Moving On

ECU Tuning Guru's last update was accompanied by a message to the effect that further test drives / data collection / tune adjustments are unlikely to be helpful until I can get out on the road for more extensive driving. I think this officially heralds my escape (long may it last) from ECU purgatory.

So now it's on to the bodywork.

Another Big Project Enters the Chat

My younger daughter loves flying and loves to work on machines. Her current (14 year old, remember) career plan is to be a missionary / emergency relief bush pilot. And by sheer random coincidence or the Grace of Providence or both, her grandfather has a half-built bush plane collecting dust in the barn. So now we have another big DIY project - finishing the airplane. Our aviation journey is documented on YouTube and this is Episode One:

Meanwhile, back on terra firma, it's gotten very cold in my garage. But there are some bodywork tasks I can do in the house where it's warm - or with short stints in the garage when absolutely necessary. 

I'd been debating what to do with the vaguely triangle-shaped recess between the front tire and the door (above). On the original Aston Martin DBR1's there were vents here, but if I put real vents in this location on my car I'd only ventilate my feet (or the passenger's feet). I plan to put a decorative metal strake across this space, but I didn't want to leave a blank wall at the back of the recess behind the strake. So something unobtrusive, that looks plausibly functional, but doesn't draw too much attention to itself. Eventually I figured out this was a good 3d printing job.

I created this object in SolidWorks then imported it into an app that converts the 3d object into a series of 3d printer instructions (I use Cura, which hard core 3d printing people sneer at, for precisely the same reasons I like Cura: it's a) free and b) easy). It's a good thing I didn't get a slightly smaller printer because this just barely fits.

Above is the 3d print as it came off the printer, just held in place by yours truly. The bottom of the recess is domed so after I cut that out the 3d printed fake vents will sit further back in to the recess. Prints off the printer need to be sanded and primed and touched up to reach an automotive level of finish (at least my 3d prints always do). I am pleased with how this came out. I plan to paint it the same color as the bodywork so it will be a little more subtle than this.

After the first print came out so satisfactorily, I mirror imaged the part to make one for the other side of the car and immediately the 3d printer declared war on me. When it works, 3d printing is almost like magic: imagine the part, send to the printer, and abracadabra in a mere instant (in this case a 9 hour instant) you have the almost-finished part in your hand. When it doesn't work, it's as if someone had programmed a machine to make your head explode in frustration. I eventually did sort out this problem and got the fake vents for the other side of the car printed.

I must throw some credit at another brother of mine, Uncle King Arthur the Reigning Grand Kahuna of 3M who, by virtue of this exalted position, possesses Complete Understanding of All Materials Real or Imagined. King Arthur Kahuna (as we call him) got me thinking it might be a good idea to try PETG again. PETG is one of the kinds of plastic filament that can be used by 3d printers. I had some... frustrations... with PETG when I first started 3d printing about 3-4 years ago. But the materials and the printers have come a long way and I am starting to think PETG might be the best material to use when printing a part that needs to be stronger and/or more heat resistant than the ubiquitous and endlessly cooperative PLA. Since these costume-vents will become a permanent part of the car, they'll need to be made of a material that will not melt into a puddle if I take the car out on a hot Summer day. In other words, not PLA. 

Fill R Up

Another bodywork feature I've been contrapting is a recess for the fuel cap. Cobras have something like this, allowing the fuel cap to settle down in its own little nest instead of having to perch atop the fender. I always thought this lends a nicely finished appearance.

Upper row, left: it seems like ages ago that I designed, 3d printed, and surface finished the plug to use in making the recess.

Upper row, middle: Made a cutout in the bodywork and glued in the 3d print. 

Upper row, right: used epoxy filler to fill and smooth the gaps between the 3d print and the bodywork.

Immediately above: This looks pretty good, if I do say so myself, but this is just midway through the job. Midway may even be optimistic. Unlike the fake vents, this needs to have some strength and it needs to be fully integrated into the bodywork - otherwise, cracks will eventually develop in the joint between the 3d print and the fiberglass. 

So the next step will be to lay fiberglass over the area painted white in this picture. Then I'll have a reverse mold of the upper fender and the recess. Except, instead of being a recess, it will be more like a lump. Then I'll cut a larger hole - probably with sine-wave edges but definitely not any sharp corners - large enough to remove the 3d print. Then, I'll attach the reverse mold to the outside of the bodywork and lay new fiberglass (probably with a layer of kevlar for strength) from the inside. Then, finally, remove the reverse mold to (hopefully) find a unitary fiberglass body surface with a fuel cap recess in the top of the fender.

Back to the upper row, right: also seen in this picture is a 3d print I made to create a recess in the rear lower valence panel with the correct dimensions for a US license plate. This will be the same process as the fuel cap recess, all over again.

Hinges of Fate

I have a set of external hinges like those seen at the front of the door in the picture below, and also a set of smaller external hinges for the boot and bonnet. 

These don't look bad to me at all and they would certainly be the quickest and easiest way to finish the car. My only objection is that I want to put a larger polished metal airfoil shape (aka 'strake') over the vents - and with the door hinges right behind them, this might be a few too many shiny darts all clustered together on the side of the car. If I can make internal hinges work I think this could lend itself to a cleaner overall look for the car. 

My yet another brother Uncle Ray suggested four bar linkage hinges for the bonnet. This would be great. I love the way boots / bonnets hinged this way move up and away from the car body. But I was unable to find space for this kind of mechanism in the engine bay. The bonnet (hood) is certainly the most challenging fit for internal hinges. So, with my natural instinct to home in on the most frustrating job, I decided to start on the bonnet hinges first. And, to make the job even more interesting, I want to see if I can get the bonnet to hinge on the front edge.

Although making prototype hinges to test is a great use case for 3d printing, I started with a different variant of CAD: "Cardboard Aided Design." I cut out some cardboard C-shapes that (I hope) will be large enough to bridge across the joint between the bodywork and the bonnet but also (I hope) small enough not to interfere with the front upper frame rail. Then I went back to CAD v.2 ("Computer Aided Design") and re-created the C-shape in SolidWorks. Then I added some hinge ears and bases and came up with this:

The bases on either side of the C-arc aren't the final design. They'll need to have a broader base so as not to create sharp stress points in the fiberglass of the hood and the car body. What actually attaches to the fiberglass will be wider and perforated to help with "glassing them in" to the existing bodywork. It may be advantageous, at least on one side, to have the wider perforated part include some threaded studs. Then, smaller bases like those in the pictures above could be drilled with oversized holes for the studs. This would allow me to adjust the alignment between the body and the bonnet/hood (and boot/trunk, and doors). An obsession in the automotive world is "panel gap" - ie, having the same amount of space around all the edges of the door (or hood or trunk lid). If the position of the hinges can be tweaked a little, this could help avoid the Heartbreak of Bad Panel Gaps.

So I added the parts in the CAD assembly above (plus two hinge pins) to Cura, to translate them into 3d printer instructions. Multiplying times the needed number of parts, I got this:

I will now send this output over to the 3d printer. And when I wake up in the morning, through the magic of technology, I will either have a set of parts that looks just like the above, or a hideous blob-like mass of misshapen plastic.

If I can convince myself with plastic prototypes that the above parts will work (or, more realistically, that the 97th revision will work) I will send the files to Send-Cut-Send and have them laser cut out of aluminum. Or steel. Maybe stainless steel. Whatever; some kind of metal that I can weld.