P48 for Cotton Belt: Roster addition SW1200

[Big Train James]

Looks good, but now you have done the outer ones you really need to add the inner ones as well or it just won't look right. It is only 8 more pieces. Shouldn't be a problem with P48 wheels to space them accurately from each face of the wheels.

It may not be so simple. I've been planning on doing both the inside and outside connecting straps on my p48 build. There is a fair amount of lateral movement in the wheelsets in the gear case and now I wonder if this will present a problem with straps on both the inside and outside of the wheel.

I'm curious whether the amount of slop is necessary? Is it a compromise to accommodate tight curves? Could I use some shims to reduce movement?I guess I'm worried that if the wheels are allowed to move, they may damage or knock off the straps and associated detail. I sure would like to have both straps per the prototype so I'll need to sort this out.

Dave, the new brake rigging is a tremendous improvement. And the crankpins seem to work well. I'll have to check into these for hardware.

 

[Yorkshire Dave]

Looks good, but now you have done the outer ones you really need to add the inner ones as well or it just won't look right. It is only 8 more pieces. Shouldn't be a problem with P48 wheels to space them accurately from each face of the wheels.

Thanks Overseer - you've put down in words what I thought last night after looking at my photographs. I've been mulling a design over in my head to mount brake assemblies to the truck keeper plate.

 

[Big Train James]

I'm also concerned about the possibility of shorting as the current plan is to have metal sideframes mounted to a brass gear case cover. So contact with the straps could be a problem. An alternative would be to use plastic brake rigging instead, but then the question is whether it will be durable enough.

 

[Yorkshire Dave]

I'm curious whether the amount of slop is necessary? Is it a compromise to accommodate tight curves? Could I use some shims to reduce movement?I guess I'm worried that if the wheels are allowed to move, they may damage or knock off the straps and associated detail. I sure would like to have both straps per the prototype so I'll need to sort this out.

The NWSL drop in wheels in the GP9 have no or imperceptible lateral movement which shouldn't give any concerns. As the trucks have a short wheelbase (9') I believe this will not give rise to any issues traversing switches or curves.

I think 'slop' in the wheels in models is there to accommodate train set track especially on steam locomotives which have longer wheelbases and coupling rods.

So contact with the straps could be a problem. An alternative would be to use plastic brake rigging instead, but then the question is whether it will be durable enough.

One way to prevent shorting is to line the insides of the metal straps with CA glue and a single layer of tissue paper, then trim the excess once dry.

Shorting is one thing I'll have to consider when I build the ATSF U23B with it's brass trucks.

 

[JimG]

I'm also concerned about the possibility of shorting as the current plan is to have metal sideframes mounted to a brass gear case cover. So contact with the straps could be a problem. An alternative would be to use plastic brake rigging instead, but then the question is whether it will be durable enough.

James,

Another option might be to use split axle/frame construction then all the bits on each of the bogie sides are at the same potential. And keep both sides clear of anything else - like a metal body.

Jim.

 

[Yorkshire Dave]

Coat, hat,etc...

You must be fast running out of these items of apparel. Winter sales start soon .

 

[Jordan]

You must be fast running out of these items of apparel. Winter sales start soon .

Yeah.... it's all mainly to cover up my own lack of real progress

I was going to comment on the sideways wheel slop issue - again something where current Atlas products are inferior to the old Atlas/Roco truck, which was only ever a 2-rail item, rather than a "one size fits no-one" compromise between 2- & *spits in disgust* 3-rail

 

[Yorkshire Dave]

Just thinking, Richard is supporting the case that WTers go the extra mile... this is a candidate for that measuring stick. Split pin, Sir?

I think I may have added another 1.60934 km.....

Following on from Overseer and James's comments regarding the inner pull rods and my musings, I came up with the idea of supporting the brake assembly from the truck keeper plate.

I made up the supports from some brass channel to which I soldered my rough home made pull rods. The 'loose' pull rods are the ones I laminated after receipt from Mickoo.



The brakes were assembled to the supports using, as noted earlier, Alan Gibson 4mm crankpins. After assembly they were mounted to the truck keeper plate. I have only made up one so far to test my idea.





These are a comparison of the trucks: Modified on the left and original on the right.



Incidentally on my way to the station this morning I called into the local sorting office to collect a package from the paranoid state California and in the immortal words of Richie Benaud 'Another fine delivery'. Two sets of couplers.

 

[Big Train James]

There's really no comparison between the before and after versions.

One additional thing you might consider is filing down the thickness of the journal keeper that spans from the bottom of one pedestal to the other underneath the journal box. The prototype is quite a bit thinner than the model rendering. Easy of me to offer suggestions for additional work.


Copyright as noted

 

[Yorkshire Dave]

One additional thing you might consider is filing down the thickness of the journal keeper that spans from the bottom of one pedestal to the other underneath the journal box. The prototype is quite a bit thinner than the model rendering. Easy of me to offer suggestions for additional work.

This did cross my mind and it's so obvious. Something to add to the work sheet.....

 

[Big Train James]

James,

Another option might be to use split axle/frame construction then all the bits on each of the bogie sides are at the same potential. And keep both sides clear of anything else - like a metal body.

Jim.

Sorry Jim, missed this the other day. I've already got two sets of NWSL geared drop-in p48 wheelsets on hand, so for for now that's what I'm going to use.

 

[mickoo]

This did cross my mind and it's so obvious. Something to add to the work sheet.....

