[smashysmashy]

That’s a good place to start
I made a stainless lugged stem (from Llewelyn’s lugs) and it eventually developed a crack where the single bolt held the bar.
But it looked cool

Cool. The crack was just on the bolt boss? Which side, thread or through hole? Can't fine a clear pic of that one, but i seems to not have much of a fillet around the boss. Mine has a bit more meat, so hopefully not a problem.

 

[smashysmashy]

Hmm.

I also notice he put some reinforcing ribs on the sharp tips to manage distortion in casting. Smart. I think I will add that. Easy to file down.

 

[#/er]

Also, if you plan to use a drop bar, the clamp will need to have a narrowed area so the curves of the bar would fit thru (usually done on the bottom by the fixing bolt)

 

[smashysmashy]

Also, if you plan to use a drop bar, the clamp will need to have a narrowed area so the curves of the bar would fit thru (usually done on the bottom by the fixing bolt)

It's 31.8, so that is no longer required (at least for MY bar, some others have more funky shapes).

Definitely needed a pop top with my older 26mm easton bar as it had angular bends.

 

[smashysmashy]

Final stem design. Needs some supports and ribs added to print. should still stay in around $44-$46. Total stem 70mm weight with tube, screws and paint will be about 205-215 grams. Not super light, but not bad for steel either. My Thomson x4 70mm is 140 ish grams.

 

[plummet]

I'm a machinist. Fits where only blue light can pass is my preferred clearance. But that's not relevant here. Bikes seems to be measured in plus or minus "close enough, I'm going for lunch". Or in the case of GT "I stopped caring after the tack welds"

Anyhow. I think we are going to do brazed lugs. So lets go for bike type and spec then:

• Gravel/XC geometry blend for drop or flat bar (to replace my GT Grade)
• 44mm head tube (just a plain tube with the lugs over it
• Tapered steerer (paragon most likely, seems pointless to make my own on the lathe)
• T47 bottom bracket shell (paragon again) INSIDE a special bottom bracket junction lug.
• Dropper and Di2 routing printed inside lugs (hoses will be external cause F that).
• 12mm through axle 100/142
• Replaceable hanger also printed in stainless.
• Post mount brake mounts
• Since I wont actually use the dropper, I can use my cut down 120mm long thomson 30.8 post with an extended seat tube. (I've seen this in steel, but I question it's wisdom)

For tubing I am leaning to columbus life which runs about about $200 for the set. 38mm down tube, 32mm seat tube for dropper fit, 32mm top tube. Round non tapered stays.

So, print wise, we need:

• 2 head tube lugs
• bottom bracket "lug"
• seat tube junction lug
• fork crown
• fork drop outs with brake mount integrated
• frame drop outs with brake mount integrated
• derailleur hanger
• head badge
• seat collar
• fittings and braze ons
• steerer brazed in "star nut"
• lower brazed on steerer fitting to take a printed nylon di2 battery holder. ( I put the battery in the steerer)

So, 9 main parts plus some tiny ones, about $100-$175. Reference price is about 25 cents a gram for the prints and in most cases they will be "net shape".

Now, to draw up the geo.

Sounds like you have a plan. Go do it and show us.

PS not all 3d metal printing is equal. Does you crowd publish material properties? Here's the ram 3d stuff. Looks like they are getting 500mpa out of 316...
The main concern i'd have with cheap 3d printing is that the quality/strength of the print is not good enough. My teeth do not want to meet the stem because the steerer tube tore off.

https://www.ram3d.co.nz/wp-content/uploads/2023/02/DJ13632_Ram3D_Templates_MaterialProperties_v4.pdf

PS. Yeah, tolerances on non machined stuff will seem MASSIVE to your machinists brain.

 

[plummet]

Made up a stem. $44 total for both printed parts. Perhaps a good part to order first and try to clean up and braze.

View attachment 2044968 View attachment 2044969 View attachment 2044970 View attachment 2044971

why not print the whole thing?

 

[smashysmashy]

why not print the whole thing?

Cause then it would not be a good test for brazing.

Would also be heavier as the walls will need to be thicker with internal support.

For the prints it is, as mentioned, SLM process. It is about 500ish tensile, 400ish yield after heat treatment which is part of print process. They use all the same printing machines anyone else does (aren't that many options), they just have dozens running only stainless and have set a super cheap price I assume to get business early on. Some people on Youtube have done sample strength tests on it and it backs up the material data sheet claims.

For reference for other people curious where it fall in the list of bike materials: Normalised 4130 tubes are in the same range. Heat treated 4130 (most of your better bike tubing) is much stronger. 7075 T6 is similar strength to the printed stainless. 6061 is around 60% of the strength. Lastly a plain old bar of 316 stainless from the metal store will be much softer and weaker as it comes annealed. I assume stainless cast lugs are in between "as cast". I also have no idea how the 900f brazing temperature will change the strength, it may partially anneal it.

