Jynn: a 7 1/4" gauge wren

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Nomis
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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Sat Jul 04, 2020 6:16 pm

A painted cylinder assembly:
(There's a lot of work in all those studs)

Image20180410_185648 by simon mace, on Flickr

Meanwhile, Joe at south west steam had been working away on the wheels and motion, which meant the rolling chassis could be assembled for the first time:

ImageFB_IMG_1528570542490 by simon mace, on Flickr

ImageFB_IMG_1528570549790 by simon mace, on Flickr

I had painted the wheels seperatley, which was exciting as these were the first parts in the final colour.

You can see the couplings I chose in these pictures. I also added eyebolts to the bufferbeams, partly to allow safety chains to be used if any railways I visit require it, but mostly to provide some secure tie-down points I can use when transporting the finished engine.

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Sat Jul 04, 2020 9:01 pm

Not suprisingly the newly assembled chassis was extremely stiff, so we undertook some running-in on the kensey valley railway (the home track of south west steam).

Here is the loco out in the daylight for the first time:

Image20180519_103502 by simon mace, on Flickr

The bearings were so stiff that extra weight needed to be added to stop the wheels from just skidding along the rails - some very heavy steel wheels were found and balanced on top of the chassis.

Dad's 2/3 scale Lister was used as motive power. Note the difference in size between a scale model and a loco built to maximum dimensions:
Image20180519_104754 by simon mace, on Flickr

A few (real) miles had the main bearings and coupling rods moving a lot more easily. However, there was an interference issue with the connecting rods, so these were temporarily removed.
Last edited by Nomis on Sat Jul 04, 2020 9:12 pm, edited 2 times in total.

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Sat Jul 04, 2020 9:04 pm

A few weeks later, and the connecting rod issue is fixed, so the wren chassis is towed around again to break in the piston rings.

A job done most effectively by my friend Lee and his loco "Tazmin":

Image20190105_121011 by simon mace, on Flickr


Nomis
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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Sat Jul 04, 2020 9:09 pm

Alongside a somewhat larger engine under construction (yes, they are both 7 1/4" gauge!):

Image20190105_154306 by simon mace, on Flickr

This was a bargain, worksplates to perfect scale for about £5 each (anyone spot where these came from? Hint, they were not intended for a wren....):

Image20180510_171911 by simon mace, on Flickr

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Sun Jul 05, 2020 9:00 pm

The next thing to show you all is probably the boiler.

Here it is, complete with cleading and brass boiler bands all made by joe:

ImageDSC_0060 by simon mace, on Flickr

The dome cover was a bit of an issue, as this large part was missing from the original pile of bits. Fortunatley Joe managed to find a suitable one intended for a different engine (of the same boiler diameter).

It had to be machined to allow the safety valves to vent. It is a thick iron casting, so adds some extra adhesive weight.

This shot shows the backhead:

ImageDSC_0058 by simon mace, on Flickr

As you can see, the boiler is all copper (so will hopefully have a long working life), and has a nice deep firebox and large firedoor, which make it a very easy boiler to manage.

The regulator handle is machined from stainless steel, and is a little overscale (at my request).

The fittings into the boiler itself are all bronze, with commercial valves etc. so I can maintain / replace them when needed.

Another change from the original design drawings is the steam turret. The drawings call for a crosshead driven water pump, and a single injector that takes steam from a valve on the side of the dome (an awkward reach).

As my loco will run mostly in short bursts around the garden, the pump would not be that useful (would be better on a long club track), so instead I requested a pair of injectors. The steam turret carries four valves; the blower (centre), the two injector feeds (left and right), and the whistle valve (mounted horizontally at the right hand end). All withing easy reach when driving, and fitted with beautiful scale handwheels.
Last edited by Nomis on Sun Jul 05, 2020 9:11 pm, edited 1 time in total.

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Sun Jul 05, 2020 9:08 pm

An unusual view; the inside of the firebox:

ImageDSC_0059 by simon mace, on Flickr

You can see how deep it is here, and the quite complex work that went into it.

The firebox has a fusible plug, which is just visible in yhe middle of the crownsheet (which makes a reassuring safety feature).

