Model Steam Engineers - Merchant Navy "spamcan"

Abby

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Merchant Navy "spamcan"
16. Jul 2010 at 23:10

With the technique for making the sprockets sorted I guess it's time to start on the loco.
The basic design will use Roger Thornber's drawings , with modifications where required.
As good a place as any to start is the frames , these are cut from 2.0mm cold rolled mild steel on the bandsaw, with straight edges and external curves done on the linisher then finished by filing .
The axle box slots were milled out with a 1/8" slitting saw , about an hour and a half and they are done so hardly worth buying laser cut frames.
The intention is to use our own castings where possible so no holes have been drilled at this stage.
A small drawing fault was found at the front of the frames where they meet the buffer beam , the measurement here should be 9/16" rather than the 1/2" stated.

here's the set-up for milling the axle-box slots.

and the finished front frames

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Dave Sohlstrom Senior Member Offline All Steamed Up! Posts: 72 Ariel, WA, USA	Re: Merchant Navy "spamcan" Reply #1 - 17. Jul 2010 at 15:43 Dan Is the merchant Navy a O-6-4 or a 4-6-O. Did you get much chatter with it in the mill cutting those pockets. Will you be building a tender or is it a tank engine. Dave
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Re: Merchant Navy "spamcan"
Reply #2 - 31. Jul 2010 at 10:33

Hi Dave , the Merchant Navy Class locomotives were 4-6-2 pacifics , built for the Southern Railway company, they were express passenger haulers and following the trend of the times had extensive , rather squarish, bodywork for streamlining , hence the nick-name "Spam-can".
These three cylinder locomotives had chain driven valve gear running in oil baths inside the frames , intended to give savings on maintenance time.
In fact the mini Walschaerts gear was a failure , mainly due to chain stretching causing strange effects on the valve timing , leaky oil pans contributed to several fires.
They were eventually re-built with conventional outside Walschaerts gear and minus the distinctive body work.
This model will try to follow the original design as closely as possible in G1 , but greatly simplifying the valve gear.
The locomotive has a tender and the axle bearing pockets cut beautifully with no chatter.
Brad has sharpened most of my milling cutters and slitting saws on the Clarkson cutter grinder and they go through steel as if nothing is there
Actually I am held up at present re-designing the inside cylinder but more of that later.
Here's a picture sent to me by Classicdelights , sure he won't mind.

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« Last Edit: 31. Jul 2010 at 18:40 by Abby »

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Abby

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Re: Merchant Navy "spamcan"
Reply #3 - 31. Jul 2010 at 18:25

I have made a few more bits for the frames , the buffer beam and bogie saddle, and cut out the rear frames which ride on the pony truck.
I have opted for steel fabrications rather than castings at this point and I have made up a tool for the fly-press to make the frame stretchers.
The rear frames have a pair of bends which were also done under the fly-press.

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« Last Edit: 02. Aug 2010 at 20:15 by Abby »

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Re: Merchant Navy "spamcan"
Reply #4 - 31. Jul 2010 at 18:36

I must say that using pressings for the "between frames" parts has proved much quicker than making patterns for castings. The horizontal mill makes short work of the tooling required as it is all 1 1/4" wide to fit between the frames , with 90° bends , when I know where the slots need to be in the stretchers I will have a go at a piercing tool.
sorry about the picture being a bit dark , right click for a new view.

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Abby

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Re: Merchant Navy "spamcan"
Reply #5 - 02. Aug 2010 at 20:02

It looks like I will have to use cylinders for the outside with conventional top slide valves .
The valves will be operated via levers passing through slots cut in the frames .
The inside cylinder will be raised and angled to clear the front axle with its slide valve on the left hand side.
It should be a fairly quick job to fabricate the cylinder from the solid and get it right before making dies for castings.
I will try to run the inside cylinder's exhaust into the left hand cylinder's exaust passageway , this should help with the plumbing and will be more prototypical .

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Abby Administrator Offline All Steamed Up! Posts: 168 coventry UK Gender:	Re: Merchant Navy "spamcan" Reply #6 - 02. Aug 2010 at 20:11 Whilst waiting for a chance to make the inside cylinder I am going to cast the drivers and the pony truck frames so that I have them ready when I need them. the drivers will be cast in brass and fitted with steel tyres.
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Dave Sohlstrom Senior Member Offline All Steamed Up! Posts: 72 Ariel, WA, USA	Re: Merchant Navy "spamcan" Reply #7 - 03. Aug 2010 at 17:21 Looks like you are making good progress. Looking forward to seeing everything assembled and running on steam. Dave
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Re: Merchant Navy "spamcan"
Reply #8 - 22. Aug 2010 at 18:14

