heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

Oh come on, you've got to pocket them for weight savings!! You're killing me smalls

Infill!

But actually, I have no idea how that works when getting a part printed in metal...

[Bry5on]

Oh come on, you've got to pocket them for weight savings!! You're killing me smalls

[heinzboehmer]

This is great, flat stock brackets would be great, I would love some of those!!
Just as long as the bar would still clear, I'll do some measurements to get a rough idea.

I don't have any information to prove otherwise but I would think the completely flat surface would protect the towers better than the OEM setup with the much smaller surface area.

I would like to go all the way someday and triangulate but I think my D.S tower has moved unfortunately. I hope to find that I am wrong there.

Those brackets with the flat bottom are identical to stock, except for the flat bottom, of course. The bar will stay in the exact same spot where it is now, so should clear just fine!

Let me know if you want the .step files. Looking like ~$150 per side for printing the flat bottom stock brackets in aluminum:

[heinzboehmer]

Aaaand FEA looks promising. Most manufacturers that can print AlSi10Mg quote around 270-290 MPa for yield strength. I don't know if I believe that? But that's what I've been seeing.

Using that same 21 kN load as before, the analysis says that the "no bosses" part will see stresses that are right up there, but not past the upper end of the range, which is good!

Brace in tension:



Brace in compression:



As expected, the "bosses" version performs worse. There are a couple points where the stress exceeds the quoted yield strength, but the rest of the part is good.

Brace in tension:




Brace in compression:




Honestly not hugely concerned. The load that I ran the analysis with is the max load the part will see (since this is when the brace would buckle), so it's unlikely that the parts will be exposed to comparable loads during normal driving. I wonder if heat treating the printed part would help, but to be completely honest, I'm not gonna give it too much more thought, since I'll be using the "no bosses" version

Worth noting that this is just the load from the E86 brace. I have absolutely no idea what loads the stock bar (between the towers) sees, so I threw the same 21 kN load on the top surface and reran the analysis on the "no bosses" version just to see what would happen:



Surprisingly, not a huge difference. Part displaces differently, but max stress is very close to the previous number.

Now, the big question is fatigue. No good way to model this, but the mounts will eventually fatigue because they'll be made of Aluminum. It's just a matter of how fast that happens. Hopefully not until the end of the cars service life!

I think it's time to stop messing around and just get these parts ordered. I'm running analyses with made up loads, which is unlikely to get me anywhere useful. Also, I've been thinking and, surprisingly, I don't think I care if these parts fail? They're dead easy to swap out, the price of manufacturing is super affordable and I've been dying to give metal 3D printing a shot. If they do fail, there's always CNC 7075 or printed Titanium

[Cubieman]

This is great, flat stock brackets would be great, I would love some of those!!
Just as long as the bar would still clear, I'll do some measurements to get a rough idea.

I don't have any information to prove otherwise but I would think the completely flat surface would protect the towers better than the OEM setup with the much smaller surface area.

I would like to go all the way someday and triangulate but I think my D.S tower has moved unfortunately. I hope to find that I am wrong there.

[heinzboehmer]

I'm liking how the "no bosses" versions turned out!




And then I might have gotten a little carried away...



From left to right:

1. Scans
2. Stock recreations
3. Stock recreations, bosses replaced with a flat surface
4. Modified with E86 pickup points and slots
5. Modified with E86 pickup points, slots and bosses replaced with a flat surface

Here's the bottom of all of them, for completion:



Yes, I know, making the "no bosses" version of the stock brackets is completely useless for this project, but I had all the geometry right there! A few booleans, some cleanup and done. Couldn't help myself.

Cubieman FYI, since I think you were looking for something like (3) above?

[0-60motorsports]

This is getting exciting. Printed out a prototype in plastic to check basic geometry and clearances.








I gotta say, even this early prototype is looking amazing. Clearances still as tight as before, but everything fits just fine.

Eagle eyed viewers might notice that this is actually a right side bracket (with the clearance for the positive terminal) that's been mirrored over to look like a left side bracket. Wanted to get a feeling for the thickness of the bracket in the area around the positive terminal and at the same time wanted to check clearances against the engine wiring harness box. Doing it this way meant I only had to print out one prototype.

Worth throwing a pic of the other side up for comparison, soo much worse:



Here's some pics of the mostly-final CAD. Biggest difference is that the holes for the top hat studs are now slotted so that the top hat can move around for camber adjustments and the strut tower brackets can stay in place:






Same pics, but this time with the stock part (purple) overlayed for comparison. Gives a good sense of where I added material to take the extra loads:





Eagler eyed viewers might notice that this version does not have the "ridges" around the rearmost stud holes for the nuts to sit in. I tried including them for max stock-ness, but the slotted geometry means they interfere with the center "///M" trim piece, so will have to go without them

Next up is printing another prototype to test the slots and running a bit of FEA as a sanity check.

I also want to try extruding the bottom surface down to get rid of the bosses and make the part totally flat underneath. Not sure how well this will work with the existing geometry, but we'll see.

That's so cool


Sent from my iPhone using Tapatalk

[heinzboehmer]

This is getting exciting. Printed out a prototype in plastic to check basic geometry and clearances.








