Author Topic: A "Stretch" Rob Roy - 3 1/2" gauge loco  (Read 7674 times)

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
A "Stretch" Rob Roy - 3 1/2" gauge loco
« on: May 12, 2016, 10:09:10 PM »
So, what happened was this:  I decided I needed some interaction with like minded individuals so joined my local Model Engineering Society in Basingstoke.  To join in the fun I really need a loco of my own.  Buying outright is too expensive (and not quite the thing for me) so, taking a leaf out of Jo's book, I've adopted an orphan.  The poor little chap is basically a 3 1/2" gauge Rob Roy designed by Martin Evans and published in Model Engineer.  It's modeled on a dock shunter of the Caledonian Railway (so there's an excuse to paint it a pretty blue).  Whoever started it had ideas of their own and extended it by an inch to give a bigger bunker and a pair of trailing wheels.  The front of the smoke box also has a rather smart Drummond like plan.











The workmanship seems to be of a good standard and most of the platework has been started



The boiler has been started but is not strictly according to the drawings



there seems to have been an issue withe throat plate



So, somewhat reluctantly, I've decided to start again with boiler kit from Blackgates Engineering.



So, all I need to do is to make a boiler, plumb it in, make and install a water feed pump or two and a lubricator, finish off the brass work and tanks, paint it and we're ready to go.  Should only take a week or two or three or...

Cheers,

Rod




Offline zeeprogrammer

  • Full Member
  • *****
  • Posts: 6375
  • West Chester, PA, USA
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #1 on: May 12, 2016, 10:22:35 PM »
 :cartwheel: :cartwheel: Looking forward to this.

Question. Picture 5. The gland coming out of the cylinder. I saw this before on another engine...wish I could remember...but in any case...
There are holes drilled around the circumference. Is that so a tommy bar can be used to tighten/loosen the gland?

So, all I need to do is

 :lolb: :lolb: :lolb:
I hear that so many times at work..."All we need to do is..."
And it never is.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Online b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13694
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #2 on: May 12, 2016, 10:34:18 PM »
The frame and running gear looks to be well done from the pictures Rod. Too bad about the boiler, but that's a nice looking replacement kit for it. Should be an interesting project.

Bill

Online Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12695
  • Hampshire, england.
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #3 on: May 13, 2016, 06:58:00 AM »
A Locomotive  :thinking: .... Joining these model engineering societies does strange things to people  ::) I'm sure I saw a hot air engine the other week in your workshop Rod and I know of a very nice set of castings I teamed you up with last year ;)

Does the chassis run on air? I have a couple of boilers of my own to make, joy  :facepalm:

Jo

P.S. I wasn't sure if the Basingstoke club was still running... Are they railway enthusiasts or do they actually make things?

Usus est optimum magister

Online Bluechip

  • Full Member
  • ****
  • Posts: 806
  • Derbyshire
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #4 on: May 13, 2016, 07:28:48 AM »
:cartwheel: :cartwheel: Looking forward to this.

Question. Picture 5. The gland coming out of the cylinder. I saw this before on another engine...wish I could remember...but in any case...
There are holes drilled around the circumference. Is that so a tommy bar can be used to tighten/loosen the gland?


Or a pin spanner / wrench :

http://www.bing.com/images/search?q=pin+spanner&view=detailv2&id=21FF1FFC71C4480B1BB663F0A86BBBDE656D93F0&selectedindex=44&ccid=N5V8tlPx&simid=607988068113515433&thid=OIP.M37957cb653f1575cd361fb2624189642o0&mode=overlay&first=1

Although there doesn't seem to be much room.  :thinking:

Dave

Offline wagnmkr

  • Full Member
  • ****
  • Posts: 661
  • Lindsay, Ontario, Canada
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #5 on: May 13, 2016, 08:50:07 AM »
Hmmmm ... reminds me of the set of Rob Roy castings that I have under the workbench. I must do something with them one day.

Tom
I was cut out to be rich ... but ... I was sown up all wrong!

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #6 on: May 13, 2016, 02:35:28 PM »
A Locomotive  :thinking: .... Joining these model engineering societies does strange things to people  ::) I'm sure I saw a hot air engine the other week in your workshop Rod and I know of a very nice set of castings I teamed you up with last year ;)

Does the chassis run on air? I have a couple of boilers of my own to make, joy  :facepalm:


I know, I know...

