Bolster clearance question

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wa6mdi
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Bolster clearance question

Post by wa6mdi » Sun Apr 14, 2019 3:46 am

Hi All,

Was finally able to get some time and I took the loco and the riding car out to a local track here in the DFW area over the weekend. Ran into a problem I have not seen with this car before and would like to ask the expertise of some others on the board here.

Seems some of the diagnostics I received had to do with the clearance on my bolster on the car. Symptoms are the car is jumping the track, mainly on curves. Currently there is about 1/8 inch clearance under the bolsters on each side. To be fair, the previous owner placed some washers under the side frames and I'm thinking this could be part of the problem.

In looking at various instructions online the information I'm getting is to have one set of trucks with about a 1/16 clearance on the bolsters, which results in the frame being more stable for riding. Then the second truck should have about 1/4 inch under it's bolsters.

Any thoughts on this please?

Thanks

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BAdams
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Re: Bolster clearance question

Post by BAdams » Sun Apr 14, 2019 9:55 am

Hi wa6mdi,
As you mentioned that this is mainly happening on curves, I would check your wheel gauge on the truck(s) that are derailing.

If it is happening on the same curve or the same point at the railroad have your track crew check the rail gauge.
I went through this with one of the passenger cars at RLS - it would derail in one direction on a curve but not the other, no other cars were coming of but this one. Fussed and fiddled with bolster clearance but nothing changed.
After watching this car come off the track at different locations within a 20 foot area of the curve I finally got the bright idea to check the track gauge.
Due to the expansion and contraction of the aluminium rail (Southern California sun) the ties had shifted and the gauge had become 7.5" and in some places less. (we use 7 5/8" on our curves).
Myself and memebr David Parrott straightened ties and re-gauged about 60 feet along that curve and we've not had an issue with that car since.

Why no other cars were coming off or why no one eles was derailing there is a mystery to me, as Car Foreman of the Club I've learned that the rolling stock, just like the steam locomotives, has there own little quirks a personalities. :wink:

Brook

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Doug_Edwards
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Re: Bolster clearance question

Post by Doug_Edwards » Sun Apr 14, 2019 2:50 pm

wa6mdi wrote:
Sun Apr 14, 2019 3:46 am

In looking at various instructions online the information I'm getting is to have one set of trucks with about a 1/16 clearance on the bolsters, which results in the frame being more stable for riding. Then the second truck should have about 1/4 inch under it's bolsters.
This difference is needed for the car to stay on the tracks. That may be your problem, there may be others.

If you look at N scale cars, you will find they also have one truck bolster bearing on the car more than the other. On a Willamette locomotive, the center truck has the hard contact between the bolster and the main loco frame, the front truck has an equalized contact that allows the front truck to roll under the loco frame (roll, as in roll, pitch, and yaw). A Climax I took measurements on had more clearance between the frame and one truck than it did between the frame and the other truck.

Regards,

Doug
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wa6mdi
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Re: Bolster clearance question

Post by wa6mdi » Sun Apr 14, 2019 5:10 pm

Thanks Guy's. That is exactly what we discussed at the track on Friday and I just wanted to independently verify the bolster question. The wheel gauge we measured and is correct, so the next exercise is to take and set the bolsters correctly.

Thanks to all that chimed in.

Dick Melcher
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ccvstmr
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Re: Bolster clearance question

Post by ccvstmr » Sun Apr 14, 2019 9:00 pm

Dick...have seen a hobby truck supplier use 1/32" clearance between the car body bolster and the side sway limits. There's two ways to accomplish this...machine the truck bolster center and the (2) side sway limits to the same plane...and install a 1/32" spacer on the center. OR...machine the 1/32" height different in the truck bolster or the car body bolster. Might have seen this in a Koster book printed years ago.

