P7 tender truck bearings: existing ball or refit for roller or needle?

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DaveD
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P7 tender truck bearings: existing ball or refit for roller or needle?

Post by DaveD »

I've begun work on the tender for my B&O 7.5" gauge P7. When I found the castings for this project some 20 years ago, the only thing that one of the previous owners had done (thankfully, as it was poorly done!) was to machine the tender truck side frames, a single bolster, the journal boxes, and a single axle. My set of castings, as many of you know, was the third of three sets that Bruce Hamilton made, and he built great-running locomotives from two of the three. Bruce had provided bearing specs with the castings that included McGill Cagerol roller bearings for the locomotive and that is what I used throughout, and he specified Torrington needle bearings with inner seals for the tender. However, whoever machined these tender trucks ignored Bruce's specs and used sealed ball bearings, pressed into the journals and onto the axles.

While in storage at the previous owner's site there was some water damage to the casting set so there is rust present in all of these journal boxes with bearings. I need at a minimum to replace the bearings and that would be cheap and easy. But there is much more to replacing the ball bearings with roller or needle bearings. First, if I decide to use the Cagerol type of roller bearing, which is designed to allow a fair amount of lateral runout, it may be difficult to find these at a reasonable price and I'm not sure this is needed on the tender. Second, I understand from other entries here that needle bearing do provide a bit of lateral misalignment. Third, fixing a roller or needle bearing to these journal boxes will require deepening the existing 1-3/8" holes and then fabricating a sleeve to press into them to reduce the diameter to accommodate the smaller OD of a roller or needle bearing.

There is very little flexibility in the bolster to side frame connection (which is a slide to accommodate the leaf springs and movement) and none in the rigid side frame to journal box connection. So flexibility has to be in the bearings or perhaps, as some have suggested, in the journal bore (I'm not crazy about that idea!).

Some of the sages in this forum are emphatic about not using ball bearings in any trucks in any case, as the truck will have a difficult time staying on the track because of the rigidity of this setup. Others say that they have used ball bearings in their tender trucks for many years with zero problems.

Edit: Right after I posted this I thought that perhaps I should leave it as is and just replace the bearings; it would be easy enough to fix later if ball bearings prove to be troublesome, a simple matter refitting the tender trucks when compared to the amount of effort required to do so on the loco.

So, considering my situation, some thoughts, please, on just how I should handle this.
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Fender
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by Fender »

Dave, I have no advice on the bearings, but I’m thrilled hear that you are moving on to the tender!
Dan Watson
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DaveD
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by DaveD »

Dan, yes, I've begun the tender. The locomotive is mostly done with only several hundred hours remaining, mostly smaller stuff with lots of figuring out how to do things, fabrication and 3D modeling/printing, and assembling. Then repainting the upper end of the loco. So I figured that while I am still able I should do the heavy work on the tender. And, to mix it up, I can alternate between the tender and that sometimes tedious finishing work on the loco. You know, of course, that this locomotive and I are in a race to the finish? I am trying hard to finish it before I it finishes me!

I started with the tender frame last week--I believe you have seen that monstrosity? Aluminum, almost five feet of total ugly! It was bad enough that the maniac who was supposed to remove the flash ended up getting carried away with his angle grinder and removing a lot of the detail (this was about 50 years ago so I can't find him to give him a bad time!). That can be fixed to a degree with a lot of epoxy filler, but worse than that the whole frame was warped horizontally, up to a quarter inch or more at each end and some in the middle. These frame problems were some of the reasons I was so reluctant to start on the tender. I thought that I might have to fabricate a steel frame.

Well, I finally came up with a plan. My calculations told me that I could press these less than one degree max warps out of an aluminum casting with no weakening or damage, but my hydraulic press will only take a piece 2 feet long, so I had to pull out my Tahoe press (I believe you are familiar with that type of press?), with only 3000+ pounds of down force but able to handle any length piece you can put under it. So I planned, placed it on the garage floor in various positions, and lowered the front end of the press carefully where it was needed, with spacers under the tender frame at the press points so as not to over-press and ultimately bend it in the other direction. It worked out great! Now total runout horizontally on the tank frame is less than 0.030". So on to machining it and filling the grinder holes and restoring the lost detail, and I'm about done with that. Machining flutes into the outer rails, much like those on the loco rods but deeper (looking like I-beams), was a hoot, with my Bridgeport able to do about 18 inches at a time and a total need for about 50 inches continuous each side. But it came out well.

