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Post by runner42 on Dec 14, 2018 7:32:51 GMT
Hi Lisa,
there appears to be a lot of help being given to this problem, much of it is work around fixes which can reduce the effect of the problem. However if I was in the same position, which happenstance I did experience the same problem, what I did was to strip everything down and measure each part that could affect the apparently too long piston rod. This inspection will give you a better idea of what remedial action is required. I don't think your proposition that the frames being incorrectly made has through a build up of tolerances caused this, as other issues would have became apparent before this. I assume you made the frames as a pair bolted together?
Brian
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Lisa
Statesman
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Post by Lisa on Dec 14, 2018 12:29:48 GMT
Hi Brian, pretty sure the piston rod length is just me miscalculating things when I changed the way the piston rod is fitted to the crosshead.
The cylinder cutouts in the frames - which are the likely cause of one motion bracket being higher than the other - were not entirely done as a matched pair, so therein lies the problem. As I said, impatient teenage me not making the best of decisions.
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Post by Jim on Dec 14, 2018 13:55:08 GMT
I used a similar method to the one that Adam describes to tighten the split pistons in my Burrell. The pistons were split so the piston rings could be fitted without the need to expand them over the piston. I drilled the two holes for the steel pegs in a short length of steel strap and used the holes as a guide to centre popping the end of the pistons for where the two blind holes had to be drilled. Once that was done I went on and brazed the short 1/4" long pegs into the strap knowing they would locate in the holes in the end of the pistons. Works just like a bought one.  Jim.
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Post by mugbuilder on Dec 19, 2018 7:00:31 GMT
Next on the 'oh bugger' list, it seems I need to shorten the piston rods:  |
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Post by mugbuilder on Dec 19, 2018 7:12:18 GMT
Good on you Lisa for having a go at finishing the Blowie.Just try to keep in mind that simple locos like this are very forgiving and will work ok without being a precision job. you are going great and i am sure that the finished engine will run well. Don't try to make everything to tight a fit as it is a recipricating engine with a floating crankshaft.a few thou clearance here and there works wonders. I have made 14 of them so am not totally inexperienced.I have seen one built by a bricklayer and it was built with the same tollerances that he lays briks and it was abit rough but ran OK.
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Post by racinjason on Dec 19, 2018 7:54:05 GMT
I didn't know you were on here Barry. It would be great if you shared some of your wisdom.
Cheers Jason
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Post by mugbuilder on Dec 19, 2018 23:25:17 GMT
Just an old mug builder Jason. Age is creeping up on me but it is great to see younger model engineers actually building stuff. It is good for the future of the hobby. Happy Christmas one and all.
BP.
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Post by racinjason on Dec 20, 2018 0:52:52 GMT
I'd like to be half as good a mug builder as you are.
Jason.
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Lisa
Statesman
Posts: 806
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Post by Lisa on Dec 21, 2018 6:45:37 GMT
Good on you Lisa for having a go at finishing the Blowie.Just try to keep in mind that simple locos like this are very forgiving and will work ok without being a precision job. you are going great and i am sure that the finished engine will run well. Don't try to make everything to tight a fit as it is a recipricating engine with a floating crankshaft.a few thou clearance here and there works wonders. I have made 14 of them so am not totally inexperienced.I have seen one built by a bricklayer and it was built with the same tollerances that he lays briks and it was abit rough but ran OK. My general aim is to be as accurate as I can where I can, and just make it work where I can't. Mostly this just involves working with younger me's impatience. But as you say, she should run well enough once done. Anyway, I did a bit this morning, and one piston rod is now the right length. It occurred to me that I need to shorten it by 6mm, and the thread in the piston is 6mm long; so I just unscrewed the piston, chopped the threaded bit off, and cut a new thread on the lathe. Once the piston was back on it all went fine, and one side is now able to turn a full revolution without banging against the cylinder ends, so I'll do the other side the same way. No pic's, as I was racing the heat this morning (39°C today!); but if all goes well I should be setting the valves soon. |
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Lisa
Statesman
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Post by Lisa on Dec 21, 2018 21:51:14 GMT
That's the left side done, and the valves set, I just need to pull it apart and do the other side.  The valve timing was a long-term worry, as the eccentrics and collars were done by 'impatient younger me'... but once I got the timing right in forward motion, slipping her into reverse showed that was spot on too, with the ports just cracking open at the dead centres, so that's a relief. Now I just need to repeat it all on the right side, and sort out that motion bracket. Then solder a 1/4BSP thread onto the main steam pipe so I can connect it all the the compressor. |
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Post by delaplume on Dec 22, 2018 1:49:13 GMT
Hello Lisa, Quote}---" with the ports just cracking open at the dead centres "...... When you set the valves, did you put the reverser at full forwards or full reverse position ??.... then with piston at the relevant dead centre the valve should be open by the lead...With your particular loco's design do you know what the lead figure should be ?? As a guide, our famed hero LBSC used to say}---- "an amount like that of a 2B pencil mark"....or words to that effect....I doubt if many modern folk have use of a 2B pencil but the nearest i can think of would be two Biro pen lines joined side by side OR perhaps 1/64" which is about 15 to 20 thou.. Whilst you have this good access now is the time to double - make sure all is well.....Incidentally a few years ago I re-set the valves on a 3.5" gauge Rob Roy rolling chassis by purely visual means.......I mention this because your steam chest design seems very similar to the Rob Roy's and is in 5" gauge.....so you should be ok later on if need be.... PS}--- Later that week I took the chassis over to Bridgnorth SVR where they had the 30 ton steam crane in steam....The Rob Roy chassis was plumbed into a steam take-off valve on the main manifold and it ran a treat !!............a slight case of over boilered I think ?..LoL !!  |
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Lisa
Statesman
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Post by Lisa on Dec 22, 2018 2:06:39 GMT
It's slip eccentrics, there is no reverser. The lead is 'just cracking open' at dead centres, which is what it does.
