99 3462 Build diary

[Roger]

That's a great result. Just a thought about a possible simple speed regulator. You might consider putting a power Zener Diode straight from the output to ground. The diode voltage would be chosen to be the output voltage you want to maintain. As soon as the generator speeds up, the voltage will try to increase, but the Zener diode will conduct and dissipate the extra energy being generated, preventing the turbine from running much faster. Nothing will happen until the voltage reaches that point.
It's crude, but I think it might work.

Something like this ought to be close. The knee isn't going to be that sharp, so alternatively you could use a shunt regulator such as this TL431 which can be bought in a package that can sink 100mA which is probably more than you'll be able to generate. That version is an adjustable voltage type.

[stevep]

Malcolm, you can host videos on Flickr, just the same as you do a photograph. You copy the link in exactly the same way too.

[mbrown]

Thanks both.

Roger, remember that my knowledge of electronics is absolutely ziltch! But that first solution could be easy and cheap to try, so I may give it a go.

Thanks Steve - I did try posting a video on Flickr once, but for some reason it didn't work. I will try again and when I have the generator running you can listen to the sound effects!

I keep putting off further work on the running gear, but I probably need to steel myself to a few repetitive sessions to get it dealt with. But if I need more displacement activity instead, I might try making a set of four headlamps, one with a red shade for the tender..... The trickiest bit of the electrics is likely to be getting the wiring through some sort of conduit about 2 mm OD. I've not yet worked out how to do that as miniature junction boxes and pull-troughs are really too small to manage.

Malcolm

[John Baguley]

Jan 30, 2022 20:20:14 GMT mbrown said:

The trickiest bit of the electrics is likely to be getting the wiring through some sort of conduit about 2 mm OD. I've not yet worked out how to do that as miniature junction boxes and pull-troughs are really too small to manage.

Malcolm

Hi Malcolm,

Can you just run a single insulated conductor through the conduit and use the conduit itself or the chassis as the return? I've got some very thin (about 0.5mm) PTFE insulated solid core wire that we used to use in TXE2 telephone exchanges that would probably do the job.

John

[mbrown]

Thanks John,

Yes, that was more or less what I was planning. The difficulty, I think, will come with the points where wires connect - such as where one feed wire splits to supply the three headlamps. The conduit is all external and the real junction boxes are about 3" square or less - you can unscrew the lids to reveal the connectors (scale size screws, probably about 0.5 mm - Roger might manage it, not sure I can!). Even then, soldering the wires without any slack in the run will be very difficult.

Never mind, the problem won't arise for a few years, so plenty of thinking time!

Best wishes

Malcolm

[Cro]

I have stainless conduit that I use for the 5" Speedos but its no where near 2mm OD. Welcome to a length of it to see if its any use, I'll measure it later on and let you know. Its encoder cable conduit but I got it from the US with an MOQ so I get 10m at a time to make it worth it.

I'll see if I can find the details as they may have other sizes and possibly sweet talk them into a small quantity.

Adam

[Cro]

Found them! It's classed as Squarelock tube and I'm fairly certain I have the SL-18N.

www.kientec.com/products/flexible-metal-conduits/squarelock/

Adam

[mbrown]

You are way ahead of me Adam! I remembered these flexible tubes from your earlier posts and was going to approach you about sourcing them as they will be ideal for the flexible parts of the electrical system on the loco - i.e. the connections between individual headlamps and the fixed circuitry on the loco and between loco and tender.

I will send you a PM shortly to enquire about getting hold of some.

The miniature junction boxes remain an interesting challenge - but plenty of thinking time before I need them!

Malcolm

[mbrown]

Finishing the Turbo Generator

It's always the final touches that take so long....

The exhaust from the turbo generator has some quite tight right angle bends in it as it runs from the front of the generator and then up beside the chimney.

!cid_part3_A6BF0909_4017D24D@gmx by malcolm brown, on Flickr

The pipe scales 4.5 mm so I used 3/16" pipe which looks OK. To get the tight bends, I used a technique that seems to work although it needs care. First I cut a series of slits in the pipe using a piercing saw, as below...

IMG_20220205_140617 by malcolm brown, on Flickr

The pipe was then bent until these closed up, then - again using the piercing saw - I cut down the same slits, only not quite so far this time. This allowed the pipe to bend a bit further, then the procedure was repeated several times until I had a tight right angle bend.

IMG_20220205_140802 by malcolm brown, on Flickr


The bends were then sealed with silver solder, being very careful to use a minimum of solder and not to let it run into the pipe bore.

The union connecting the pipe to the generator is fitted with a prominent square flange on the prototype. This would have been incredibly fiddly to fit up and dismantle, so I used a 1/4" x 40 union and intended to make a square union nut. However, I hadn't enough clearance to allow a 3/8" square to rotate, so I had to approach it another way. I turned down a standard union nut for half its length, then made a 3/8" flange, bored a push fit onto the nut, and fitted with four 12 BA dummy studs. This allows the nut to be tightened then the flange can be pressed into place without turning it.


