Model Engineer issue 4737 **FREE 20 PAGE PREVIEW**

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THE ORIGINAL MAGAZINE FOR MODEL ENGINEERS Vol. 232 No. 4737 23 February – 7 March 2024

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Leaf Springs

How to make them

Turbine Loco

5 inch gauge model of 18,100

Bodo Museum We visit Norway’s air museum

FIRE QUEEN

Tender completes the locomotive

309

325

Published by Mortons Media Group Ltd, Media Centre, Morton Way, Horncastle, Lincs LN9 6JR Tel: 01507 529589 Fax: 01507 371066 © 2023 Mortons Media ISSN 0026-7325 www.model-engineer.co.uk EDITORIAL Editor: Martin R. Evans MEeditor@mortons.co.uk Deputy editor: Diane Carney Designer: Druck Media Pvt. Ltd. Club News: Geoff Theasby Illustrator: Grahame Chambers Publisher: Steve O’Hara CUSTOMER SERVICES General Queries and Back Issues 01507 529529 Monday-Friday: 8.30am-5pm Answerphone 24hr help@classicmagazines.co.uk www.classicmagazines.co.uk ADVERTISING Group advertising manager: Sue Keily Advertising: Craig Amess camess@mortons.co.uk Tel: 01507 529537 By post: Model Engineer advertising, Mortons Media Group, Media Centre, Morton Way, Horncastle, Lincs LN9 6JR PUBLISHING Sales and distribution manager: Carl Smith Marketing manager: Charlotte Park Commercial director: Nigel Hole Publishing director: Dan Savage SUBSCRIPTION Full subscription rates (but see page 306 for offer): (12 months, 26 issues, inc post and packing) – UK £128.70. Export rates are also available, UK subscriptions are zero-rated for the purposes of Value Added Tax. Enquiries: subscriptions@mortons.co.uk PRINT AND DISTRIBUTIONS Printed by: William Gibbons & Son, 26 Planetary Road, Willenhall, West Midlands, WV13 3XB Distribution by: Seymour Distribution Limited, 2 East Poultry Avenue, London EC1A 9PT EDITORIAL CONTRIBUTION Accepted photographs and articles will be paid for upon publication. Items we cannot use will be returned if accompanied by a stamped addressed envelope and recorded delivery must clearly state so and enclose sufficient postage. In common with practice on other periodicals, all material is sent or returned at the contributor’s own risk and neither Model Engineer, the editor, the staff nor Mortons Media Ltd can be held responsible for loss or damage, howsoever caused. The opinions expressed in Model Engineer are not necessarily those of the editor or staff. This periodical must not, without the written consent of the publishers first being given, be lent, sold, hired out or otherwise disposed of in a mutilated condition or in other unauthorised cover by way of trade or annexed to or as part of any publication or advertising, literary or pictorial manner whatsoever.

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Vol.232 No.4737 23 February –7 March 2024 308 SMOKE RINGS News, views and comment on the world of model engineering.

309 HERCULES – A TWIN CYLINDER COMPOUND ENGINE Chris Walter describes a condensing marine engine first featured in Model Engineer 100 years ago.

314 LNER B1 LOCOMOTIVE Doug Hewson presents a true to scale fiveinch gauge model of Thompson’s B1.

318 1934 McDONALD TRACTOR George Punter tackles another tractor construction project.

321 INVESTIGATING PARTING TOOL CHATTER Neal Raines investigates and causes and cure of a common machine tool problem.

325 BUTTERSIDE DOWN Steve Goodbody returns with further tales of the trials and tribulations of a model engineer’s life.

327 SMEE NEWS Martin Kyte reports from the Society of Model and Experimental Engineers.

328 WANDERINGS IN SOUTH ISLAND NEW ZEALAND Colin Hill comes across an interesting locomotive relic.

for details.

331 THE WILLIAMSON ENGINE REVISTED Ray Griffin discovers a book by Tubal Cain from 1981 and builds the engine described in it.

334 A FIVE-INCH GAUGE 0-4-0 PADARN RAILWAY TENDER LOCOMOTIVE Luker builds a tender for Fire Queen, a Welsh slate quarry locomotive.

337 BODO AIR MUSEUM Geoff Theasby ventures north of the Arctic Circle to visit Norway’s air museum.

341 THE STATIONARY STEAM ENGINE Ron Fitzgerald tells the story of the development of the stationary steam engine.

344 WORKSHOP TECHNIQUES – MAKING LEAF SPRINGS Chris Rayward begins an occasional series with tips for making leaf springs.

