Date   

Re: Model brake component size comparison to prototype

Dennis Storzek
 

A couple of things are not being accounted for in this discussion. Yes, metal shrinks as it solidifies, as does most things, water excepted. But in the investment casting process, the molds are at somewhere around 1000 deg. F when the metal is poured, so thermal expansion has made the molds bigger.

Shrinkage does not have to be equal in all directions; if the part is constrained as it solidifies, most of the shrinkage will be in the thickness of the part. An example would be painting your house. Paint shrinks as it cures, but that doesn't mean that you house gets smaller as it dries. Since the house is sturdier than the shrinkage forces, 100% of the shrinkage is in the thickness of the paint film.

The big problem calculating size with the traditional lost wax process is accounting for the size change in all the steps; the master is used to make a rubber mold, and traditionally it wasn't RTV, but some heat cure rubber, which shrinks. Wax is poured into the mold, and it shrinks. The wax part is then used to make a plaster mold, which is then heated to burn out the wax and drive any moisture out of the plaster, so it doesn't flash to steam when the metal is poured, causing voids, or worst case, causing the mold to burst open. Finally, the metal shrinks as it cools. The shrink rate of each of these steps is only an estimation unless the job is such a long run that actual data was tracked for the purpose of adjusting the final part size. That just doesn't happen in model railroading. 

Another story, told to my by a professional modelmaker who was a friend of Bill Clouser:

Clouser modeled in 1/4" scale using the prototype track gauge, what we now call P:48. One of the nicest freightcar trucks available in those days was made by Carl Auel (sp?), but it was five foot gauge. Bill took one of the bolsters and used ti as a pattern, had enough cast in brass to provide multiple patterns to fill the typical spin casting mold, and then used that mold for waxes to have parts cast for himself and some friends who also modeled to exact scale. The resulting parts were 5% shorter than the original, which corrected the width of the truck.

Dennis Storzek


Help with a B&O document

Eric Lombard
 

Good Morning, Fellow Stay-at-Homes,

I would appreciate some help. I have a carefully arranged document archive system. The following document was so carefully archived almost 20 years ago that I can't find it. The journal issue is where it should be but the supplement is not with it.  I would be indebted to anyone who could provide me a scan of:

Daniels, R. K., 2001, [B&O] Freight Car Equipment, 1917-1927. Supplement, 12 pages, to The Sentinel, Vol. 23, No. 01: Baltimore & Ohio Historical Society

I am particularly in need of pages 1-3 at this moment.

Thanks in advance....

Eric Lombard
Stymied on a project in Homewood, IL
elombard@...


Re: [Non-DoD Source] [RealSTMFC] CB&Q 110193 Truss Rod boxcar

Gatwood, Elden J SAD
 

Really nice build, Bill!

 

Elden Gatwood

 

From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of Bill Welch
Sent: Saturday, April 4, 2020 12:18 PM
To: main@RealSTMFC.groups.io
Subject: [Non-DoD Source] [RealSTMFC] CB&Q 110193 Truss Rod boxcar

 

CB&Q 110193 Truss Rod boxcar is a Westerfield kit. My modeling date is Oct. 1955 and by then these were probably all gone but I occasionally cheat and so the car has a re-weigh date in 1952. The underframe has not been glued as yet so the body is not yet sitting firmly nested on the U/F. I have also not yet attached the brake wheel. To help keep the turnbuckles taught as well as provide more comfort for someone "riding the rods" a wood plank has been lodged through the four turnbuckles on each side of the underframe. The scratch built Running Board and Latitudinals will receive replacement boards after sandpaper is used to peel some paint up.

Bill Welch


Re: Model brake component size comparison to prototype

Dennis Storzek
 

On Sun, Apr 5, 2020 at 09:04 PM, Tony Thompson wrote:
  Richard Hendrickson did the same to get some durable bracket-mount grabs. I still have a couple dozen of his parts, very nice brass. Don't know what reject rate occurred.
Those may well be my parts, I intended to sell part of the run to recoup some of my cost, but when Richard heard about it, he bought all I wanted to sell.

Dennis Storzek


Re: [Non-DoD Source] Re: [RealSTMFC] Model brake component size comparison to prototype

Gatwood, Elden J SAD
 

Nice work, Paul!

