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LTM 51

Boiler cradle

When most parts had arrived and when I had completed NBDS 118, I intensified preparations for LTM 51. I had been staring at the etches for several times and at one moment I noticed I was procrastinating.

So I took a deep breath and made a first cut in this exceptionally rare etch and with that these etches become even more rare as mine was no longer untouched. It almost felt like sacrilege.

 

History was written on 8 May 2020, 75 anniversary of VE Day, end of WW2 in Europe.

 

Usually I start a project with the frame and drive. This is the most critical part of the build and often the most tedious one. The superstructure is the fun part and I reserve that for last. But at the start of this project I am still waiting for the gearboxes to arrive despite being ordered on 30 March. So far I have not even had so much as a response from High Level Kits despite reminders. I do have good experiences with them and their products though, so I will wait. In the mean time I started with the boiler cradle.

Getting acquaintanced and figuring it all out

The very first part. The project now officially has started!

After cutting all parts out of the boiler cradle fret I tried to figure out what went where.

Remember I have no building manual whatsoever, so the parts should be more or less self explanatory. I studied each and every part carefully and really most parts are obvious. In the process I cleaned the parts up, removing burrs, etch cusps and fret bridges.

 

I was quite puzzled by the frame though.

The "frame" of the boiler cradle, that is the running board, it supporting both vertical longitudinal braces and the lateral stretchers, left me with many questions.

  • Which longitudinal brace was left or right. The little hole on one of them was the clue. The drawing showed a handle under the cab on the right side. So I marked that brace with an R(ight) in the middle and V and A for front and aft on the end, and the other of course with a corresponding L.
  • Where should the Y-frame plates go (yellow arrows).
  • Why was the only one "sagging" spacer (most left white arrow). Where should it be placed? If the sagging spacer was to go on the outer end then it would not match the top of the drive unit. There was no space.
  • The triangular pieces (yellow circle) first puzzled me until I realised that they had a curved section with the radius for the boiler, so they were boiler supports net tot he tab-like slotted strips on the inside of the running board etc.
  • The six "hooks" (green circle) were soon identified as supports under the running board.

A look at the drawing helped locate the Y-plates, but the location of the short Y-plate remained more or less a mystery.

A conversation with a valued colleague builder revealed that the short Y-plate was presumably supporting the wooden cab floor. Note that the long Y-plate is halfway the spacers about to clear the boiler.

 

This conversation also confirmed that the sagging spacers really needed to go on the end of the running board. The fact that they would protrude into the surface of the top plate of the drive unit had kept from accepting that but as it turned out the drive units had a recess at the rear end. Once you know it you can see it in the drawings.

 

This meant I had to make a choice: keep the spacers and cut out the top plate of the drive unit, or shorten the spacer. As space is at a premium below the top plate the cutting out and lowering the top plate will almost certainly interfere with the gearbocI chose the latter.

I had only one sagging spacer. The conclusion was that this was an error in the etch. There really should be two, one at each end of the boiler cradle.
So I got to work. An attempt to drill the holes on the Proxxon MF70 was unsuccessful. I mis-drilled by a huge 0.2 mm! Being not all to happy with the other hole I discarded it.
So out came the old fashioned piercing saw cum files.
And after two hours of delicate and careful sawing, drilling and filing I had a reasonable copy. Just guess which one is the original.

So now I could go for a Blu-tack demonstration assembly.

Constructing the actual cradle

I have a habit of soldering running boards on a flat surface, in this case a sheet of safety glass. After each soldering action I can check if the running board is still flat.

First I tack soldered the longitudinal braces on four spot ind the order (from left to right) 2, 4, 1, 3

It is of utmost importance to prevent heat build up in the three parts. They are long and they heat up they extend considerably. If let that unchallenged the running board will distort. So after each tack let the running board cool down and then put the next tack down quickly.

Aaaaaaaahhh!

More tacks added inbetween the existing ones, each time letting the heat dissipate.

I checked the width between the braces. Where the short Y-plate neede to go everything was okay.
But at the front end a gap showed up. That was odd. I checked if the braces had followed the inner rim of the running board. I could find no fault.

Measuring confirmed: 17.8 mm behind the boiler and 18.2 at the front. Now what? After careful consideration I decided to live with it. It will be invisible, in fact it already is, it only came to light when I checked. Altering the alignment would mean I would have to fill up the gap between the brace and the inner rim of the running board which might prove impossible to hide from sight. So get over it.

So I filled in the soldering between the tacks and soldered the two Y-plates in place.

