Making Proto:87 Drivers

[Jake S.]

Hey all,

I'm in the process of designing a steam locomotive to scratchbuild, using Kalmbach's Build a Brass Steam Locomotive as a reference guide. While I've never done anything like this, everything shown in the book seems to be relatively doable, and it all seems like it would be a very fun and rewarding experience, even if I make mistakes or fail along the way. Since I will be scratchbuilding and currently don't have an established layout, (curse you, apartment living!) proto:87 seems like a great option to indulge my obsessive attention to detail. While proto:87 wheelsets for freight cars, tenders, and diesel locomotives are readily available, (albeit somewhat pricey) proto:87 steam locomotive drivers are hard to come by pretty much nonexistent. I've found some spare brass drivers on Green Way Product's brass builders corner, and noticed that the core of the driver is brass, while the tire is some other material, presumably one with better electrical conductivity. (Nickel silver, I'd guess.) This makes me think that it should be possible to press a brass driver's core out of its tire, and simply fit a new proto:87 tire. I went ahead and designed a driver tire with the proto:87 flange profile in Autodesk Fusion360, stuck a few of them on a rudimentary sprue, and uploaded them to my Shapeways account to see if it was feasible to have them cast. As it turns out, it is!

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8 72" proto:87 tires on a sprue. I went with the sprue concept because there is a minimum charge for each cast object regardless of size, and I wanted to make this as economical as possible.

Only thing is, my options are pretty limited. While this design could be printed and cast in any of the metals Shapeways offers, the only really sensible selections are brass, stainless steel, and sterling silver. Brass isn't great though, because its color is totally wrong for a driver, and even once painted will look awful thanks to the tread having to be unpainted for electrical pickup. Yuck. Brass is out.

That leaves stainless steel and sterling silver. Both are of the appropriate color, but both also have their advantages and disadvantages.

Stainless steel's main pro is that it is cheap, it's $12 for that sprue of 8 drivers, what a steal! The problem is that it's a very hard metal (so cutting away the sprue and filing down the nibs may be difficult.) and it also has relatively poor electrical conductivity, which is kind of necessary.

Sterling silver's main pro is that it is very electrically conductive and easier to work with when removing tires from the sprue and filing them down to be fitted to a driver. The downside is of course... price. More than 5x the cost of the stainless steel tires. (Though still a price I'd be willing to pay because while expensive, it's not THAT unfeasibly exorbitant.)

So as it stands, I've reached an impass and would like some advice. What do you guys say: steel or silver?

As time goes on, I'll continue to update this thread with my progress on this project.

[Lemosteam]

IMHO, none of the above.  If you plan on doing machining anyway, just go buy rods or tubes of nickel silver. @narrowminded will have some thought on this I am sure.

1- brass is soft and will wear quickly on the nickel silver rail

2- printed stainless has three issues for what you are trying to do (I have a tender frame made of this material for my loco kit)
        -There are shrinkage factors in all three dimensions and the sprue may worsen this
        -The material is not pure stainless and not a hard as you might think- it is printed with stainless pellets, held together with a resin, and then the sintering process replaces the resin with bronze- this from a direct sources
        -The Shapeways cleanup process is somewhat random, ground down areas, rough areas, extra material in areas, etc.

3 Silver is simply too soft.

[Jake S.]

Thanks for the input! These are exactly the sort of things i need to know. So stainless steel is clearly out, but is sterling silver really too soft? Obviously fine silver would be, but I hoping the sterling silver might be okay since it's an alloy which is specifically made to be harder.

Unfortunately machining is likely not an option for me unless there is some Shapeways-like service for outsourcing machining. I'm actually not half bad with a lathe, but the expense, size, and weight of even a very small lathe is not something I can overcome in my situation. (Again, apartment living.  )

Anyone else have any ideas? I've thought of casting, but that would likely be subject to shrinkage eproblems too, and also not doable in my situation.

[C855B]

Machining will be absolutely necessary regardless of material. 3D printing processes simply are not capable of the precision roundness needed for wheels, and John already mentioned the relative imprecision with the standard post-printing processes. I guess it would be possible to make rough billets this way, but you would still need to chuck them into a lathe for final profiling and roundness.

See Max's thread about turning tires on a scratchbuilt steamer, among a zillion other "do it this way for best results" examples.

[peteski]

John, I have to disagree with you about brass being too soft. Majority of N scale metal wheels are made from brass - sometimes even unplated - just blackened. The Walthers Mallet's tender wheels are just blackened brass. Most manufacturers do plate the brass wheels with some silver color metal - possibly nickel-silver or nickel. But that plating wears off, exposing the brass colored metal underneath it. Atlas locos are a prime example. I have lots of those wheel-sets where the tread is brass-color.  But Kato wheels do not seem to show any brass color, even on wheels with lots of wear. I wonder if they use nickel-silver for the wheels.

[Jake S.]

Machining will be absolutely necessary regardless of material. 3D printing processes simply are not capable of the precision roundness needed for wheels, and John already mentioned the relative imprecision with the standard post-printing processes. I guess it would be possible to make rough billets this way, but you would still need to chuck them into a lathe for final profiling and roundness.

