Best Material for Locomotive Frames

[metalworkertom]

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).

I found this that seems to explain this well. Although it shows that the oxide is not really conductive but very thin and allows contact easily . Which in the context of this thread that Nickel plating can be very beneficial to parts we do want conductive.


http://www.mdpi.com/2075-4701/2/4/450/pdf

[Sokramiketes]

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

Maybe I'm confused, but centrifugal casting of the brass itself?  I'd call that spin casting.  Like the parts from Showcase Miniatures, and usually in white metal.

When you said lost wax, I pictured shooting wax in rubber molds, treeing the waxes, surrounding in investment, and pouring brass into the mold. 

Shrinkage can be accounted for in the lost wax process, yes, but lost wax brass parts needing to hold tolerances for N scale mechanisms is where I started getting confused.  The root of the tolerance in this process is a rubber mold.  Maybe Bob has a better handle on what tolerances can be held, since he was doing a bunch of lost wax detail parts.  But in my experience working with a jewelry firm on this Z scale flatcar, there was a bit of fluctuation in the straightness of the parts and overall dimensional stability.

[Sokramiketes]

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

Valley Brass & Bronze (CA) will take your wax shots and turn them into brass, if that's what you're asking.  If you're planning on treeing them and setting in investment as well, which is doable, I'm sure they'd pour the brass.

Best Cast (NJ) is another option on the other side of the continent.  I've had them run full production from 3D cad to brass parts, and they are good to work with.

[peteski]

I figured that it might also be worth mentioning at this point that Shapeways will also take your 3D design and cast it in brass. According to their description of the process, they print the part in wax then investment-cast it (lost-wax casting). But they are quite pricey.

[robert3985]

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

First, how big is your run?  Second, how large is the part?

If your run isn't too big and if your part isn't too large, a local jewelry store or rock shop may be able to do your casting for you if you supply them with the wax masters for much cheaper than $200-$300 for one run.

The way to get the price down would be to make your masters from machinable wax, taking into account the shrinkage you'll get during the casting process.  You won't need to apply any sprues, runners, gates, risers, etc., to your master...the person who will do your casting will do that, and tree it up in the investment flask too.

You can also make them from Styrene...but because of shrinkage, and the non-standard thicknesses you'll be dealing with, using Styrene stock will be less exact and it doesn't machine very well.

I have all the equipment for a complete investment casting foundry, but it's a lot easier for me to get the actual casting done elsewhere. I supply a local rock shop with wax masters (which I have made a flexible vulcanized rubber mold for, and injected them with my wax injector), and the brass.  They tree the wax masters up and invest them, burn 'em out and cast them for between $20 and $35 a shot.  However, my parts are small (caboose marker lights, switch stands, etc.) and have no requirement for dimensional accuracy and I get several hundred parts per throw.  I also finish the de-investing at home in my big ultrasonic cleaner, so basically the rock shop trees up the parts, invests them, burns them out, casts them and tosses the hot invested parts into a bucket of cold water for less than $35 a throw...and I supply the metal.

My parts are invested in a small/medium sized flask, so the cost of investment is minimal, and I supply enough wax masters to pretty much fill the flask up after they're treed up. 

If the rock shop had to do all the work required to produce flexible rubber molds from my brass masters, then inject the molds to produce the wax masters, the cost would go up exponentially, so I'm saving a shirt-load of money by supplying the rock shop with both the wax masters and the metal.

If I were to want to cast up locomotive frames out of brass, I'd engineer them so that they'd allow themselves to be machined to my tolerances where they needed it.  I'd also add whatever exterior details that won't interfere with clamping the part to my mill's X-Y table.  Then, I'd calculate the shrinkages and cut the wax master accordingly.  A word of advice..."shrinkage" can only be calculated approximately, so make your part a little larger than you think you need at the points it needs to be machined after casting.

Also, I would be very surprised if you get usable parts the first try.  It's a learning process and the cast parts will show you where you need to change your wax masters to get an end-product that meets your requirements.

Good luck!...and I am sure we'd all like to see more details about this project.

Cheerio!
Bob Gilmore

[robert3985]

Maybe I'm confused, but centrifugal casting of the brass itself?  I'd call that spin casting.  Like the parts from Showcase Miniatures, and usually in white metal.

When you said lost wax, I pictured shooting wax in rubber molds, treeing the waxes, surrounding in investment, and pouring brass into the mold. 

