Best Material for Locomotive Frames

[peteski]

Must I worry about brass corrosion over time? It looks like the best material so far plus it's fairly common and relatively cheap. The only other thing I can think of would be silver. More expensive, but for small frames it is much more dense than brass. Maybe as a "premium option"

Not at all - brass will tarnish, but is pretty much corrosion resistant.  That is why it is used for fittings and other sea-going ship hardware. (where steel or aluminum would just corrode away).

You might be thinking of Zamak (which is the white metal used for making many die-cast items (like Hot Wheels cars or model loco frames). Zamak can be afflicted by "Zinc Pest" which corrodes the parts and makes them swell up and fall apart.

I have some small N scale models from Dapol (British manufacturer) where the metal weights are made from Tungsten. When I examined them they appear to be made from powdered (sintered) metal compressed into molds. I wonder of that process could be used for making complete frames (not just simple-shaped weights)?

[nickelplate759]

Not at all expert in metals, but here are criteria I would like to see met.

1. heavier than the material used by Kato and various Chinese contractors on behalf of Atlas et al.
2. Machinable by mere mortals with hand tools or a Dremel tool so we can kitbash it or find ways to squeeze in additional electronics or audio equipment.   (no tungsten)
3.  Stiff enough not to accidentally deform  (no lead, or pewter.  Probably not silver either)
4.  Not toxic enough to require special handling (no lead or uranium, depleted or otherwise).
5.   Easy to use as part an electrical circuit.


From what I know of alloys [typo corrected],  Brass would meet all these requirements, but is perhaps a little soft for requirement #3.  Bronze would be stiffer and maybe easier to use for electrical connectivity, but I believe it would be harder to modify with hand tools.

[peteski]

Not at all expert in metals, but here are criteria I would like to see met.

1. heavier than the material used by Kato and various Chinese contractors on behalf of Atlas et al.
2. Machinable by mere mortals with hand tools or a Dremel tool so we can kitbash it or find ways to squeeze in additional electronics or audio equipment.   (no tungsten)
3.  Stiff enough not to accidentally deform  (no lead, or pewter.  Probably not silver either)
4.  Not toxic enough to require special handling (no lead or uranium, depleted or otherwise).
5.   Easy to use as part an electrical circuit.


From what I know of allows,  Brass would meet all these requirements, but is perhaps a little soft for requirement #3.  Bronze would be stiffer and maybe easier to use for electrical connectivity, but I believe it would be harder to modify with hand tools.

While I have not done any stress tests, I suspect that brass is stiffer than the white metal currently used for model locomotives frames.  There is soft (annealed) brass and hard brass. I'm talking about hard brass.

[dcutting]

1. Heavier than the material used by Kato and various Chinese contractors on behalf of Atlas et al.
2. Machinable by mere mortals with hand tools or a Dremel tool so we can kitbash it or find ways to squeeze in additional electronics or audio equipment.   (no tungsten)
3. Stiff enough not to accidentally deform  (no lead, or pewter.  Probably not silver either)
4. Not toxic enough to require special handling (no lead or uranium, depleted or otherwise).
5. Easy to use as part an electrical circuit.

It looks like brass is indeed our animal. Very good way to sum it all up!

I'll be working over the next few days to finalize plans so that I can write up a post on the process I intend to use later this week.

David

[narrowminded]

Brass, bronze, and nickel silver are basically the same weight and cost is in the same order listed with nickel silver measurably more expensive and more limited in bar size selection.  Brass also has the broadest selection of standard sizes available and with such favorable machinability and solderability quickly becomes a good choice for these purposes.  If you're worried about finish it can be nickel plated at a reasonable cost.  Bronze might have a slight advantage when a part will be used directly as a bearing but brass is often plenty adequate when reviewed. 

Steel is slightly lighter and lead free pewter is over 15% lighter than brass.  I think many of the commercial train chassis are similar to pewter in weight or maybe a little less as I think they are basically one of the zinc/ aluminum alloys.  That is very castable at relatively low temperatures and as such can be cast in graphite permanent molds that are much easier to machine and therefore lower cost than metal molds, hold good tolerance similar to die cast, and have a decent life especially in hobby quantities (500-1500 pcs?).  It doesn't mean the molds are cheap but they are a lot less than fine steel molds.

Tungsten is basically twice as heavy as brass.  Tungsten is not machinable but there is machinable tungsten alloy that is 90% tungsten and as such is very near to the weight of pure tungsten (within 2 grams), still twice the weight of brass, but it is wildly expensive.  It is also not that great to machine but it can be done.  I have made tungsten wheels from this and they're nice but are very expensive as wheels go.  It is the material cost but is also the tool life.  Also material sizes are not as readily available so when trying to make component parts you're often stuck with buying much larger stock than a finished part might require and then having to machine away a lot more of that very expensive material and with the machining being tougher, all resulting in costs that increase exponentially every way you come at it, sufficient to cause convulsions when quoted to hobbyists.  Maybe for some components that use the material efficiently and are primarily cuts with sufficient room for rigid tools but expect costs to easily exceed 5x for the same part in brass, bronze, or even nickel silver and it can go right off the charts for some more intricate or heavily machined shapes. 