On to the two trucks, a decent winter project. Then I've got to think seriously about a tank with over a million rivets, and what to make it out of--steel or brass?

Lastly Dan, I really didn't appreciate you publishing a photo on Chaski of me and my project. My project OK, but me? Who want to see that? :oops:
Dave Dalton
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by Fender »

Dave, your reputation precedes you! I'm sure the readers appreciate seeing the "artist" as well as his work!
Dan Watson
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by DaveD »

I'm going forward with using the journal boxes as is with new 1621-2RS ball bearings. These ball bearings are radial load only; Bruce Hamilton used roller bearings--JTT-1212 and IR-812--for the radial load and thrust washers between the inner journal face and the wheel flange. I will be getting high quality 1621-2RS bearings. Will these bearings take the thrust load on the tender, which will normally be a small amount consisting of pulling the train around curves, or should I use a brass thrust washer between the journal and the wheel flange? If I do so the bearing inner diameter to axle fit will have to be slightly loose to allow the axle to move a bit laterally in the journal.
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by Harold_V »

DaveD wrote: Mon Dec 06, 2021 8:45 am <snip> or should I use a brass thrust washer between the journal and the wheel flange? If I do so the bearing inner diameter to axle fit will have to be slightly loose to allow the axle to move a bit laterally in the journal.
I have no experience with what you describe----but I'm of the opinion that providing a sliding fit isn't a great idea. It promotes the possibility that the axle will spin inside the bearing instead of the bearing rotating with the axle.

Just sayin'

H
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by Steggy »

DaveD wrote: Mon Dec 06, 2021 8:45 am I'm going forward with using the journal boxes as is with new 1621-2RS ball bearings. These ball bearings are radial load only; Bruce Hamilton used roller bearings--JTT-1212 and IR-812--for the radial load and thrust washers between the inner journal face and the wheel flange. I will be getting high quality 1621-2RS bearings. Will these bearings take the thrust load on the tender, which will normally be a small amount consisting of pulling the train around curves, or should I use a brass thrust washer between the journal and the wheel flange? If I do so the bearing inner diameter to axle fit will have to be slightly loose to allow the axle to move a bit laterally in the journal.

The 1621-2RS (an industry-standard part number) is a filling-slot-style ball bearing, which although not rated for axial loads, will tolerate them at the relatively low speeds you will be running them. On some bearings, the side from which the balls were loaded is identified in some way. That side should face inward toward the axle's shoulder.

Be sure to obtain fully sealed bearings, not shielded. Also, the bearing should be a press fit on the shaft and a close but not tight fit into the bearing box.
Last edited by Steggy on Tue Dec 07, 2021 5:03 am, edited 1 time in total.
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by Pontiacguy1 »

BL Deep Groove Ball Bearings (Inch) 1621-2RS, Sealed, Light Duty, 0.5" Bore, 1.375" OD

These ball bearings Absolutely CAN take thrust. Do not use the thrust washers, they are unnecessary. The Torrington catalog stated that the typical radial ball bearing (conrad) could absorb up to 30% of it's rated radial load in thrust, making them perfect for use in our applications. Bear in mind that these are typically electric motor rated bearings, so they should be able to do their rated loads/thrusts at 1750 or 3400 RPM. You won't be anywhere near that speed, or at least I hope you are not. If you used needle roller bearings, you would have to use something to absorb the thrust, and your thrust washers would come in handy doing that.

Also, good ball bearing practice dictates that the revolving member be locked to the bearing, while the stationary member can be a loose or sliding fit. everyone wants to make this backwards, pressing the bearing in the axle box and letting the axle slide through the bore of the bearing. That isn't the way it should be done according to bearing manufacturers. That is why wide inner ring pillow blocks and housed units all have shaft locking mechanisms (collars, setscrews, etc...) to lock the revolving shaft to the inner ring of the bearing.
On some bearings, the side from which the balls were loaded is identified in some way.
The only time I have seen that is if the inner ring had a grease hole drilled in it, or it was an angular contact bearing. All of the radial flat OD bearings we made and assembled, it didn't matter which way the inner/outer ring were oriented, they were symmetrical. Most of your spherical OD bearings did have to be oriented because of the grease hole. Rare to have grease holes drilled in a Flat OD outer ring. Ditto on getting sealed rather than shielded bearings.

