Brass vs Bronze for heat sink backing?

[Xyphota]

I'm going to fabricate a heat-sink for a bicycle seat tube similar to the one in the link below. It'll will be fitted inside 0.035" wall thickness chromoly tubing while it is welded up. I have not machined any brass or bronze before, is there a particular flavour of either brass or bronze that people think would be appropriate for this use case? Or any flavours to definitely avoid?

Fixture: Heat Sink Seat Tube — TI CYCLES FABRICATION

TiCyclesTubes design Complete units include draw bolt, purge fitting, one brass insert, and all hardware as shown.

www.ticycles.com

 

[Proxule]

Leaded brass is 100% machinable - On the machinability reference chart.
Also being easier to locate and cheaper to buy vs, bronze, ( manganese, phosphorus or beryllium bronze )

I would say your choices are as vast as you want, Throw in some pure copper to your choices. As brass and bronze are majority copper.

My exp in bronze has been bearing bronze, ( leaded ) and machines very easily and the surface is gorgeous with positive rake tooling.

Others can insert their opinions

Gluck

 

[Janger]

Have you priced the brass? I believe it is very expensive. Anyway according to engineering tool box (below) brass is not an especially good heat conductor - better than steel but aluminium is twice as good and copper almost 4 times better. Please post your progress @Xyphota sounds like an interesting project. Is the air fitting in the commercial one to keep the heat sink cool? Do you make bicycle frames or aspire to?

Heat Exchanger Materials - Thermal Conductivities

Typical heat exchanger materials and their thermal conductivities.

www.engineeringtoolbox.com

 

[Xyphota]

The air fitting is to provide back purging of argon to the welded joint. Its good practice on steel, and necessary on titanium from what I've read. I think copper would probably be best material choice for the heat wicking, and it's similar in price to brass, but I've read copper is quite challenging to machine? Maybe I'll do a bit more research on that lol.

Currently in the aspiring phase to build some bikes, I'm just about to start my first one

 

[Proxule]

The air fitting is to provide back purging of argon to the welded joint. Its good practice on steel, and necessary on titanium from what I've read. I think copper would probably be best material choice for the heat wicking, and it's similar in price to brass, but I've read copper is quite challenging to machine? Maybe I'll do a bit more research on that lol.

Currently in the aspiring phase to build some bikes, I'm just about to start my first one

My exp is positive rake tooling like CCGT or DCGT inserts for copper. The chips fly off nice and curly and leaves a mirror finish. With appropriate RPM of course, Nothing difficult about it at all!

I have heard welding inside a purged fume hood for titanium, but never for steel. Interesting

 

[trevj]

If choosing between brass and bronze, choose brass, for ease of machining!

Some bronze alloys rival some particularly miserable stainless steels, for issues to adapt to!

In the shops I worked and welded in, we had all manner of backing gas fixtures and blocks, all made of brass, for ease of machining. Copper may be slightly better for heat transfer, but not cheaper to get, for the most part.

 

[Xyphota]

I have heard welding inside a purged fume hood for titanium, but never for steel. Interesting

The back purge is a good idea on bicycles because the steel is so thin, and there is a high likely-hood of melting the back side of the tube. Are there any problems drilling copper? I'll likely end up drilling a 1/2" through-hole that is 4-5" long

If choosing between brass and bronze, choose brass, for ease of machining!

Some bronze alloys rival some particularly miserable stainless steels, for issues to adapt to!

In the shops I worked and welded in, we had all manner of backing gas fixtures and blocks, all made of brass, for ease of machining. Copper may be slightly better for heat transfer, but not cheaper to get, for the most part.

I'll probably end up purchasing this from metal supermarkets and the price for copper is only about 15% more it looks like. I might end up needing 4 or 5 of these so I'll price it out

 

[trevj]

The back purge is a good idea on bicycles because the steel is so thin, and there is a high likely-hood of melting the back side of the tube. Are there any problems drilling copper? I'll likely end up drilling a 1/2" through-hole that is 4-5" long


I'll probably end up purchasing this from metal supermarkets and the price for copper is only about 15% more it looks like. I might end up needing 4 or 5 of these so I'll price it out

Drilling can range from easy to miserable, depending on, it seems, the phase of the moon and the way you hold your lips at the time... Seriously, never had the same experience twice. Have strong suspicion that how work hardened (from being rolled to shape at the mill), or how annealed (from exposure to high heat) the bar stock was.

Tapping the stuff was absolute hell, up until we used animal fat as a lube. Try butter, or dip the tap in high fat coffee cream. Bacon fat will likely work at least as well. Real lard too, if you can get it!

Did a project that required several hundred tapped holes on a grounding strap 1/4 inch x 2 inch, by 6 feet long, in an air traffic control tower radio room.