Does it run on air?  As purchased, no.  The gear is Stephenson's link.  The eccentrics had not been set.  Each eccentric has 2 4BA socket grub screws to hold it in place on the axle.  On one of these the screw was locked solid onto the axle.  I managed to break an Alan key (not "Unbrako" I assume) trying to undo it  and even the application of heat refused to budge it.  A drill wouldn't touch it but I managed to use a burr in the Dremel to get rid of most of it, so the eccentric is now moveable and there is the other screw available to set it in place (the drawings only call for one screw for each eccentric).  My next task was to immerse myself in the complexities of Stephenson's link motion which has involved a lot of head scratching but I think I'm there now (it's really quite straightforward, I think I was overthinking).  What isn't quite so straightforward is getting at the valves to see where they are in relation to the steam ports.  So the smokebox came off:



and the the inlet and exhaust pipes removed together with the steam chest covers.  The thing was, the steam chests and covers are held on by through bolts and there isn't enough room to remove the bolts enough to get the covers off so the whole assembly has to be slid out.  The steam chests were then replaced without the covers



I could now see the valve movement with the aid of a dental mirror



The rear of the eccentric straps also had to be removed to allow access to the grub screws.  Lots and lots of trial and error later I seemed to have adequate (mostly!) valve events..  So, take it all apart again and re-assemble (destroying 2 gaskets in the process -I've left them out for the moment) and after making some connections for my newly acquired airbrush pump:

<a href="http://www.youtube.com/watch?v=pt_nsRQBcDw" target="_blank">http://www.youtube.com/watch?v=pt_nsRQBcDw</a>

 That was yesterday :cartwheel:

The compressor runs out of air fairly quickly and the engine stops running at about 20psi but I'm sure there must be leaks.  I haven't looked at the pistons yet to see what they are packed with and the glands will need tightening (with a tommy bar Zee - or as I call it, a drill bit!).  But at least I don't seem to have wasted my money, which is a big relief.

Rod

« Last Edit: May 13, 2016, 02:42:24 PM by tangler »

Offline 10KPete

  • Full Member
  • ****
  • Posts: 1564
  • Nordland, WA, USA
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #7 on: May 13, 2016, 04:10:35 PM »
Well that's a big step forward! Quartering, etc. seems to be OK. I'm like Zee in that I've always wanted to build and run a
railroad around the house but I have no hands on experience with the hobby. That said, the arrangement of the engines on
that loco seem to make building and working on them a real pain in the arse with the valve chests inside the frames like that.
To be honest, that's the first loco (pictures) I've seen that way, I'm only familiar with the ones having the valves (slide or spool)
outside the frames. Is there some advantage to having the valve chests inside like that?

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline NickG

  • Global Moderator
  • Full Member
  • *****
  • Posts: 1430
Re: A &quot;Stretch&quot; Rob Roy - 3 1/2&quot; gauge loco
« Reply #8 on: May 13, 2016, 06:00:43 PM »
Looks good Rod, bit different to the norm. Seems to run well with a good exhaust beat to draw up the fire! My Mabel that i bought many years ago has inside cylinders so the valve gear is even more fiddley to get at. It has 1 grub screw, the same which is rubbish and doesnt give a very positive locking action. I was planning on  putting another in, is the axle dimpled? Was thinking of doing that once set correctly.

Sent from my LG-H340n using Tapatalk


Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #9 on: October 10, 2016, 05:10:08 PM »
Hello again folks.  Mrs T and I seem to have had rather a lot of holidays this year  8).  However, some boiler making has taken place so here is the progress to date:

You'll remember that I bought a boiler kit that included the main tube, all the necessary ready flanged plates, the boiler tubes, various bits of copper plate and bronze for the bushes.  The main tube needs trimming to length and the ends squaring so the first job was to make a pair of good fitting plugs from some scrap beech.  Roughed out on the bandsaw.



The bolt is used as a centre for trimming the plug to a good fit



I took the opportunity to scribe 4 lines at 90 degrees to each other to act guides for the various bushes that will be brazed in (note:  for the purposes of this thread, "brazing" means using silver solders with melting points of 600C plus.)



One end of the tube needs to be opened up to provide the vertical sides of the wrapper.  The plugs were pushed into the tube to provide support to stop the tube being distorted by the vice.  I made the 2 saw cuts with a nice new 32 tpi blade in a hacksaw.  I wa quite surprised how much the residual stresses in the tube have opened out the saw cut on their own.



This is my brazing hearth.  I've got a Sievert propane torch with various nozzles, you can just see the one I used in the bottom of the picture - plenty of heat available from that one  :o.  The first annealing heated the tube to dull red.  I'd forgotten how malleable it becomes once annealed.



The wrapper cheeks were opened out with the aid of this pistol action clamp - very useful



Then tweaked a bit by hand



I used one of the firebox flanged plates as a former



The bottom ends of the wrapper need extending by adding a piece of plate which is brazed to a butt strap.  The assembly will be held together for brazing by a few 1/16" copper rivets so holes need to be drilled for these.  As I mentioned, the copper is now very soft so good support was needed to drill the holes.



These show the assembly, temporarily held together with 10BA nuts and bolts.





More to come  :)














Offline joe d

  • Full Member
  • ****
  • Posts: 308
  • Montreal, Canada
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #10 on: October 10, 2016, 06:02:54 PM »
Looking good, Rod.  Will be following along.... :popcorn:

Joe

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #11 on: October 10, 2016, 06:18:19 PM »
Thanks, Joe

The throat plate needs fitting to the barrel.