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Post by delaplume on Dec 22, 2018 2:52:40 GMT
Hi Lisa,
Sorry about that---habit I'm afraid, mentioning about the reverser I mean..........
Yes, it's slip eccentrics so you have to push the loco forwards a wee bit before opening the regulator....but your eccentrics are secured via a grub screw or similar to the axle ??... so the Point of Admission can be varied and thus the lead as well.......But "just cracking open" sounds like the 15 to 20 thou I mentioned earlier so that should be ok then....
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stevep
Elder Statesman
Posts: 1,073
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Post by stevep on Dec 22, 2018 10:12:03 GMT
Alan,
I think you will find that with slip eccentrics, they are free on the axles, and stop collars, which are held to the axles, provide the drive for the eccentric.
One of the big issues when building steam engines to published designs is that the valve gear parameters are not known. In Lisa's case, I think she has done the right thing and, having made everything to the drawings, made sure the valve is 'cracking' by the same amount at both ends, and in forward and reverse.
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Post by delaplume on Dec 22, 2018 10:42:05 GMT
Hello Steve,
I really must re-visit the basics more often !!........I've just this moment had a look at a couple of Wilesco models that I have...and they demonstrate quite nicely the slip eccentric idea.........Sorry Lisa, I hope you haven't been distracted by this ??...We are all supporting your efforts and look forwards to the loco's first steam trials...
Alan
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Post by mugbuilder on Dec 22, 2018 22:30:26 GMT
Hello Lisa, What you have done setting the valves is spot on. The thing that you need to be carefull of is to make sure that you have both sides set to run the same way . Beleive me, with slip eccentric it is easy to have one side going in forward and the other going back. I have done it a couple of times before , Very embarrasing.
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Post by delaplume on Dec 23, 2018 3:16:34 GMT
Hello Lisa, Earlier I mentioned about how the GWR crossheads were atached to the piston rods via an oval hole and a tapered wedge... I found these photos just recently and post them for interest sake only... What you can't see is that the end of the Piston rod is tapered also and is drawn into a tapered hole by the action of the tapered wedge (or glut ).. The slideways are white-metaled.. Alan   |
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Lisa
Statesman
Posts: 806
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Post by Lisa on Dec 23, 2018 4:23:44 GMT
Hello Lisa, What you have done setting the valves is spot on. The thing that you need to be carefull of is to make sure that you have both sides set to run the same way . Beleive me, with slip eccentric it is easy to have one side going in forward and the other going back. I have done it a couple of times before , Very embarrasing. Reminds me of that blow-fly-blow garratt someone did an outline drawing of in AME ages back... with a comment that it could end up going both ways at once! |
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Post by steamer5 on Dec 24, 2018 1:53:29 GMT
Hi Lisa,
The old Garratt column in AME covered that very point! Setting both engines to run forward is fine, but remember that ONE HAS to run backwards helps to improve things!
Have to remember that when I get to that point!
Cheers Kerrin
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Post by mugbuilder on Dec 24, 2018 5:43:43 GMT
Hello Lisa. People seem to forget that if a slip eccentric engine is pushed either forward or backward that it will then continue to run in that direction.
Therefore if two blowfly chassis are used to make a garratt they will both work ok as the ecentrics will set for the direction travelled. The front one will go forward and the rear one which is the other way around will technically be in reverse gear but travel in the same direction as the front.There is a blowfly garratt running in NSW and it goes very well and seems to steam well with the original boiler even though the boiler is feeding 2 sets of cylinders.
Also some people beleive that a slip eccentric engine has to have a push in the desired direction before it will run. This only applies to the firsr time that the regulator is opened. The engine can be stopped and started at will simply by opening the regulator provided that it has not been inadvertantly moved in the other direction more thar about a 1/4 turn of the wheels.
Happy Christmas. BP
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