IMG_20220205_161255 by malcolm brown, on Flickr


Here it is, temporarily mounted on the bracket attached to the smokebox.

IMG_20220205_171736 by malcolm brown, on Flickr


And here is the little bracket to bolt the exhaust pipe to the chimney (10 BA screw). Of course I soldered the bracket onto the pipe before dropping the square flange into place - so it had to be unsoldered and re-done... we live and learn.

IMG_20220205_170446 by malcolm brown, on Flickr


Finally, especially for Steve, here is a short video of the generator on its test rig. Sorry the compressor cut in and spoiled the soundtrack.... It needs a bit more air to get it going than the early turbine I made, but this scale version has a smaller turbine wheel and more convoluted passage ways, which probably explains it. I shall have to wait some time to see how it works on steam.


VID_20220205_155241 by malcolm brown, on Flickr

Best wishes

Malcolm

[Roger]

that's a really interesting way to get the sharp bends, I rather like that. It's a crackiong mini project all on its own, and a fantastic result.

[mbrown]

Thanks Roger - although,of course, the generator itself was "bought in". When I picked it up for a song, maybe 30 years ago, I thought I might get around to making a steam turbo generator out of it one day! It's good to have got there at last.

Malcolm

[steamer5]

Nice work Malcolm!
Runs well, like you said be neat to see it on steam.

Do you plan on doing any night running at all? if so then a light for the sight glass make life much easier, do you think it could power another 1 or 2 LED's?

Cheers Kerrin

[tony9f]

Malcolm,

Absolutely outstanding work on the genny (not to say that the rest of it isn't).

Tony

[mbrown]

Hi Kerrin,

Two of the LEDs are for a water gauge lamp and a lamp in the roof which will illuminate the pressure gauge. The lamps in the cab were quite prominent so I am hoping to reproduce them.

On the real thing, there is also a light over the shovelling plate and one over the driver's timetable holder - standard DR equipment, but the former would be on the removable part of the cab roof and not many of our tracks run to timetables, so I plan to leave them out!

There are connections for three lamps on the rear of the tender, for tender-first running, and these are all used on the WEM. But the MPSB always ran trains loco first so the tender just carried one tail lamp for light engine movements after dark.

So that's why I needed to prove the generator could run six lamps - three headlamps, a tail lamp and two in the cab.

Malcolm

[mbrown]

Re-making the spring pins

Since getting the turbo generator to work, my enthusiasm for the job has waned somewhat, knowing that I really need to strip the loco right down, and reassemble with some new parts and the final fixings before I can make any more progress on the chassis. First of all, the spring pins needed remaking.

The problem here was that I made the threads 3 mm x 0.35 - using 3 mm rod and a fine thread as 1/8" looked too thick and the standard 3 mm thread looked too coarse. My undoing was that, having silver soldered the pins into their bosses, I decided to clean up the threads by running the die down them again - and thereby reduced them just enough that the nuts tend to strip. As these pins bear the whole weight of the loco, that didn't seem a good idea....

In fact, 3 mm was still over scale but 3/32" was under scale by a greater amount and I couldn't find any material in between. Then I discovered 12 swg stainless motor bike spokes - dirt cheap and good material. So I made replacement pins in this, threading them 6 BA, for which 12 g is just about right, and which doesn't look too coarse. I decided to use the old bosses and screw the pins into them with a dab of high strength Loctite.

While I was at it, I made a set of 6 BA studs for the dome. That made a total of 36 double ended studs - 16 for the loco spring pins, 8 for the tender and 12 for the dome. It took most of last weekend's workshop time.

Today, though, I decided to get on with it, but rather than strip the loco (a friend came round this evening and I wanted him to see the progress!) I did the tender.

To drill and tap the bosses accurately for the new pins, I held the old pin in a tailstock chuck, offered it up to the 4 jaw, and gently closed the jaws onto the rectangular boss.


IMG_20220220_143043 by malcolm brown, on Flickr


I then parted off the old pin, centred, drilled and tapped it 6 BA.


IMG_20220220_143502 by malcolm brown, on Flickr


Then, holding the new pin in the tailstock chuck, I put a dab of Loctite on the end and screwed it hard into the boss.


IMG_20220220_143603 by malcolm brown, on Flickr


Here are one of the old pins (top), one of the renewed ones, and two of the stainless studs which form the new pins. The old ones were too long anyway, so this gave me a chance to get the length right. When I made the originals, I wasn't sure of the camber of the springs and left too much leeway.


IMG_20220220_144808 by malcolm brown, on Flickr


And, although the light for this picture is very poor, here is one side of the tender chassis and I think it is an improvement.


IMG_20220220_154040 by malcolm brown, on Flickr


I am on the Talyllyn next weekend for some of the first trains of the season, but after that there is no real excuse for not stripping the loco chassis down and completing the other 16 spring pins.

