Black & Tan 332iT

[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.

[Bry5on]

No problem, I'm 99% that hole is drilled there for that exact reason, just got lucky we can see the structure. 10mm higher and the structure wouldn't be seen, lol

I got real lucky then in this case! Definitely did not design with an impeding structure in mind.

[Obioban]

Ummm… never saw this matte screen protector technique before. Adding it to the project list!

[George Hill]

Thanks for taking the time to check for me!

No problem, I'm 99% that hole is drilled there for that exact reason, just got lucky we can see the structure. 10mm higher and the structure wouldn't be seen, lol

[karter16]

I think you should be fine everywhere except the lower (2) rear holes. Right below that hole I have drilled is some structure. With the calipers flat, tons of room, angle them down ever so slightly and contact.

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!

[George Hill]

I think you should be fine everywhere except the lower (2) rear holes. Right below that hole I have drilled is some structure. With the calipers flat, tons of room, angle them down ever so slightly and contact.

[karter16]

3) I got to installing the fender brace with these awesome new rivet nuts (definitely recommend). Fitting up:

Do you happen to know what the minimum clear air is on the other side of the bolt holes? I'm looking at riveting rather than bolting, but would need about 30mm of clearance to fully insert the rivets before crushing them. Wondering if it's clear air back there or additional layers of sheet metal etc. that might be in the way.

[Bry5on]

Also would the rubber resin grip the rotary encoder shaft well enough?


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I’ll keep thinking on this as I think all printing methods are out for one reason or another. Maybe a tiny mold and pourable silicone or TPU would do it. Mold the soft stuff right on to a plastic center

[karter16]

Farm out is the plan. Looks like they're about $30 a piece or so. Am I crazy for considering just printing the whole thing in 60A rubber-like-resin?

Also would the rubber resin grip the rotary encoder shaft well enough?


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[heinzboehmer]

Oof, thanks for sparing me the pain of that mistake. Now I'm trying to convince myself that this ABS plastic is good enough

Single data point, but my phone holder is printed in ABS and has seen many, many hours of direct sun. No warping or deformation that I can see.