348 GAS TURBINE ELECTRIC LOCOMOTIVE 18,100 Tim Coles reports on progress to complete a 5 inch gauge model of an experimental locomotive.

352 CLUB NEWS Geoff Theasby compiles the latest from model engineering clubs around the world.

355 CLUB DIARY

329 POSTBAG Readers’ letters.

Future Events.

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THE ORIGINAL MAGAZINE FOR MODEL ENGINEERS Vol. 232 No. 4737 23 February – 7 March 2024

ON THE COVER...

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Traction motor, gearbox, axle and wheel set for a 5 inch gauge turbine locomotive (photo Tim Coles).

Join our online community www.model-engineer.co.uk

Leaf Springs

http://twitter.com/ modelengineers

How to make them

Turbine Loco

5 inch gauge model of 18,100

Bodo Museum We visit Norway’s air museum

Tender completes the locomotive

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£5.10

FIRE QUEEN

This issue was published on February 23, 2024.

The next will be on sale on March 8, 2024.

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Members of Rochdale SMEE meet the mayor, Mike Holly.

Rochdale SMEE MARTIN EVANS Editor

DIANE CARNEY Assistant Editor

Bob Hayter writes with the following news: ‘Following a very successful charity running day late last year members of Rochdale SMEE met yesterday with Mike Holly, Mayor of Rochdale, where they received a certificate of achievement and thanks for their charitable work. Over a cuppa and biscuits the Mayor emphasised the contribution made by model engineers to the local community, not only giving rides on the miniature railway but also promoting engineering and providing valuable training and experience to young people.’

Medway Queen Centenary

Medway Queen Preservation Society

Martin Evans can be contacted on the mobile number or email below and would be delighted to receive your contributions, in the form of items of correspondence, comment or articles.

07710-192953 MEeditor@mortons.co.uk

308

Richard Halton of the Medway Queen Preservation Society has sent me the following.

PS Medway Queen was built by the Ailsa Shipbuilding Company of Troon, Scotland, and launched on St. George’s Day (23rd April) 1924. Her maiden voyage across the Thames Estuary was on Friday 18th July of that year, under the flag of the ew edway team Packet Company. Medway Queen’s standard route was then from Strood and Chatham

career in all chapters of her history are extensively covered in books published by the Medway Queen Preservation Society, and available online (www.medwayqueen.co.uk ) or from the Medway Queen Visitor Centre on Gillingham Pier.

Medway Queen is moored at Gillingham Pier, ME7 1RX, and is open to the public on Saturdays from 11am to 4pm (last admissions 3pm) starting on February 17th. Naturally, in this centenary year, the Medway Queen Preservation Society plans appropriate celebrations, and these begin in earnest on Sunday April 21st with a Memorial Service in Rochester Cathedral for an invited crowd of people with family connections to the ship at any stage in her career.

Tuesday 23rd (the actual launch anniversary) sees a reception for invited guests on board Medway Queen.

To accommodate visitors to the ship over this period the vessel will be open as usual on Saturday 20th April, and she has a second public day on Monday 22nd. Then on Saturday 27th the usual public open day will be enhanced with the added attraction of a visit from some Dunkirk Little Ships and the Chatham Cruising Society. The fund-raising possibilities have not been forgotten and a summer draw is planned with ticket sales from the beginning of April until the end of June and some exciting new merchandise which will be available to personal visitors and also via the society’s website www. medwayqueen.co.uk. There will be other events through the year and details will be posted on the Medway Queen Preservation Society website.

to Southend and then back across the estuary to Herne Bay. Additional trips were made to Clacton and Margate at times and several private hirings took her upstream to the Pool of London, especially in later years. The excursion service was seasonal, usually starting at the Whitsun Bank Holiday weekend (now the Late May Bank Holiday) and terminating in September.

She worked these routes from 1924 until the beginning of September 1939 and again from 1947 to 1963. Variety was created by special excursions and events such as Chatham Navy Week and the 1937 and 1953 Spithead Naval Reviews.

During the Second World War, HMS Medway Queen was a commissioned minesweeper and took part in the evacuation of the BEF from Dunkirk.

Working out of Ramsgate most of the time Medway Queen and her crew made seven return trips to the beaches or the East Mole at Dunkirk. They rescued thousands of men and seven officers and crew received gallantry awards.