 

Elden Gatwood

 

From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of Paul Woods
Sent: Monday, April 6, 2020 7:43 AM
To: main@RealSTMFC.groups.io
Subject: [Non-DoD Source] Re: [RealSTMFC] Model brake component size comparison to prototype

 




An example of the casting work I have done - O-scale freight truck with functioning equalisation - and genuine American black walnut bolster.  I had expected to find some shrinkage in the axle-boxes because they are a big lump compared to the arch-bars but they were fine, all portions of the sideframes turned out at intended size.

Regards
Paul


Re: Model brake component size comparison to prototype

Paul Woods <paul@...>
 




An example of the casting work I have done - O-scale freight truck with functioning equalisation - and genuine American black walnut bolster.  I had expected to find some shrinkage in the axle-boxes because they are a big lump compared to the arch-bars but they were fine, all portions of the sideframes turned out at intended size.

Regards
Paul


Re: Model brake component size comparison to prototype

Paul Woods <paul@...>
 

Tony

I am greatly insulted by your tone and it appears that you have not put any thought into your comment.  Seriously?  You are trying to tell us that ALL the metal in a casting cools to freezing point at exactly the same moment?  You might know a lot about metallurgy but I know a bit about building things from metal.  I hadn't bothered mentioning that the brass caster's tale matched my own experience gained building steel ships because it didn't seem important, but fine: the metal might eventually shrink equally, but not all at the same time because cooling happens from the outside in, and this can be used to our advantage.  I have dealt with plenty of  castings, such as A-frames for supporting ships' propeller shafts, with significant variations in section size.  The orientation of the casting as it is poured is quite important, with the thicker part intentionally placed above the thinner part so that it acts as a reservoir keeping the thin section filled as it cools....as a metallurgist you should be aware of the high density of metals such as steel and brass, and thus the pressure that will be exerted that can keep pushing semi-molten metal down towards the bottom of a mould when it is cooled slowly enough - that is the key, achieving a slow enough rate of cooling.  You can't tell me it doesn't work because I've already done it; yeah sure, the metal shrinks but if it's done right it is possible to control WHERE the shrinkage occurs.  The column that lost-wax brass parts are stuck to when they are cast serves as one heck of a big reservoir of molten metal as the 'branches' are freezing so I don't have any reason to doubt what the caster said.

Paul Woods
retired mechanical engineer


Re: Greg Martin

james murrie
 

Schuyler;
What is the best way to reach out and send our good wishes, or the name on the Facebook account they are using?
Jim Murrie
Durham, NC


Re: Model brake component size comparison to prototype

Tony Thompson
 

Dennis Storzek wrote:

I've only ever done one investment cast project; I wanted some bracket grabs that were more robust than the typical styrene parts, so back when Intermountain was still molding parts here in the US, I bought a hundred detail sprues from their PS-1, clipped the runner with the grabs out of them, and sent them out as investment masters. I was warned about the potential for ash to plug the long narrow cavity, and indeed, the reject rate was someplace around 20%, but the properly filled parts were nice.

    Richard Hendrickson did the same to get some durable bracket-mount grabs. I still have a couple dozen of his parts, very nice brass. Don't know what reject rate occurred.

Tony Thompson




Re: Model brake component size comparison to prototype

Dennis Storzek
 

Well, we certainly have agreement here, don't we? Over the years I heard anywhere from "don't worry about it" to 7% shrinkage from pattern to investment cast part, although I dismiss both ends of that range. It does point out that investment casting is still somewhat of a 'black art' as far as the short runs typical in our hobby.

And some firms ARE using styrene as the burn-out material, although it typically isn't very hard and doesn't contain much colorant. Injection molded styrene also has a shrinkage factor, appx. 1/2%, which has to be added to the metal shrink factor.

I've only ever done one investment cast project; I wanted some bracket grabs that were more robust than the typical styrene parts, so back when Intermountain was still molding parts here in the US, I bought a hundred detail sprues from their PS-1, clipped the runner with the grabs out of them, and sent them out as investment masters. I was warned about the potential for ash to plug the long narrow cavity, and indeed, the reject rate was someplace around 20%, but the properly filled parts were nice.

Of course, the nicely molded acetal parts from Kadee have made that no longer worth doing.

Dennis Storzek


Re: Model brake component size comparison to prototype

Tony Thompson
 

Paul Woods wrote:

My casting supplier tells me the shrinkage occurs in the rubber mould, not the metal casting because the column of molten brass in the cast keeps pressure on the mould as it cools, helping reduce shrinkage.  

      Sorry, this is nonsense. The entire volume of the metal is shrinking as it solidifies and cools, and nothing in ordinary life can constrain it. The molten column AND the part are all shrinking equally.