The box is about 5 1/2" wide and 7" long (internally). Not huge, but enough to hold a decent amount of fuel.

The next shot is well out of sequence, but makes sense here. This is the grate & ashpan assembly:

ImageDSC_0172 by simon mace, on Flickr

Again, all stainless steel, designed and welded by Joe. The ashpan is all laser cut, so is a very precise assembly.

The ashpan is held up by two long pins that pass through the horizontal tubes. The grate then rests on the tubes, sitting inside the rectangular cutout.

It's a shame that these parts are all hidden!

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Re: Jynn: a 7 1/4" gauge wren

Post by tom_tom_go » Sun Jul 05, 2020 9:14 pm

The steam turret on the boiler is nicely machined (I want to remake mine one day) and a pair of injectors over a hand or axle pump backup should be fine providing you have good quality injectors that are reliable (I use Chiverton type as recommended by my club).

Nomis
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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Mon Jul 06, 2020 12:01 pm

The injectors are a pair of "number 4s" from polly model engineering.

Pretty reliable, although I have had some issues with the feedwater warming up (hopefully fixed now).

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Mon Jul 06, 2020 12:07 pm

Here is the boiler cleading & dome cover all painted up and curing in my van (makes a nice hot greenhouse when the sun gets on the windows):

ImageDSC_0080 by simon mace, on Flickr

And re-fitted to the boiler:

ImageDSC_0079 by simon mace, on Flickr

The nameplate came from http://steamplates.co.uk/
The website is well worth a good look around.

As they say, they are not cheap, but the quality is truely impressive. I have my choice of name, font, size, edging, material, and finish.

They are cnc machined, but there are absolutely no machining marks - you would swear they are polished brass castings.

I chose to stick them on using double sided gorrila tape, as I didn't want to risk drilling holes in the water tank.

And the name?
Its cornish for engine. Seemed about right for this one (GWR font too)

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dewintondave
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Re: Jynn: a 7 1/4" gauge wren

Post by dewintondave » Sun Jul 12, 2020 8:35 am

Lovely loco Norris! That was a great Rustoleum tutorial too. What a great finish he got :thumbup:
Best wishes,
Dave

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Mon Jul 13, 2020 5:50 pm

I don't have any pictures of the rest of the build (but can answer questions if anyone has any).

A few pics of Jynn's first weekend in steam:

ImageDSC_0118 by simon mace, on Flickr

ImageDSC_0122 by simon mace, on Flickr

ImageDSC_0121 by simon mace, on Flickr

ImageDSC_0129 by simon mace, on Flickr
Last edited by Nomis on Mon Jul 13, 2020 6:21 pm, edited 1 time in total.

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Mon Jul 13, 2020 5:52 pm

And back home after initial breaking in:

ImageDSC_0119_1572243224484 by simon mace, on Flickr

ImageDSC_0123 by simon mace, on Flickr

ImageDSC_0122_1572243224052 by simon mace, on Flickr

Nomis
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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Mon Jul 13, 2020 5:55 pm

Despite being a (relatively) small engine, Jynn is still quite a heavy object to move around, so I built a simple trolley to make things easier:

ImageDSC_0174_1582404742027 by simon mace, on Flickr

In full flight in the garden:

Image2020-02-23_09-14-11 by simon mace, on Flickr

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Mon Jul 13, 2020 6:07 pm

There have been some (minor) teething issues, but nothing I wouldn't expect from a new engine:

- getting the suspension & valve timing to work together. With hackworth gear the distance from the weigh shaft to the rear axle has quite a bit of effect on the valve events, so getting the "ride height" correct is important. The wren has leaf springs all round with short push rods to connect to the axle boxes. Shortening these rods lowers the chassis on the wheels.

- there was a tigh spot in the motion that turned out to be connecting rod bearings being slightly too tight tolerances. Fortunatley these are marine style split bearings, so easy to introduce a little "slop" until things loosen up.

- the blower was pretty weak at first. On wrens the piping for this runs from the cab, under the left hand side of the saddle tank and into the smokebox; about 4' of pretty small bore copper pipe making a pretty ideal condenser. Mostly just hot water coming out at the business end. Fixed by wrapping the whole pipe with string to insulate (held in place by soaking in thin superglue)

- some injector trouble resulting from the water in the saddle tank getting hot. I have added a couple of layers of gasket material where the tank brackets meet the boiler and smokebox. This blocks the worst of the conducted heat, and increases the air gap underneath the tank itself.

