mbrown
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Post by mbrown on Oct 21, 2017 20:06:25 GMT
My Lyn has working Ramsbottom safety valves on the dome. They have coned wing valves on 3/16" seats with the wings reduced as far as possible to give maximum flow through the valves - I did this by plunging a 3/16" end mill down the stem to produce three thin wings.
I got the tension spring from MJ Engineering who advertised it for one of their 2" scale traction engines - and although I made provision for fine adjustment of the tension, it opened precisely on 80 psi at the first steaming - no idea if this was designed into the spring or mere luck... the boiler is quite small at 3.5" dia with about 7 sq ins of grate. It is important, by the way, that the dimple in the top of the valves, on which the pins of the lever rest, are below the level of the valve seat. Otherwise they tend to tip when they open and won't seat squarely.
The safety valves work very well, opening and shutting cleanly although the pressure drop is inevitably a bit more than with pop valves. They passed the boiler steam test fine. The only oddity is that when they blow for the first time after raising steam, they go up very suddenly taking a lot of water with them. Thereafter, they blow much more gently - I've no idea why this is.
For that reason, and because my latest engine has a much bigger grate area, I made soft pop valves inside the Ramsbottom-type columns.
Many congratulations on your fine model!
Malcolm
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miken
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Post by miken on Oct 21, 2017 20:11:25 GMT
That's interesting Malcolm. Thanks.I won't be changing what I've made.
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Post by Jim on Oct 21, 2017 20:44:03 GMT
Lovely work Mike. You are a master craftsman with the file and emery paper which goes show what fine work can be done with basic hand tools.
Enjoying watching your progress.
Jim
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mbrown
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Post by mbrown on Oct 21, 2017 21:13:23 GMT
That's interesting Malcolm. Thanks.I won't be changing what I've made. I am sure that's the soundest decision. Ramsbottom valves can be done - but they're not ideal. Malcolm
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miken
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Post by miken on Oct 22, 2017 17:56:35 GMT
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jma1009
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Post by jma1009 on Oct 22, 2017 19:20:15 GMT
Drool drool drool!
Another masterpiece looking very complete by Mike!
So pleased to see you back at the loco again Mike.
This is going to be something very special and a most important miniature replica - on a par with Dr J Bradbury Winter's Como in Brighton Museum.
Cheers, Julian
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miken
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Post by miken on Nov 2, 2017 20:58:47 GMT
Ive been making the rear corners and cab steps.
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miken
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Post by miken on Nov 3, 2017 20:17:57 GMT
Ive been thinking about how to tackle the screw reverser for a while. On these engines it protrudes out through the spectacle plate so its got to look right. I haven't turned a multi start thread since I was an apprentice 40 years ago I dont think Ive ever made a square form thread. In the end I bit the bullet and it all went quite well. 5mm diameter, L/H, 2 start, 4mm pitch, square thread. I made the screw in stainless steel and a bronze nut. I now have no excuse for using a 3/16" whitworth thread if I build another loco with a screw reverser!
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Post by Oily Rag on Nov 3, 2017 20:42:18 GMT
The Wrought Iron Nut case hardened on the drawing intrigues me. Is is common to case harden a nut in full size back in the day ?
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Post by Deleted on Nov 3, 2017 20:49:30 GMT
lovely work, I wish that I could turn threads, my lathe just isn't up to the job...I would love to have a go at something like this...perhaps one day I'll get another lathe more suitable for jobs like this...as I said, lovely job sir...
Pete
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mbrown
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Post by mbrown on Nov 3, 2017 20:50:09 GMT
Lovely work. Did you screwcut the nut or make a 2-start tap? I made my reversing screw (similar dimensions) the latter way, but the tap was very flimsy and actually snapped on the very last turn and had to be worked out of the nut very carefully.
Malcolm
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miken
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Post by miken on Nov 3, 2017 22:50:06 GMT
Lovely work. Did you screwcut the nut or make a 2-start tap? I made my reversing screw (similar dimensions) the latter way, but the tap was very flimsy and actually snapped on the very last turn and had to be worked out of the nut very carefully. Malcolm Malcolm, I cheated a bit when I made the nut. I didn't even try to make an internal screw cutting tool. I started to make a tap from silver steel. I was about to mill the cutting flutes in it when I thought to myself"this is never going to work". Then I had another idea. I made the bronze nut part as a much larger square block but in 2 halves. I drilled the tapping size hole through so that there was half a hole in each half block. Then I took the part finished tap (which at this point was just a threaded mandrel) and with the bronze blocks either side i squashed them in the vice. This embossed the thread almost perfectly in each half. Then I silver soldered the 2 halves together. I finished the tap by milling the flutes and sharpening them a bit with an oil stone. I was going to harden and temper it but I tried it in the hole and with a bit of force i was able to clean out the thread. I Then used the tap as a mandrel in the lathe to turn the nut round.
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Post by simplyloco on Nov 3, 2017 23:43:20 GMT
I've cut quite a few multi-start threads in my time, but thankfully the Brit required only a single start 4mm Acme LH thread in stainless steel...However, i did manage to cut the nut in one piece! John
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miken
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Post by miken on Nov 4, 2017 8:49:33 GMT
Excellent Jim. I wouldn't have thought it possible.
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mbrown
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Post by mbrown on Nov 4, 2017 14:24:21 GMT
Malcolm, I cheated a bit when I made the nut. I didn't even try to make an internal screw cutting tool. I started to make a tap from silver steel. I was about to mill the cutting flutes in it when I thought to myself"this is never going to work". Then I had another idea. I made the bronze nut part as a much larger square block but in 2 halves. I drilled the tapping size hole through so that there was half a hole in each half block. Then I took the part finished tap (which at this point was just a threaded mandrel) and with the bronze blocks either side i squashed them in the vice. This embossed the thread almost perfectly in each half. Then I silver soldered the 2 halves together. I finished the tap by milling the flutes and sharpening them a bit with an oil stone. I was going to harden and temper it but I tried it in the hole and with a bit of force i was able to clean out the thread. I Then used the tap as a mandrel in the lathe to turn the nut round.
I don't call that cheating - I call it a stroke of genius! I will remember that method in case I have a "next time".
Malcolm
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miken
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Post by miken on Nov 8, 2017 20:44:05 GMT
I have done some more work on the screw reverser assembly. Note the highly technical workshop drawing I worked from.
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Post by noggin on Nov 8, 2017 21:10:25 GMT
Lovely workmanship
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Post by arch1947 on Nov 8, 2017 22:39:03 GMT
Beautiful work, I am envious.
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miken
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Post by miken on Dec 11, 2017 21:19:11 GMT
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r707
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Post by r707 on Dec 12, 2017 9:26:52 GMT
You're absolutely smashing it Mike -
The reverser is a jewel and the platework so crisp - you'll be steaming in no time :-)
All the best - ~ Phil
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