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GWR 'Paddington'
by Barry Leach

Latest Update 05-August-2018

Barry Leach
It's been a number of years now since this project was started. Progress has been positive but maybe not spectacular.

One thing that does not make sense is why over the same time frame the price of a pair of Cylinder Block Castings (just the blocks - no end covers etc) has risen from about £280 to £1113.

However, things have recently (April 2016) changed considerably. I bit the bullet and bought the cylinder castings when they were offered at 15% discount. However, during machining it was found that they were 'not suitable for purpose'. On returning the castings for replacement I was offered a refund as the suppliers had no intention of supplying any more castings as they were too difficult for the foundry. These particular castings have now been removed from their website. Modellers of 'Paddington' - you're on your own!
Someone else's 'Paddington' at Donnington 2004

However, an advert on the 7.25"G Society website has paid dividends. Contacts made via the website have supplied me with Wheel Castings at a price substantially below that required by our normal model suppliers. Unfortunately, several of the castings that I have already purchased could have been supplied by the same contacts at a substantially lower price than what I'd paid! It does show the advantages that can be gained by joining a group of fellow enthusiasts.

In addition, Polly Model Engineering produce a number of Lost Wax castings for their locomotives which are the same as those required by 'Paddington' and are at prices substantially below the prices charged by other suppliers, i.e. Brake Hangar Brackets £42 (£177), Brake Hangars £66 (£260), Brake Blocks £42 (£184), Brake Shaft Split Inner Bearing and Inside Weightshaft Split Bearing (same casting) £12 (£72).

When I first started 'Paddington' I noticed that many dimensions on Sheet 1 of the drawing pack were specifically marked as "Use dimension marked DO NOT scale drawing". I naively thought that this meant that someone had 'proved' the drawings and there should be few problems. How I was wrong. I have listed below the concerns that I have with areas of the 'Paddington' drawings so hopefully others can perhaps be better prepared than me. Please take my comments for what they are, they are MY comments. Please feel free to e-mail me if you would like to comment on any of them (or warn me of any I've yet to find).

As I have found the dimensions of many piece parts to be suspect I have taken to redrawing them with CAD before cutting metal. This has enabled me to build up a 'library' of parts and 'assemble' them on paper in order to give more confidence that the parts will go together. I now have a very effective CAD General Arrangement drawing. This CAD work has worked especially well with the valve gear. From my CAD drawings I estimate that the maximum cut-off in forward gear is 75.6% and in reverse gear is 77.0%. Don't know whether these are a little low for an engine that was designed to pull empty stock out of Paddington.

My CAD work has even given me new drawings for the frames, but I don't think I'll get a new pair laser cut.

Sheet 1

The location of the buffer beam brackets is questionable. Photographs of all 1500T Class engines clearly shows that the buffer stock is the same height as the front buffer beam. However, the two are not the same on 'Paddington'. I have decided the best course of action is to centralise the front buffer stock vertically in the buffer beam.

There is a group of ten 'G' holes along the top of the frames, behind the centre axlebox position, that are for the Rear Side Tank Support bracket. The relative positions of the ten holes DOES NOT match the hole positions dimensioned on the Rear Side Tank Support bracket on Sheet 4.

Also, the datum dimension which has been changed to 4" seems incorrect. With the dimensions of the location of the matching support plate on the tanks, I think the dimension should be nearer 3.75" (which may have been the original dimension).

The group of five holes ahead of the centre axlebox position and immediately behind the large weighshaft hole for the Rear Motion Bracket Support have had the datum dimension changed to 2.875". With this dimension the lower hole of the front row falls into the weighshaft hole. Also, the Front Motion Bracket Support position of 1.750" behind the front axle, and the Motion Gear Stretcher position of 2.5625" ahead of the centre axle, is correct for the size of the Motion Bracket. However, the resulting position of the Rear Motion Bracket is completely wrong. A fixing screw position of 2.625" seems more correct than the amended dimension of 2.875". This would certainly correct the problem with the weighshaft hole. So many holes in my frames to be possibly filled and re-drilled :(

Just ahead of the 'M' hole, there is a group of 17 holes (top row of 5 holes that also hold the cab floor, plus two rows of 6 holes). The drawing asks for a No.29 drill hole (4BA Clear). The bottom 2 holes of the back row of 6 holes would be better drilled for a 4BA tapped hole, as 4BA nuts on the inside of the frames foul the Sander Handle Support Bracket fitted to the 'K' holes inside the frames.

There is a line of four holes (No 29 drill 0.5" apart) directly above the brakeshaft inner bearing holes for fixing the Cab Step Stretcher (marked 'z'). As they stand these four fixings are offset to one side of the stretcher and need moving 0.062" to the rear (right on the drawing) in order to centralise them (perhaps they should be offset?).