When her excursion work ceased the ship’s future was extremely uncertain but, in 1965, she was purchased to be a club house and restaurant on the Isle of Wight, at what was then called the ‘Medway Queen arina’ at Binfield.

The ‘Medway Queen Club’ opened in May 1966 and ran in various guises until the end of 1974. All Medway Queen, now berthed at Gillingham Pier aspects of the ship’s (photo Colin Matthews).

Model Engineer 23 February 2024

HERCULES

A twin cylinder

compound condensing marine steam engine.

PART 8

157

Main stop valve on the left front of the engine in front of the high-pressure steam chest.

Chris Walter builds an engine described in Model Engineer 100 years ago.

Continued from p.261 M.E.4736 February 9

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Main stop valve (regulator) and simpling valve This was a reasonably simple fabrication of various sizes of brass tube (photo 157). It was easier to make it in two distinct parts, the main body to attach to the inlet manifold, and then the valve and handwheel assembly. I experimented a bit at first to clarify its exact finished position in front of the high-pressure steam chest, so that the hand wheel was reasonably accessible to the driver and didn’t conflict with anything else.

The joint to the inlet manifold is just a screw pipe fitting

with a brass lock nut, as is the connection for the steam feed from the boiler. This can be modified to suit any installation as necessary. A four-stud flange joins the body to a matching flange on the hand wheel assembly. There is no gasket required as a boss on the hand wheel unit carries an ‘O’ ring seal (photo 158).

The actual valve is an elongated bronze cone on the end of the stainless handwheel shaft. I experimented with various shapes of valve, and indeed with various materials including PTFE, and the bronze cone came out best and gave a suitable amount of control.

When I started on this model, I had never heard of a simpling valve, much less know what it was for. Looking it up in the model press gave me some sort of idea (for simpling

158

Component parts. valve read starting valve) but from the various comments expressed it was apparent that I was not the only ignorant person. A compound engine is not self-starting as the inlet of the second or subsequent cylinders is fed from the exhaust of the primary cylinder. No movement no steam, no movement! A simpling valve provides a short injection of steam to the second cylinder to start the whole thing moving.

Once movement takes place >>

309

159

160

The simpling valve. This is just a conventional blower valve screwed into the top of the valve body feeding the receiver via a 5/32 inch copper pipe. there will be exhaust steam available. The name ‘simpling’ is because momentarily you have converted a compound engine into a simple engine.

Again, from the chat pages of the modelling press, there are a multitude of comments as to how this ought to be achieved.

I am afraid that I took rather a simplistic view (sorry about the almost pun) and stuck a commercial blower valve on top of the main stop valve and then connected it via ⅛ inch

copper pipe to the inlet side of the receiver. It worked very well indeed, the engine starting immediately every time.

Admittedly you have to turn the valve on and off but this is only momentarily (photo 159).

If this becomes a pain, I see no reason why the blower valve can’t be changed for a lever operated spring-loaded whistle valve, which are readily available, and which would give the required momentary operation.

162

LP inlet now with a threaded bush for the pressure gauge pipe.

310

161

The HP and LP manifolds were similar.

Trial fit of LP exhaust on the block.

Manifolds

therefore modified with silver soldered collars furnished with threaded bushes for this purpose (photos 162 and 163).

These are all brass fabrications, flanges and stems being machined separately and then silver brazed together.

The exhaust manifolds were screwed into the threaded passages in the cylinder block with sealing compound. I was glad that I had made a steel drilling jig for the flange holes as this helped with some repetitive tedium (photos 160 and 161).

Each inlet was secured by a two-hole flange, there being short extensions on the inside of the flanges made to bear on silicone ‘O’ rings in counterbores in the valve chest passages. When I came to it a lot later, I ran out of available options as to where I could pick up connections for the high and low steam pressure gauges.

Both inlet manifolds were

Air pump Once again, I have to admit that, at the start of this model, I knew less about air or vacuum pumps than I did about condensers and that wasn’t a lot!

Some concentrated research online and the old engineering books passed on to me by my father did something to enlighten me. At the very least I now knew what an Edwards air pump was and what other types of pumps were available.

As it transpired it was a choice of one of two pump types - a fairly conventional single acting three valve type or the Edwards air pump, which had just a piston and a single valve.