- I am still trying to get the delivery rate from the mechanical lubricator right, it is adjusted by moving the drive rod between different holes on the ratchet arm. Hopefully I am getting close now....

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Mon Jul 13, 2020 6:18 pm

I took a few close-up pictures of various parts of the engine to show some of the fine detail.

I have no idea how Joe managed to machine some of the more complex shapes in the motion work.

You can see the wrapped blower pipe running up to the smokebox here:

ImageDSC_0174 by simon mace, on Flickr

This is the lubricator drive, set here for maximum delivery (which meant a very oily exhaust, and getting covered in sooty black oil spots after driving!).

You can also just see the balance pipe between the two "legs" of the saddle tank. This has a T piece with a large ball valve that makes it quick & easy to drain the tank (either at the end of a run, or the dump hot water & replace with cold).

ImageDSC_0176 by simon mace, on Flickr

A driver's view of the cab. Everything is nice and easy to reach. I cut an opening in the cab roof to give a better sightline of the gauge glass, and Joe mounted the pressure gauge as low as possible for the same reason.
Apart from these things it is all laid out as per the prototype. The small brass handles either side of the boiler are the water controls for the two injectors, and the lever on the floor (left of the firedoor) actuates the draincocks.

ImageDSC_0175 by simon mace, on Flickr

Not sure how visible it is here, but the front part of the footplate is hinged. It flips up to give access to the boiler blowdown and ashpan.
Last edited by Nomis on Mon Jul 13, 2020 6:23 pm, edited 2 times in total.

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Mon Jul 13, 2020 6:20 pm

The finished engine, pretty as a picture :)

ImageDSC_0173 by simon mace, on Flickr

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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Tue Jul 14, 2020 12:06 pm

And here she is in action:


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Re: Jynn: a 7 1/4" gauge wren

Post by Nomis » Tue Jul 14, 2020 4:56 pm

And better one of a full lap:


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Re: Jynn: a 7 1/4" gauge wren

Post by bambuko » Tue Jul 14, 2020 5:34 pm

very nice :thumbright:
thank you for sharing

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Re: Jynn: a 7 1/4" gauge wren

Post by tom_tom_go » Tue Jul 14, 2020 7:03 pm

Nomis wrote: Mon Jul 13, 2020 6:07 pm
- getting the suspension & valve timing to work together. With hackworth gear the distance from the weigh shaft to the rear axle has quite a bit of effect on the valve events, so getting the "ride height" correct is important.
My Sweet Pea also uses Hackworth gear which required the suspension and valve timing to be adjusted when I first got it to get it spot on (it now runs in forward and reverse with no issues and does not need a push to get going even when pulling passengers, only tested with 8 people so far).
Nomis wrote: Mon Jul 13, 2020 6:07 pm
- the blower was pretty weak at first. On wrens the piping for this runs from the cab, under the left hand side of the saddle tank and into the smokebox; about 4' of pretty small bore copper pipe making a pretty ideal condenser. Mostly just hot water coming out at the business end. Fixed by wrapping the whole pipe with string to insulate (held in place by soaking in thin superglue)
The blower pipe arrangement on your Wren is similar to that on my Sweet Pea, however, I have not experienced any condensate issues. Trying to think what would cause this on your loco?
Nomis wrote: Mon Jul 13, 2020 6:07 pm - some injector trouble resulting from the water in the saddle tank getting hot. I have added a couple of layers of gasket material where the tank brackets meet the boiler and smokebox. This blocks the worst of the conducted heat, and increases the air gap underneath the tank itself.
I drilled a small breather hole through the plug of my saddle tank on my loco as the fit was very snug.
Nomis wrote: Mon Jul 13, 2020 6:07 pm - I am still trying to get the delivery rate from the mechanical lubricator right, it is adjusted by moving the drive rod between different holes on the ratchet arm. Hopefully I am getting close now....
I also had to adjust the arm on my mech lubricator when I first ran my loco as it showered me in oil. Too much oil is better than too little though!

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