I agree about the various irritating bits in the Evans design, however i do take my hat off to the man for doing what he has for the model engineering world. As you say it is a 60's design, and models have steped up a level since then.
As for the machining of the motion plate, i am a precision patternmaker by trade, making dies and patterns on CAD/CAM systems with the aid of cnc machines.. however i do like to get away from the computer, so challenge myself by maching bits the old fashioned on my bridgeport. In order to get it to look like a casting i run it through the bead blast cabinate.
The model i am doing as of the loco 'Gypsy Hill' when it was converted to motor train work (A1 class). It will be painted in the Marsh livery with LBSC on the tanks. The reason for doing this prototype is the loco had one of the more interesting paths of life, running on a number of railways. Also, hardly anyone paints thier engines Brown.. so going for somthing a little different.
It may supprise you that i am only young, which makes it all the more pleasing to see your positive coments.
a pic of STEPNEY's nearly completed cylinder assembly taken a few days ago.
i had machined the cylinders out of solid with a fabricated steamchest to drawing nearly 20 years ago as a machining excercise whilst making some other cylinders, without knowing whether i was actually going to build a 5"g terrier. quite a lot of work has been done recently to get the cylinder assembly up to a stage when it can be fitted as a complete and sealed unit to the frames. i have made a few modifications, milling out the drilled steam passageways into 2 slots with a dental burr in a hand held dremel engraver. i also re-positioned the exhaust passageways closer together and opened them up to give a freer exhaust which is otherwise rather restricted at this point.
the valve rod guides/gland housings are bolted on as per jim scott. i have used my usual method of making fabricated glands to save valuable bronze!
i wasnt happy with the fit of the original pistons, and so have lapped the bores (a wooden rod with 1500 wet and dry paper cellotaped and wrapped around to form a tight lap can be seen in the background), and made new pistons. the valves and their buckles are of course hidden, but im pleased to say everything seems to be ok with no friction or slop. packing not yet fitted to the glands or pistons. the cylinder block is also tapped underneath for drain valves each end of the cylinder. the rear covers needed altering and fabricating to produce the lugs for Stroudley type channel section slidebars.
the cheesehead screws on the valve rod guides are only temporary and have been replaced with studding and nuts to secure them and the glands.
setting the valves 'central' will be via the drain cocks, as this is far more sensitive than sight and i dont think the 'sight holes' suggested by martin evans will give much visibilty anyway!
Hi Julian, hope you are well, it's been a while since we last spoke?
It's great to see you are making good progress with your terrier. The Cylinders look great!
Unfortunately my Gypsy Hill has had to take a back seat at the moment as other projects have taken over! However I did finalise my design for the valve gear. And As i checked it against Don Ashton's dimensions it surprised me that I had managed to get it very close.
Hi Julian Wouldn't it have been lovely if the rear covers could have been cast as per your modification - just a machining job then instead of a reconstruction. I'm still looking at the possibility of retro-fitting Stroudley pattern slidebars but it will be very tight, given that all the existing valvegear is made to 'Boxhill' dimensions. Progress to No 83 has been slow but steady, but I am now at a stage where I can temporarily mount the sidetanks and some of the cab platework and can see a Terrier emerging at last. Pity it all has to be taken down to the frames again to correct some basic dimensioning errors, but I'll try to get a decent photo before then...
John, good to hear from you. I hope you will find time to make a more little progress during these cold winter months.
hi john, good to hear from you too! as jim knows i havent done much on STEPNEY for the last 6 months till a few weeks ago.
the other modification i made which i forgot to mention is that the valve rod centres are now 7/16" apart instead of 1/2". there is a rather pointless 1/8" gap between the 2 sides of the valvegear as designed, and as clearances are so tight everywhere else the odd extra 1/6" makes all the difference!
jim's terrier has been my inspiration over the last 18 months, and his standard of workmanship far superior to mine. i hope jim can be persuaded to post some pics of his completed cylinder block and nearly completed loco No. 83 EARLESWOOD.
richard, i havent any pics of machining the cylinders im afraid. the exhaust passageways were done quite easily in my dore westbury mill with a 3/16" endmill angling the head of the mill. it was a job i'd been dreading and had put off, but only took a few minutes when i got round to it. the exhaust passageways are 5/16"x3/16" which is quite a bit bigger percentage wise than as designed and equates pretty much with a 9/32" diameter hole in cross-section which will be maintained up to the blast nozzle.
