Engine Mount Progress

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.

3D Printed and Carbon Fibre Engine Mounts fit

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.

xmas holiday summary

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.

When Engine Cranes Attack

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.

Behold!

Final fitting of the tub

 

So, here is everything laid up as a reminder of where this started. I think it’s a good reminder of how far the tub has come, but at the same time it’s also making me think the duratec is photobombing everything in my garage.

 

 

 

Now, here it is in the car:

It’s pretty close to where I want it now, and I’m doing the final fettling. I made this with a positive mould, which has meant the outer surface (that fits to the chassis) isn’t perfectly flat. I’ve had to take it back a little at a time with the flap disk in the appropriate areas to be sure it fits. I developed a methodology to do this after I’d removed the obvious obstructions.

I go around the gap with a feeler gauge set to 0.7m, and look for areas it traps. When I find a trapped area, I set the gauge to 0.05 mm and see if that still sticks, and anywhere it does, I mark with tape (hence the packing tape on the tub at the back top) and take it back about 1mm with a flap disk. I deliberately only mark the jamming points rather than the tight points so I can avoid making gaps unnecessarily larger than they need to be.

Once everything is marked, I lift the tub out (it’s only 13kg, so two adults can easily lift it with fingertips) and do the sanding. When it goes back in it fits a little better. Everywhere is pretty much where I want it, apart from the back where it’s still a little high. Everytime I advance the fit, the back lowers down a bit. I have about 3-4mm left before it’s flush and I’m happy.

This one is a little more difficult to wrap your head around, but it’s the mating surface between the tub (carbon on the right, starting in the top right corner) and the chassis rail. As you can see, the gap is pretty uniform now, and I’m aiming for between 1 and 2mm.

It unfortunately means I’m doing to have to remove some of the powder coat with a flap disk.

 

 

 

Here is the birds eye view. You can just see the lip at the back. I don’t want to just sand it off – I think I can make the tub a better fir before I have to do that.

Then the final act before bonding it in is to have it lacquered and cured. Then I will have an awesome finished product.

The tub is out of the mould

So, it’s been a while since I posted, but a lot has been achieved, and there are videos below to share the love. So, the tub has been infused, it’s been extracted, the peel ply and infusion mesh have been dragged off the back (that was a sweaty day), it’s been partially fitted and baked.

I’ve got three videos below to show what happened. There’s the infusion setup, followed by the resin going in, and finally the lovely tub once it’s out.

The infusion setup

The actual Infusion going in

The Tub out of the mould – ta-daaaaa

Ready for the bag

 Here is the spiral, with an extra layer of infusion mesh to carry it up on to the part. I’ve also ran my finger through the spiral to separate it a bit.

 

 

 

Spiral is down the middle, jointed by the t-pieces I printed.

 

 

 

 

 

 

Here you can see the spiral as it’s jointed and is taken around corners. It’s much easier to do it this way than bend the spiral through such tight radii.

 

 

Here’s the final part ready for the bag. I’m going to envelope bag it this time – I had a lot of struggles with a bag on the flange. I usually do better when I envelope bag it. The blue bits on the top are little cone-hats I made to give the bag some relief from the socket-headed cap screws. They’re in there against a modified t-nut so I can both use air to get the part out, and have a drain-hole afterwards. The red bit on top is one of the two vacuum exhausts. They’re positioned equidistant between the resin feeds. If I need to direct the flow of resin, I have four inputs, one at each corner.

3D Printing improves degassing

So, Degassing is the process of getting all the air out of the mixed resin. This leads to stronger parts with a better cosmetic finish – you aren’t fighting tiny bubbles that appear in the resin, or that start to appear as the resin warms through the exotherm and the gas expands.

It’s simple to do – you put the resin in a chamber – evacuate it and watch the resin bubble up as the air comes out. As the bubbles near the surface, you let a little air in to equalise the pressure, the bubbles subside and you continue until under full vacuum, no bubbles appear.

However, it’s NOT SIMPLE TO DO: I lied. There are subtleties to this, and if you just open the tap carelessly,it’s easy to let the air in too fast and get resin everywhere. Also, you end up shooting air into the resin you were trying to clear of the damn stuff. This is also how you trash a degassing chamber, and they aren’t cheap.

The following youtube video I made illustrates this with water. Read on to see how I fixed this with a simple 3D Printed part.

So, I designed and printed a part that moved the air and vacuum over to where it was needed:

So, using some gum-tape to fix the air-guide in place, I now have a degassing chamber that lets air in without worrying about shooting it back into the resin.