3D printed 316L lugs thermal expansion and first build planning

[Hananas]

Hi everyone, I’ve been lurking around here absorbing information about framebuilding and also about 3D printed parts but I haven’t found anything about this yet so sorry if it’s been talked about but I just didn’t find it.

I’d love to build a modern allroad frame with classic looking lugs as my first frame and would like to print lugs for that, but I’ve been looking at some data that sort of worries me. I found that 316L has a lower rate of thermal expansion than chromoly, so wouldn’t that pose problems with the gap between the tube and the lug getting tighter as both materials heat up, making it harder for silver to flow in?

The reason I’d like to use 316L is that my first step in the direction of frame building was that I used a 316L printed custom coupler to convert my Surly Straggler daily driver to belt drive. That worked great, been using it daily for a year, worth about 3000-4000km without issues and the price of the prints was also super reasonable.

I’d use relatively big radii in the lugs to beef it up and reduce stress concentrations as much as possible.

Context about what I want to build:

The bike would be an allroad bike with 35 or preferably 38mm tire clearance, 12mm TA wheels and flat mount disc brakes. I still need to see if my lbs has tools to face and chase stuff, that’s an investment I’m not ready for.

I don’t know if it’s relevant but so far I’m thinking about Zona tubing because it’s relatively affordable, easily available in Europe and seems to fit my use case. TT 28.6mm 7/5/7, DT 35mm 8/5/8, HT 36mm 1.1, ST 28.6 0.8/0.6 (not sure if that’s right for me?) SS 14mm 0.7 CS ZON114OV425.

Geo context:
Reach 395-400mm (for use with 80-90mm stem)
Stack 570-580mm
Seat tube c-t 500-520mm
STA 73.5-74 deg
CS 410-420mm
HTA 72.5-73 deg

I’m 183cm, 65kg and currently ride a Surly Straggler 700C 56cm which fits me pretty well with a 75mm stem and gravel handlebars. I created the geometry numbers and chose tubing by keeping in mind what I like from the Straggler and what I like from my 1988 hardcore Columbus SLX race bike and what I miss in both.

[Daniel_Y]

Your lug modeling looks great! How did you get those cutouts shaped so nicely?

@Hananas

I found that 316L has a lower rate of thermal expansion than chromoly, so wouldn’t that pose problems with the gap between the tube and the lug getting tighter as both materials heat up, making it harder for silver to flow in?

Interesting. I never thought about that! I believe in reality it is OK. Lugs are not a press fit, and there have been many real-life examples of people having success with 3D printed lugs.

@Hananas

TT 28.6mm 7/5/7, DT 35mm 8/5/7, HT 36mm 1.1, ST 28.6 0.8/0.6 (not sure if that’s right for me?) SS 14mm 0.7 CS ZON114OV425.

This all sounds good to me!

@Hananas

The bike would be an allroad bike with 35 or preferably 38mm tire clearance.

The shortest chainstay I could comfortably get with 700x38mm was 418. Otherwise, the tire hits the seat tube.

I would start looking at the dropout and flat-mount solutions. I think that will be the biggest challenge for this build.

I don’t think it would be out of question to 3D print the non drive side dropout with flatmount. It will be expensive (~$100), but you know it would work!

[Hananas]

Hi Daniel, thanks for your feedback! Good to hear it won’t be a deal-breaker.

I used surfacing in Fusion to model my lugs, I have a bachelor’s degree in industrial product design with a minor in engineering which helps.

And yes… I’ve played around with making 3D models of 5 or 6 frames so far to get a feeling for it, and the only part I’m still really struggling to get right is the rear dropouts.

Maybe I should have sliding dropouts like the All-city super professional so I can have 410-415mm chainstays when running a road setup with 30-32mm tires and 420-425 for when I want to clear a 38. Then I can also split the challenge into a printed mounting system and separate dropouts with brake mounts/hanger. I’m okay with spending a bit extra on those parts to make my life a little easier.

[Luniz82]

Hi Hananas,

great first build, looking forward to the process!

@Hananas

I found that 316L has a lower rate of thermal expansion than chromoly

It’s the other way around, 316L has about 18.5 (10^-6/K), 4130 has about 13 between 20°C and 500°C.
This is the reason it is so difficult to weld large stainless sheet metal panels. It expands/contracts more, while having significantly less thermal conductivity. This leads to extreme buckling when it cools down.

So, if anything this means that the seat of your lugs will get more sloppy while heating up, and probably some residual tension when it cools down with the gap being filled with silver. I wouldn’t worry too much about it though…

[Hananas]

Ah I must’ve switched things up in my brain, or I was thinking about plug style printed parts when I looked at those numbers lol.
But cool thanks! At least it’s nice to know any residual stresses wouldn’t be trying to pull the silver apart.

-Han

[Spencermon]

If you’re looking at thru axle and dropouts to allow for chainstay length adjustment, here is some inspiration:

Egress Bikes - Leftover Tubes Hardtail Build

Thanks! It does consist of a few parts and ideally I’d like it a bit simpler, but I think I’ve pared it down as much as possible to still work with the concept I have in mind. I saw your first (unedited) comment and figured I’d respond to that last bit, but I have a feeling you have already figured it out. The hanger, bolt and washer are standard SRAM parts. The washers you noted are necessary to make up the thickness of the dropout - both are still needed when using a Transmission derailleur. …

I don’t know how to link the forum post so that it shows the images, but click on it to see the beauty.

[Hananas]

That is amazing, thanks for sharing! It’ll certainly help me design a system that works!

I’m so grateful for this forum, so much incredible information on here.