Tony Thompson
retired metallurgist




Re: Model brake component size comparison to prototype

spsalso
 

Paul,


I will disagree with your statement that shrinkage does not occur in the metal casting process.

If we assume the mold is filled out with molten brass, and the brass cools down to its phase change temperature of 920 degrees C., thermal contraction will occur as the solid cools from just under 920 degrees to 25 degrees C.  The piece will pull away from the walls of the mold.  The "column of molten brass", if it even still remains liquid, will be trying to compress a solid.  That solid will not compress significantly.

As I said, the shrinkage during the casting process for brass is 1.7%.  Roughly.


Ed

Edward Sutorik


Southwest Scale Productions Boxcar Doors

Steve and Barb Hile
 

Following on on some previously posted material, attached are two formats of a document describing the post WWII boxcar doors produced by Southwest Scale Productions, with photos of both the prototype and model for each one.
 
I am unable to load them to the files area, but hopefully they will find a home there.
 
Steve Hile


Re: Illinois Central 40' ss boxcar information

Chuck Cover
 

Thanks Tim.  Nice photo.

 

Chuck Cover

Santa Fe, NM


Re: Model brake component size comparison to prototype

Paul Woods <paul@...>
 

Hi Folks

For the benefit of anyone not familiar with the brass investment casting process: I do CAD design work for cast brass model railroad parts, along with other methods (laser, photoetch); the 3D-printed master is made 2% oversize and a rubber mould is made from it.  Today the rubber is transparent, and the mould is poured as one block then cut in half with a scalpel.  I always do my 3D-printed patterns with sprue gates but sometimes an area won't fill with metal properly, and any additional sprue gate can simply be carved out of the mould to correct the problem.  A special hard wax is then injected into the mould, making as many wax copies as required.  These waxes are then 'treed up', that is, stuck on a wax cylinder so that they look like branches on a tree, then the whole lot is dipped in high-temp plaster repeatedly to build up sufficient thickness.  The plaster mould is heated to run the wax out (hence the term 'lost wax'), so that molten brass, bronze or whatever can be poured into the resulting cavity.

My casting supplier tells me the shrinkage occurs in the rubber mould, not the metal casting because the column of molten brass in the cast keeps pressure on the mould as it cools, helping reduce shrinkage.  I usually see shrinkage i.e. low spots where the surface should be flat, where a large cavity is filled through a smaller sprue gate and so the metal in the sprue gate can freeze before the metal in the cavity, preventing more metal from flowing in.  Uneven cooling is the sworn enemy of metal casting of any kind, so large thick sections should be avoided; it will usually give a better result if a large part is either hollowed out or assembled from smaller parts.

It can be an expensive waste of time trying to burn styrene parts out of plaster moulds because styrenes can include fillers to make them harder, and these are not always combustible.  The ash can get pushed into the smaller nooks of the mould by inflowing metal, preventing the fine details from filling.

To the best of my knowledge, wax masters cannot be used for spin-casting pewter, because the type of rubber compound used (at least, by my local supplier) to make the mould produces heat as it sets, sufficient to soften or even melt styrene, so wax doesn't stand a chance.  This similarly rules out the use of 3D-printed resin masters, so if metal masters cannot be made by hand then the process has to be plastic master - brass casting - pewter casting.  This can still be worthwhile but you have to require huge numbers of something, such as tieplates, to justify the effort.  The tricky part is judging the amount of shrinkage to allow for because the brass casting process involves shrinkage and then so does the pewter casting process, so one multiplies the other.  I would love to find a spin-caster who can use wax patterns because that would reduce the costs quite a lot.

Regards
Paul Woods

Whangarei, NZ
NYCSHS #7172


Re: Reboxx 1.035 wheels

Schleigh Mike
 

How many sets do you need, Brian?

Mike Schleigh in Grove City, Penna.

On Sunday, April 5, 2020, 05:37:17 PM EDT, Brian Carlson via groups.io <prrk41361@...> wrote:


Does anyone know where any Reboxx 1.035 33“ wheels might exist on a hobby shop shelf or workbench someplace never to be used. I am looking for some for a project, either single or double insulated.

I miss reboxx wheels.

Brian J. Carlson



Re: Reboxx 1.035 wheels

Dave Parker
 

I found the same website last week,  They only seem to offer 0.110" wheels.  Reboxx were all 0.088" IIRC.