The top two 'H' holes for the sanding gear Bellcrank are superfluous if the bellcrank bracket on Sheet 8 is correct.

The two right hand fixing holes for the upper Rear Drawbeam Stretcher (i.e the two fixings that DO NOT hold the Corner Bracket) on the Right Hand Side frame only need to be suitable for countersunk screws as these positions foul the fixing brackets for the Rear Frame Toolbox.

There are two holes slightly above and to the left of the 'ac' fitting (Brakeshaft Bearing). I have NO IDEA for what these holes are used.

The large rectangular slot through which the rear sandbox levers pass does not have a dimension for its position from the top of the frame. I think the top of the slot should be 1.907" from the top of the frame.

There is a pattern of six (6) fixing holes for holding the Front Beam Support Bracket which are dimensioned 1 31/32" back from the front axle centre line. This dimension brings the front fixing screws right in the corner of the brackets. I think this dimension would be better increased to 2 1/16".

Sheet 2

Verify the required positions of the buffer stocks.

Sheet 3

No obvious problems found on this sheet.

See note on Sheet 1 for the Cab Step Stretcher (shown on this sheet) fixing holes.

Sheet 4

Rear Tank Support Bracket fixing holes do not match those dimensioned on the frames (see Sheet 1). The dimensions on this sheet appear to be the correct ones.

The Rear Support Beam for Side Tanks shows 8 holes of No.35 drill which is a hole size for a large fixing. I reduced the hole for a 7BA bolt (8BA head) which seems to fit the beam much better.

The Rear Drawbeam Steps were fixed direct to the rear buffer beam when the locomotives were new built and this is how 'Paddington' is drawn. Within a few years most of the locomotives had been modified to have the steps turned through 90degs. However, a dimension on the drawing is incorrect. The lower of the two 0.5" dimensions should be 0.656" for the 1.562" dimension to be correct.

Pictures of various members of the Class 1500T shows the design of the Lower Front Side Steps to be different between engines (at least when they were a few years old). Look at a picture of your particular model to see how your steps should look.

Check whether the specific locomotive being built does have Upper Front Side Steps.

Cab Side Step. The overall dimension of 5.562" does not match the sum of the individual dimensions. Actual height on my locomotive steps was only 5.5" with the 0.875" dimension being 0.750". This allowed the individual dimensions to match the new overall size (i.e. 5.5").

The dimensioning of the Brake Crossbars is questionable. The overall length of the crossbar seems correct at 8.75" but the key dimension should be the distance BETWEEN the brake hangers (7.312" assuming the Brake Hanger Bracket is 0.437" (checked from job)). Also, the threaded end sections need only be 0.344" long rather than 0.406". This gives a 0.031" extension after fitting the required 0.062" washer, and 4BA and 5BA nuts. These 'amendments' maintain the dimensioned 8.75" overall length.

There is no detail for the Brake Operating Lever, only a side view. A photograph of 1501 shows the lever to be forked with an offset to align with the pull rod.

The 'Brakeshaft Assembly Plan' shows a dimension of 1 11/32" for the distance from the mainframe to the Steam Operated Lever centre line. From my locomotive I believe this dimension should be 1 1/32" (i.e 5/16" less).

Front and Rear Life Guards - the drawing shows these as 5/32" thick. Who can bend that? Model Engineers Laser supply these as 3/32" thick, much more sensible.

Sheet 1 shows the bottom of the Front and Rear Life Guards to be 7" from the top of the frame. As drawn the Front Life Guard is too short to meet this dimension and needs to be 3 23/32" instead of the 3 5/8" shown.

Sheet 5

The Sandbox Operating Levers have a 0.125" spacer below each of the forks. These spacers were superfluous with my 'Reeves' laser cut frames (their slot was lower). However, with the rear sandbox lever slot positioned 1.907" from the top of the frame (as stated on Sheet 1 notes) the spacers are needed.

The General Arrangement of the Sandbox Location fails to show the Front Tank Support Angle Brackets which makes the Operating Lever more complicated than shown. The bracket for the Bellcrank is drawn on Sheet 8.

I found that the link between the Rear Operating Handle Assembly and the Left Rear Sandbox required a 0.5" vertical step in order for the link to correctly fit into the two forks. This is not shown on the drawing.

Sheet 6

Pump Piston - length is suspect. I had to decrease mine by 1/8" (4" overall length).

Sheet 7


Sheet 8

The Connecting Rod is drawn as 0.312" thick with a 0.093" web thickness. I think this should be 0.093" web DEPTH from both front and back giving a 0.125" web thickness, although it may be considered that this is rather thin.

