Scattergun Roller Bearings

[farnetti]

For roller bearings to work efficiently the outer ring must not rotate within the axlebox, and the inner not rotate around the axle otherwise the rollers are redundant.

I can see how this would work in an 0-4-0 or BoBo situation but we usually need some side play when a loco with more axles is modelled. I think Tony Reynalds has used and Adrian on his 4MT.

Can anyone share any light on how they work with 3 or more axles?

Ta very much,

Ken

 

[Steph Dale]

Yup:

They don't. Primarily for the reasons you describe.

BTW <pedant mode = ON> I think you mean ball races. Roller bearings are available with 3/16" bores, but I can't get them under about $20 a shot. <pedant mode = OFF>

Steph

 

[Osgood]

.....Can anyone share any light on how they work with 3 or more axles?

Ta very much,

Ken

More side play in axle box/frame relationship?

A small amount of side play is required on outer axle sets if axleboxes are to oscillate up and down, but centre boxes can have any amount of side play (or be fitted with those expensive roller bearings which would have more side play?)

 

[mickoo]

More side play in axle box/frame relationship?

A small amount of side play is required on outer axle sets if axleboxes are to oscillate up and down, but centre boxes can have any amount of side play (or be fitted with those expensive roller bearings which would have more side play?)

Hole in one

In a plain bearing set up the axle floats laterally in the bearing to give side play, in a roller bearing set up the bearing outer casing floats laterally within the frame, On the Britannia the cannon box has about ¾" (dredging memory as can't lay my hands on the actual value right now) lateral play.

 

[Steph Dale]

That's interesting. I don't doubt there is more clearance in the horns for a roller-bearing vs plain-bearing loco - but in the real thing the frames bend to get round curves; in model form they don't.

In fact, it occurs to me that in the case of 7mm 'finescale' the clearance is probably between the flange and rail head. And before anyone takes issue with that, I'll remind you guys I build to that standard!

@mickoo,
Actually, one thing I can't get my head round is how the typical use of cannon boxes with roller bearings works when the loco has an inside cylinder, like an A1, for example. Any thoughts/ info? Wide bearing? Self-aligning?

Steph

 

[mickoo]

Steph, if the Britannia frames flexed and bent to go around curves they'd be in really serious trouble . Unlike earlier designs the Britannia and Standard 5 have a massive flat longitudinal plate stretcher from the cylinders to the firebox throat, the Fowler 4MT tank has a similar affair but plain bearings.
On the Brit and Std 5 the cannon boxes have to have side float as there's virtually no flex in the frames, look at any Std 5 rear wheel rim under the firebox and see where it has been touching the frames.

Other Standard engines may also have this frame trait with the large flat longitudinal stay (I know the 9F does but only as I've had my head in there), but as I've no GA drawings, photos or interest for those I'd rather not commit.

Regarding the five A1's with roller bearings, I suspect they went the same way as Stanier on 6256, 6257 and used self-aligning roller bearing boxes on the axle with the crank and cannon boxes on the other two.

MD

 

[Steph Dale]

True for later locos I guess. Once you ditch the inside motion then you have all sorts of options for frame strengthening. Even then you might be surprised how even very big lumps of steel can move around under high mass dynamic loads; but I suspect you're actually well aware - we know what big toys you play with for a living!

It'd be interesting to know whether there were significant frame differences between the roller bearing and plain bearing versions of the same class, such as the Brits and Std5 you mention.

Steph

 

[mickoo]

All Britannia's and Std 5 engines have roller bearings through out, so there are no frame changes within each class that I'm aware of, there may well be on the Peppercorn A1 and the Princess Coronations, Black 5's as well as I recall some of those were roller bearing fitted.

Flexing, absolutely, the tip of the boom on our crane flexes up to +- 3m side to side laterally if you crash stop when gantrying, even a normal ramped stop will produce a lateral flex.

MD

 

[Osgood]

That's interesting. I don't doubt there is more clearance in the horns for a roller-bearing vs plain-bearing loco - but in the real thing the frames bend to get round curves; in model form they don't.

Steph - I think I interpreted Ken's question wrongly - I had assumed he was asking about how it is done in model form and my response was penned accordingly. On reflection, and given that he creates such wonderful miniatures, I guess he meant the real thing!

I would regard sloppy horn guides as a modelling fudge, and not an engineering solution. Axial clearance would be designed into either the bearing or the primary bearing housing, the secondary housing (axle box) / horn guide design then being independent of bearing choice.

But surely plate frames only bend as a result of going round bends at speed - not in order to? Flexing is a given benefit of plate frames, since stresses can be relieved by the flexing. In the real thing, running clearances for wheel / curved rail must be designed in, just as with models.

Whilst flexing is often designed into structures to relieve stress - in the case of American-style cast steel bar frames, flexing is a definite no!

Tony

 

[Steph Dale]

Tony,

Quite right. Your correction is not purely semantics. None the less in many years of trolling through archives I've yet to see a calculation or drawing showing that sideplay was ever designed into a set of steam loco frames. Ergo it was all rules of thumb and therefore some allowance was made for frame flex in working assumptions about getting locos around bends.

As an aside, once conventions were set it would then be difficult to translate them to alternative approaches; hence bar frames not being used in the UK after WW2.

Steph

 

[mickoo]

Not related to bearings, but frame flex, one of the biggest issues with Thompsons Pacifics was frame flex around the cylinder area due to traction forces, the result being broken bolts on the smokebox saddle, looking through photos there's plenty of evidence of these engines with one, two or even three bolts missing in service. The flexing of frames also had an effect on valve timing and uneven wear in bearings and to some extent even Gresley engines suffered the same.