Just trying to help, and I hope this does.
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by rkcarguy »

I like the simplicity of the ball bearings, and they can tolerate adequate thrust for this application. I would press them on the axles and let them float inside the axle boxes. If you're picky like me and wouldn't like the rattle, groove the axle box bore for an O-ring so it will grip the outer bearing race while still allowing some movement.
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by Fender »

Pontiacguy1 wrote: Mon Dec 06, 2021 5:58 pm
Also, good ball bearing practice dictates that the revolving member be locked to the bearing, while the stationary member can be a loose or sliding fit. everyone wants to make this backwards, pressing the bearing in the axle box and letting the axle slide through the bore of the bearing. That isn't the way it should be done according to bearing manufacturers. That is why wide inner ring pillow blocks and housed units all have shaft locking mechanisms (collars, setscrews, etc...) to lock the revolving shaft to the inner ring of the bearing.
I have a Craftsman bandsaw that I have used many years. It had a weird characteristic of making a terrible racket when starting and stopping. After several years, I took it apart, and found that the lower wheel shaft had been spinning inside the ball bearing, instead of turning the actual bearing! The fix was to loctite the shaft to the bearing!
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by DaveD »

Thanks to all for the comments, especially by Pontiacguy1 who tells me
Pontiacguy1 wrote: Mon Dec 06, 2021 5:58 pm These ball bearings Absolutely CAN take thrust. Do not use the thrust washers, they are unnecessary. The Torrington catalog stated that the typical radial ball bearing (conrad) could absorb up to 30% of it's rated radial load in thrust, making them perfect for use in our applications.
That is the info I was looking for.

The bearings I will be using are, of course, the sealed type. That is indicated by the "2RS" suffix in the 1621-2RS part number.

Recall that these trucks are part of a set of castings I bought about 20 years ago, not part of a once-running locomotive--only the tender truck parts were messed with. I don't plan to re-bore the boxes, as whoever did the rather sorry tender truck work did that part well. The existing bearings are a light press fit into the journal boxes and I'll keep it that way. As I mentioned in my original post, these trucks came with sealed bearings already pressed into the journal boxes. That work is probably 45 or so years old and I am replacing the bearings because of age and some rust. I am re-machining the boxes, side-frames, and bolsters to be properly aligned with the axle shafts that I will be making, so I won't have any significant lateral misalignment in the assembly. Hopefully any twisting motion because of track unevenness will be taken up by the lateral runout, which I did measure on a couple of these old bearings, (again, they have never been used), and It appears that with no load the lateral movement is in the area of 0.090 across the axle width. That runout, I expect, would be a bit more under load. But how much bearing lateral runout is really necessary? Some of that will be taken up by side frame twisting and tilting at the bolster connection and perhaps in other places.

It's a lot easier to machine something from scratch than to re-machine some else's bad work!
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Re: P7 tender truck bearings: existing ball or refit for roller or needle?

Post by Pontiacguy1 »

I have a Craftsman bandsaw that I have used many years. It had a weird characteristic of making a terrible racket when starting and stopping. After several years, I took it apart, and found that the lower wheel shaft had been spinning inside the ball bearing, instead of turning the actual bearing!
I probably have the exact same band saw, and it did a very similar thing! Mine got to where it was making noise, and the blade wouldn't stay in position on the drive wheel down below the work rest. I tore the thing down and found that the shaft had been rolling inside of the bearing, and had done it long enough that the shaft was worn down about 0.030" where the bearing rode. It was loose from the manufacturer, and it just rolled inside the inner ring. Once some dirt and grit got in there, it ate up the shaft causing a lot more play. I made a new shaft, got a new bearing, pressed them together, reassembled everything, and it works just great now.

To be perfectly clear, the original bearing was still turning and was fine. I could have re-used it, but didn't. The inner ring of the bearing is a lot harder than the shaft, so once any kind of dirt got in there, it just ground down the shaft as it rolled along inside of the inner ring of the bearing.
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