Shrinkage can be accounted for in the lost wax process, yes, but lost wax brass parts needing to hold tolerances for N scale mechanisms is where I started getting confused.  The root of the tolerance in this process is a rubber mold.  Maybe Bob has a better handle on what tolerances can be held, since he was doing a bunch of lost wax detail parts.  But in my experience working with a jewelry firm on this Z scale flatcar, there was a bit of fluctuation in the straightness of the parts and overall dimensional stability.

There are a few ways of getting the brass into the hot flask.  The crudest way is to simply pour molten metal into the "cup" on the end of the invested tree and let the brass run down into the mold...burning out the wax at the same time.  This will work for small, not-too-detailed objects, but when commercially done, the way is a little more complex.

First, the flask with the invested tree is put into a burn-out oven, and a relatively exact heating regimen is followed to not crack the investment in the flask and ruin the tree inside it.  When I was doing it, the investment was required to still be "wet" to enable superheated steam to thoroughly clean the void.  After the flask is burnt out...and in the same operation heated to the temperature of the metal that's going to be put in it...it's transferred to the spin caster, which can be either electrically operated or wound up using a special spring base. 

When the hot flask is placed in the spin caster, a specially shaped ceramic crucible with the appropriate amount of molten metal is placed in its holder and is adjacent to and fits against the "cup" now cast into the plaster that used to be the base of the tree inside the flask.  For small amounts of metal, you can melt it directly in the crucible with a torch, but for larger amounts, you have to melt it in your melting oven and transfer the hot crucible full of molten metal to the spin caster. 

Then, the spin caster (or centrifugal caster) is activated, either by switching it on or dropping a pin on the spring mechanism, and it spins like crazy...the crucible and flask rotate outward sharply on a hinge built into the spin caster's arm, shooting the molten metal into the void in the burnt out investment being held inside the flask, and applying additional centrifugal force to the molten metal to hopefully fill all the voids in the investment left by the burnt out wax.

When I was casting, at this point I'd let the metal solidify for a few minutes, then I'd toss the still very hot flask into a big bucket of cold water, and the investment cracks and disintegrates (mostly) away from the part...I'd also hose it down for a while, washing away as much investment as I could.

I'd do final cleaning using my big ultrasonic cleaner filled with a couple of gallons of de-investment solution.

The other way is to use a vacuum casting machine, which I have never done.  The hot metal is sucked into the void in the investment caused by burning out the hot wax master beforehand.  Be aware that above a certain altitude, these don't work.  So, if you live in a high altitude area, you'll get better results using a centrifugal casting machine.

Notice that I'm using "spin" and "centrifugal" interchangeably.

Spinning zinc or other similar alloys in rubber molds involves a different technology, and the molds are shaped like pizza pies with a hole in the center where the hot metal is poured as the rubber molds spins away sandwiched between a couple of metal plates.

Investment casting produces superdetailed parts with no concern about complexity because the "mold" or the investment, is destroyed when removing the finished part. 

Rubber molds into which molten metal is poured and spun degrade after a while, and highly detailed parts can only be produced along certain aspects of the finished part because the part has to be removed from the two halves of the rubber mold, which you don't want to destroy in the process.

The vulcanized rubber molds I've made for producing wax masters or "shots" last virtually forever.  I've got some that are over 30 years old and are still flexible and fully functional.

Cheerio!
Bob Gilmore

[Sokramiketes]

Thanks for the run down, Bob.  No matter how the brass gets into the investement mold, it's still only as dimensionally stable as a rubber mold and shrinkage guesstimates. It seems like you agree that high tolerance parts will need post-machining, and that's all I was trying to warn about.

[robert3985]

Valley Brass & Bronze (CA) will take your wax shots and turn them into brass, if that's what you're asking.  If you're planning on treeing them and setting in investment as well, which is doable, I'm sure they'd pour the brass.

Best Cast (NJ) is another option on the other side of the continent.  I've had them run full production from 3D cad to brass parts, and they are good to work with.

I beg to differ.  Sure, you can tree up your wax shots, but that involves a certain amount of previous experience and involves knowing what size flask you're going to use, buying and using a flask base and probably a flask too to make sure it all fits properly inside it.  Then, if you can't take it all down to where you're having the casting done, you have to ship it, and unsupported wax trees won't hold up to shipping because they are EXTREMELY FRAGILE.

Secondly, you don't just mix up and dump investment into a flask with a tree inside it.  There's a definite protocol to mixing investment, and then de-airing it, then how your pour it into your flask, then having the equipment...which involves special mixing bowls, a vibrating table, a vacuum table and bell jar.  This equipment is going to run about $500 if you can find a good deal.