For simple back purge fittings, I suggest making some plugs from aluminum, drilled and tapped for gas fittings, and with a couple O-rings to seal around the inside surface of the tube. Cheap as chips to make, and you can make them as required, depending on your tubing sizes used. Just an idea. Less dicking about than dealing with aluminum tape.

 

[PeterT]

I'm not a copper expert but have experienced some if its not so fun surprises. It can be very grabby during drilling especially larger holes, so dub the edge angle like for brass. Tapping can be challenging too, things appear normal & then it squeaks & wont let go. Not sure if its gumminess or local friction heating. I didnt have swarf extracting taps back then, those might work better. Turning is pretty straightforward with very sharp tools. On slender profiles best to err on using tailstock support when possible & not push the stick out ratio. WD-40 works pretty good as a cutting lubricant. And different grades of copper may well behave differently so maybe check that out. I think my unlabeled copper Mysterium from Metal Supermarket could have contributed to the excitement.

 

[Rauce]

The nice thing about bronze is that you can get it in hollow bar form to save you drilling it out.

The difference in heat sinking ability between brass/bronze/copper/aluminum isn’t critical in this application. It’s more about the heat sink providing outward pressure to prevent the tube from ovalizing and dissimilar material so it doesn’t get welded in place.

I’ve made 5 of these, 31.6mm and 27.2mm for seattubes, 34mm and 44mm for headtubes and one for BSA BB shells. I also have the paragon ones for T47 BB shells.

I wouldn’t sweat Argon purge on steel even if its thin. There are plenty of pros who don’t bother. I visited a builder in the US who’s been building 100+ frames a year for the last 3 decades and has never back purged on steel.

 

[Susquatch]

Sometimes I hate this forum.

I have a mountain bike I have not driven in years. It gives me scrotorectal eruptions. The seat was made for normal humans. I want to put a big tractor seat on it to cushion the vitals. But that will require a new seat post and some fabrication.

I hadn't even thought about it till you guys started yakking about bike tubing. Now I have another damn job to do.

 

[Dan Dubeau]

Make me one too, would ya? I started biking again with the kids this past year, and found bike seats aren't as comfy as a portly adult as they were when I was a scrawny kid......Stamina isn't there like it used to be either......

 

[Xyphota]

The nice thing about bronze is that you can get it in hollow bar form to save you drilling it out.

I’ve made 5 of these, 31.6mm and 27.2mm for seattubes, 34mm and 44mm for headtubes and one for BSA BB shells. I also have the paragon ones for T47 BB shells.

Do you know what flavour of bronze you used? 'Bearing Bronze' tubes on mcmaster (https://www.mcmaster.com/bushing-stock/material~bronze/) is about 1/2 price of the brass and copper, so maybe I should go this out.

I did purchase the paragon BSA bb shell,, so I have some dimensions to use for inspiration.

 

[Xyphota]

If you ride you bike for less than 15 minutes at a time and are pretty casual about it, you'd probably love a big comfy seat. If you ride for longer than that, a highly padded seat might actually be more uncomfortable than a less padded one.

 

[Rauce]

Do you know what flavour of bronze you used? 'Bearing Bronze' tubes on mcmaster (https://www.mcmaster.com/bushing-stock/material~bronze/) is about 1/2 price of the brass and copper, so maybe I should go this out.

I did purchase the paragon BSA bb shell,, so I have some dimensions to use for inspiration.

932 I’m pretty sure. It has a bit of lead in it so keep that in mind. I got it at metal supermarkets. For a couple of them I used scrap brass I got from work.

I used a 15deg angle (30 included) on the cones. Did the keyholes and slots with endmills (faster and more forgiving than a slitting saw). And when I turned the bronze center I took it to 0.3-0.5mm smaller than nominal to make removal/install easier.

 

[Susquatch]

If you ride you bike for less than 15 minutes at a time and are pretty casual about it, you'd probably love a big comfy seat. If you ride for longer than that, a highly padded seat might actually be more uncomfortable than a less padded one.

So 10 minutes would prolly work fine then?

Zero interest in one of those skinny seats. I like my deep rumbly voice just fine.

 

[Rauce]

So 10 minutes would prolly work fine then?

Zero interest in one of those skinny seats. I like my deep rumbly voice just fine.

Don’t confuse padding and width.

Too much padding can put more pressure on soft tissue instead of supporting your weight on your sit bones. Generally the more upright you sit on your bike the wider your seat should be.

 

[Xyphota]

I've pulled the trigger on the 932 Bearing Bronze from Mcmaster. It is 7% lead, what extra safety precautions should I be taking while turning this in my garage?

 

[Proxule]

Yup your typical bearing bronze, with lead content as you mentioned, I have machined quite a bit of this stuff for bushings.
Turns like a dream - but makes a awful mess, the chips fly off, like an explosion. With positive rake tooling.

I have never worn PPE for turning the bronze, I assume its risky wile its being poured vs. machining. I do not know. I will update you in 20 years.

 

[Dan Dubeau]

Don't lick it, and you should be fine.