Black & Tan 332iT

[Bry5on]

Quick and easy 4lb weight savings by removing the ski pass:

[heinzboehmer]

This looks way better:




Ribs in line with loads and has space for fasteners in the corners of the topmost + frontmost surfaces.

The above parts should weigh ~300g if made of 7075. Add in weight of welds + rivnuts and you're getting awfully close to the 428g weight of the machined part. So yeah, really only worth exploring this route if you want to drive cost down. Otherwise, I'd stick with the proven machined design.

[heinzboehmer]

The cost of drill bits and rivet nuts (or rivets), plus the cost of Heinz's design Just shoot a few strategically placed holes through it - although I think one of those holes would have to be right under the plastic windshield cowl which is not super great.

+1. Just add some holes and run some bolts through.

All of the red locations look like they'd be fair game in the sense that the bolts wouldn't run into anything in the chassis:




Blue spots would land under the cowl, like Bryson said. Maybe some (big) rivets in these spots would be low profile enough to not interfere with the cowl? You definitely want fasteners up front though, that's the part of the mount that most wants to peel away from the chassis.

If you're going through the effort of redesigning for bolting, I would be inclined to attempt a sheet metal version. You don't need material along the top if you're not bonding, so a "sideways J"-shaped piece might work (maybe add a couple weld-on ribs for extra strength). The resulting parts is probably gonna be similar weight, but should be much cheaper to produce.

Give me a sec, let me draft up something real quick, just to explain the idea better.

Edit: Super rough, but something like this:


Maybe rotate the ribs inwards a bit to have them be more in line with the loads.

Here's the machined version overlaid, for reference:

[George Hill]

The cost of drill bits and rivet nuts (or rivets), plus the cost of Heinz's design Just shoot a few strategically placed holes through it - although I think one of those holes would have to be right under the plastic windshield cowl which is not super great.

I wasn't sure if the bracket would need to be redesigned for a bolted method, but I guess as long as its bolted through something solid it should be fine.

Sounds like I need to fire up the printer and report back.

[Bry5on]

What do you think the manufacturing costs and easability would be for a bolt on piece?

I can have a heater case out of an E46 in under 1.5hrs 👀

The cost of drill bits and rivet nuts (or rivets), plus the cost of Heinz's design Just shoot a few strategically placed holes through it - although I think one of those holes would have to be right under the plastic windshield cowl which is not super great.

[George Hill]

If I ever want to change the layout of any of this, all I need to do is redesign the piece that bolts on. Achieves 90% of my maintainability/scalability/extendability goals with 10% of the install effort.

What do you think the manufacturing costs and easability would be for a bolt on piece?

I can have a heater case out of an E46 in under 1.5hrs 👀

[heinzboehmer]

What about if the heater case was removed?

Yeah, I think pulling the dash + the whole HVAC unit and using a right angle drill is the only way to make the install of a fully bolt in solution palatable.

Still didn't want to go through all that trouble, though

I compromised by designing the mount in two pieces, one that's bonded to the chassis and one that gets bolted to the first piece. If I ever want to change the layout of any of this, all I need to do is redesign the piece that bolts on. Achieves 90% of my maintainability/scalability/extendability goals with 10% of the install effort.

[George Hill]

Honestly I wasn't about to pull the engine to get that thing installed.

What about if the heater case was removed?

[heinzboehmer]

Hmm you raise a good point here. I'd kind of thought about it as being the same as epoxying the firewall bracket for the braces (e.g. kinda permanent). But you're right, the risk of a fender bender is much higher and removability would be an advantage in this situation. As you say might depend on how much damage and to where exactly, but still. Thanks for this, this is good for me to ponder!

Honestly, if I could have designed the firewall bracket to be bolted/spot welded in, I would have. Problem is that the access back there is abysmal with the car put together and I wasn't about to pull the engine to get that thing installed.

[karter16]

Fender benders are always a possibility, as well.

Hmm you raise a good point here. I'd kind of thought about it as being the same as epoxying the firewall bracket for the braces (e.g. kinda permanent). But you're right, the risk of a fender bender is much higher and removability would be an advantage in this situation. As you say might depend on how much damage and to where exactly, but still. Thanks for this, this is good for me to ponder!

[heinzboehmer]

A single M8 bolt would hold the entire car’s weight with margin (so 4.x G’s in compression). Bolts are fine

Yep! I remember you and my other ME buddies running me through that same exercise when I was designing the mounting point for the E86 braces. Was pretty eye opening to see the numbers down on the paper.