the rear covers had the original boss machined off in the lathe and the existing hole for the piston rod enlarged to 3/8" dia. the new bosses were machined out of brass with a 5/16" hole through. having the bosses separate from the covers aided accurate milling of the slidebar lugs. a stepped gunmetal plug was then added and the whole lot silver soldered together. the covers then needed to be carefully set in the chuck 'inside facing out' and the holes for the piston rods drilled and reamed concentric. then everything turned the otherway round and a similar proceedure used to bore out the gland recess concentric.
i have used castings for glands in the past but find it much easier to turn down and drill and ream bronze bar with a step on the end in one go, then make the rest of the gland from 1/8" brass and silver solder together.
jim's valve rod guide arrangement can be thoroughly recommended and also provides increased bearing surface and more support for the rods. as jim has commented previously last year it enables the completed valve buckle and valve rod to be assembled and fitted as a complete unit rather than try and assemble the two parts together accurately in the steam chest. i added some 1/8" strip to the bottom of the valves so their weight is transfered to the bottom of the steam chest as per fullsize, though whether this adds anything in reducing wear im not sure.
jim very kindly gave me some spare valve castings he had, and ive machined them so there is a 5 thou gap between the backs of the valves (i was tempted to make them sort of balanced!). by my reckoning there is still full steamchest pressure on the valves whether there is a 5 thou or 1/4" gap.
ive got to plug a few redundant holes on the top of the steamchest and fix a new steam entry connection into the steamchest as far forward as possible then i think its time to fit the packing and bolt everything together for the last time!
I bought all the 'Boxhill' castings back in the early 70's as this is what it said to do in the book! (ME) I really didn't give a second thought to machining the block from the solid, although for a close scale model it allows for better fitting of a 'proper' smokebox as per the original A1's. (see earlier photo of John's Gypsy Hill block).
It was very fortuitous for me that you started this thread when you did, as it coincided with my restarting work on No 83 after more than two decades. The information input by all contributors has been most useful and it is doubtful that I would have taken as much care to get things as close as possible to prototype had you not pointed out the none-scale dimensions in the original ME plans . On the other hand I might well have had a finished and running 'Boxhill' by now...
Too cold to take photos in the workshop just now but I have attached a photo of my block from earlier this year. Not finished but the valves etc are ffitted. Overall construction is as per Martin Evans and shows his rear cylinder cover arrangement.
a bit more progress with STEPNEY... for various reasons i became sidetracked into making the smokebox saddle which is the Marsh A1X type. it is fabricated out of odds and ends and silver soldered together...
in the middle of the saddle is a fabricated exhaust manifold bolted to the top of the steamchest. i dont like bits of pipe going into the smokebox for the exhaust especially as in the BOXHILL design this leaves huge gaps in the bottom of the smokebox and the pipes are easily knocked throwing the blastpipe out of allignment. the blastpipe is partly made and screws into the top of the exhaust manifold. my exhaust passages are quite a bit more than the BOXHILL design which has very restricted exhaust passageways.
the coupling rods have been lying around partly machined and roughed out for ages, so i reckoned it was about time i finished them and stuck them on the loco.
so here's a pic after i'd been playing pushing the chassis up and down a short bit of display track. a few jobs remaining...brass oil caps required, and the temporary knuckle joint pins need replacing. i can push it along with my little finger.
the valve spindle bearing block is also made and temporarily fitted.
one of the jobs i'd been dreading were the crankpin collars. in fullsize these are plain, pushed on, and secured with taper pins. i decided to thread the ends of the crankpins 1/4 x 40 tpi and fit threaded collars flush so the threads cant be seen, and add a taper pin. drilling for the taper pins was the job i'd been dreading.
anyway a pic of one of the collars being drilled 1.55mm for the pins.
all went surprisingly well with nothing broken and everything being in line, despite the collars and crankpins being quite tough steel.
some more progress with my 5"g terrier to report...
the attached pic shows the motion plate fitted with correct Stroudley 'channel' section slidebars fitted and all the associated gubbins. machining the slidebars was quite trying, as was getting everything else to fit ok including the crossheads. the crossheads were milled out of meehanite cast iron.
quite a job in quite a small space! anyway on with the valvegear, which apart from making boiler fittings is my favourite job!
Julian, The boiler will shortly reach the top of the boilersmith's queue and the chassis should be ready to receive it when delivered in a few months. Well, as a simple assembly of mainframes/ buffer beams, that is. Currently machining the hornblocks so still very early days. All the best Jamie