Casting thin "overlay" sideframes for the Atlas S2

[mark dance]

Hi all...Geoff Gooderham ("Angus Shops") and I have recently started discussing the feasibility of a small, but likely challenging, project to cast replacement AAR sideframes to go on top of the Blunt truck sideframes. 

I wanted Alco S type switchers to replace my tried and true LifeLike SW1200s in the C&W's Nelson yard.  After testing both the Bachmann S4 and the Atlas S2's I went with the S2s for their performance although what I really wanted was S4's to match the CP units in 1970.  I bought the S2's and planned to look into converting them to resemble S4s.  Now it seems to me the two primary spotting features of the CP Nelson units are a propane heater on the engineer’s side of the hood and AAR Type B switcher trucks in place of Blunt trucks.  Geoff will be putting on a clinic on resin casting at the upcoming Railway Modellers of BC Meet in May (More coming on this exciting event soon!) and while thinking about the heaters I began thinking about whether the sideframes could be cast as well.

My original intention was to cut off the Atlas side frames and replace them with suitable AAR sideframes either from Atlas or Bachmann and so I purchased extra sideframes as well as lots of extra pre-wired Blunt truck assemblies from Atlas.  I looked at these pieces for a few days, and tried a couple of things, but then parked the entire project...it just looks too risky to me given how the new trucks are assembled into the new Atlas design...for example the dimples on the back of the Blunt side frames look pretty critical to the functioning.  To be honest, I am even afraid to try and get the trucks off the model!  It isn't obvious to me how to take the model apart nor whether I would trust it would run well when put back together.

While thinking about the limits of casting I wondered about creating a very thin, double sided casting which could be glued over the existing Blunt truck side frame.  Such a casting would have the AAR truck detail in positive elide on one side and the mating Blunt detail in negative relief on the other.  Yes it would make the trucks "deeper" and it would likely depend heavily on the final overlay thickness as to whether the resulting thickness is too noticeable and "displeasing".

Geoff Replied:

“Well, this would be a bit of a challenge. However, one of the things I've learned about resin casting is that you won't know if something works until you try.

There doesn't seem to be any limit on how thin the casting can be, the limit is whether or not you can get it out of the mold with breaking it. Casting with detail on both sides would also typically be considered a 'no go', but I've cast complete trucks with typical truck detail on the outsides and the axle dimples on the insides without issues. This would be a bit more tricky but I've had an idea on how to overcome this in the back of my mind for some time now. This seems to be good time to try it out.

We'll need a good master. That seems to me to be the hard part. How to get the Blunt detail into the back of the AAR fronts. I gather from your notes that the typical strategy of filing the Blunt details of the side frames to provide a flat surface to mount the AAR castings won't fly because of the way the model is assembled. Hmmm....

We could make an impression of the Blunt side frame in some sort modelling clay (a material I'm not familiar with, but it can't be that difficult). Then we make a rubber mold of that and make a casting in resin. This will give us a negative in resin of the Blunt side frame, but it will be a fairly large chunk of resin. So we'll file this down until we have what we need.

Then I think what we should do is glue this to one side of a piece of .005 styrene and the AAR side frame to the other side (making sure we get everything lined up properly). Next we make up a box out of styrene, open on the top. We take the piece out .005 with the sideframe and glue it to the bottom of the box so that the sideframe is sticking up into the centre of the box, and fill the box with rubber. We should end up with a little block of rubber with a slot in the middle that has a void the shape of our desired sideframe. If we squeeze on the ends of the block of rubber this slot should open up enough to pour resin into the void. We may have to poke around with a toothpick to tease out any air bubbles, but when we let go of the block of rubber it will return to it original shape (might need a little pressure on the side) and squeeze out the excess resin. Let this set up and then extract from the mold and clean up. No problem. It's this "block with slot" idea I've been thinking about for making flat castings with detail on both sides.

Geoff”

I have Geoff’s permission to post these ideas to this forum for feedback. 

Has anyone tried something like this, specifically a double-side, thin resin casting?

Are the any suggestions for a non-shrinking clay like material to create a good negative of the blunt truck surface?
Thx
md (and gg)

[Ed Kapuscinski]

It may defeat the purpose of the clinic, but there are replacement truck sideframes of a number of varieties on Shapeways. This simply allows you to replace the entire OEM casting with the sideframes at one clip.

See: https://www.shapeways.com/product/888BU9RGF/flexicoil-n-kato-early-production-sd40-2?optionId=57556023

[mark dance]

That would be great, but I couldn't find an AAR truck side frame for the Atlas S2 on the Shapeways site.  Does anyone know if one exists?
 
In the back of my mind is that it would be logical for Atlas to do it if they were going to offer an S3/4 but I don't know what their economics to an S3/S4 would be given it would not likely increase switcher sales for them significantly. 

md

[Ed Kapuscinski]

I haven't seen one either, but there are folks out there who do stuff like that...

@Lemosteam: "Mapleleaf Customs"??