If your wheels are in gauge, can the truck side frames move "loosely" with respect to the bolster? If the springs are so tight, the side frame gets locked in position and won't "flex" for track peaks and valleys. Are you familiar with the 1/4" rule? With the truck on the track or steaming bay...can you roll one wheel over something like a 1/4-20 nut and the other 3 wheels stay on the rail? If not, the springs are usually too tight.

Might add too...if these are NOT new trucks...if the trucks were machined/assembled by someone else...are the axles parallel?

Just trying to offer several areas to examine for consideration. Hope that helps. Carl B.
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Greg_Lewis
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Re: Bolster clearance question

Post by Greg_Lewis » Sun Apr 14, 2019 9:17 pm

Carl makes some good points. Something I've done is to put a round-head screw at the top of the bolster where it contacts the frame. Thus when the car is empty and the bolster is at the top of it's slot in the frame, the screw provides a pivot so the truck remains flexible regardless of the strength of the springs.
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ccvstmr
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Re: Bolster clearance question

Post by ccvstmr » Mon Apr 15, 2019 10:16 am

Greg, I have done that on some old alum frame trucks where someone used any old set of springs they had, but the springs were too loose. Not only does the round head screw on top of the bolster bearing up against the inside of the side frame bolster pocket to provide a pivot point, it's also intended to "pre-load" the springs slightly so they stay in place and don't vibrate out of the spring pocket. Still, the springs should not be locking up the bolster so tight that it can't pivot/gimbal slightly in the side frame. Who would have thought there would be so many parameters to consider just to get a truck to roll around railroad? (don't answer that). Carl B.
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Greg_Lewis
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Re: Bolster clearance question

Post by Greg_Lewis » Mon Apr 15, 2019 4:37 pm

Well, Carl, I'll answer anyway for the benefit of those who may not have thought of this: the loaded to empty weight ratio of our cars is much greater than the prototype so we need to play some games to make things work.
Greg Lewis, Prop.
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cbrew
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Re: Bolster clearance question

Post by cbrew » Mon Apr 15, 2019 6:01 pm

I have adapted the three point design methodology when it comes to building rolling stock with both "show" cars and butt haulers. it makes a very stable yet flexible car. one truck is setup with very close clearances between the car and truck bolster side bearings and the other truck is either missing the car side bearings or have a clearance of .1". this addresses issues with twist in the roadbed and any twist in the car body.
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Re: Bolster clearance question

Post by Glenn Brooks » Sat Apr 20, 2019 1:52 pm

Here’s how the old time car builders supported the frame on the bolster circa 1890. the rub plate appears to be replaceable.

Seems like This concept would work fine on miniature cars, perhaps using Teflon or poly plates, instead of cast iron, if the, springs are soft enuf to allow proper movement of the axle set.

Glenn
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Bill Shields
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Re: Bolster clearance question

Post by Bill Shields » Sat Apr 20, 2019 4:53 pm

i like riding cars that are just pivots instead of springs for many of the reasons described above.

Idea came from the Puriton family and doesn't let me down - 3/4" to 1 1.5" - always works no matter how 'heavy' the passenger load.
trucks side 1.jpg
These tender trucks, while they have 'springs'...are really nothing more than a pivot for the equalizer
finished truck 4.jpg
how much clearance do you need on the bolsters? It depends on the track and the length of the car.

I always carry spare washers so that if I get to a new track (rare), or there has been settling / heaving during the winter (common), I can always modify the clearance as needed on the one truck that I setup to rock side to side.
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Re: Bolster clearance question

Post by rkcarguy » Mon Apr 22, 2019 10:59 am

This is a problem with scale operation, as the weights are so much different between an empty and full piece of rolling stock. I followed BigDumbDinosaurs method of having bearings atop the bolster so they pivot similar to what Bill has shown above. This allows the truck to conform to track conditions INDEPENDENT of spring travel, critical for stiffly sprung rolling stock that is running empty.
Real trains encounter a fraction of the grade changes that our models do, and also are much heavier empty so it's not much of an issue.

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