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5" gauge Britannia
The numbered part of the menu to refers to the drawings and each has its own page containing information on how I made all of the parts on each of the drawings, including assembly information where appropriate. Although the drawings generally describe what is in the title, the draughtsman used any spare space to add bits and pieces so there are sometimes components that one would expect to find elsewhere.
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Assembly & Alignment Drawing Errors 1. Mainframes 2. Pony Frames 3. Main Axles 4. Coupling Rods
5. Bogie 6. Pony Truck 7. Brakes, Sanding Gear 8. Cylinders9. Link Motion 10. Oil Pumps, Saddle
11. Smokebox 12. Boiler Detail 13. Boiler Fittings 14. Superheater, Ashpan 15. Valves, Pipework 17. Cab Fittings, Clothing
18. Cab & details 19. Footplates & details 21. Tender Frames, Axles 22. Tender WPU, Brakes 23. Tender Body 24. Tender Body, Filter
Drawing Errors and Omissions
Below is a list of all the errors that I have found on the drawings, and they are quite numerous. Most are of minor concern and easily rectified but some have lead to extensive reworking when the error came to light. I would recommend that all who plan to build a Britannia from this set of drawings spend some time reviewing these errors and confirming for themselves that they are, indeed, errors and that they make provision accordingly. They are listed in drawing number order.
There is also a section at the bottom covering authenticity issues which will be added to at time goes by.
The locomotive drawings are from Norman Spink, as redrawn from the Perrier drawings by Mr Gilbert. There is no drawing no. 16
Drawing No. 1 The footplate support bracket holes adjacent to the slidebar bracket are too close to it. I had to thin my brackets to fit.
A means of supporting the front section of the footplate is required, maybe two more footplate support brackets either side of the cylinder mounting plates.
The 3/16" dia cylcock shaft holes are too close to the cylinder and need moving at 45 degrees as close to the edge of the frames as possible. Because I had already drilled mine, I made a pair of brackets. There is a picture on the "Assembly" page.
The draughtsman forgot to include a hole in the frames to access the blowdown valve. I have drilled mine on the right-hand side with access for an Allen key between the spokes of the rear driver.
Drawing No. 2 By-pass body overall length incorrectly labelled 1.1/8", should be 1.3/8".
Pump and pump stretcher - ignore the 7/16" dimensions and use the 8-hole PCD dimensions instead (0.442" for the 45 degree holes)
Drawing No. 3 The spring mounting holes in the toe of the spring brackets appears to be incorrectly positioned on the drawing and need to be nearer the centre to fit the cast springs. I offered up my springs to the mounted brackets before drilling and spotted through accordingly. Thanks to Alan W. for pointing this one out.
The driver's side wheel fouls the expansion link bracket when the suspension bottoms out. See the "Assembly" page.
Drawing No. 4

Slidebar bracket - the six frame mounting holes are 4BA, not 6BA.
Why do these lazy draughtsmen not put overall lengths of components on drawings? Front rod is 9.202", rear rod is 7.265", con rod is 12.208"
Return crank (as drawn) is 2.213" overall length.
The pins joining the front and rear rods need a screwdriver slot in the rear to aid assembly / disassembly.
The oil pump platform needs to be extended by 5/16" to 2.9/16" but the stiffening piece below stays as drawn..
Drawing No. 5 Sanity check - bogie frames 10.3/8" overall length, 5.3/8" between inner bearing faces
Bogie stretchers - easier to use 6BA bolts to fix, with 3mm dia. holes in frames and 6BA tapped holes in stretchers
Axle boxes - use sealed-for-life bearings, oil channels not required.
Drawing No. 6 Spring sockets 3/16" high
Drawing No. 7 The frame mounting holes of the footplate brackets leave the brackets approx 5/32" too high. I have used 1.243" from the top of the frames to the top of the brackets as the reference size. I have made six of the short brackets and two of the long brackets.
Drawing No. 8 The valve spindle shows 7/32" x 40 thread, then specifies 2BA nuts to fit.
Drawing No. 9 If using the expansion link bracket castings, the driving wheels foul the underside of the castings at maximum depression of the suspension. A cutaway needs to be made in the castings to clear the wheel (see the Assembly page). The fireman's side bracket also needs a cutout to clear the link at maximum throw.
Drawing No. 10 The blast pipe nozzle cannot be made as drawn. It needs to be made as two parts and fitted / soldered together.
Reversing box - the centreline of the driven shaft is 19/32" from the rear face, not 9/16" as shown. Updated below.
The width at the bottom of the pump operating lever is 9/64", not 3/8" as shown.
The reverser box is rubbish and doesn't fit the space! I have remade mine more in line with the prototype with dimensions that fit.
Drawing No. 11  
Drawing No. 12A & 12B Not an error but it is worth making the inner girder span the full length of the firebox crown. My crown deformed downwards a little under the shell test pressure and full-length girders would have prevented this. See the "Assembly" page.
Drawing No. 13 The major O/D of the small regulator valve is 3/8" dia, not 5/16" dia as shown.
Drawing No. 14 The snifter valve is shown with a 1/4" x 40 thread in the bore and 3/16" x 40 on the base. This should be 3/16" x 40 at the top ( with a 5/32" bore) and 1/4" x 40 at the bottom to fit the 1/4" dia hole in the smokebox.
Drawing No. 15 Now drg no.15 but still printed with drg no.21 in the bottom right corner.
Drawing No. 16 I have been advised by Alan W. that drawing 16 refers to the tender but this may be a legacy from the Perrier drawings. My set, redrawn by Gilbert, uses the Warnett drawings (see below).
Drawing No. 17  
Drawing No. 18  
Drawing No. 19 The smokebox footplate is drawn with the side mounting flanges projecting downwards. They were upwards in full-size.
The tender drawings supplied by Blackgates are for the BR1G tender as used on the 9F and are by Les Warnett
Drawing No. 21  
Drawing No. 22  
Drawing No. 23  
Drawing No. 24  
Drawing No. 25  
Authenticity Issues
Tender One correspondent, Don, has reminded me that the Timken covers from Blackgates are smaller than prototype. Adam Cro (see the Links page) sells a more accurate version. The look of the axle boxes can be much improved also.
     

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