I have seen some references and I think drawings that allow for sideplay in engine frames, mostly eight and ten coupled, I'm sure the 9F has side play designed into the middle axle and I'm also sure the 8F has side play designed into the rear axle and some NER eight coupled freight engines as well, possibly also the WD's, being at work I cannot confirm any or either.

Where side play is designed in there also has to be corresponding alterations to the knuckle joint in the coupling rods, some having semi spherical bushes / bearings as opposed to straight or flush.

I accept there is going to be some working clearance but the gap on the Britannia cannon boxes visually appear much larger than just running clearances, especially when compared to the bogie which show virtually no gap between the cannon box and horn guide face. I didn't have a chance last night to dig out all of my Britannia notes and references but it'd be nice to know if it is tabulated somewhere and what the tolerance actually is. There may also be more information in Wild Swan on the Princess Coronation engines 6256 and 6257 as well as the 8F and I think the roller bearing Black 5's are covered in one of the sections as well in the Wild Swan Black 5 books.

I have never seen the cannon boxes modeled on any Britannia or Standard five model, real or simple psuedo covers. They are certainly visible on the leading bogie axle, but accept that on the drivers they are less visual and of course you cannot add one to the models driven axle.

Apologies to Ken for the distraction and diversion.

MD

 

[JimG]

Tony,
None the less in many years of trolling through archives I've yet to see a calculation or drawing showing that sideplay was ever designed into a set of steam loco frames. Ergo it was all rules of thumb and therefore some allowance was made for frame flex in working assumptions about getting locos around bends.

Steph,

I've seen allowances being made in driving wheel tyre profiles - witness the tyre profiles for the Caledonian 498 class dock tank...



Note the different flange width between leading/trailing and driving (centre) tyre and the different tyre widths. It's interesting to note the adjustments as well.

Jim.

 

[farnetti]

Steph,

Nothing wrong with a bit of pedantry, and enjoyed nattering to you and Simon at Warminster.

Osgood,

I can see the benefits of your suggestion as it also allows the axle to rotate around the longitudinal centre line of the chassis more freely but, at the same time might potentially upset coil or CSB springing. Maybe the movements are so small it doesn't matter.

I was referring to models rather than full size but it has unleashed an interesting dialogue between Steph and Mick on full size practice which I will have to read again a couple of times to fully understand.

I appreciate your comment about my models but this is more down to choice of kits than my abilities, luckily kits from MMP, Finney, and Slaters fall into my chosen era and area, and probably a MOK 4MT soon. Hopefully a Kemilway kit of some sort for my NPCS rake at some point.

Anyway back to read through this thread again,

Ken

 

[simond]

I'm going to bet the (Brit &) 9F frames flex measurably with every piston stroke. Not by much, perhaps, but given the piston thrust at zero speed is (in the 9F) is something approaching 80,000 lbf 35 tons, or 365kN, and the piston rod is offset by at least half the piston diameter, say 250mm plus the wall thickness, there's a huge bending moment.

Best
Simon

 

[mickoo]

I'm going to bet the (Brit &) 9F frames flex measurably with every piston stroke. Not by much, perhaps, but given the piston thrust at zero speed is (in the 9F) is something approaching 80,000 lbf 35 tons, or 365kN, and the piston rod is offset by at least half the piston diameter, say 250mm plus the wall thickness, there's a huge bending moment.

Best
Simon

I fully expect you're right, but it'll not be as near as much as a conventionally stayed engine frame and I'm not sure the thrust is that high, considering that the maximum tractive effort is only 40,000 lbs. The piston may well be able to develop 80,000 lbs of thrust but as soon as the wheel slips that force is reduce to minimal and that wheel will slip governed by the weight and tractive effort of the engine. I may be totally wrong on that mind but it appears to me that the maximum effort you can ever assert is limited by the grip of the wheel on the rail.

 

[mickoo]

Right, side play, both the black five and 8F have built in side play, the tomes fail to say exactly what it is but side play is designed into the axle boxes. In 1940 in an effort to 'increase' the side play, a directive was issued to machine 1/8" from the inside of the wheel leading and trailing wheels and relevant axle box faces.
Job 5171 refers to the 8F and Job 5168 to the Black fives (source Wild Swan) this did not reduce the minimum curvature of the engines but eased the passage through existing rated curves. The directive may also have been applied to other LMS locomotives at the time, not researched those yet.

I'll dig through some more books and see if I can find the original tolerance purely as a matter of interest.

MD

 

[simond]

Mick,

I fully agree, max TE is limited by wheelslip.

My estimate of the piston thrust was based on the ratio of wheel diameter to piston stroke (or radius of wheel to that of crankpin, which is the same number: about two) multiplied by the max published TE, which, iirc, is calculated by piston area, full boiler pressure, and that ratio inverted.

It would certainly be possible to make a first-approximation calculation on the back of the proverbial fag packet, given a set of drawings and a fag packet, but to get a comparison that you'd hang your hat on would probably benefit from a decent FE program, and a bit of time.

Best
Simon

 

[Martin Shaw]

Simon
TE is usually calculated using 85% boiler pressure. I've never yet managed to get the boiler pressure gauge and the steam chest pressure gauge to read the same.
Regards
Martin

 

[farnetti]

Just on the issue of frames and flexing, this video is interesting even though on a cargo ship. (hope it works).

Ken

 

[Eastsidepilot]

Loco's were certainly built with side play on axle boxes, the GER built C32 ( LNER F3) 2-4-2t and T26 ( E4) 2-4-0 tender loco's had 1" of side play on their carrying wheel axle boxes, the top of which had a sliding wedge device which put pressure on the springs bearing on them.
These were not pony trucks or radial boxes.
Although these loco's had conventional frames the leading and trailing axles had an outside frame with an extra bearing on the end of the axle, they had trouble with flexing as cracks did appear in the frames, plates being welded over them in later days.

Col.