I gotta say, even this early prototype is looking amazing. Clearances still as tight as before, but everything fits just fine.

Eagle eyed viewers might notice that this is actually a right side bracket (with the clearance for the positive terminal) that's been mirrored over to look like a left side bracket. Wanted to get a feeling for the thickness of the bracket in the area around the positive terminal and at the same time wanted to check clearances against the engine wiring harness box. Doing it this way meant I only had to print out one prototype.

Worth throwing a pic of the other side up for comparison, soo much worse:



Here's some pics of the mostly-final CAD. Biggest difference is that the holes for the top hat studs are now slotted so that the top hat can move around for camber adjustments and the strut tower brackets can stay in place:






Same pics, but this time with the stock part (purple) overlayed for comparison. Gives a good sense of where I added material to take the extra loads:





Eagler eyed viewers might notice that this version does not have the "ridges" around the rearmost stud holes for the nuts to sit in. I tried including them for max stock-ness, but the slotted geometry means they interfere with the center "///M" trim piece, so will have to go without them

Next up is printing another prototype to test the slots and running a bit of FEA as a sanity check.

I also want to try extruding the bottom surface down to get rid of the bosses and make the part totally flat underneath. Not sure how well this will work with the existing geometry, but we'll see.

[heinzboehmer]

That would be solid modeling, versus shell (or surface) modeling. Some of the contours looked pretty 3D so I thought you might have been practicing shell. I find it much harder.

Oh! I've briefly played around with surface modeling and agreed, it's much harder. Something about the infinitesimally thin objects makes my brain trip out.

[Bry5on]

That would be solid modeling, versus shell (or surface) modeling. Some of the contours looked pretty 3D so I thought you might have been practicing shell. I find it much harder.

[heinzboehmer]

What style of modeling did you use for this one? Hilarious that the price is within a few bucks.

Hmmm, I don't know how to answer that question. I feel like I'm missing some formal eduction on this topic to be able to do so. I'd describe the style as stumbling through the design and backtracking a bunch until I have something that looks good

In all seriousness, the approach was to start with the two objects from a few posts ago and then extrude a bunch of cuts in them. Not entirely sure what style that would constitute.

Also, both stock brackets recreated now:



The cut for the positive terminal looks it would compromise the strength of the bracket a bunch. The thinnest point measures right at 3.6mm, which is not terrible, but still.



My plan is to get rid of the bosses on the bottom entirely and extrude the bottom surface of the bracket down all the way to the strut tower surface. Will yield another 3mm of material and more bearing area to take the extra load from the E86 braces. If anyone with the early style strut towers wants to recreate this, they could always give the version with bosses a shot.

And now onto the fun bit: modifying them!

[Bry5on]

What style of modeling did you use for this one? Hilarious that the price is within a few bucks.

[heinzboehmer]

Stock left bracket recreated:




This is mostly a 1:1 copy, but not quite. The one key difference is the geometry where the "ledge" with the two studs for the strut bar meets the main body of the bracket. The stock part has a huge chunk of material missing from that area and I opted to keep most of it and throw a big fillet at it. This should make it a little stronger with no impact on packaging:




Additionally, I did not include any of the weight savings features on the bottom of the part. I'm pretty set on 3D printing the final parts, so I can skip that altogether and gain the savings back with infill.

Next up is recreating the right bracket, which is basically the same, except it has an extra cutout for the positive battery terminal. After that, I can work on grafting the E86 brace pickup points onto the brackets and slotting the strut tower nut holes so that these work without camber plates.

Out of curiosity, I quoted a print in aluminum (AlSi10Mg, specifically) and it came out comically close to the price of the real BMW part:




Last thing worth discussing is that this CAD work was much more straightforward than I expected. I think the sheet metal approach was great for prototyping and validation, but this approach is much more inline with the rest of the parts that make up this project. I'm excited to get these done and manufactured. In hindsight, I should have gone down this path from the start.

[heinzboehmer]

Posted this in the E86 braces DIY thread a few days ago:

Alright I'm calling this project (including documentation!) 99.9% done. Just have two small TODOs to get through before I can call it 100%:

1. Weigh the modified cabin air filter housing/firewall plug + a stock cabin air filter housing and add to documentation.
2. Sand and paint the strut tower brackets.

Was thinking about the best way to approach (2) and quickly came to the realization that my hate for painting is so strong, I'd rather find a way around that altogether.

So, instead of spending a couple hours painting my existing brackets, I have decided to spend tens of hours redesigning the brackets so that they can be printed/cast/machined in one piece. Here's where I am right now:



Progress will likely be slow, since the existing brackets work just fine, but it's nice to have a low stakes project to work on whenever I have a few hours to sit on the couch. Will post more updates when I have them.

[heinzboehmer]

Love a good squeak fix. Haven't heard of Krytox before, interesting. Is that your go-to for lubricating door seals and stuff too?

Krytox is awesome, I keep a needle nose bottle of the 103 (thinner, runnier) and a tube of the 207 (thicker, more of a paste) handy in the garage. It's compatible with virtually all materials and has a wide temp range.

It's super inert and safe to use on rubber, but not sure I would use it for door seals. It never dries, so seems like it would get messy pretty quick in that area. I think a rubber safe lubricant that dries out is a better choice.