Hope that helps a little.

[Sokramiketes]

What about for lost wax casting? That's the direction I'm going in here.

I'm afraid that lost wax won't hold the tolerances you'll need for a locomotive chassis, unless you plan to do some post-machining.

[dcutting]

I'm afraid that lost wax won't hold the tolerances you'll need for a locomotive chassis, unless you plan to do some post-machining.

I'm referring to professional centrifugal or vacuum assisted techniques with shrinkage accounted for in the master.

[robert3985]

As you've already determined, brass is it.  That's why model train engines have been made out of brass for a very long time.

Cheerio!
Bob Gilmore

[metalworkertom]

http://www.alb-copperalloys.com/silicon-bronze/c65500/

http://www.olinbrass.com/resources/alloy-data-specifications/C26800-%28ASTM-B36%29-Yellow-Brass



http://www.concast.com/files/C83600.pdf

http://www.dura-barms.com/bronze/aluminum-bronze/c95400.cfm


From comparing data and experience I would say Yellow Brass . Conducts good , Casts easy , Solders well and Not hard to machine. I recommend picking up a Machinerys Handbook I find this book very handy for comparing all materials used by many of us in this hobby.

[mmagliaro]

Another vote for brass.   As Robert pointed out, it's no accident that brass locomotive imports have been made from , well... brass!   Those parts are not weak of flimsy (unless they are cheaply made and too thin.
I have no regrets about making my 0-6-0 locomotive frame from brass.  It was good to machine, solders well,
and it's strong.

If I were machining another one, I do think I would try nickel silver, however.  It is more conductive even when tarnished, and it is harder and stronger than brass.  I don't know if you can use it for casting, however.

[peteski]

If I were machining another one, I do think I would try nickel silver, however.  It is more conductive even when tarnished, and it is harder and stronger than brass.  I don't know if you can use it for casting, however.

You know Max, we keep on saying that nickel-silver oxides are conductive, but maybe it is just one of those things someone said years ago and it has been passed along through the generations of model railroaders (even by me)?  Where is the proof? I want to see the proof!  To be honest, I am a "doubting Peter". 

I did some Internet searches for proof but found none pointing either way (except for some anecdotal statements, usually in reference to model RR rails).  If you have some positive proof of the conductivity let me know where you found it.

I'm not singling you out as being incorrect - just being tired of this info being passed along  the model RR circles with absolutely no poof.

As far as casting NS goes - I believe that it can be cast - I have some automotive model parts which liik to be lost-wax cast from NS.

[Missaberoad]

You know Max, we keep on saying that nickel-silver oxides are conductive, but maybe it is just one of those things someone said years ago and it has been passed along through the generations of model railroaders (even by me)?  Where is the proof? I want to see the proof!  To be honest, I am a "doubting Peter". 

I did some Internet searches for proof but found none pointing either way (except for some anecdotal statements, usually in reference to model RR rails).  If you have some positive proof of the conductivity let me know where you found it.

I'm not singling you out as being incorrect - just being tired of this info being passed along  the model RR circles with absolutely no poof.

As far as casting NS goes - I believe that it can be cast - I have some automotive model parts which liik to be lost-wax cast from NS.

Well the empirical evidence often cited is nickle silver track requires less cleaning then brass track did. Which I found to be correct in my limited experience with brass track.

I guess the question that needs to be answered is, does this indicate that nickle silver oxidizes more slowly then brass or is the oxidization conductive?

Perhaps an experiment is in order...

[peteski]

Well the empirical evidence often cited is nickle silver track requires less cleaning then brass track did. Which I found to be correct in my limited experience with brass track.

I guess the question that needs to be answered is, does this indicate that nickle silver oxidizes more slowly then brass or is the oxidization conductive?

Perhaps an experiment is in order...

I know all about the benefits of NS rails. "Empirical evidence" is the problem for me. We know the track needs less cleaning, but is it really because the oxide is conductive?  That is my gripe. It might just be that NS oxidizes slower then brass, or maybe the layer of oxide is thinner or softer?  That would result in the same outcome without the oxide being conductive.  Actually, if the oxide was really conductive (in mili-ohms) then we would never have to clean the rails (except for light wiping of the greasy gunk).

[dcutting]

So the next question for me becomes... assuming I have an investment component, does anyone know of a cheap supplier that could get me the parts? I called one today and a run of one would cost $200-$300, with production being cheaper by a long shot. Problem is, I'm not up for a huge run as these are supposed to be custom frames as one-offs. No, I am not setting up a garage foundry. Sorry. Too much risk and too many $.

David

[Missaberoad]

I know all about the benefits of NS rails. "Empirical evidence" is the problem for me. We know the track needs less cleaning, but is it really because the oxide is conductive?  That is my gripe. It might just be that NS oxidizes slower then brass, or maybe the layer of oxide is thinner or softer?  That would result in the same outcome without the oxide being conductive.  Actually, if the oxide was really conductive (in mili-ohms) then we would never have to clean the rails (except for light wiping of the greasy gunk).

Agree with you completely in fact alot of what you say here is in my last response... 

Like I said we need someone with a curious mind and the intelligence to back it up to conduct an experiment... hint hint