See Max's thread about turning tires on a scratchbuilt steamer, among a zillion other "do it this way for best results" examples.

Looks like a a few weeks of double shifts and a $900 mill may be in my future then. And probably shoring up my flat-pack "work bench." Or maybe (probably) building a new work bench entirely.

Oy, what have I gotten myself into. At least there are a ton of things I can do before getting tires done is a priority.

Thank you kindly for all the advice and resources. If there are any other resources you all know of that I may not, I'd love to see them.

[Lemosteam]

John, I have to disagree with you about brass being too soft. Majority of N scale metal wheels are made from brass - sometimes even unplated - just blackened. The Walthers Mallet's tender wheels are just blackened brass. Most manufacturers do plate the brass wheels with some silver color metal - possibly nickel-silver or nickel. But that plating wears off, exposing the brass colored metal underneath it. Atlas locos are a prime example. I have lots of those wheel-sets where the tread is brass-color.  But Kato wheels do not seem to show any brass color, even on wheels with lots of wear. I wonder if they use nickel-silver for the wheels.

Ok can't argue with that but a driven wheel takes a lot more abuse than a non-driven wheel.

There is a reason that Max plated his brass driver tires in Nickel.

[CVSNE]

Some good techniques for making drivers here -
http://www.proto48.org/p48_art_05.htm

I agree with previous posters, I don't think 3d printing is going to produce a consistently round, durable set of drivers.

Good luck,

Marty

[peteski]

Ok can't argue with that but a driven wheel takes a lot more abuse than a non-driven wheel.

There is a reason that Max plated his brass driver tires in Nickel.

As I mentioned, the Atlas diesel models have plated brass wheels. The thin plating wears off after a while, then it is only brass left and the model still performs well (except for needing the wheels to be cleaned more often).  Those are all driven wheels.  I have serviced many Atlas diesels with no plating on the wheels left.

[Jake S.]

@CVSNE, That was a very interesting article, thank you! I'll be sure to check the Proto:48 page for more cool stuff. Originally I was planning on having Shapeways do them in brass, and doing an interference fit by heating the tire up like on the prototype, however this thread makes me unsure that that would be an option. Does anyone know if Shapeways brass parts are cast or sintered like the stainless steel? Also, do you guys think a FUD/FXD wheel center would work? (Albeit, it would kind of negate the whole thing about building a brass engine, but I digress.) What about resin casting?

I know I'm probably asking a lot of silly questions, but I'm new to this and I'm the kind of person who likes biting off a little more than they can chew. Life's more fun that way.

[peteski]

@CVSNE, That was a very interesting article, thank you! I'll be sure to check the Proto:48 page for more cool stuff. Originally I was planning on having Shapeways do them in brass, and doing an interference fit by heating the tire up like on the prototype, however this thread makes me unsure that that would be an option. Does anyone know if Shapeways brass parts are cast or sintered like the stainless steel? Also, do you guys think a FUD/FXD wheel center would work? (Albeit, it would kind of negate the whole thing about building a brass engine, but I digress.) What about resin casting?

I know I'm probably asking a lot of silly questions, but I'm new to this and I'm the kind of person who likes biting off a little more than they can chew. Life's more fun that way.

Brass is done using the lost-wax casting method.  For all the details see https://www.shapeways.com/materials/brass . I highly recommend that you go to the materials landing page https://www.shapeways.com/materials then click on each material you are interested in. Al the technical details and production details are provided there for each.

[Jake S.]

Brass is done using the lost-wax casting method.  For all the details see https://www.shapeways.com/materials/brass . I highly recommend that you go to the materials landing page https://www.shapeways.com/materials then click on each material you are interested in. Al the technical details and production details are provided there for each.

Ah, thanks. I'd been to the materials page for brass, but only to check the minimum feature dimensions for my designs. I missed the bit about lost-wax casting.

[CVSNE]

Some company - who's name escapes me - offers drivers made from wax masters that I believe he 3D prints and then casts. Look around on the Proto48 site, since it's likely mentioned there.

It's also possible it's on Matt Forsyth's web site -

http://mattforsyth.com/?paged=2

BTW, be prepared to be amazed at a Proto 48 I-class PRR Decapod.. impressive work to say the least.

Marty McGuirk
Manassas, Va.

@CVSNE, That was a very interesting article, thank you! I'll be sure to check the Proto:48 page for more cool stuff. Originally I was planning on having Shapeways do them in brass, and doing an interference fit by heating the tire up like on the prototype, however this thread makes me unsure that that would be an option. Does anyone know if Shapeways brass parts are cast or sintered like the stainless steel? Also, do you guys think a FUD/FXD wheel center would work? (Albeit, it would kind of negate the whole thing about building a brass engine, but I digress.) What about resin casting?

I know I'm probably asking a lot of silly questions, but I'm new to this and I'm the kind of person who likes biting off a little more than they can chew. Life's more fun that way.