So after scribing a line from the barrel



I clamped the plate to the drill table which I was able to adjust to give me a good working height and used a piercing saw to cut out the profile



After some work with a file, the throat plate protrudes just enough to give a good butt join for the braze to penetrate



The sides of the throat plate were then joined to the wrapper sides with some more 10 BA screws



I used the backhead to guide various bits of trimming and folding to get everything close to the correct shape



These are all the bits ready for the first braze.



I've purchased 2 grades of Silver Solder:  38% Ag which melts between 650 and 720C and 55% Ag which melts at 630 - 660C (we're cadmium free here in the EU).  The idea is to use the higher melting point solder for the initial steps and the lower one when joining the various assemblies together.  I replaced the bolts with copper rivets and just bent the rivets over rather than forming proper heads - the idea was to just keep the assembly together rather than squeeze everything tight.  I applied high temperature (HT5) flux to all the joints and brazed away. (sorry, no pics - too much juggling of hot stuff)





Looks a mess but penetration of the braze looks good so I'm quite pleased.

The next job is to braze the tubes to the front firebox.  The tubes are mostly 3/8" diameter with 2 x 3/4" for the super heaters. The flanged plates were supplied with all the holes already spotted.   I used a step drill for the holes and did some trials on some scrap copper.  The 3/8 holes were a tightish sliding fit on the tubes but the  3/4 holes were slightly too small.  A standard jobber drill just cut triangular holes.  I relieved the diameter of the ends of all the tubes so that they were a couple of thou undersize which was fortuitous since it stopped the tubes from sliding through the plate.



I drilled all the holes in the smokebox tube plate as well so that I could use these as a jig to help position the tubes.  Some of the holes were too close to the flange to drill all the way through so I had to drill partly through then turn the plate over to finish the hole to size.



The firebox wrapper was annealed, formed and rivetted to the tube plate in similar fashion to the boiler tube.  This time I finished off the rivets in conventional fashion but still didn't make the joint really tight.  I tried the method of putting a centre pop in the metal with the hope of raising enough burr to make adequate space for the capilliary action.  Sadly the copper seemed too soft and the centre pop raised a dome on the other side of the plate and no burr at all.  I coiled up a spring from some thin solder wire and then cut rings off to go around each tube.  The whole assembly was fluxed inside and out and heated up till the silver flowed.  More solder was fed in to the various joints, encouraged occasionally with a steel poker.





With some trepidation I showed the progress so far to my boiler inspector and he was very encouraging.  Penetration is good on all the joints.  He will want to see it again before the final operation which is attaching the backhead.  This will allow him to inspect the quality of the crown stay joints.  After that he will want to witness an hydraulic test and finally a steam test.

The latest progress was a bit of woodworking, to make a cradle to hold the boiler shell while I drill the various holes for the various bushes which will be located on the lines that I scribed earlier.



That's it for now,

Rod










Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 4013
  • Switzerland
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #12 on: October 10, 2016, 06:51:43 PM »
Looks like you are having fun  :) nice work on the boiler  :ThumbsUp:  :ThumbsUp:  :wine1:
Best regards

Roger

Online b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13694
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #13 on: October 10, 2016, 09:22:54 PM »
Seems I have missed a good bit of progress on this Rod. Its coming together nicely though...well done

Bill

Offline crueby

  • Full Member
  • *****
  • Posts: 9014
  • Rochester NY
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #14 on: October 10, 2016, 10:05:50 PM »
Great job on the boiler - you make it look so easy!

 :popcorn:

Offline Barneydog

  • Full Member
  • ****
  • Posts: 87
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #15 on: December 08, 2016, 01:29:30 AM »
Nice looking build mate.

I recently joined my local society, along with my mate Rich, for several reasons and got bitten. We are more interested in traction engines as they can run in our gardens without needing track. Had a look at some of the locos at the society and we were both like you....."We got to build one of these!!!"  Understand you completely. Like the fact that you got hold of a very good quality part build. I am experimenting at the moment with some parts and just about to start a topic for the build from scratch. Will watch yours with great interest. Once its done and running we may have to come down to Basingstoke to see it running.

Keep going. Rob Roy appears to be very well documented on the internet. It sounds like it is a very unforgiving engine build and needs great attention to detail especially the slide valves, excentrics and their setting. It looks like the chests are very close together. Have you considered replacing the through bolts with studs and nuts to make removal of the lids easier?

Julian

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Re: A "Stretch" Rob Roy - 3 1/2" gauge loco
« Reply #16 on: January 01, 2017, 05:44:30 PM »
New year and new resolutions:  I've got a boiler to make (I won't mention the wobbler broach and linishing disc kits that were delivered from Hemingway yesterday) so today I made the various bronze bushes.


When it stops raining here it looks like the weather is going to be good for boiler making - providing my pickle doesn't freeze.

Happy new year,

Rod