The Bellcrank Bracket vertical pin length is dimensioned at 0.5", this is too short and should be nearer 0.75". The bracket only shows a single fixing hole which correlates with the bottom hole of the three holes shown as 'H' holes on Sheet 1. The top two 'H' holes are incorrect (or superfluous) for the bracket as shown.

Reversing Arm Bush. The drawing states 6 off at 0.5" diameter. Based on the Reversing Arms shown on Page 9 there should only be 2 off at 0.5" diameter and 4 off at 0.437" diameter.

The Weighshaft Assembly shows a centre distance of 11 1/2". To correctly align with the Cylinder Valve centre line this should read 11 9/16" (6 7/16" (Outside Frame dimension) + 2 9/16" + 2 9/16").

The Weighshaft Assembly includes a Weighshaft Compensating Lever, however, nothing appears on any other drawing to show how/where this is connected. All my detail locomotive pictures appear to be from the LH side so further investigation of the RH side Motion Bracket is required.

Motion Gear Stretcher. Drawn as 1 7/8" wide but should be 1 29/32" wide to align the Motion Bracket centre line with the Cylinder Valve centre line (2 9/16" = 21/32" (Half Motion Bracket @ 1 5/16") + 1 29/32").

The front Coupling Rod shows the centre lines offset by 3/32". To maintain the crank bosses at the sizes drawn and get the crank bosses to align with the drawn crank pins the offset needs to be only 1/16".

The two views of the top of the coupling rod centre boss each show dimensions that do not correlate with one another :(

Outer Weighshaft Bearing. The top line of three fixing screws are shown as 1/8" from the top face. However, the 7BA head of the centre 6BA screw will foul the body of the circular bearing. Reducing the 1/8" to 7/64" allows a 7BA head to clear the bearing.

Sheet 9

Expansion Link Oilbox - should be round NOT square.

Sheet 10


Sheet 11

Several errors found regarding the Reversing Lever:
The drawing states the lever pivot point is 4 3/8" to rear axle centre. The dimensions from sheet 1 (Frame Drilling) make this dimension 4 1/2".
Regarding the Pole Reversing Frame the key point here is that the pivot point for the Reversing Lever is 2 5/16" below the TOP of the cab floor (i.e. 2 1/4" + 1/16"). This dimension concurs with the frame drilling and the Pole Lever Fulcrum Bracket. To get the frame and indexing plates to correctly align, the 2 5/8" dimension for the heigth of the right hand hole on the frame should be 2.547" NOT 2 5/8" and the height of the PAIR of Gear Indexing Plates should be 1 3/16" NOT 1 1/4".

The Hanging Bracket holes in the Pole Lever Fulcrum Bracket are 5/16" from the front face and with 1/4" for the bearing on the bottom of the Reverser Lever gives 9/16". The distance to the matching holes on the Reverser Main Frame is only 3/8" (i.e. Gear Index Plate (1/8") + 1/4" offset on the bottom of the frame). This offset needs to be increased to 7/16" and the width of the bottom of the Reverser Main Frame increased to say 5/8" from the 1/2" drawn.

The long thin detent slot in the Reverser Lever is shown as 5 1/4" above the pivot point. I believe this should be 5 5/16".

The offset of the Reach Rod is suspect. I believe the offset at the Reverser Lever end needs to be considerably increased in order to give the maximum movement of the Radius Rod in the expansion link with full forward and back movement of the Reverser Lever. Consequently the reach rod hole in the Reverser Lever will need to be higher. I believe that the offset at the cab end of the Reach Rod is 1.312". This gives a Reverser Lever dimension of 4.436" for the Reach Rod hole above the Reverser Lever bottom pivot point. This gives maximum movement of the weighshaft within the Motion Bracket Assy.

The Draincock Operating Lever is shown as 9 1/4" from the rear of the dragbeam. If the drawing is to be believed (i.e. the support bracket is centred on the forward edge of the Cab Floor Stretcher) then I believe this dimension should be from the rear of the frame, else increased to 9 3/8" to allow for the thickness of the dragbeam.

The hanging bracket shows its fixing holes 1/4" from the back face. This dimension is OK for the Pole Lever Fulcrum Bracket fixing holes but needs to be 5/16" for the holes on the opposite end which locate with the holes in the Pole Reverse Main Frame.

The Drain Cock Pull Rod is very different than that implied by the drawing. Both ends of the Pull Rod need to be cranked (in opposite directions) not just the front end as stated in Note 9. This is to ensure that over its length the Pull Rod runs parallel with the bottom of the frame.

The Pull Rod drawing shows a spacer silver soldered to the cab end of the pull rod which connects with the Primary Crank. The drawing shows an amended dimension of 1/8". From my CAD drawings I have this dimension as 0.281". This allows the pull rod to clear all the axlebox components and fit neatly along the bottom of the frames. I have also fitted two small support brackets behind the centre and leading wheels (as per prototype) to keep the long, thin, pull rod from swinging around. These brackets are not shown on any drawings.