This is why brazing seems the best starting point, because we already know exactly how a stainless brazed lug works in use, and this should be the same. With bonding, there is a lot more to test and work out before winding up with an actual frame.

 

[plummet]

Personally I wouldn't mix 316 and 4130. That's a recipe for galvanic corrosion. But if you are in a dry, cold inland location your will probably get away with it.

 

[smashysmashy]

Personally I wouldn't mix 316 and 4130. That's a recipe for galvanic corrosion. But if you are in a dry, cold inland location your will probably get away with it.

There are thousands of frames with stainless lugs, 304 or 316. Does not seems to be a significant issue.

 

[smashysmashy]

Models prepped to print. I added in a SLS nylon print for mitering. Slip it over the tube, spray paint the exposed area, then cut the painted area away, most likely with a little dremel grinding wheel to get right to the line. Seems plausible anyway. On the main tubes of a frame ill do the same thing, although most likely I will try to CNC the mitres.

$42 for the 2 steel parts. $2.50 for the mitre sleeve. I wont order them until I get my test prints next week. Gotta see how they turn out.

 

[CHONBoy]

Definitely test your pieces out real well for safety's sake. 304 and 316 lugs have been used in the past but I think a lot of the 3D printed SS on bicycles is actually 17-4 which is way way stronger. I imagine 3d printed parts being more prone to failure. I could be wrong though.

 

[smashysmashy]

Definitely test your pieces out real well for safety's sake. 304 and 316 lugs have been used in the past but I think a lot of the 3D printed SS on bicycles is actually 17-4 which is way way stronger. I imagine 3d printed parts being more prone to failure. I could be wrong though.

Obviously you need to test.

304 and 316 are standard cast lugs on thousands of bikes. They work fine. Lugs on a frame are kinda like a built in fixture. The tubes are actually still brazed to each other with a miter. You are not relying on the lug itself for much tensile strength. The exception becomes the bottom bracket, and drop outs, brake mounts, etc, which you need to size accordingly. The print is about half the strength of 4130 so you can't simply copy a paragon part machined part. More plausible to take inspiration from the proportions of a 7075 part.

3D prints are not more prone to failure. This isn't your home plastic printer where the layers are not bonded well and they are full of air. An SLM print is 99.9% just solid stainless steel just like a casting.

My test prints are in the mail, tracking says friday. This will be interesting

 

[CHONBoy]

Obviously you need to test.

304 and 316 are standard cast lugs on thousands of bikes. They work fine. Lugs on a frame are kinda like a built in fixture. The tubes are actually still brazed to each other with a miter. You are not relying on the lug itself for much tensile strength. The exception becomes the bottom bracket, and drop outs, brake mounts, etc, which you need to size accordingly. The print is about half the strength of 4130 so you can't simply copy a paragon part machined part. More plausible to take inspiration from the proportions of a 7075 part.

3D prints are not more prone to failure. This isn't your home plastic printer where the layers are not bonded well and they are full of air. An SLM print is 99.9% just solid stainless steel just like a casting.

My test prints are in the mail, tracking says friday. This will be interesting

interested to see how this goes as well! I think you might be onto something pretty cool

 

[smashysmashy]

interested to see how this goes as well! I think you might be onto something pretty cool

I hope so, haha.

A few people seems to have tried this before, (316 stainless SLM) so it is not totally new territory. But is was always unreasonably expensives. $100's of dollars per lug etc. People would make 1. it would work or fail, and that would be it. At $15 you can make revisions and tests and wind up with a proven "production" part I am hoping. Not that I intend to produce them.

The biggest failures I see online with prints on bikes are just from poor design and not because the print process or concept was bad. You tend to see big thin hollow structures, and while FEA is done, they leave too little of a safety factor. Obviously they are trying for ultra light weight, etc. With the lugs, I will be happy to simply replicate the proven performance of a cast lug set in a way that you can customise each lug for each frame for minimal cost.

 

[plummet]

Exciting sh1t.

Side note. I'm seriously thinking designing and 3D printing TI cranks.

 

[smashysmashy]

Exciting sh1t.

Side note. I'm seriously thinking designing and 3D printing TI cranks.

Someone did. uh. cant remember who. Last year nahbs maybe? In principle they should be awesome, but at $2-3k its not something easy to experiment with.

 

[plummet]

Someone did. uh. cant remember who. Last year nahbs maybe? In principle they should be awesome, but at $2-3k its not something easy to experiment with.

Printing ti from my supplier isn't as expensive as yours. I'm expecting $300 to $500 nzd.

Got to find time to design them. Not a 5 min exercise and I'm riding my new bike every spare second I have.

 

[smashysmashy]

Woo. Very promising for thin walls and details, although the big concern for the lug will be supports and resulting distortion.

 

[smashysmashy]

So the stainless hanger is 20g. and the Pilo cnc'd aluminium one on the bike is 9.5g.

Ordered a tap and will install it on the frame tomorrow and try to align it and see how it behaves.