I really miss Reboxx.
--
Dave Parker
Swall Meadows, CA


Re: Reboxx 1.035 wheels

James Brewer
 

Brian,

I don't  have any Reboxx wheels in my stash; but I've noticed an ad in the last few issues of RMC for "JB Wheelsets" that says "slightly different name...same great product!"  There is a web site listed www.jbwheelsets.com

Other than noticing the ad I have no connection with this vendor.  Good luck on your search.

Jim Brewer


Reboxx 1.035 wheels

Brian Carlson
 

Does anyone know where any Reboxx 1.035 33“ wheels might exist on a hobby shop shelf or workbench someplace never to be used. I am looking for some for a project, either single or double insulated.

I miss reboxx wheels.

Brian J. Carlson


Re: circa 1946 freight car images

BRIAN PAUL EHNI
 

A color photo of these two has made the rounds before.

 

 

Thanks!
--

Brian Ehni

 

 

From: <main@RealSTMFC.groups.io> on behalf of Eric Hansmann <eric@...>
Reply-To: <main@RealSTMFC.groups.io>
Date: Sunday, April 5, 2020 at 2:12 PM
To: <main@RealSTMFC.groups.io>
Subject: Re: [RealSTMFC] circa 1946 freight car images

 

The second handhold on the left end of the car sides became a practice in the early 1930s.

 

I model 1926 and I need to remove the second handhold detail from many resin and plastic models.

 

 

Eric Hansmann

Murfreesboro, TN

 

 

From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of Tim O'Connor
Sent: Sunday, April 5, 2020 1:25 PM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] circa 1946 freight car images

 


And wouldn't that be a violation of the Safety Appliance regulations of the 1920's ??

I am amazed - thanks for pointing that out. The shop date is clear - dated 1950.




On 4/5/2020 2:14 PM, John Larkin via groups.io wrote:

For a fan of details, note the single handhold on the first car versus the double handhold on the second.  These are two otherwise similar (in gross detail) cars and the picture is a great way to show the sometimes minor differences off.

 

John Larkin

 

On Saturday, April 4, 2020, 11:49:12 PM CDT, john oseida via groups.io <xseinc@...> wrote:

 

 

There was a recently concluded eBay listing that had a number of images that might be of interest to the group including one of those not often photographed poultry cars:

 

 

Eight (8) b&w negatives of Vintage Freight Cars (PFE & Western Union inc...

Find many great new & used options and get the best deals for Eight (8) b&w negatives of Vintage Freight Cars (P...

 

 

 

 

Regards,

John Oseida

Oakville, ON

 

 

On Saturday, April 4, 2020, 2:06:52 p.m. EDT, Tim O'Connor <timboconnor@...> wrote:

 

 



Thanks Drew for the clarification. I'd love to see this done. It seems to be an
almost forgotten art at least for HO models.


On 4/4/2020 11:35 AM, Drew wrote:

Tim,

   I worked in a prototype model during my high school years. We used lost wax a few times. First a master is made and a mold made off that master, the mold was usually RTV rubber. Wax was poured in to that mold to make a second master which did shrink a bit. That wax master was then placed in foundry sand and hot metal poured in to the sand mold. The wax melted/vaporized and metal took its place, hence the name lost wax. It's been 20 years since I last did that but I do recall there was a bit of shrinkage in each step.

Drew Marshall in Philly, PA

Modeling the pre-Depression years.

Sent from TypeApp

On Apr 4, 2020, at 09:15, Tim O'Connor <timboconnor@...> wrote:


As I recall, all Cal-Scale detail components were OVERSIZE because they were used
for lost wax casting! In that process the plastic parts are for the molds and are
destroyed in the casting process, and the shrinkage produces parts that are closer
to scale.

Or am I wrong? :-)

Tim O'Connor

========================================

On 4/4/2020 9:00 AM, Lester Breuer wrote:

A comparison of several manufacturers’ model brake component measurements to Westinghouse prototype brake component measurements prepared by George Toman was sent to me for my use.  I asked George to share his measurements comparison on my blog.  If you are interested in the  comparison measurements, they are now available on my blog I have to share photos and writeup of projects on my Minneapolis & Northland Railroad Company. If would like to take a look please do at the following link:

 

http://mnrailroadcab100.blogspot.com/

 

Lester Breuer

 


--
Tim O'Connor
Sterling, Massachusetts


--
Tim O'Connor
Sterling, Massachusetts


--
Tim O'Connor
Sterling, Massachusetts

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