Sheet 12

Rear Slide Oil Boxes are rather too square. On photographs the oil boxes look much wider than their depth.
Rear Oilbox Bracket is completely wrong. The oil boxes are held by brackets on their sides not by screws through their backs.
Also, the drawings do not show oil boxes fitted for the Motion Brackets. There should be a total of eight (8) oil boxes not four (4).
Front Valvespindle Oilbox is wrong. It should be round and the oil pipe must feed into the outside of the gland, not into the pressure side.

Draincocks - the drawings do not make it clear but the draincock assembly on the left cylinder is different to that on the right cylinder. On the left cylinder the steam chest drain cock is front of centre of the cylinder whilst on the right cylinder it is rear of centre (effectively like the left cylinder turned through 90 degs.).

The drawing shows the bottom of the Brake Column tight against the rear of the cab. Using my amended cab dimensions I believe the bottom of the Brake Column is at least 3/32" behind the rear of the cab.

The drain cock Lever Support shows it is fixed with four (4) 6BA screws. However, in the positions shown 6BA screw heads will foul the bracket. I have used 7BA with no problem.

Sheet 13

The Rear Frame Toolbox position is questionable. The drawing shows the toolbox 1.375" from the rear buffer beam. For the toolbox to fit as demanded by its brackets etc., the toolbox needs to be 1.562" from the rear buffer beam. The position does look correct to that shown on General Arrangement on Sheet 1.

Sheet 14
Sheet 15

My Boiler was manufactured by Swindon Boilers so no proving of the information on these two sheets.

Sheet 16

Reeves casting for the Petticote Pipe is totally unfit for purpose. The 1.6875" choke diameter was oversize before any turning was undertaken and on completing the 1.8125" push-fit diameter a wall thickness similar to a cigarette paper remained. The job had to be salvaged by silver soldering a large brass ring to the top of the casting.

Reeves casting for the Manifold does not allow for the 0.0625" offsets on one end of the manifold. I've omitted the offsets which I hope will not be a problem.

Smokebox Handrail Stanchions - I think their positions are wrong. As the dimensions stand the rear stanchion enters the smokebox directly behind the cast flange on the smokebox rear ring. I have scaled a Swindon drawing and a photograph of 1501 and have matching results. I think the 1.5" dimension for the front stanchion from the front of the smokebox tube should be 1.125" and the 4.6875" for the distance between stanchions should be 4.875".

Sheet 17

I assume that part of the 'Smokebox Blower Bush and Nipple' at the top of the page is a duplicate of the 'Smokebox Tubeplate Blower Connection' at the bottom of the plate.

Blast Pipe & Blower Ring Assembly - the drawing shows an 11/16" and 3/8" dimension with an overall combined dimension of 1 3/16" (which does not equal 11/16" + 3/8"). The combined dimension is correct, the 3/8" dimension should be 1/2" .

The smokebox side view does not give a dimension for the position of the chimney and I cannot find a suitable dimension anywhere else in the drawing pack, although it is assumed that the chimney is in the centre of the smokebox but this cannot be guaranteed. Taken from a Swindon drawing, the dimension from the front of the smokebox door front ring to the centre of the chimney is 3.476".

The front view of the smokebox door and front ring shows two dummy rivets at the 9.00 o'clock and 3.00 o'clock positions. These rivets are shown on a 3.375" radius. However, compared to pictures of 1501 these are very near the outside. I have used a radius of 3.218" and I think this looks much better.

Sheet 18


Sheet 19


Sheet 20


Sheet 21

A 'typical' Air Vent is drawn. The design of this vent is different for locomotives 1500 and 1508.

Sheet 22


Sheet 23

The dimensions for the build up of the cab side plates do not all concur. The sum of the individual plate dimensions do not match the overall dimension given. This is taking some sorting out as to which is correct and determining whether there are clearances necessary (e.g. around the door) which are not mentioned.

Sheet 24

The dimensions on the upper cab side plate (2.6875" + 1.1875"Rad + 2.125" + 1.1875"Rad = 7.1875") do NOT match the lower cab side plate dimensions (5.3125" + 2" = 7.3125"). The upper cab plate dimensions should only be 1/32" greater than the lower cab plate to allow for the doorway trim. Either the upper or the lower side plate has an error of 3/32" which needs to be investigated.

Sheet 25

Rear view shows the only illustration of the Brake Operating Lever. However, the Brake Pull Rod is shown in line with the wheel flange which means the rod must have a 'set' in it but this is not shown on the rod illustrated on Sheet 5.

Sheet 26



Work continues........



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