Sorry for the break , I have had to completely re-design the inside cylinder due to an oversight on my part.
Anyway I have gone for a conventional slide valve cylinder and machined it all from brass sliced off an ingot.
The main body is the inside width of the frames i.e. 1 1/4" and is just a few thou longer than the stroke which at 13/16" is 1/16" less than DOT.
The front and rear covers are counter bored 1/16" and the steam passageways are milled into the covers.
the ports in the port plate are milled and filed to the same dimensions as per DOT to give a 50% cut-off.
The remaining bits of passageway are drilled before the port plate is soft soldered in position.
O'ring seals are retained in seal carriers and the clearances are as already described in previous build posts.
Just got to make a piston and rod and it can be finally assembled.
All threaded holes are M2.0 and I will use studs and nuts to hold it together.
The exhaust passage is not drilled yet as the plan is to share the outside cylinders exhaust and so cut down on plumbing. In fact this is true to the full sized loco.
I will most probably have to use brackets to support the cylinder between frames as once the outside units are fitted it becomes difficult to get access for screws.
Anyway let's worry about that later , I just re-installed OSX on my IMac and have to re-register ViaCad 2D/3D to get it working again so that I can look at my drawings Grrrr.
Here's the block and covers

You can see the passageways milled in the end cover!

A shot of the porting and rod seals , the rear cover is doweled with 1/16" pins to keep the rods in true position.

and an idea of what it looks like when assembled.
This type of construction needs a lot of screws to make it steam tight and you need to think ahead on the positioning so not to run into existing holes.
After marking out I used an eye loupe to position the centre punch , reckon it's time to buy a magnifying punch .
All of the milling has been done using a Chinese made compound table from Axminster's bolted onto my Medding's Drill-tru bench drill , The holes in the seal carriers were drilled after adding a rotary table on top and I am pleasantly surprised with the accuracy.

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« Last Edit: 22. Aug 2010 at 21:38 by Abby »

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Dave Sohlstrom

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Re: Merchant Navy "spamcan"
Reply #9 - 23. Aug 2010 at 02:10

Dan

Been sitting here for ten minutes trying to understand the steam passages. I do not understand how the steam is getting from under the valve port plate into the cylinders.

I feel your pain with the OSX. I have been increasing my memory from 1 meg to 2 meg and yesterday things went sideways and the computer would not restart.

Spent several hours laying in bed trying to figure out what may of gone wrong. This morning I logged on with the lap top and searched for answers. I had changed the power supply a few weeks ago so I was looking that direction. when I went to test the main plug in the mother board just fell out. plugged all the connections back in and it restarted and has not given me any more trouble today

keep up the progress reports.

Dave

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Abby Administrator Offline All Steamed Up! Posts: 168 coventry UK Gender:	Re: Merchant Navy "spamcan" Reply #10 - 23. Aug 2010 at 09:49 Dave there is a drilled hole , four holes in fact , two for each steam inlet port. The holes channel the steam below the port plate and out at either end to the passages in the end covers. Can't show a drawing as I have not installed ViaCad yet but this sketch should make it clear.
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Dave Sohlstrom Senior Member Offline All Steamed Up! Posts: 72 Ariel, WA, USA	Re: Merchant Navy "spamcan" Reply #11 - 23. Aug 2010 at 17:13 Dan Ok that helps. I've been playing with the Alibre Ver 13 beta and it has some neat new features. If the PC you have is new enough you may want to download the free ver and take a look at it. I really think you would like how it does 3D. Dave
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Abby

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Re: Merchant Navy "spamcan"
Reply #12 - 23. Aug 2010 at 20:37

I have been having problems due to overheating on the Imac , you can't easily take them apart so I connected my workshop vacuum cleaner to the various vents and gave them a severe sucking , reset the disc permissions and lo' and behold , temperature is down by 25°C and ViaCad is working again so no new Mac needed yet and no re-installation of ViaCad necessary either.
Managed to get the inside cylinder located between the frames so that I can determine where the exhaust passage needs to be to connect with the outside cylinders. It looks good, but I have to decide how to fix it to the frames next.
May have to be by external brackets , however I do it I will have to make new frames because the first set have been cut for the fitting of my first inside cylinder attempt.

the connecting rod is is well clear of the leading axle now

I really need the driving wheels before I do much more so it's time for some castings.

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Dave Sohlstrom

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Re: Merchant Navy "spamcan"
Reply #13 - 23. Aug 2010 at 22:34

Dan

It's looking good. It looks like you will be holding the outside cylinders with counter sunk screws. Would it also be possible to use counter sunk screw for the center cylinder when you make the new frames. Then you could mount the outside cylinder steam chests that would cover the screws holding the center cylinder in place.

Life with drivers will be better for getting all the angles where you want them.

Good news on the computer.

Dave

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Abby

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Re: Merchant Navy "spamcan"
Reply #14 - 24. Aug 2010 at 04:11

Dave if the outside cylinders are screwed on first, then there is no access to do the same with the inside cylinder. The same applies if the inside cylinder is mounted first.
This is of course if c/s screws through the frames are used.
Only the lower section of the inside cylinder, below the bore , is thick enough to take any depth of screw thread.
For easy assembly the most sensible approach would be to mount each outside cylinder on its respective frame using flush fitting C/S screws through the frames , with the inside cylinder mounted slightly backwards ,nearer the axles , it should be possible to fit a C/S screw either side and a pair of small angle brackets should secure the front.
Well that's the plan , but as you agree having the drivers will make things easier to work out.
I am also going to make the front bogie , the drawings show that there is very little clearance if any between the wheels and cylinder front covers so better to sort these problems early.

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