MODEL ENGINEERING

IN THE STYX - 16

By Journeyman

We had a short break in Dawlish at the end of August, mainly to enjoy travelling on Brunel’s famous coastal railway line. Neither of us had ever travelled along it so it was an enormous pleasure to find it to be as spectacular as it’s reputation. Dawlish station stands right by the beach, so we had the best of both worlds while waiting . One of our trips was to the Paignton and Dartmouth Steam Railway, and we bought the all inclusive tickets for a trip up the River Dart  on the P.S. Kingswear Castle, Britain’s only coal fired paddle steamer. Newly arrived on the Dart this year from the Medway, she was immaculate, and the engines were truly magnificent, powered by a Scotch boiler burning half a ton of coal a day.

Autumn is upon us, and with it the end of the running season. Having sorted out Gooch’s boiler feed problems, we had a good problem free time at the club barbecue, but it was difficult to maintain a full head of steam without undue use of the blower. I was putting this down to the coal, of which I was using a somewhat mixed bag, until I happened to look down the chimney after disposal to discover that the blast nozzle was 5/8” off centre! Not having the drawings I was unable to see why this should be so, assuming that John Clarke the designer and builder would not have made such a mistake. The only solution that I could see was to make a new blast pipe with a dog leg to bring the nozzle into proper alignment, and then a run on the last day of the season should show if there is any improvement.

   

Boxhill  9 Oct 2013

I’m now working on the pipe work, and very largely having to work this out for myself. There is no provision for  three clack valves on the boiler drawings, one each for the crosshead pump, hand pump and injector, so the two pumps will have to share one with connecting pipes running under the boiler, and the injector have the other. It’s all a bit of a jigsaw puzzle, as it would be a lot easier to do it with the boiler removed giving better access to the connections on the top of the crosshead pump, but with anything removed it would be all too easy to run a pipe only to find that on reinstatement a pipe is in the way preventing re-assembly, spaghetti junction with dead ends!

I made up a loco inverting jig to enable me to turn it upside down easily and it has been invaluable. It’s amazing how one’s lefts and rights become confused between obverse and reverse (to use coinage terms) and a lot of concentration was needed to ensure that all the pipes went from their correct A’s to B’s and didn’t interfere with anything untoward.


Midlands Exhibition

We went to this show for the first time this year. In all the years I have been doing model engineering I have only been to 4 shows, and this made the fifth. It lived pretty much up to expectations and it was nice to make the acquaintance of one or two new helpful traders, but not such a pleasant experience dealing with those who plainly see us as a source of  easy money with no significant level of advice or service : it wouldn’t take much effort to treat us in a friendly and helpful manner; but fortunately they are a very small minority.

For me the star exhibit was the running of Tim Coles’ GT3 gas turbine locomotive. Each run was preceded by an informative description of the engineering behind the project. Two return runs on the track were an exciting experience to watch, with the scream of the turbine and the exhaust wash as it passed giving a real sensation of the power available. Had it been run at full power, 160,000rpm, it would have had 7.5 hp available, approximately 15 times that of an equivalent sized steam loco !


The big difference between this show and The Model Engineer Exhibition at Sandown Park lies in the smaller number and range of top quality models on display, and I suspect that this is due to the long history and range of awards on offer at MEX. Having said that, there were many fine models, and perhaps the fact that they were mostly dispersed throughout the whole show diluted the impact. Another difference is the absence of some of the principal traders at MEX, and one wonders why this is so. Both exhibitions are very well attended and it must be worth their while to be there. And while on the subject of exhibitions, why are those attending kept waiting until 10.00 am before being allowed in: many travel long distances and need to make full use of a whole day.


How do you set yours ?

At long, long last Boxhill has successfully ‘passed’ her first air test. If you have never set valves on a Stephenson’s link motion there are several critical parts to take into consideration. I found it difficult to visualise the sequence of admission and exhaust, but fortunately I have a factory-made Stuart 10H. Removing the steam chest cover enabled me to observe the relative positions of the eccentric and crank, i.e. 90 degree advance + the lead angle, and how these together move the valve across the ports to create optimum admission and exhaust. Following my mentor’s instructions I had already set  the eccentrics on the crankshaft but hadn’t really understood these positions, although I knew that the ports had to be open to the steam equally at both ends of the stroke (as observed on the 10H).

First attempts were complete failures, despite care in setting the valves, and this lead me to thinking that I had set the eccentrics incorrectly. One odd thing was that although I could manually turn the wheel though 180 degrees there seemed to be no exhaust. Then a bell started to ring in the back of my mind that I had fitted the exhaust manifold gaskets but had not made the hole to match the port, thereby completely blocking said passageways!  Sure enough that proved to be the case. I went through several attempts to get things running , including doing each cylinder separately (yes, daft idea), and so with everything bolted together the little loco sprang into life.

How did I see to set the slide valves?  Well, I adapted a Maglite torch. It has a very bright bulb and as you can see illuminates the inside of the steam chest brilliantly!



Year’s end

The wet autumn has encouraged the growth of masses of mosses and weeds on our paths so I’m waiting for a dry day to attack them and generally clean up all round with my pressure washer. There is real danger of a fall which I can do without, and choosing the right day is a matter of careful timing. I mentioned in an earlier Styx that being surrounded by saturated farm land means that the humidity remains high most of the time in winter, so a few dry days will be most welcome. It’s amazing to see so many of the trees still in leaf at the beginning of November, so a sharp frost or two will see to their fall. They were useful during the late October gales in providing shelter, so the results of such a warm autumn have been beneficial.

Since the air test, Boxhill has been reduced to a pile of bits ready for painting. In fact it is all laid out on a table with each part in correct juxtaposition to it’s neighbour, being very careful to ensure that left and right is strictly observed. It would be very easy to muddle bits up and finish with a nightmare situation of things just not re-assembling properly, as my level of skill does not run to interchangeability of say the four crosshead slide bars, they must go back from whence they came. Future projects may well be better engineered!

This will be the last Styx of 2013, and I must once again thank my Mentor for his amazing support, and for new friends from the Midlands Ex. whose enthusiasm for model engineering gave me a boost when I most needed it. Have a good winter in your workshops and dazzle us all next year with your latest creations.