Palmerston - Small England Loco as built

[philipy]

Philip

If you want the stl files for the Birmingham coaches - just ask. ......

What resin are you currently using?

Trevor

The F & B Birminghams are, I think, slightly different to the FR ones, not least because the wheels are up inside the body, under the seats, but I haven't looked in great detail. I'll keep it in mind though, thanks.

For some time I've been using the Sunlu ABS-like Water Washable in grey, but it seems to have become unobtainable recently. I used my last bit of it last night and I have a bottle of the Anycubic version being delivered today. Never used before so will have to see what happens. I did have some Elegoo water washable but that was rubbish and I wouldn't touch it again for all the resin in China!

[Trevor Thompson]

Philip

Yes the coaches you are interested in are more akin to the Ashbury 4 wheel coaches on the Festiniog, but of course they are slightly different.

However the Ashbury drawings might be a good starting point - and I have drawn those. Sketchup drawings available if required.

The coal insert is now in place and I think it does what I was looking for:

IMG_4196.jpeg (2.45 MiB) Viewed 53352 times

Trevor

[philipy]

Your coal looks great now it's finished.

I have the F & B coach drawings in the book, so I'll be able to compare when I get that far.

[philipy]

Philip

Yes the coaches you are interested in are more akin to the Ashbury 4 wheel coaches on the Festiniog, but of course they are slightly different.

Actually, I'm an idiot and got my Birmingham and Ashbury mixed up. The F & B ones ARE Ashbury, not Birmingham. Sorry.

[Trevor Thompson]

It is a long time since I finished this model - but I still haven't been able to get it to run properly. It ran for a few laps at Peter's railway a couple of weeks ago pulling the new ballast wagons - but then it stopped - ceased solid.

The issues are to do with the resin printed chassis - and the way I assembled it.

Namely:

• Connecting rods bending
  connecting rods binding
  chassis warping

I have "gone off" resin printing somewhat!

So I have been applying my new found skills with fusion 360 to re-design the chassis, wheels, connecting rods, and motor mount. In particular I want to be able to replace the motor if required, and adjust its position accurately. Testing the assembly will be easier if I can separate the chassis form the footplate for testing. So to that end I am about to filament print these re-designed components:

Screenshot 2025-09-17 at 11.06.29.png (361.23 KiB) Viewed 41521 times

I have made the motor mount in 2 parts screwed together, and the whole arrangement then screwed to the chassis via a slot each side so that it can be slid along to engage the gears properly.

I will let you know how I get on!

Trevor

[Trevor Thompson]

I can't say that my modifications have resulted in success yet. When I put it all back together it didn't take long for one of the wheels to slip on the axle, causing the mechanism to stop.

I remember from my days modelling in 4mm scale using axles that have a squared end, and wondered if this might be a way forward.

So I have found appropriate axles made by Slaters Plasticard. They are intended for their 16mm scale locomotive kits. Expensive, but if this works it will be worth it, and become a standard way of working for me.

So the axles:

IMG_5222 2.jpg (1.07 MiB) Viewed 3953 times

And the wheel I have drawn to fit it:

Screenshot 2026-07-29 at 10.07.37.png (503.49 KiB) Viewed 3953 times

I have also altered the hole for the crank so that I can use heat fitted inserts.

The wheels printed out overnight so I'm off to see if they fit!

Trevor

[philipy]

Be interesting to see how you get on.
I had a similar slipping problem and solved it in a similar but different way. Not having lathe skills, I opted for D-shaped 3mm axles from AliExpress and then printed the wheels with a D-shaped axle hole. It just needs to print two versions with the D's at 90 deg. It works fine on my Quarry Hunslet and the F &B MW also has them although so far its only been test run. The slight downside is that the axle is not a full circle in the bearings, but that doesn't seem to matter so far, but the other positive is a flat face on the axle for the gear grub screw to lock against.

[Trevor Thompson]

Be interesting to see how you get on.
I had a similar slipping problem and solved it in a similar but different way. Not having lathe skills, I opted for D-shaped 3mm axles from AliExpress and then printed the wheels with a D-shaped axle hole. It just needs to print two versions with the D's at 90 deg. It works fine on my Quarry Hunslet and the F &B MW also has them although so far its only been test run. The slight downside is that the axle is not a full circle in the bearings, but that doesn't seem to matter so far, but the other positive is a flat face on the axle for the gear grub screw to lock against.

An interesting alternative - which I am sure will be much cheaper. I will keep that in mind. The CAD and printing makes little difference - square holes and countersink face - or a "D" all the way through.

Thanks for alerting me to the alternative solution.

The down side of the Slaters axle is the odd diameter of the axle - 4.7 mm diameter. That might be some obvious imperial measurement, but it does mean that I need a 4.8mm drill to make brass bearings

Trevor

[GTB]

The down side of the Slaters axle is the odd diameter of the axle - 4.7 mm diameter. That might be some obvious imperial measurement, but it does mean that I need a 4.8mm drill to make brass bearings

Slaters website states their loco axles are 3/16" dia. This seems to be the common O gauge size of driving axle and Walsall sell a similar design to the Slaters version.

There is also a note on Slaters website claiming there are undersize counterfeit axles in ciculation being sold on Ebay.......

3/16" is approx. 4.76 mm, but the nearest metric standard sizes of bright mild steel bar are 4 mm and 5 mm.

How did you measure the axles? I don't much trust digital calipers, as I checked the calibration of mine and it reads low across most of it's range. If I want accuracy, I use a micrometer.

Graeme

[Trevor Thompson]

It measured 4.72mm on my digital calipers. So I suppose you are correct 3/16'. I have always found my digital calipers to be agree quite closely with my micrometer - so close that I rarely get the micrometer out. I have 4.8mm drills to make bushes.
Trevor

[GTB]

It measured 4.72mm on my digital calipers. So I suppose you are correct 3/16'. I have always found my digital calipers to be agree quite closely with my micrometer - so close that I rarely get the micrometer out. I have 4.8mm drills to make bushes.
Trevor

There are manufacturing tolerances on metal bar dimensions, drills and measuring instruments. Sometimes the errors add up, sometimes they cancel out.

My standard loco axle is nominally 1/4" (same as Roundhouse), but between bar size tolerances, drill size tolerances and measurement errors they always turn out to be a nice running fit in a hole reamed with a 1/4" reamer. I suspect BMS rod is made slightly under the nominal size.

The reading errors on my callipers can be up to 0.03 mm. Digital callipers aren't as mechanically rigid as a micrometer and don't have an equivalent to the clutch on the micrometer spindle. The calliper jaws can take up a slight angle which varies with the closing force, how far apart they are and where they contact the workpiece, all resulting in a variable reading.

Most of which is largely academic to the average model engineer, who hand makes model parts to fit and isn't much concerned with the tolerances necessary on parts for mass production. I remember seeing a quote from an early engineer writing to a friend and he was ecstatic that the cylinder bore of his new stationary steam engine was circular to within the thickness of a penny when machined.

Graeme