Best wishes

Malcolm

[ettingtonliam]

What a coincidence! I've just started a thread called 'stainless steel', because I need to make some 6BA studs for valve chests and cylinder covers, and the nearest size I could find was 3mm which is 8 thou over size, making extra work for a poor little 6BA die, especially in stainless steel. Now you've come up with the solution! I shall take myself off to the local motorbike repair shop and see what I can find!

[mbrown]

I've no idea what grade they are, but I got nice threads with a far-from-new carbon steel die.

Malcolm

[mbrown]

Regulator flange


I have had a few weeks off from the workshop - partly to do other things, partly recovering from a minor op.... but mainly because most of the jobs I needed to do next didn't appeal particularly. You know the feeling...

But today I ventured forth and found myself a small job that needs doing before I get my boiler officially tested. I intend to use a Gordon Smith-type ball regulator (it works well on the Burma Mines loco) and planned to mount it on a flange which sits in between the dome bush and the inner dome.

First job was to make up a dozen 6 BA studs from 12g stainless bike spokes.


IMG_20220319_164241 by malcolm brown, on Flickr


Then I prepared a disc from 1/8" brass sheet - mounted on a 10 mm bolt to turn the edge to size. The hole will be opened out in due course to take the regulator body. A second hole accommodates the standpipe which feeds the turret. There is a gasket between the mating faces. Once the regulator is fitted, I intend to drill an array of smaller holes in the plate which will allow plenty of steam into the upper part of the dome but may deter priming to some extent.


IMG_20220319_164852 by malcolm brown, on Flickr


And then the inner dome cover goes on top of that, again with a gasket. I always smear Rocol molybdenum grease on the sides of gaskets which makes it much easier to dismantle the parts without the gasket tearing. About 40 years ago, I was allowed to fill a 35mm film canister from a friend's big tin of Rocol anti-scuff paste - I am barely half way through it three and a bit locos later - a little goes a very long way!


IMG_20220319_170545 by malcolm brown, on Flickr


When it all comes apart again to fit the regulator, I can trim off the two studs which are a tad long. But it is now all sound for the official test later in the summer.

Tomorrow I may find a few more odd jobs to get on with - but, sooner rather than later, the whole chassis is going to have to come to pieces before everything goes back together permanently. I will psych myself up for that eventually....

Best wishes

Malcolm

[mbrown]

Smokebox saddle end plates


One more job done today. As on the prototype, the smokebox is supported at the front end by sturdy plates on either side, and these are closed in at front and back by thin plates giving the appearance of the usual square saddle. I made the side plates some time ago, and today I did the front and rear covers from 1 mm steel sheet. A straightforward enough job, just needing some care to fit the curve of the smokebox and the side plates.


IMG_20220320_170956 by malcolm brown, on Flickr


IMG_20220319_180220 by malcolm brown, on Flickr


Those rust spots on the buffer beam and frames are more visible in the photo than in reality - but having spotted them I have now dealt with them!

Best wishes

Malcolm

[mbrown]

Regulator

Time in the workshop has been at a premium lately, and so, as another piece of displacement activity before I gird up my loins to strip the chassis down, I have made up the regulator which is the Gordon Smith cam-operated poppet type, with a ball valve. It is exactly to his drawings as shown in EIM, but with a 7/32" dia passage, as on his smaller design, rather than the 1/4" one he specified for a Simplex.

The vertical part of the body was machined from 3/4" gunmetal. The main steam passage and ball chamber have already been machined in the 4-jaw chuck and, below, I am drilling the 5/32" hole for the lifting spindle. This needed more offset than my small 4-jaw could really cope with, but with care it worked out OK.


IMG_20220402_161312 by malcolm brown, on Flickr


And here is the body finished - the lower section is from 5/8" gunmetal with one end threaded for the main steam pipe and the other bored to make a socket for the cam.


IMG_20220403_162610 by malcolm brown, on Flickr


Here are all the component parts - the ball with its spring and adjuster (just like a safety valve), the operating rod and link at the top, and the cam. Having made this cam, I realised I had made it to open in the wrong direction, but it was an easy job to make another - just a silly waste of PB rod!


IMG_20220403_171354 by malcolm brown, on Flickr


And here is the finished job. The cam at the right lifts the operating rod which in turn lifts the spindle for the ball valve. You can see a small clearance under the nut which lifts the ball so that the ball seats nicely and gives a small amount of play before the cam engages the ball. The short steam pipe goes through the tubeplate bush and is sealed with O rings when finally assembled.


IMG_20220403_175018 by malcolm brown, on Flickr


I have a similar regulator on my Burma Mines loco, although as that has a pull-out handle, the cams lift the ball valve via a different mechanism. But it is completely weep-free on test and quite sensitive when driving - so I hope this one will be too.

In due course, the regulator will be attached to the mounting plate in the inner dome as shown a few posts ago, but that can wait until after the boiler has had its main shell test by the BI.


Best wishes

Malcolm