7mm Scale DJH/Tower Models Streamlined Coronation

Following my query on York Paul's Standard 4 thread about the Slaters extended crank pins I promised to photograph my method (it's not my idea just one I have picked up from other builders).

For this build the front and rear drivers have the standard 12ba crank pin as provided by Slaters with their wheels. The centre axle has had the 12ba cheese head screw replaced with a 10ba countersunk screw. This is to allow the crank pin bush to be tapped 10ba and an additional bush to be added and again tapped 10ba so that they can be screwed in opposite each other to house both the couple and connecting rods (on this particular kit the extra bush was available because a pair of smaller bushes had been provided for the front axle to ensure clearance for the crossheads).

As well as tapping the crank pin bushes 10ba, I also tap the wheel itself allowing the screw to be tightened and retained.

I must admit for my own builds I tend to replace all my crank pins with 10ba and blacken the wheels but I was told not to for this build.



You can see the difference in screw sizes from the back of the wheel.



I also drilled and tapped the return crank itself but it will be soldered to the bush once I have cut it to the correct length and made sure that the crank is in the right orientation.

 

Despite many distractions recently I have made slow progress on the Coronation.

One of the easier wins over the weekend was to epoxy the balance weights on - the instructions have you do this much earlier in the build but I seem to have a tendency to do them as late as possible and I am not sure why.

Then on to the fun bits, I wanted to make the valve gear removable for painting so some mods were needed

This is what the front of the frames looked like with slots where the cylinders fed through to attach to the top of the frame spacer.



This was what they look like after a visit from my piercing saw.



Then I needed to make some spacers to attach the two cylinders together



Doing this meant that the 2mm diameter screws provided were not long enough so I retapped the holes 8BA and added some longer 8 ba screws. to hold them on.

next I soldered the slide bars to the motion bracket frame and started to assemble the valve gear



DJH provide 14ba screws/nut to assemble the valve gear which I have used but I have also done a belt and braces approach by tapping all the holes 14ba too which allows the nut to be locked on. Most of them also needed to be filed back for clearance purposes.



Last night I fitted the motor into the basic chassis and ran it for a while with the connecting rods attached. It was a good sign that nothing decided to unscrew itself while it ran (which can be a sign of something amiss).

Hopefully tonight will see the valve gear fitted and tested before stripping it back down ready for Warren to paint.

 

Hi Toto,

That depends on whether you include the preparation and soldering together of the layers that make up the parts of the valve gear. Including that then around a couple of days. Actually assembling what you see took most of Monday.

To be fair it wouldn't have been quite as long to assemble if I hadn't broke a drill bit when I drilled out the valve guide casting. This meant quite a bit of measuring and shortening of one of the valve stems. I had hoped that there was enough of the valve stem left to still work because it doesn't look to move that much. Sadly it didn't work - photos later and I will now have to backtrack and either get the broken drill out or get a replacement casting.

 

From "Woe to Recovery", it sounds like the title of a book or film

Where do I start, when assembling the cylinders, one of the jobs was to drill out the valve guides. When I drilled the first one I managed to break a drill bit of in the middle of it. I attempted to get it out by cutting off the rear spigot and drilling small holes around the end of the drill bit but didn't succeed in getting it out. I popped a bit of rod in the other end and it went a fair way in so I reasoned that I might get away with shortening the rod because the valve stems don't appear to move that much.

This was what was peeking out of the end of the casting but it wasn't quite enough to grip.



When I broke the drill bit off in the first casting, I decided to make a collet to allow me to better grip the second casting without damage and I was able to drill the second one without issue.
This is the collet and another view of my attempts to remove the offending drill bit stub



I advised the gent that I am building it for what had happened and that we may need a spare casting but I was going to attempt to work my way past it. During the assembly of the valve gear I carefully measured the amount of valve stem and progressively shortened it until it fit.

Fast forward to giving it a test run and it dropped out of the guide jamming up the valve gear.


When this happened on Tuesday evening I took the wise course and stopped to ponder.

First thing yesterday morning as I was getting up for work, Chris said I have the solution to getting the drill bit out and proceeded to explain the idea that she had dreamt while asleep. The idea was basically, to cut a cut down the side of the casting to relieve the grip from the whitemetal and then drift the stub out.

After dinner I went into the workshop to take the valve gear to bits and unsolder the valve guide casting. I then out the casting in the collet and after a bit of a fiddle managed to get the seam of the casting lined up with the slit in the collet and gripped in the vice.





That done and using an old Exacto Blade, I proceeded to cut through the side of the casting using some odour free white spirit as a lubricant (made more essential by the fact that this Exacto blade has a slight kink at one end). I kept steadily cutting until I felt the blade grating on the side of the drill bit stub (why I used an old blade) and then removed the casting from the vice.



The next bit's I forgot to take photos of but using another broken drill bit as a drift I placed the bottom end of the casting on a block of wood which I have on my bench with the protruding stub of the drill over a hole that I had drilled when going through something previously (it doesn't quite look like swiss cheese but there are a good few holes in it).

The drift moved the drill bit out a few millimetres further, to the point where I was able to grip it in a pin vice. I was then able to grip the casting in my hand and a twist of the pin vice had it free.



I then filled the seam with 70 degree solder and using the collet as a heat sink I soldered the casting back on and cleaned it up. In the photo below the seam is uppermost and is to all intents and purposes invisible.



Lastly I dismantled and remade the valve stem. The original is two layers of etch. I made the replacement from a piece of 1.10mm brass rod. I am not too happy with the boss so I plan to have another go later this morning.

This is the shortened version.


This is with the bit that I had cut off


Lastly this is the replacement.

 

Thanks Keith,

I only wish that I had thought of it first time around, and then I wouldn't have had to make a valve stem too. That said if the hole had been a tiny bit deeper I think my first recovery would have been good enough.

 

I agree, particularly when those who have no inclination to build anything, ask for a price for someone else to build an item and then think that they are being robbed at the price quoted.

That said, when you can get an O Gauge RTR loco for under £200 you can see how they might think it. But as an example,I noted earlier in the build that I had spent 47 hours building the tender on this build. The 47 hours didn't include adding the tender axleboxes either which were left off until after painting.
Using that example If I were to charge £200 pounds for building the tender there would be those who thought it expensive to 'just' build a tender when compared to the RTR loco

However when you translate that to a price per hour it works out at £4.25 per hour. How many people would be prepared to work for £4.25 an hour doing anything these days - I just had a look on the .gov website and the current minimum wage is £7.38 so an employer who offered £4.25 p/h would be regarded as wanting slave labour.

Thankfully, I haven't encountered anybody who thinks I am robbing them when I quote for a build but I know a few fellow builders who have.

 

After Wednesday's woe today is Sunshine and Joy. She runs at last. There are a couple of the fixings to sort out but the motion all works as intended after my repairs. I still need to add the reversing shaft and the speedo but then I think that I am onto the body.

 

And then there were two!

I have made a start on the backhead and as I mentioned on another thread it makes sense to do them both together now that I have the second kit to build. - Although I may also do the body in tandem I won't be doing the tender or chassis until later.