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Post by springcrocus on Aug 31, 2015 15:07:02 GMT
Hi Steve I think your build is terrific, and I love looking at your method of doing things gives me some good ideas, just one question not a criticism as I am building a 5" 9F am I right in thinking that the Brits and 9Fs wheels were not fitted with keys. Stan As David said above, normally just a good press fit. However, you need a pretty accurate and sturdy arrangement to set the angular position of the wheels and keep them there while pressing them on OR you can have a looser fit and use adhesive. As I explained a few posts back, the reason I chose to use keys is because I no longer have to devise a method of quatering the wheels, this happens automatically, and I don't have to worry about an adhesive setting before I have pressed the wheels fully home. If I ever need to press a wheel off, it will be relatively simple whereas, with an adhesive (read "Loctite") things can be a bit more complicated. An adhesive can fail and the wheels could shift on their axles and a good press fit could go awry during the pressing operation and not be truly quartered but a key ensures that the angular position of the wheels is perfect from the start and will always remain that way. The original Britannias had hollow axles and the wheels were just pressed on but after a few instances of wheels shifting on their axles, they were all replaced with solid axles albeit with the wheels still just pressed on. I've always understood that the original problem was due to the axle deforming inwards, similar to swaging but in the other direction, during the pressing procedure, and hammer-blow agravating the situation which the solid axle overcomes. However, I can't state this with any degree of certainty and may have been misinformed. Steve |
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Post by donashton on Aug 31, 2015 16:47:23 GMT
Well I just love Dave's 'serious press fit'.
It paints a facial expression to give credence to the seriousness being applied.
It beats 'Agh', 'Hmmm', 'oooo' and lots of others!
Cheers,
Don.
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Post by vulcanbomber on Aug 31, 2015 18:08:39 GMT
A serious press fit at work is usually sorted out with Ed, his 3 handed hammer and a bit of a run up.
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Post by springcrocus on Aug 31, 2015 18:38:40 GMT
A serious press fit at work is usually sorted out with Ed, his 3 handed hammer and a bit of a run up. LOL, the mind boggles...  Steve |
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Post by donashton on Aug 31, 2015 18:59:58 GMT
.....and a bit of a run up.
Yeah, I've seen it: brilliant! I watched as the guy (not Ed, mind) grabbed a centrepop and the hand shook as the position was determined. Meantime, and out of sight of the centrepop, the hammer built up adrenalin. A sudden crash, a dull thud, and the costly casting collapsed in a heap of bits. It's gloriously funny as long as it's not you!
Thanks for brightening a dull bank holiday.
Don.
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stan
Seasoned Member
Posts: 110 
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Post by stan on Aug 31, 2015 21:11:43 GMT
Thank you Steve and Dave that is something I didn't know I thought all wheels were keyed, I do remember reading about 70039 Sir Christopher Wren developing a bad vibration which was found to be a loose wheel, seems a long while ago now.
Stan
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Post by suctionhose on Sept 2, 2015 11:48:38 GMT
Looks like you've done a good job with the keys - not easy but satisfying when it works out. The coupling rods will confirm your quartering!
FYI I usually put my keyways at 45 degrees to the crankpin. When you turn one wheel over to put on the other end of the axle, it is automatically quartered to 90 deg. (axles have keys for both ends machine in the same setup - the vice - on the same alignment which eliminates jigs or dividing. All wheels and axles are the same)
Actually, an even better way is to cut keyways first and bore crankpin holes second. The wheel is located in angular terms from the finished keyway for drilling / reaming the crankpin hole.
Fullsize, I believe, are only roughly quartered when fitted to the axle and finally quartered by machining the crankpins on the quartering machine. About a 1/4" was left for finishing IIRC.
Actually, in later practice (American I guess) the wheels were fitted without keys - press fit only. A railway fitter explained the process to me once. He spoke of scribed lines on wheels and axles that were kept aligned during the pressing operation. Should the wheel begin to rotate, as press fits often do, a wedge was driven under the wheel to bring it back on line.
The final quartering was done on the quartering machine. With a 1/4" allowance on the crankpin for finishing, some small error could be accommodated. Interesting work though!
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Post by ettingtonliam on Sept 2, 2015 19:30:32 GMT
I hesitate to disagree with all you knowledgeable chaps, but according to Eric Langridge, discussing the shifting of wheels on BR locos, he quotes a report written at Derby in October 1951, on an incident where 70011 had moved its wheels, and the report definitely refers to the wheels having been keyed onto the axles. These were the original hollow axles, possibly when solid axles were used later, the keys were omitted, because they don't seem to have been effective in preventing movement.
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Post by Deleted on Sept 2, 2015 20:48:56 GMT
In his treatise on the BR standards, under "Design of the mechanical parts", E.S. Cox simply says:
"The wheels and axles showed no departure from current practice on one or other of the regions".
Furthermore, in discussing the loose wheels problem in a later chapter, he says:
"The former L.M. practice had been adopted for the B.R.engines in which a 1 in 500 taper on the axle had been pressed into a parallel wheel seat bore to assist an even fit over the length of the assembly. This arrangement caused by its geometry a slightly tapered keyway when machined by available methods...........Instructions were given for parallel wheel seat fits, deeper and longer keys and the hand fitting of keys to be made standard for all B.R. engines".
There is no suggestion that the keys were ever omitted, before or after the axle modification.
