Author Topic: One more for you guys - Bachmann Steam question  (Read 2677 times)

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daniel_leavitt2000

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Re: One more for you guys - Bachmann Steam question
« Reply #15 on: December 09, 2016, 02:31:23 AM »
+1
So this old 0-6-0 served as a good learning tool. This was my first tear down of a steam engine, including valve gear.  A few lessons learned:

1. The chassis is elegantly simple.  A plastic sub frame keeps the gears in place. Plate metal covers on the side act as current collection and bearing surfaces for the drivers. Everything screws together and there are no wires.

2. But the plastic sucks. The chassis parts look like they were injected over-temp. This creates an orange peel effect in the plastic and leads to distortions. This usually occurs when the plastic is too hot and not allowed to cool long enough before demolding. Then there are the driver gears/axles. All were split.

3. It's not the quartering that will get you. Quartering is pretty simple. I stick a flat screw driver in the gear and use an open needle nose tweezers to "twist" the driver face into correct position. I was able to quarter all drivers within 30 seconds.

4. It's the damn valve gear. Christ almighty. Side rods smacking into drivers. Cranks popping loose. Balancers unable to clear the rod pins. And all of this could be avoided if Bachmann made the hangars just .25mm wider. It took me a good hour getting everything to operate smoothly in my fingers before reinstalling the motor.

5. The MDT gears DO work in the drivers BUT... But one also split during assembly! So much for the black plastic being better than white nylon. The cheap and easy fix was to put the broken gear in the middle driver that is not attached to the siderods and therefore would not throw quartering off should it work its way loose. I secured the now somewhat loose wheel with thread locker applied inside the gear with a pin. If I were to do this again, I would just use threadlocker on the white gears and call it a day.

6. It's not a bad motor. I replaced the old skew wound 3 poler with a 5 pole Mashima but swapped it back when the Mashima didn't work as well. I might try a 5 pole Kato motor from their 4 wheel chassis next.

7. Those MTL conversion pilots for the Rapido 0-6-0 are gold. Nothing else improves the look of this model more than a good pilot in my opinion.


So after more than 15 years in a junk box, this little engine will live on. This will become a backup to the B&M G11 I am building from a newer run.
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mmagliaro

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Re: One more for you guys - Bachmann Steam question
« Reply #16 on: December 12, 2016, 12:12:11 PM »
0
With apologies to all non-SPF's for hijacking this thread:

Thanks for the input, Tony.  Really nice looking tender, too.  At least one of the PRR switchers used a straight-sided tender from about 1950, so my current plan is to use the short Bachmann Spectrum tender, to save some work.

(Attachment Link)

Max, you forgot to add that the valve gear needs work, too.  That's just too much effort, for too little in return.  The layout scenery division has been demanding more attention.

Okay, how about this idea?
Use the Bachmann 0-6-0 mechnism, but fit a Trix B6 shell on it, use the Bachmann USRA tender, but use the Trix B6 tender shell on there.  That would get you an approximate "Pennsy looking" profile of a B6 on a good mechanism with fine-flanged drivers and nicer valve gear. 
The thing is, there were 10 times more B6's than B28's, and the B6 is far far more typical of what you'd see in a PRR scene.

nscaleSPF2

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Re: One more for you guys - Bachmann Steam question
« Reply #17 on: December 12, 2016, 05:40:11 PM »
0
Okay, how about this idea?
Use the Bachmann 0-6-0 mechnism, but fit a Trix B6 shell on it, use the Bachmann USRA tender, but use the Trix B6 tender shell on there.  That would get you an approximate "Pennsy looking" profile of a B6 on a good mechanism with fine-flanged drivers and nicer valve gear. 

Ooooh.  Now there's a pregnant idea, Max.  I will definitely investigate this, when I get back into the shop.  Thanks, Max!
Jim Hale

Trying to re-create a part of south-central Pennsylvania in 1956, one small bit at a time.

narrowminded

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Re: One more for you guys - Bachmann Steam question
« Reply #18 on: December 13, 2016, 02:34:25 PM »
0
Sometimes I think it's not just the material but also a press fit that's too much.  Affords all kinds of tolerance on assembly but those that have too much tension finally split over time.  And if bad enough, a very short time.  Like the time it takes to push it in. ;)

I don't have enough pieces to confirm this as a trend but of the few I have, I have a minimum to maximum difference of around 3/4 of a thousandth (.00075").  When you think about it that's a HUGE difference in these small dimensions.  Especially if .0002"  gets the job done. 
« Last Edit: December 13, 2016, 02:36:23 PM by narrowminded »
Mark G.

peteski

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Re: One more for you guys - Bachmann Steam question
« Reply #19 on: December 13, 2016, 04:17:05 PM »
0
Sometimes I think it's not just the material but also a press fit that's too much.  Affords all kinds of tolerance on assembly but those that have too much tension finally split over time.  And if bad enough, a very short time.  Like the time it takes to push it in. ;)

I agree.  I have also seen nylon gears which are injection molded around the axle. You can tell it was molded over the axle by seeing some flash around the axle.  In that example the plastic shrinks as it cools (more than the steel axle) creating additional stress on the plastic gear (as it tightens over the axle). Over time that stress will cause the gear to crack.
« Last Edit: December 14, 2016, 12:05:18 AM by peteski »
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mmagliaro

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Re: One more for you guys - Bachmann Steam question
« Reply #20 on: December 13, 2016, 10:07:58 PM »
0
Sometimes I think it's not just the material but also a press fit that's too much.  Affords all kinds of tolerance on assembly but those that have too much tension finally split over time.  And if bad enough, a very short time.  Like the time it takes to push it in. ;)

I don't have enough pieces to confirm this as a trend but of the few I have, I have a minimum to maximum difference of around 3/4 of a thousandth (.00075").  When you think about it that's a HUGE difference in these small dimensions.  Especially if .0002"  gets the job done.

Roger that!  When I've made things to press-fit, .001" is the difference between it being so tight I can't get it in without a press, or being so loose it will flop right off in my hands.  And .00075 is almost .001

narrowminded

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Re: One more for you guys - Bachmann Steam question
« Reply #21 on: December 14, 2016, 01:01:08 AM »
0
The tolerance I was referring to is the axle diameter.  I never measured the gear ID as it was split so I don't really know what that would have proved and I didn't get the pin gauges out to check the gear ID in the new ones but they were also pressed off of assembled wheelsets so again, not a terribly useful inspection.  I guess I should have but I'll bet they're pretty good from a mold. 

There are so many things that can effect this beyond tolerance, especially the material and molding temps, that I really don't know what they're doing to have this trouble.  It shouldn't be that hard and I know splitting hasn't been a problem for me on parts machined from delrin bar with a 1/2 thousandths (.00025"/ .0005") press.  Some early experimental parts where I wasn't actually testing that detail were even tighter but used anyway and none over the last three years or so have split and I know some were way tighter than I would normally make them.  I wonder if an annealing might be done to new gears to relax any internal stresses if it's a known problem and maybe was caused by improper heating and/ or cooling in the process.  It would be a crapshoot but couldn't hurt and info that might help with some annealing guidelines might be found searching Dupont's material applications technical data sheets.  If it seemed like there might be any benefit, or at least no harm, a crude home rig could probably be made up using either hot water or a low oven heat.  I know in other data searches from times past that I've seen reference to annealing delrin although it wasn't applicable to my use at the time so doesn't stick with me.  Maybe place them in boiling water for a few minutes before to assemble would help.  Maybe what I'm doing right now is speculating and outlining what my research might look like if I really needed to figure this out.   :D
Mark G.