Yeah so to be clear I don't anticipate gaining anything in terms of strength, rigidity, etc. As Bryson says the bolts are more than sufficient (The sheer strength of the 07333 across those surfaces works out about twice what the 6x M8 bolts achieve, but it's irrelevant as the bolts are more than sufficient anyway). To your point heinzboehmer about permanence - I've tried to keep such things to a minimum, but where I do make such changes I try to do it as well as I can so I don't have to revisit it in the future. In my mind I've permanently modified the chassis at the point I drill holes in it anyway, so I figure if I'm doing these braces I might as well do them and never think about them again given they're hidden.

The thinking with epoxy bonding is that I'll have the 07333 to hand when I do the firewall bracket for the strut braces anyway, and if I do the same for the fender braces then I have a sealed join where I don't have to worry about corrosion prevention in the future. It's more of a "I might as well" as opposed to expecting any further gains out of it. Likewise thinking pop rivets rather than bolts in that they're then there and fixed for forever. In my defence over-thinking things runs in my family lol.

Ah, I fully misjudged your intentions with the adhesive, my bad! The corrosion argument makes total sense. It is quite nice to go overboard with something just so you never have to worry about it again.

Buuut just cause I like making other people's life's more difficult, the third side of the argumental coin is maintainability.

Even with an overboard install, there are things that remain fully out of anyone's control, which might warrant repair or replacement of the parts. Unbolting the part to fix some surface rust caused by accidentally leaving a bit of exposed metal is much easier than peeling/grinding/cutting the part off. Fender benders are always a possibility, as well.

Although at that point, you might be looking at replacing the entire chassis/car anyway, so maybe a moot point. Nonetheless, just offering up something more to overthink

[karter16]

Hmm, I'd be inclined to do the math and find max bearing load the bolted joint can take before committing to the structural adhesive.

Gut says you'll see very little (if any) gains with the adhesive, but you'll be stuck with a permanently modified chassis.

Maybe Bryson already ran the numbers.

Getting good numbers would require knowing a lot more about the associated structures unfortunately. You can approximate a sort of ‘worst-case-ish’ analysis since these fasteners are essentially in pure shear. What’s that analysis? A single M8 bolt would hold the entire car’s weight with margin (so 4.x G’s in compression). Bolts are fine

Apologies - am now talking about my car on Bryson's thread... Yeah so to be clear I don't anticipate gaining anything in terms of strength, rigidity, etc. As Bryson says the bolts are more than sufficient (The sheer strength of the 07333 across those surfaces works out about twice what the 6x M8 bolts achieve, but it's irrelevant as the bolts are more than sufficient anyway). To your point heinzboehmer about permanence - I've tried to keep such things to a minimum, but where I do make such changes I try to do it as well as I can so I don't have to revisit it in the future. In my mind I've permanently modified the chassis at the point I drill holes in it anyway, so I figure if I'm doing these braces I might as well do them and never think about them again given they're hidden.

The thinking with epoxy bonding is that I'll have the 07333 to hand when I do the firewall bracket for the strut braces anyway, and if I do the same for the fender braces then I have a sealed join where I don't have to worry about corrosion prevention in the future. It's more of a "I might as well" as opposed to expecting any further gains out of it. Likewise thinking pop rivets rather than bolts in that they're then there and fixed for forever. In my defence over-thinking things runs in my family lol.

[George Hill]

Or maybe jus a shorter rivet? 30mm past both pieces of metal is a huge rivet.

[Bry5on]

Hmm, I'd be inclined to do the math and find max bearing load the bolted joint can take before committing to the structural adhesive.

Gut says you'll see very little (if any) gains with the adhesive, but you'll be stuck with a permanently modified chassis.

Maybe Bryson already ran the numbers.

Getting good numbers would require knowing a lot more about the associated structures unfortunately. You can approximate a sort of ‘worst-case-ish’ analysis since these fasteners are essentially in pure shear. What’s that analysis? A single M8 bolt would hold the entire car’s weight with margin (so 4.x G’s in compression). Bolts are fine

[heinzboehmer]

Amazing - thanks George Hill that's super helpful! good to know re the lowest holes. My thinking is to structural epoxy for the shear load with rivets to deal with any peeling load. So even if I can't hit those lowest holes it should be fine. Thanks for taking the time to check for me!

Hmm, I'd be inclined to do the math and find max bearing load the bolted joint can take before committing to the structural adhesive.

Gut says you'll see very little (if any) gains with the adhesive, but you'll be stuck with a permanently modified chassis.

Maybe Bryson already ran the numbers.