Thirdly, when I was producing investment cast brass HO scale detail parts, there is a definite time window when flasks and invested wax trees can be burnt out...because the burning out process utilizes superheated steam from the still wet (but hard) investment to clean the voids of any residue.  I don't believe you could feasibly invest your tree, pack it up and ship it and have it still be usable whenever the casting company gets around to burning it out.

Just sayin'...

Cheerio!
Bob Gilmore

[mmagliaro]

Peteski, I'm with you on wanting proof.  I suppose we do not know at all if the nickel silver oxide is conductive, or if it forms more slowly, or if it comes off easly with a little rolling pressure from rolling stock.  All we really know is that nickel silver track generally conducts better and needs less cleaning than brass.

I did find this:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4680879/

... a paper that claims that allows of Cu and Ni (which is what nickel silver is... copper and nickel) remained conductive where straight copper did not.

We also know that people use nickel-copper alloys to plate things to protect them from corrosion.
http://www.nickel-alloys.net/copper_nickel_alloys.html

That would imply that the secret is that nickel-silver things don't oxidize as much --- not that the oxide itself is conductive.

[robert3985]

Thanks for the run down, Bob.  No matter how the brass gets into the investement mold, it's still only as dimensionally stable as a rubber mold and shrinkage guesstimates. It seems like you agree that high tolerance parts will need post-machining, and that's all I was trying to warn about.

Yup, you're entirely correct.  What really makes it complicated is when you need to cast up multiple brass masters to produce a multi-cavity vulcanized rubber mold for your wax masters.  This means that your initial brass master needs to compensate for the shrinkage of the first cast, which produces the brass masters from which the multi-cavity vulcanized rubber mold is made, then compensate for the last cast, which produces the end products.

For the OP's problem, I'd seriously consider having Shapeways (or a similar company) produce the wax masters, or even do the lost-wax investment brass castings.  All he'd need to do would be to produce the 3-D model, which can be easily modified if necessary...which I think will probably happen, and let Shapeways take care of the rest.

Of course, it depends on the size of the run and the size of the part if this is economically feasible at Shapeways...two facts we are not privy to yet.

Cheerio!
Bob Gilmore

[peteski]

I found this that seems to explain this well. Although it shows that the oxide is not really conductive but very thin and allows contact easily . Which in the context of this thread that Nickel plating can be very beneficial to parts we do want conductive.


http://www.mdpi.com/2075-4701/2/4/450/pdf

Thanks - looks like interesting reading (and I haven't gone through all the pages yet).

Max: looks like the nickel is the key. Like you said, it is not that the oxide that is conductive - it is that the nickel doesn't easily corrode.  Looks like we can finally throw that "old modeler's tale" out of the window.   

[railnerd]

Out here on the West Coast, there is also Pacific Locomotive Works— they make a lot of O-Scale castings which could be larger than many pieces of N-Scale rolling stock. Not familiar with the cost structures, but have friends who have used his O-Scale parts.

http://www.pacificlocomotive.com

[robert3985]

...  Looks like we can finally throw that "old modeler's tale" out of the window.   

Can we throw the "the three foot rule" out the window too along with the other "old modeler's tale"???

Just askin'...

Cheerio!
Bob Gilmore

[Missaberoad]

Can we throw the "the three foot rule" out the window too along with the other "old modeler's tale"???

Just askin'...

Cheerio!
Bob Gilmore

I almost wonder if that's one that just needed to be scaled down.... Three feet to 1:48 would be just under 11 inches to 1:160, seems more appropriate 

[mmagliaro]

Can we throw the "the three foot rule" out the window too along with the other "old modeler's tale"???

Just askin'...

Cheerio!
Bob Gilmore

Wow... talk about thread drift.   Here's where I stand on the 3-foot rule.   There are a lot of things that we cannot really see at 3 feet, that will give us a sense that something is wrong!
I discovered this about my own modeling in about 2007 (around the time I did the PRR I1s, and started religiously using optivisors for everything).   Our ability to perceive things that are not straight, or out of proportion, is a lot better than our actual ability to see things sharply.  So for example, maybe you can't see a certain rivet line on a model at 2 feet, but if it's crooked, I bet you will notice that, or at least have this sense that something is "off".  It's like listening to a band where the drummer or bass player can't quite keep their timing dead on the beat (and you other amateur musicians KNOW what I'm talking about ... LOL!)  Audience members may not be able to tell what the problem is, but they can tell "something is wrong."

That's when I abandoned the "3-foot" rule.  When I realized there were things I couldn't see clearly enough to model, but clearly enough to bother me if they weren't right.