Boiler making, a reconnaissance exercise

This is where I got to the stage where I wanted to fit the boiler. I have ordered a suitable brass tube to turn but that has not arrived yet. So I tried my new turning skills on a steel tube. That did not end too happy. For some mysterious reason the new carbide tool kept only scratching the surface. So I will have to wait for the brass tube to arrive.

 

The setup here was only experimental, it was not put to work. A fried of mine advised to make a mandrel to take the tube on the live centre. I made one from wood and it worked. For the final brass tube I will make a mandrel in brass.

Bending the cab sheets

 

One of the future jobs is to bend the roof line of the cab's side sheets. This roof line has a relatively sharp bend that gradually eases into the roof itself. No easy bend to make.

 

I decide to make a bending jig which would be profiled using a template taken from the cab's backplate.

 

I scribed the roof contour on a scrap piece of 0.75 mm brass. I filed it out and made sure it matched the backplate's contour as close as I could get it.

I took a piece of angled aluminium and cut it somewhat longer then the roof top.
I filed the aluminium angle to match the brass template I had made. Time and again I touched the angle with the brass template. Especially against the light any discrepancies immediately came to light.
When I was satisfied I matched the aluminium jig against the original and approved the result. Then why the template? Well, you can match the roof only on both outer ends of the aluminium jig. Even the most perfect match does not say anything about the rest of the profile. The template however can be held in any place to check the profile over the entire length of the jig.
I scribed a nearly invisible line on the cab's backplate where the corner started. I transferred the height of that line onto the cabside. I also scribed a corresponding line on the aluminium jig.
I clamped the cab side in the vise with the aluminium jig behind it and aligned the two scribed lines. I checked for parallelism with my calipers.
Then I rolled the protruding end of the cabside over the form exerting even pressure with the another piece of aluminium angle.
Preparation: one and a half hours, actual operation: 10 seconds
If I may say so: a next to perfect fit. The other cabside followed suit.
While at it, I also shaped the roof to fit the rear and the front sheet of the cab. Again a line was scribed to locate and align the centers of both sheets. The curve is very shallow so when starting out to form the roof start gently.

Making the pivots

At this stage I turned my attention to making the pivots that will connect the boiler cradle to the power units.

 

This became an adventure and project in itself so I dedicated a separate page to the subject of making the pivots. For here I suffice to show the end result.

Boiler making

By now the brass tube I had ordered had arrived so I could get to work on the boiler. (28-05-2020)

Turning a boiler may be a challenge in itself but the first puzzle to solve is how to hold the tube in the lathe. As said, a friend of mine advised to make mandrel.

I found a suitable piece of scrap brass (actually it is the business end of clack valve from the boat of my brother-in-law, of his toilet to be exact.....). I had to do a bit of sawing and turning to get a reasonable lump of brass that was more or less suitable.

 

I am a beginning machinist and I could not get the finish much better than this. I am worried it might show up through the paint work.

On the same day I wanted to machine the mandrel to size and start work on the boiler I received two tools with carbide inserts landed on my doormat sent by the same friend.

I tried them on the would-be mandrel and boy did that give a decent finish, see the left side en judge for yourseld. Out of curiosity I took it to the spray booth and gave it a primer coat.

The difference is apparent in streaking light, and yes, yesterday's work does show up through the primer, where as today's work does not. Wow! Happy boy I am!

I now took a cut in the boiler-to-be brass tube. It is not difficult if you do not have a band saw. Just mark the tube off at the desired length, about eight marks around and follow the marks with the saw, first cutting in about two thirds of the thickness of the wall all around and in the second pass going all the way through. Not one hundred percent accurate but you will get the tube within half a millimeter.

I dialed in the end of the tube and faced off the sawed end of the tube. This is a delicate operation as the tube is only held in the chuck far, far away from the cutting action. Only light cuts will not distort the setup of the part in the chuck.

Then I turned the mandrel to a snug fit over the mandrel.

And there we have a boiler nicely snuggled in the lathe.

The mandrel holds the tube concentric on the live centre on the right. My dial indicator said there is less than 0.05 mm (2 thou) difference between left and right. Run out of the boiler is 0.15-0.25mm (6-10 thou). Not bad for a beginner. It will be concentric after turning but there will be a slight taper of about 0.1 mm (4 thou) which is well within what I find acceptable for a boiler of a model locomotive, nobody will see it. As a beginning engineer it hurts, I should do better than that. I will learn, I will learn.