Because of its apparent simplicity the Edwards air pump seemed to be the most popular choice of many ship builders and in the past several writers in the modelling press have enthused about its suitability for modelling use. I am afraid that, after reading their descriptions of its operation, it appeared to have, for my own use anyway, several distinct disadvantages, the main one being the difficulty in making the conical chamber which is the basis of the pump.

Without a casting I could find no viable way of machining this shape and I speak advisedly for I had several attempts at it and failed. I tried various shapes of cutter or boring tool, but given the small opening through which they had to work they were insufficiently rigid.

I also tried making it as a multiple layer sandwich, machining the conical void in

Model Engineer 23 February 2024

HERCULES

163

165 Top view of cylinder showing the inlet holes in the base of the head valve.

HP inlet with pressure gauge bush.

164

Finished air pump and water feed pumps. three separate pieces and in fact I did complete a pump with this method. On test this worked slightly but not well enough to be used so, having spent a considerable amount of time and effort getting nowhere, I decided enough was

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enough and opted for the more conventional three valve design (photo 164).

As the build had progressed it had become more and more apparent that, whatever detailed planning I had carried out, I was going to have

problems with positioning the air pump. Lots of components had been redesigned en route, so to speak, and everything had appeared to grow in the process.

Instead of mounting the air pump upon the bed plate

as originally intended, this was now totally unfeasible.

Somehow it would have to be positioned and fixed to the back edge of the bed. In addition, I found that I was short of the height needed and the stroke of my pump required to be shortened, also affecting the dimensions and ratio of the operating levers and their pivot point!

Now I will admit here and now that mathematics in all its forms is not my strong point, so I spent a long time trying to calculate the ratio between the front and rear arms of the levers, to give me the required stroke. Although this seemed to work, I found that I still had to alter the pivot position to get it right. Perhaps I should have stuck to trial and error in the first place!

The main cylinder of the pump is made from a brass tube with a flange at either end, to connect to the base unit and the head valve cover respectively. Inside the tube is a fixed brass plate with a hole in the centre for the piston rod, surrounded by eight 3/16 inch diameter holes which form the base of the head valve (photo 165).

In operation there are three one-way valves: the foot valve, the piston valve and the head valve. The foot valve in the base unit allows water/air from the condenser to be drawn through it into the base of the cylinder by the action of the piston rising.

When the piston descends the foot valve closes and this water/air is trapped so has to travel upwards through the piston and piston valve. At the bottom of the stroke the piston starts rising and the piston valve closes forcing

311

>>

166

Bottom view of cylinder. the water above it to rise with it and be pushed through the one-way head valve. There it is free to escape through a pipe to the hot well, to eventually be filtered and re-used in the boiler.

The base of the pump is machined from a block of aluminium and is held to the engine bed plate by two M4 set screws, the heads being on the inside of the bed. In addition, there is a pair of countersunk

167

Main body showing the well for the foot valve.

4BA screws, one at each end, which are hidden behind the brass feed pump bases.

The cylinder is held to the base by eight 8BA hex screws through its bottom flange. The cylinder extends for 1/16 inch under this flange to provide a register in the foot well bored in the base. Fitted in the top of the foot well and held in position by the cylinder is the foot valve unit. All three valves are basically the same, being

168

Bottom view of top cylinder cover. The centre boss acts as the limit stop for the head valve.

169

Piston and rod. The plain disc valve is a sliding fit on the piston rod and its limit stop is a circlip fitted in a groove in the rod. This valve is identical to the head valve - just a brass disc lined on one side with 1/32 inch neoprene.

312

fixed brass discs with eight orifices under a movable disc valve made of brass with a 1/32 inch lining of neoprene. I was unsure what to secure the neoprene with but initially tried super glue and, so far, it has survived and given no trouble.

The foot valve moves up and down on a short 3/16 inch pin secured to the bottom disc but the piston and head valve have the piston rod passing through

them. This is probably clearer from the pictures than from my endless wittering (photos 166 to 169).

Where the piston rod exits the top cover there is a conventional two stud gland using a 3/16 inch inside diameter ‘O’ ring as packing.

Secured to the base of the pump by small flanges, and either side of the main cylinder, are two vertical bronze ⅜ inch diameter cylinders. In these run stainless ¼ inch rams whose primary purpose is to act as a cross head for the air pump piston rod, both being secured at the top to the ends of the pump cross bar.

