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Model brake component size comparison to prototype

Lester Breuer
 

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
 


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

Jim Hayes
 

Lester, I read your review of brake equipment sizes and the following one on the SF boxcar and was impressed by both. I should read your blog more often.

JimH

Schuyler Larrabee
 

Tim, I believe you’re correct about this process.  I’ll have to look at the information on Lester’s blog and measure a few things.

 

Schuyler

 

From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of Tim O'Connor
Sent: Saturday, April 04, 2020 9:15 AM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] Model brake component size comparison to prototype

 


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

Ralph W. Brown
 

Hi Tim,
 
My understanding is that the sacrificial material used to make the molds for casting is, as the name of the process implies, wax, which melts and is absorbed by the mold when it is first heated leaving the void later filled with molten brass or other casting metal.  I doubt plastic detail parts made by Cal-Scale or others would or could preform the same function, although I suppose they could be used as “masters” for casting the sacrificial wax patterns, copyright issues notwithstanding.
 
I suspect there are others here who are more familiar with the process and could provide a more detailed description of the process.
 
Pax,
 
 
Ralph Brown
Portland, Maine
PRRT&HS No. 3966
NMRA No. L2532

rbrown51[at]maine[dot]rr[dot]com
 

From: Tim O'Connor
Sent: Saturday, April 4, 2020 9:15 AM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] Model brake component size comparison to prototype
 

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

Schuyler Larrabee
 

Ralph, I believe that lost “was” is, except for unique individual items made by artists casing in silver or gold, no longer used for mass production of parts like model railroad brake gear.  That has become a “lost plastic” process, where many plastic parts are glued together in a “tree< which is then inserted into a can of wet plaster.  When dry the plaster cylinder is heated to get the plastic to run out, and then brass is poured into the middle of a spin casting machine, which forces by centrifugal force, the metal into all the voids in the plaster cylinder.  After cooling (and shrinking) the plaster is broken away and the parts harvested.

 

I presume that the plastic used has a lower melting temperature than that used for injected molded parts from metal dies.

 

I have received lost plastic parts that still have plaster on them.

 

Schuyler

 

From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> On Behalf Of Ralph W. Brown
Sent: Saturday, April 04, 2020 1:34 PM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] Model brake component size comparison to prototype

 

Hi Tim,

 

My understanding is that the sacrificial material used to make the molds for casting is, as the name of the process implies, wax, which melts and is absorbed by the mold when it is first heated leaving the void later filled with molten brass or other casting metal.  I doubt plastic detail parts made by Cal-Scale or others would or could preform the same function, although I suppose they could be used as “masters” for casting the sacrificial wax patterns, copyright issues notwithstanding.

 

I suspect there are others here who are more familiar with the process and could provide a more detailed description of the process.

 

Pax,

 

 

Ralph Brown
Portland, Maine
PRRT&HS No. 3966
NMRA No. L2532

rbrown51[at]maine[dot]rr[dot]com

 

From: Tim O'Connor

Sent: Saturday, April 4, 2020 9:15 AM

Subject: Re: [RealSTMFC] Model brake component size comparison to prototype

 


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
 



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

Dennis Storzek
 

On Sat, Apr 4, 2020 at 10:36 AM, Ralph W. Brown wrote:
My understanding is that the sacrificial material used to make the molds for casting is, as the name of the process implies, wax, which melts and is absorbed by the mold when it is first heated leaving the void later filled with molten brass or other casting metal. 
Wax was used when the masters were being "spin" cast in rubber molds. For higher production numbers the masters are injection molded from styrene. Precision scale Co. plastic parts are the same; investment casting masters sold as parts. Come to think of it, Grandt Line once sold their parts in brass, also.

Dennis Storzek

Randy Hees
 

One thought... While AB control valve portions are going to be about the same size...  noting that some current portions (there are three parts to a AB control valve, the pipe bracket, the service portion and the emergency portion), The pipe bracket hasn't changed... but some [portions have gotten larger... requiring longer mounting studs...    and there are lots of sizes of brake cylinders... you match them to the car's weight....  So the cylinder on a caboose is much smaller than on a 40 or 50 ton box car, with cylinders for a 70 or 100 ton car much larger...  I am not sure about reservoir size...   

In the era for this list, probably only two common sizes... one for the typical 40 or 50 ton freight car, and one for cabooses... 

Randy Hees

steve_wintner
 

High quality castings for aircraft engines are usually "investment cast" which is pretty much lost wax by another name. A variety of materials can be used - wax, plastic, stereo lithography or other 3d printed resins. Burn them / melt them out, then pour - under vacuum for highest quality. The plasters used withstand very high heat, so high melting point plastic is irrelevant as long as it burns out leaving no ash behind.  All metals shrink when they solidify, but it's only a few percent. Depending on how it's done, the wax may shrink too. .97*.97 = still only a little bit. If you are making aircraft engines, that few percent matters. 

Aside from jewelry, model railroad gubbins, and aircraft engines, there are cheaper processes for most applications.

Steve


Randy Hees
 

The late Dave Braun once investment cast a road kill rabbit...  It apparently was almost cartoon flat, but very much recognizable as a rabbit...   He sold it as a piece of art... Apparently the odor when it was being "burnt out" was particularly memorable...   not in a good way...

Randy Hees

spsalso
 

While Cal-Scale (Bowser) may well use their plastic parts to investment cast their brass AB brake parts, they still have the wrong dimensions.

Shrinkage during the casting process is 1.8%.  If you multiply the prototype dimensions in the chart under discussion by 1.018, so as to predict the proper size of plastic piece that will produce the proper sized brass one, the numbers just don't work.  The dimensions are just wrong.  Unless there are errors in the table.

So any errors in the Cal-Scale parts are not based on making properly oversized parts for casting.


Ed

Edward Sutorik

Ralph W. Brown
 

Hi Dennis,
 
Live and learn, I guess.  Admittedly, what know of the process was learned a few decades ago, so I stand corrected.  It would be interesting, to me anyway, to know what types of plastic are used and how the shrinkage of the various materials compare.
 
Pax,
 
 
Ralph Brown
Portland, Maine
PRRT&HS No. 3966
NMRA No. L2532

rbrown51[at]maine[dot]rr[dot]com
 

From: Dennis Storzek
Sent: Saturday, April 4, 2020 2:06 PM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] Model brake component size comparison to prototype
 
On Sat, Apr 4, 2020 at 10:36 AM, Ralph W. Brown wrote:
My understanding is that the sacrificial material used to make the molds for casting is, as the name of the process implies, wax, which melts and is absorbed by the mold when it is first heated leaving the void later filled with molten brass or other casting metal.
Wax was used when the masters were being "spin" cast in rubber molds. For higher production numbers the masters are injection molded from styrene. Precision scale Co. plastic parts are the same; investment casting masters sold as parts. Come to think of it, Grandt Line once sold their parts in brass, also.

Dennis Storzek

ron christensen
 

Interesting comparison
I wondered what the cylinder should look like if the brakes were off, so I modified a cylinder.
As far as I know no one manufactures a cylinder with the push rod in.
Ron Christensen

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

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

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



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

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



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