Simply cut the old keeper plate off and add a new metal one from thin shim, you can then also add the slack adjuster emergency retention strap as well

I reckon with all these bits your getting close to filling a minimum sheet size for PPD

Doubling the half etch pull rods to solder together takes up a lot of etch space but does remove the need to have to file any cusps off, so some basic math, for a GP9 you need 64 half etch slack adjusters for inner and outer pull rods, then add in the eight keeper plates ohh and you really need decent etched step plates then I think your going to be close to filling a 12x6" sheet or at least two complete engine sets would fill that area.

On a re run I'd close up the holes and slots a little, I forgot that when etching holes and slots on a half etched part it over etches so that'd need tidying up and I suppose all this talk of Blombergs measn my pulling the MP15 off the shelf and progressing, the more I look at the cab and it's great big thick windows frames the more I am inclined to etch a whole new one.

MD

 

[Yorkshire Dave]

Oh Blombergs ! Another 1,760 yards later.....

I purchased some 3 x 3 mm brass angle today in order make journal keeper plates and representations of the slack adjuster emergency retention brackets. Mickoo's suggestion means the entire brake assembly is mounted on the truck sideframe - brilliant .

Firstly I made up the keeper plate from the brass angle and cut away most of one 'leg' of the angle leaving two legs, one at either end to represent the emergency retention brackets. To this I soldered the slack adjuster.

Next was the assembly of the brake gear. I soldered 14BA bolts to my original home made slack adjuster (as these are being used on the inner face) followed by tube, brake, tube. Then this was married to the keeper plate with the outer face slack adjuster and secures with 14 BA nuts.

Bravely I cut the moulded keeper plate from the truck and mounted the new brake assembly and is secured with two M1 8mm hex bolts

Below is the result which still needs a bit of tweaking. Just another 7 to go ..........

 

[Yorkshire Dave]

I've already got two sets of NWSL geared drop-in p48 wheelsets on hand, so for for now that's what I'm going to use.

Have you tried these in the trucks yet to see how much lateral movement there is?

 

[Big Train James]

I've been doing some (3d)modeling....these are for Flexicoil switcher trucks, but most of the details are similar to the Blombergs.



Everything is built off prototype info gleaned from the Fallen-Flags website. You can see in the third shot that the backside connecting strap is very close to the back of the wheel. I will widen the drum at the base of the inside lever and the slack adjuster at the outside lever to push the backside strap further away from the wheel.

Several details left to finish including various nuts and bolts, journals, springs, and fillets to represent a casting. Then I will have to decide how to output everything. What can be printed, cast, or etched, and whether to create molds for casting as opposed to direct burnout one-for-one castings. I feel like you can achieve more complex parts by direct burnout, and mold shrinkage issues are reduced as well. It just depends on how many I might need (not that many), versus whether I might offer for sale as well.

I'm thinking of trying to just print the brake rigging in plastic to avoid possible electrical continuity issues. But I'm concerned about durability. Something to yet be determined.

 

[Big Train James]

Have you tried these in the trucks yet to see how much lateral movement there is?

I have a set assembled to test the new p48 cover. What seems like "a lot" of slop is probably only .0625", but it seemed like a lot when I was sitting there envisioning how it might work. And a sixteenth actually isn't entirely insignificant with the extra detailing we are adding.

 

[Yorkshire Dave]

I haven't seen the Atlas (can't remember whether it's an MP15 or SW1500) switcher close up. Does it have flexicoil (cast metal?) trucks or are you making these yourself?

 

[Big Train James]

Atlas makes an mp15dc, which has Blomberg trucks with diecast metal sideframes which suffer from the same brake rigging issue that you are remedying now. They also make diecast Flexicoil sideframes as found on the sw1500, although theirs are developed for their sw1200 model.

I'm kitbashing the mp15dc into an sw1500, cutting down the frame and swapping in the 8'-0" gearboxes found on the Atlas sw8/9/1200 models, and had planned on using the Atlas flexicoil sideframes. But then I started pursuing p48, and several glaring issues with the Atlas sideframes became apparent. First, the sideframes are designed to accommodate 3-rail wheels. When p48 wheels are used, the sideframes end up too far from the wheels by a ridiculous amount. This can be fixed with a replacement gearbox cover with mounting tabs that bring the sideframes in closer. However, the remaining issue is that the sideframe casting is too thin, so that even when the brake shoes are located over the wheels, there is still a significant gap between the wheel face and the back of the sideframe.

So I decided to make my own new ones with full thickness. I've since come to realize that the Atlas frames are flattened in front to back depth quite a bit, with just enough relief and edges to convey the look of the prototype, while allowing the frames to clear the gearbox cover originally design for the AAR type A sideframe for the sw8/9 models. I should have expected compromise, but I was still disappointed to discover this.

As noted, I'll have to figure out what parts will be made via which methods, and for personal use versus "commercial" availability. I think the Atlas sw1200 is much less common than the sw8/9 model, and the number of people doing a kitbash of a sw1500 seems limited as well, so I'm not convinced there will be a market of any sort for a p48 drop-in sideframe fix. But the beauty of the 3d model is once in hand, it can be used multiple ways if the need arises.

 

[Jordan]

The sound you just heard was all this information whistling it's way right over my head...

I just like American trains.

 

[Yorkshire Dave]

I've just finished all eight of the brake assemblies for trucks.... .

There's still some work to do before final assembly of the trucks namely the end stretcher bars, installation of the pickups, sand hoses, speedo cable etc. Managed to get as far as painting the one on the left. Apologies for the lighting.





After seeing this it's a shame Atlas/Roco did not model the truck with the springs under compression given the weight of the loco. And no. I'm not moving the journals upwards......................... yet.

Picture below for illustration. Copyright as noted.