David Andrews Princess Royal – A Romford Screwdriver Never Goes Out Of Style

Still working my way through getting the chassis running and I now have the inside motion running forwards at least.

As an aside I have reversed the front crankpin bushes to look more like the prototype and to give additional clearance for the motion. I was wondering about how to tighten the reversed bushes and remembered the late David Smith talking about making peg spanners as he called them. I chose a similar route but instead of pegs I used the same approach as the 4mm scale Romford screwdriver (I still have one in my modelling toolbox).

For those who haven’t a clue what I am talking about this is a Romford screwdriver

Original Romford Screwdriver

This is the leading crankpin bush that I am talking about

Front crank pin nut

This is the custom big boy’s ‘Romford’ Screwdriver that I made to tighten them. The business end is 3/16 silver steel and the end was shaped with a 3mm end mill with the rod held in a square collet block so that I could keep flipping it over to take the same amount off each side.

8BA Romford Screwdriver

If I wish to use this method of securing the coupling rods to the front wheels again in the future I will probably need to make another one with a smaller diameter to fit reversed Slaters bushes. The crankpins on this build are 8BA so bigger than most builders make them (the wheels were already tapped 8BA for the crankpins when I received them with the kit). Continuing my current ‘Dremel’ tool theme I used a ball burr in the mill to make the grip. Previously I have used the ball burr in a similar manner to an end mill by cutting into the top of the work piece. This time I did it differently and side milled it. This gave a much better finish and was easier to do. I milled the grooves before turning the taper.

MOK 8F 8425 – Replacement Brake Clevis

In between times I have managed a little more on the 8F. The next job was reassembling the brakes. One thing that has bugged me for a few years is that one of the clevis castings hadn’t fully formed when casting.

Misformed Clevis casting

It would have been easy enough to just solder it on and have done with it but I remembered fellow modeller Tony Geary making some clevises to add detail to the brakes on one of his builds so I decided to have a go at one myself.

I started with some square bar and turned a round spigot on the end. Then I reduced the next few millimetres down to the size of the arms of the clevis using a small Dremel burr as a milling cutter

Dremel Type Burr

a bit of hand filing gave me the basic shape

Basic Replacements

Then I drilled a couple of holes in either end of a stub of brass bar and temporarily soldered the two parts into it.
This allowed me to cut the slots. I do have a full sized slitting saw for the mill but a couple of years ago while in one of the cheapo trading stores I bought a set of slitting saws for a Dremel type tool (notice a theme here?). I think they were a fiver for the full set.


I fitted it into the mill with a 0.8mm blade (the pack has several different thicknesses from 0.4 – 0.8mm) and I was really surprised at how little run out it had.


This is the end slit and then finally the finished clevis


David Andrews Princess Royal – Return Cranks and Eccentric Rods

I got around the problem last night by modifying a 12BA screw and soldering the etched covers on, making a small bush from tube threaded 12BA and a small spacer. Once I get them assembled, I may not need the spacer but if I don’t they will go in the spares box.

David Andrews Princess Royal Return Crank and eccentrics
David Andrews Princess Royal Return Crank and eccentrics – Constriuent parts

I still need to add oil corks to the eccentric rods.

David Andrews Princess Royal – much ado for nothing….

Recently there has been much work but not a lot to show for it. I returned to the chassis in an attempt to get that running before carrying on with the body and cab. much of the time has been spent fine tuning the fit of the gearbox so that it doesn’t rub and getting the rear axle to pass through the gearbox and be a tight fit but still be removable for painting etc. This is more interesting because of the wheels being fixed to the axle stubs and the gearbox having ball races which want to grab onto the axle.

I also had a rather frustrating time trying to make a pin for the outer end of the return crank which attaches the eccentric rod. I had tapped the small end of the return crank 12ba and the plan was to make a small shouldered pin threaded 12BA with a large flat head that I could attach an etched cover to.

Return Crank Pin

This gives an idea of the desired pin with the etched covers below

The observant amongst you will note that the threads look very undernourished on the pin. This was possibly my fifth or sixth attempt and I kept putting it down to my having the pin too thin, too thick etc. as each time the thread came out too small for 12BA. Eventually I examined my 12ba die under some magnification and realised that one of the three cutting edges is out of line with the rest and is what I am sure was causing all the failures.

I can’t actually recall if I have used the 12BA die at all (I use the 12 BA tap set regularly but generally for fitting bought hardware) and if I have I would have only used it on brass or nickel so I very much doubt that I have deformed it. It has been consigned to the bin and a new one ordered from Chronos. in the meantime I will probably modify a a couple of 12BA set screws to get on with the job but when the new die arrives I will have to make another to prove once and for all that it’s not something that I am doing wrong.

Drill Chuck Key Comfort Handles

This may not be as relevant to some in these days of keyless chucks but here goes.

I have got into the habit of watching Youtube videos on my phone while having coffee, usually on lathes or machining of some sort. During one such video yesterday a guy in the US had made comfort handles for for drill chuck keys and when he explained why it struck a chord.

Today while at the lathe making return crank bushes for the Princess I decided to have a go at a handle for the chuck key for the drill chuck that I use on both my lathe and mill.

Chuck Key Handle
Chuck Key Handle

Really quick to make and it doesn’t need a lathe to do it. A Drill and a file would suffice. I made it so the handle was a tight interference fit and I did such a good job that I had to drill a 1mm hole in the end to let the compressed air out to allow it to push into the bottom of the main hole in the handle. It got quite a bit of use while making the bushes so this evening and it was so much more comfortable to use that I made a second one for the much smaller chuck key for my Proxxon Mini Pillar Drill

Chuck Key Handle

Both handles are made from offcuts of Delrin rod that I had in stock but they could be made from pretty much anything. I had eyed up wooden dowel, aluminium bar and brass rod before remembering the Delrin.

David Andrews Princess Royal – Cab Details

More detailing of the cab has ensued since my last update. The reverser is a mixture of David Andrews and Ragstone castings. 

David Andrews Princess Royal Cab details
David Andrews Princess Royal Cab seats

The David Andrews Seats are reasonable castings but I was struggling to work out how best to fit them. They look like the idea is that the two pegs fit into holes but I didn’t really want to be drilling holes in the cab side sheets for them. With the pegs removed there is very little to secure them so I made some replacements with a rear strip to solder to the cab side.

David Andrews Princess Royal Cab details

What is unclear is whether they fold up or down. At the minute They just drop down but if they fold up I can make a couple of stays to hold them when folded down.