Now I happen to have in front of me the BR works drawings for the smaller 5'-8" driving wheels fitted to the 4MT engines, and these have a keyway 2" wide by 5/8" to 7/8" deep depending on the application. And yes, Don is quite right, the keys are adjacent to the crankpin, which seems to have been general practice elsewhere.
The keys are generally difficult to spot, because it seems to have been a practice to skim the ends of the keys when the wheelsets were in the lathe for tyre turning, leaving a step in the end face of the key. However, I have several photos which confirm their presence.
For confirmation of the key position, go to the 82045 Trust website and look for the December 2013 and February 2014 news updates.
Ron
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Post by springcrocus on Sept 2, 2015 21:04:35 GMT
Good heavens, I'm starting to wish I had used Loctite now, all this fuss over a simple keyway.  Actually, it's pleasing that people are showing some interest and adding their knowledge to the pool for the rest of us. I was under the impression that the wheels were unkeyed in full-size but am obviously wrong in this assumption. However, with regard to my 5" gauge model, I am not trying to mimic exactly the original, nor do I give a monkeys where the keys are supposed to be. I chose to key the axles for the simple reason that, based on the tools and machinery available to me, this is the easiest way to ensure accurate quartering of the wheels and, more importantly, they will not move at a later date. However, I am not trying to show disdain for the purist and if another builder is aiming for full authenticity, then I applaud their efforts. An interesting discussion, please keep your comments coming. Steve |
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Post by ettingtonliam on Sept 2, 2015 21:08:09 GMT
Further reading on my part indicates that as part of the axle modifications, the keys were made parallel instead of the standard 1 in 96 taper, and the keyways made deeper, so yes, the axles had keys both before and after modification.
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Post by springcrocus on Sept 2, 2015 22:02:20 GMT
This is a photo from the Nigel Fraser Ker site and shows the rear right-hand coupled wheel.  Damned if I can see any sign of a key. Steve |
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jj
Active Member
Posts: 47
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Post by jj on Sept 3, 2015 8:28:40 GMT
Hi Steve Here's a photo of Oliver Cromwell's driver, and although I'd never noticed it before, I think you can just make out the key in line with the crankpin, or at least the break in the circular edge of the axle. Regards, John  |
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Post by ettingtonliam on Sept 3, 2015 9:23:33 GMT
Too much grease in the first photo and too much paint in the second one,both would need cleaning off properly to be certain, all I can say is from the info I have, both should be keyed. Apart from preventing the wheel moving on the axle in service(which they don't seem to have been very good at), wouldn't the keys be needed to keep the wheels aligned during the pressing on process?
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Post by donashton on Sept 3, 2015 10:01:44 GMT
'Key' and 'Lock' usually signify a measure of control as to the outcome. Neither key nor lock do the locating. I see some difficulty in expecting a small key to locate a wheel radially. What did they do on turbines, where it is necessary to jack up the shaft on oil pressure before you dare move it?
Don.
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hudson
Involved Member
Posts: 92
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Post by hudson on Sept 5, 2015 5:34:00 GMT
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Post by Roger on Sept 5, 2015 7:57:54 GMT
That's an interesting article, although it does specifically state that this method can only dismount bearings on parallel shafts, so that's not applicable here. |
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Post by springcrocus on Sept 5, 2015 14:09:17 GMT
The pony truck wheels were made in the same way as I made my main wheels (see HERE for a full description), that is using soft jaws in my 3-jaw chuck. First op was to hold on the tyre, face the back, drill bore and ream the axle hole and skim the O/D of the flange. All subsequent opeations were done holding on the flange until the wheels were finished.  The axle was also done in a similar fashion to my main axles which were covered HERE. I used EN8DM material because that is what was in stock at the time. However, they don't need quatering so there are no keyways to worry about.  I had made them a light press fit but one side was a tiny bit undersize and the wheel went on far to easy, so I employed a trick from my production engineering days which was to knurl the bearing diameter with parallel knurls. I only use caliper knurls on my lathe because they don't put anything like the stress of pressure knurling on the headstock bearings. There are gunmetal castings available to make the axle boxes but, as with the main axle boxes, I have made mine from 2" diameter mild steel billets. As described HERE the back face was first cleaned up on the lathe using the 3-jaw chuck and a 7/16" hole drilled through before the billet was then reversed and loaded to soft jaws with all other turning operations completed in one visit. Using a small boring bar and using the compound slide for varying the depths, I faced the front to length, finished the bearing bore to size and depth, bored the bearing relief at the bottom and finished the 17/32" hole through. I aimed for a light press fit on the bearing bore. Then they were milled to size the same as before  I have made the axlebox covers from some mild steel flat bar. The edges were milled to size on the Cowells mill and then the front faced off in the lathe with a small hole to locate the "Timken" covers followed by reversing and turning the spigot for the bearing bore and the bearing relief.  Finally, the edges were rounded off on the linisher and the 8BA clearance holes marked out and drilled.  This is a top view of the built-up truck although there is more work to do yet.  Thanks for looking in Steve |
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hudson
Involved Member
Posts: 92
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Post by hudson on Sept 5, 2015 18:38:35 GMT
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Post by Roger on Sept 5, 2015 20:11:32 GMT
As I pointed out, the video only talks about 'dismounting' bearings or railway wheels. The coupling it describes uses tapers and that's the reason it can be assembled with oil pressure. You can't do that with parallel bearings. |
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