[randgust]

I've done that stuff before several times - my Climax sideframes, I did a set for Baldwin roadswitcher cast three-axle trucks, GE 70-tonner sideframes.    This shot shows the resin 70-tonner sideframes when I was still making that kit - the wheelbase was adjusted slightly to precisely fit the 5'6" wheelbase of the Kato 11-105 truck: http://www.randgust.com/GE70%20Kitparts.jpg

Oddly enough, that one just came back to life a couple weeks ago when I was doing a 3' gauge 65-ton Whitcomb and needed different sideframes.

However I've never tried to make a two-part mold to overlay an existing truck and fit the one under it.   I've always made the new sideframe as thin as I could make it (usually the base is .020 or so) as drip/pour one-part mold, and then simply filed the existing sideframes flat and thin with a mill file.   The nice part about resin is that you simply can glue these on with a light touch of Goo.

I'm 'assuming' dangerously that you want this:  http://www.bownas.net/albums/public/trainfest2004/Img2857_S4_20040801.jpg
laid over top of this:  http://www.readingmodeler.com/images/locos/s246.jpg
And my first observation is that there's enough relief there that you really need to file things flat first.

Atlas lists the trucks but they don't seem available:  http://shop.atlasrr.com/p-38860-n-s-2-locomotive-truck.aspx

I'd also guess that somebody, somewhere, from Atlas to Life-Like to Kato, has a sideframe casting with the right wheelbase that could be whacked off a truck, filed thinner, and used as a master.   If you were selling these commercially, you'd have to scratch the master.   If you're doing them yourself, no such rules apply.  I've had to scratch all mine.


Nothing against Shapeways (as I sell some Shapeways stuff myself) but you wouldn't want to do that stuff in FUD.   Just too brittle, I think you'd break all kinds of stuff off putting them on.  Maybe a different material.   With resin, for example, I was able to embed the Baldwin brake rods right in the casting - .010 wire - things you can't do in Shapeways.   I have a love-hate with FUD - I've broken so much stuff printed with perfect fidelity and no structural integrity.

I'm seeing a lot of really excellent work for design in Shapeways, but I do have to wonder how anybody can justify their design time on something like this to make about 50 cents a shot.

[mark dance]

Thank you for your wisdom Randgust.  Yes you have it right. 

I was able to get a bunch of pre-wired S2 trucks from Atlas for this purpose as soon as they became available...and now it looks like they aren't any more.

lucky me

md

[up1950s]

Wasn't Atlas to do the S1 S2 S3 and S4 series ?

[Lemosteam]

I haven't seen one either, but there are folks out there who do stuff like that...

@Lemosteam: "Mapleleaf Customs"??

Ahahahahaha.  That would really peeve @chicken45 off!

Seriously though Mark, if you are willing to mail the truck to me I can design any sideframe you want to clip over the truck assembly just like the OEM version.

It may take a while as there are may pans on the fire.  PM me to discuss further if you want.

[drgw0579]

I had hoped that Atlas would at least offer an S4, but we haven't heard anything more on their plans so I decided to temp the "scratch build something (or kitbash) and a vendor is certain to come out with a RTR version" fate and do my own.

Ironically I had a pair of AAR trucks from an Atlas "SW1500" in my scrap box, so I thought it would be appropriate to use those.  The end result is satisfactory, but barely.  I didn't want to thin the original side frames too much, so I believe the modified trucks are about a 1/16" too wide.  I had to ensure that there were no clearance problems where I run it.

Remember James Train Parts'  work from a couple years ago?  I am using his RT624 as my regular yard switcher, and the truck side frames from Shapeways have worked well, despite being FUD.  The sideframes don't have any regular pressure on them, so they should hold up.   You wouldn't  want to try to offer a FUD gearbox, but the sideframes should be okay.

Where is James anyway?  He did good work!

Bill Kepner

[C855B]

... Where is James anyway?  He did good work!

Still around, still doing good work: https://jamestrainparts.com/

[chicken45]

Ahahahahaha.  That would really peeve @chicken45 off!

Seriously though Mark, if you are willing to mail the truck to me I can design any sideframe you want to clip over the truck assembly just like the OEM version.

It may take a while as there are may pans on the fire.  PM me to discuss further if you want.

As I understand it, it would still be a Keystone Customs item since it is ...you know what? Forget it..I still have no idea. LOL

[AKNscale]

The S2's are pretty simple to disassemble, you just want to be careful when taking it apart. If I remember correctly, to take the the trucks off you just have to pop the side frame off(like any other Atlas truck), move the contacts away from the truck, then you slide the truck over or turn it and pull it out. If you look at the underside of the frame you'll see the grooves.

[mark dance]

The S2's are pretty simple to disassemble, you just want to be careful when taking it apart. If I remember correctly, to take the the trucks off you just have to pop the side frame off(like any other Atlas truck), move the contacts away from the truck, then you slide the truck over or turn it and pull it out. If you look at the underside of the frame you'll see the grooves.

I'll print and file that advise away. Thx!

Md

[Angus Shops]

Mark,

On thinking about it a bit more, I think Randgust's comments are wise. An AAR sideframe glued over an unmodified Blunt sideframe is going to place the AAR sideframes too far away from the face of the wheels, giving your S4's a 'fat truck' look.
Geoff

[mark dance]

Yep, that was the risk and it seems that risk would be borne out. Time to investigate alternatives.

Thanks for the advice everyone

EOT

md