it. This time, in order to make my life easier (ha!) I had it on an engine crane pivot mount because there was only me. The pivot mount has a cranking handle that lets one change the angle of the engine. However, what it doesn’t do is give one the same pivoting as a nylon strap.
Long story short, I toppled the crane over, into my tool chests, and smashed 5 drawers over two tool chests, and covered the floor in nuts and bolts.
So, here is the tub out of the mould. I had a lot of issues infusing this, and I’ve learned quite a lot whilst doing it. It’s gutting to scrap it, but it’s the right thing to do. Next time it’ll be right.
There are some high level fuck-ups that were mine, and they led to some lower level quality issues. It’s the first time I’ve done an infusion of this size and at the same time with a positive mould, rather than the usual negative mould. Doing it on a positive mould means I have to be very careful about the layer thickness otherwise I have a too large or too small gap between the part and the chassis rails I want to bond it to.
Some of the fuckups were down to layup technique, and some were down to getting the infusion wrong. I infused over a hexagonal core, and the hexagons were too large to not have a hole put through the middle.
Here’s another picture of the quality issues up close – now for the lessons learned:
I over engineered the part – too much carbon meant it was too heavy. When I cut it open I had great consolidation – all the issues are cosmetic.
In the spirit of making it ultra strong, I had core everywhere. Next time it’s going to be core in the floor, up the back and the top of the tunnel only. The core interfered with the close fit needed to bond it to the chassis. Again, this is due to a male mould. Normally I’d overlay layers in certain areas to achieve this. In this instance, I have to stick to the required layers to achieve a 2.5mm thickness up the sides and at the bonding areas.
More holes in the core, and a thinner core
The catch-pot imploded. I made one out of plastic. Air got in. A lot of air. I made one out of plastic and tested it for a week – it was strong. With the heat of the part (I had the tub heated to 35C) the pot weakened and imploded. Back to my all steel pot.
The tubing sucks up a shit load of resin. I had 6kg mixed and it flew into the part. This caught me off guard and I didn’t have enough mixed. A small amount of air got in. If I’d had really strong vacuum (i.e. No pot death) I might have recovered.
Have one KG of resin and hardener ready to mix. Even two.
I took 4 attempts to get the bag on – next time I’m going to make a huge envelope bag instead – it should increase my chances of a perfect vacuum.
No gel-coat. It’s a long layup and I was up against the clock. This drove some of the other mistakes. I’ll not be up against a schedule this time.
If I get another output that isn’t cosmetically great, I’ll spray it and be done. If it’s of a cosmetic quality, I’ll have it sprayed in two-part lacquer. This will give a great finish.
This is a vacuum exhaust fitting. I’ve designed it to be deliberately flat so the release film will stretch around it. I’ve previously used these silicone connectors from easy composites. They’re quite good and just over 3 pounds each. The connector I’ve printed has a hole for a 6mm hose and a stop at the bottom so the hose just doesn’t sit on the mesh. They also have a larger surface area sat on the mesh to help pull vacuum out. Mine aren’t reusable, and only cost 19p each to print, and take about 15 minutes.
I did a large infusion for the tub recently, and had no end of problems, to the point of scrapping the tub. I’ll write that up later, but one of the issues was that one of my pipes jumped off the clamp and sucked air in. Rather than use a simple OTS clamp, I’ve printed something specific for a 10mm hose and a 10L bucket. The hose is a snug fit and the height from the bottom of the bucket can be nicely set and held just with friction. No more springing hoses ever again.
So, I can expect to need 5.4kg of resin to infuse this part, assuming a load of 40% by the time you include pipework, mesh, etc. The actual part itself should only take a load of 30%, but I can measure the weight of the part afterwards to see what the actual load is.