heinzboehmer's 2002 Topaz 6MT Coupe

[Obioban]

^that sheet metal version doesn't look like it's going to fit in a brake
(not manufacturable)

[heinzboehmer]

Also, been learning as much as I can about designing this piece for strength, while also having it be light and relatively easy to manufacture. Lots of learning to go, but I'll get there. I'm very much the wrong kind of engineer to be designing these kinds of things, but luckily, I have a decent chunk of mechanical engineer friends (a lot of them automotive as well)!

There are a few things that are of concern to me right now (there's likely more points of concern, but I have yet to identify them...):

1. The ribs are placed randomly. I tried my best to put them in the load paths, but the corners of the piece don't line up with them, so there's a bit of a compromise there. I don't know what the implications of this are, need to figure that out.
2. The surface area for the CF to bond to is decreased because of said ribs. Again, not sure what the full implications of this are, maybe it's fine? But I will sleep better when I know what analysis to do to make sure it's good enough.
3. My fillets and bosses are picked kinda randomly. I just guessed at wall thicknesses and stuff for them in the version posted above. I've gotten some feedback from friends and they look much better now, but I need to keep these constraints in mind going forward.

Anyway, in an attempt to address the above concerns, I quickly drew up a couple (wacky) alternative ideas for the mount. Figured I'd document them even though I might not implement either.

First up, a split machined version of the mount:





The idea behind this is that I can keep the full surface for the adhesive to bond to on both the top and the bottom. The two halves would have to be machined with no threads, bonded together along the ribs, post processed (tap holes, clean up any excess adhesive) and then get bonded to the CF sheet.

The extra material on the bottom only adds ~50 g, which sound like a worthy tradeoff. The problem is that I don't actually know how splitting this thing in half and then bonding it back together will affect its strength. Again, more learning required.

Second alternative is to make the entire thing out of sheet metal. Would look something like this:



This design would also require two end caps to box in the sides, along with a bunch of locating tabs everywhere so that it's easy to fixture for welding. Some sheet metal ribs inside along the load paths would probably not be a bad idea either.

Big issue with this is that even without the end caps and ribs, the design already weighs roughly the same as the machined + CF version. Making it this way would really only help with cost and I'm not exactly trying to optimize for that factor with this project (especially after seeing that the CNC'd quote was <$500). Assembly would also be harder as it requires knowing how to weld well instead of just smearing a bunch of adhesive on.

Anyway, alternative #1 is appealing, but more thinking is required before any decisions are made.

[heinzboehmer]

What's your timing? I have 2 more roofs, hood and a mold, and a dashboard mold, and front thrust plate for George Hill to do - 3-4 more weeks for me?

I have about 20lbs of casting resin and it has a limited shelf life. So far, I plan to a compression mold for race seat floor mounts, jack pad, and maybe seat mounts. I should have plenty of material left to do your mount. If you want to give it a try then all I ask is to get rid of the ribs on the backside...I'd have to fill all of that stuff in which would take forever. Estimate about 2-4 weeks to get done. Again, it's going to cost less than $50 in materials...if that.

It would be an honor to contribute something to this build!

That timing should work. I can print you a piece and send you that.

To be completely honest, I'm not sure that forged carbon is gonna be the best material for this application. This piece will see a decent amount of load and the random nature of the forged carbon makes me a bit uneasy. Would gladly hang the piece on the garage wall if you're still interested in the practice!

[bigjae46]

What's your timing? I have 2 more roofs, hood and a mold, and a dashboard mold, and front thrust plate for George Hill to do - 3-4 more weeks for me?

I have about 20lbs of casting resin and it has a limited shelf life. So far, I plan to a compression mold for race seat floor mounts, jack pad, and maybe seat mounts. I should have plenty of material left to do your mount. If you want to give it a try then all I ask is to get rid of the ribs on the backside...I'd have to fill all of that stuff in which would take forever. Estimate about 2-4 weeks to get done. Again, it's going to cost less than $50 in materials...if that.

It would be an honor to contribute something to this build!

[D-O]

"Just went with what the eyecrometer said looked good."

I am using that one. Far superior to the old "calibrated eyeball."