Picky, Picky, Picky

Getting Fussy about the Gauges

Going way out on a limb, I will hypothesize that anyone willing to go to all the trouble and expense of making his/her own toy car is likely to be really demanding about some features of the project. And, likely, there will be other features they really don't care about all that much. I don't really care about big horsepower, or maximizing performance generally. "Sporty and fun to drive" is my target - whereas other builders will want acceleration that crams their eyeballs to backs of their heads or will get really intense about shaving a half second off their lap times on track day.

One of the things I am really exercised about is avoiding, as much as possible, anything that glaringly conflicts with the aesthetic vibe of a 1950s British sports car. And the more often I see it, the more an obvious anachronism is going to grate on me. Modern ECU hidden behind the dash? Don't care. But the dash itself is always in the driver's view so I wasn't going to be able to cope with the OEM Miata instrument cluster. The 90s graphics. The gauges all crammed together in one tiny hemisphere. Immediately identifiable as "not a 50's British Sports car."

One solution would have been to get a set of real Smiths gauges but I was not eager to spend $4000 on that option. So what I settled on, and which has turned out to be a fairly major project of its own, has been re-styling the OEM Miata instrument cluster.

First on the agenda was to move the small gauges into their own housing. So I used Solidworks to re-create the standoffs for the OEM Miata fuel, oil pressure, and coolant temp gauges and create a box around them.

Above is one of the earlier version of the part. It's gone through a number of corrections and iterations that I do not care quantify.

Here's the latest 3d print. Which actually needed some more corrections so technically I suppose the latest version is the one that is being printed right now. Right behind is the dashboard faceplate that goes with these gauges (also has most of the car's electrical switches).

Here we have the gauges and gauge faces installed. I designed the gauge faces with Corel Draw and had them laser etched on a two-ply black/clear acrylic. The laser etches away the black, leaving clear for the backlighting to shine through.

I am still using the OEM Miata pointers... which I can live with... I think.

Of course the instruments and the lamps that illuminate them have to be wired. This was my first idea - using copper tape as a conductor for the lamp contacts. Still not sure exactly why, but only one of the lamps had reliable electrical connection with this method. Will need more work.

Here's the temp gauge, unevenly lit by just one lamp. I do think this is going to look good when I get all the lamps working. Note: the 2 ply acrylic only produces black and clear. For the colors, I used transparent colored tape on the back side of the acrylic. It's a little blotchy up close but looks fine at normal viewing distance. The OEM pointers aren't as annoying when they fade into the black background.

Here are the speedo and tach with their corresponding face plate. These face plates were laid out on Solidworks, then laser cut in stainless steel by SendCutSend. I used a drill press, a brass brush, and valve lapping compound to make the engine turned finish. The black parts of the gauge bezels are 3d printed ABS. The shiny trim rings are designed to fit on the OEM Miata instrument cluster and are available on eBay from a supplier in Poland. For switch guards, I just used stainless steel u-bolts. The brass trim at the bottom ends of these are brass knurled nuts. The cutout at the bottom of the face plate is for the steering column. I do have a rubber grommet to finish this off.

Fuel Tank Update

Another excursion into Pickypickypickyland has been my insistence on making my own fuel tank. I do think it will be worth it - primarily for the more useable trunk (boot) space - but it has been a major project of its own.

After designing the tank in Solidworks, then using Solidworks sheet metal utilities to separate it into individual parts, I uploaded the resulting .dxf files to SendCutSend. There was some back-and-forth as the SendCutSend techs asked me to modify the files in various ways to make them executable in real life. Then the parts arrived and.... one of them was bent the wrong way. 

Yeah, that's not going to work. Astonishingly, this problem was NOT due to a mistake that I made. After uploading the .dxf files to SendCutSend, the customer has to specify the direction and angle for each bend. When I went back to look at my order I discovered that, against all the odds, I had spec'd this bend correctly. It's the first time SendCutSend has made a mistake on any of my projects. Of course they are remaking the part and I should have it by the end of the week. 

Fortunately, this mistake was made on the very last part that gets welded on the tank. So the plan is to head out to Pops' Shop this afternoon and get started with the other parts.

Update to the Update

Here are the tank's center baffle and top laid out on the welding bench. I can't use this top for the actual tank, being bent the wrong way, but it did work nicely as a fixture to hold the fuel pickup/pump/sender assembly. Here the baffle is in position just below the assembly. When designing the baffle I neglected to take into account the movement of the fuel level sender, so my biggest job today was cutting an opening in the baffle to allow the sender's float to describe its arc from full to empty. 

This big hole will of course make the baffle will less effective in limiting the fuel's side-to-side sloshing inside the tank. This could cause fuel starvation problems if I'm in the last lap of a big race, almost out of fuel, and have to take a left hand corner really hard to keep ahead of a hard-charging Max Verstappen. On the other hand, if I'm facing a fast right hander, this could actually help keep me ahead of Max. So I'll have to just take my chances on that eventuality.

Even if it isn't a terribly effective baffle, I think it will make assembly and welding of the tank a lot easier. I plan to rivet it to the front and bottom panels (eventually welding over the rivets, of course, to prevent leaks). The hardest part of welding is holding the parts in position until they're tacked in place. This middle part should help.

I also got the holes punched for the fuel filler flange. If I'd known what flange I was going to use ahead of time, I could have included this hole pattern in my Solidworks design and the part would have arrived with these holes already laser cut in place. But a 2" chassis punch and drill press took care of the job without too much fuss.

Not-pro tip: using wax on the chassis punch really makes this job easier. Especially if it's a really old chassis punch that isn't very sharp any more, and especially if you're punching a relatively large hole in relatively stiff material.