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.

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.

Making a vacuum manifold

I suppose your first question is “what are you even on?”,  and your second question, is “why bother?” If you need a vacuum manifold. Well, to answer them in order:

  1. I am on a chair, in my office.
  2. If you want to double bag, or hold down vacuum whist you degas, isolate a catch-pot or pat your head whilst rubbing your tummy, you need a vacuum manifold.

I mentioned making this in the infusion stations post and showed how I’d connected it to my vacuum reservoir, also known as “my old compressor tank”.

Basically, I’d hoped this doodad that I’d wombled off eBay would work (it’s a CO2 gas splitter with valves for the unclicking) and hoped it would fly straight out of the packaging, but it turns out it has non-return valves in, which means it won’t work for vacuum. 

I tested it against my vacuum gauge and it’s great – seals well and holds vacuum both ways.

Here it is, in the vice after I’ve taken it apart to see what gives with the valves, and can I somehow get them out.
They were only turned in with PTFE tape, so were an easy extraction. It’s worth noting that the steel is either polished stainless (probably) or chromed. Either way, the finish was great.

If you look at t’photo ont’ right, you can see the on-return valve, and as I hoped (but didn’t have a clue about before I dismantled it), the housing for the valve (ball on a spring) is a press fit. All I then did was get the right sized drill in there, and started drilling it out. Sure enough, it went pop, and the whole thing turned out.

Here it is, open and ready to go. You can easily see through to the white foam I used as a backing material for the shot.

 And the the detail-obsessed amongst you, here is the spring, cap, o-ring and ball to seal it. Very neat and simple.

A study in cores for my tub

Problem

So, I need to decide which core to use in the sides of the tub, where I don’t really need huge stiffness like I do with the base, but I still need to do a trade-off between thickness, ease of working, stiffness and weight.

Weight wasn’t going to be my only trade-off here. I have some others to think about

  • Ease of preparation started to become important when I started calculating the time required to prepare a standard foam such as the Airex. It needs to be scored every 20mm as a grid, and then at each intersection, needs to have a hole pit in (only 2mm or so) to allow the resin to flow through to the other side of the core. I did a square metre of it, and it took over two hours. Very tedious to do accurately.
  • Ease of layup is also a significant factor. Some cores are very bendy, some are very rigid, and some will thermoform. I don’t want to choose a core of marginal better physical properties if it takes me days of frustration to get it into the stack. This isn’t just a simple flat sheet, but a large female mould with complex curves in multiple planes.
  • Physical strength

Method

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  • do a flex-test to see how rigid it is (clamp one end to a flat surface – hang a standard weight off the other end). You can see how the steel rule is horizontal, and the part has deflected.. 24g is the weight.

Results

  • Weight – Soric (24g), 3D Core (23g), airex (29.5g). So, the airex is 2/5 thicker than the other two, and is 26% heavier.
  • Deflection (therefore infer stiffness) – Soric 30.9mm, 3D Core 31.6mm and airex – 20.5mm

Ease of layup

  1. Soric first – it’s more or less like a thick cloth, and will bend into most angles without being damaged
  2. 3D Core second. It’s a bit like hexagons of foam which are stitched together. It will easily follow simple curves, and can be thermoformed into the tighter ones. It’s not great in tight curves and will separate at the meeting points between the hexagons
  3. Airex last. It has some flex but does thermoform very well. However, getting the hot-air gun in there and pushing and shoving to thermoform it is going to be an arse.

Conclusions

  • I was surprised a bit between the 3D Core and the Soric. Deflections were very similar for very similar weight, which is what one would hope to see. This means the cores were performing as a function of the distance they separate the cloth. I thought the Soric would hold a lot more resin than the 3D core mind, and the results were so close.
  • The airex outperformed for stiffness, which is a symptom of the thickness it separated the cores. Interestingly, i could hear the fibers snap when i weighted this core, and it deformed at the end. Not sure why – further thought is needed.
  • I will use Soric for the side pieces. The ease of putting it into the stack and having it follow tight curves makes it far better for me than the foam. The time and effort to score, hole, form and shape these pieces isn’t worth the extra 600g of weight the chassis will carry as a result.

Hard Point design for the tub

Here’s the design for my hard-point for harness mounting bolts. It’s 3mm thick steel, and the channels are 2x1mm cuts. What you’re looking at is the underside. The channels and holes are to allow resin to flow through and past the hard-point. The big hole in the middle is where the 7/16 insert will go and get welded. Each channel has been tapered down at the entry point so the resin can easily flow into the part.

I’m hunting around now for prices to get them CNC’d. I need 6 per side (six point harnesses) and I’m getting a couple of spare for welding practice.

When they actually go into the part, they will need a layer of glass-cloth either side to insulate them from the carbon to avoid any galvanic issues.