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.
I’ve created the front engine mount in CAD (another post to follow) and now I need to test the engine height with the mount and the bonnet fitting – it’s no good having a beautiful mount if the engine then doesn’t clear the bonnet. I’ve gone for a trial fit of the mount (several hours of CAD and printing) to be sure it works before I go through the process of moulding and making the CF part. What I wanted to do was put the mount in place (it cradles under the front of the sump and bolts on to the front of the dry-sump). It also needs to curve around the awkward external dry-sump pump which seems to get in the way of everything.
Having fitted it, here are a set of photos that attempt to show the bonnet in place, and the engine having about 30mm of clearance between the top of the engine and the bonnet. One of the other interesting things about doing this is it’s the first time in a couple of years that the car has had any bodywork attached. It’s gone (in my head) from an abstract chassis concept back to something that relates to being a car again.
From a reference point of view, the sump will sit between 115 and 125 mm from the floor, and my suspension is height adjustable so on a track I can lower it a bit more. Right now, I’m safe to go over a house-brick without writing off the engine.
Here you can see the bonnet resting on a clamped large table-mat as a reference line. (Clamped to the top chassis rail). The mat and clamps weren’t strong enough to handle the weight of the bonnet, so I needed another idea. So, what you can see sticking down is a piece of (cut to size) wood that represents the chassis rail height to the floor as a relative position. The table mat is now just sat there without any vertical load – it works well as a reference point.
With the bonnet properly propped, this a bit of a scrappy shot down the bonnet. There’s loads of clearance here, and you can see the CF footwell and gearbox.
More of the same here and you can make out the 3d printed blanking plates I made.
And again – hopefully you can see the oil filler cap at the front a good 30mm below the bonnet.
Here it is from the top down. It looks a tiny bit like a car again.
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.