As is the norm in this type of engine design, these two rams perform a second function, being utilized as the pistons for feed pumps fitted to either end of the main air pump body. Each ¼ inch diameter ram piston is fitted with an ‘O’

170

One of the two pump cylinders and rams which also act as a crosshead for the air pump piston rod.

171

Components of the main pump.

Model Engineer 23 February 2024

HERCULES

172

175

Drive levers with the weight shaft, brackets, and valve gear.

The feed pump components.

176

173

Main pump unit.

174

Trial fitting the air pump.

Main pump unit, showing the hot well pipe and its support bracket. ring and at the base of each cylinder a drilling connects to the brass pump units at either end of the main pump base (photos 170 and 171).

These are both simple pump units, each fitted with two oneway gravity operated bronze ball valves. The reciprocating action of the rams causes the

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pumps to suck in liquid through the first valve and then expel it through the second (photos 172 to 174). These are then conveniently available for boiler feed or coolant feed for the condenser.

Air pump drive levers The drive for the air pump is

taken from the high-pressure cross head wrist pin, its outer ends being reduced from ⅜ to 5/16 inch diameter to accommodate two short links with split bronze bearings.

These links are connected to a double pivoted lever, its pivot being a bearing mounted on the rear support column. At its outer end these levers have two more short links which are attached to the air pump cross bar (photo 175). The pivot bearing of the two levers is provided with a capped oil cup.

One of these two levers carries a clevis pin and bearing with a short rod connected vertically to the drive shaft for the mechanical lubricator.

This shaft runs the width of the engine just behind the condenser, and parallel to the weigh shaft (photo 176).

The two levers are cut from ⅛ inch steel sheet and are attached to the pivot pin by 8BA bolts into flanges on the pivot shaft.

To be continued.

313

LNER B1 Locomotive PART 39 – ASH PAN – PART 1

erby track where I uizzed him about it. e told me that it had been in his engine for ten years and it had never been a problem all the time it had been in there. I thought that sounds good to me, so I had to have one in my T as all B tandards have them and, of course, the B s.

I am going to describe both ash pans as there is so little difference in them that no one is going to see! I would make the ash pan 1 to 15 ) from 8swg stainless steel without hesitation and I have found that it silver solders very well if you use the correct type of silver solder i.e. silver solder . As B used to say, the solder runs like water once the joint is at the correct heat, a

e will have a look at the fire grate at this stage. owever, all B s are fitted with rocking grates so what I intend to do is to describe a plain fire grate for a start and I will deal with the rocking grate in the next few issues. owever, I would go to the trouble of fitting the rocking fire grate as I can say that they are brilliant, having fitted one to my T even though ddy has had a few problems. opefully I have cured these design faults now so it should be a little more of a plain sailing job. I copied mine from a heffield member who fitted one in his American . I thought he seemed to be rocking his fire grate so I went over to speak to him on our annual visit to

W

Doug Hewson presents an authentic 5 inch gauge version of Thompson’s B1 locomotive.

Continued from p.278, M.E.4736, February 9

1/16

3/16

Fig 149

nice dull red. I put my ashpan together using asyflo o. and it is still all in one piece, so I don’t know what that tells you!

I would cut the top plate out for a start which is about . 8 inches long and .8 inches wide. I would leave another .8 inch inside to bend down for the taper inwards. ou will, of course have to cut the two triangles off where the two side pieces need to be joined.

This plate can be silver soldered together once it is bent. I was going to suggest that you find a piece of inch plate and clamp the top plate to that, but that is no good is it That was how I built up the ash pan on my T but then I realised that the top plate on that is perfectly flat. owever, you can always

9 15/16 damper rod 9 3/16 1/2

1/8 s/s bar thru

23/32 1 25/32

3/16 3/16

1 11/32

25/32

5/8

r1/4

1 3/32 3 3/4 2 off 8BA bolts to underside of spring hanger

9/16

1/2 3/16

2

1/8 1/8 strip on outside as stiffening Note this bracket is fixed to inside of loco frame plates

r3/16

6

7/ 3

1 1/16

1 5/

1/4

2 off 10BA studs

2

r1

See detail

r1

23/3

17/32

16 r3 /

line out

1/4

1/2 19/32

5/16 17/32

for de rod Guimper a d

1/4

1/8 copper tube with 10BA bolts thru to support heat shield

1 1/16

16 11/

5/32

13/64 1 3/8

1 9/32

17/32

Bend line

3/64

ting Set

2 13/3

5/16

1/32

1

1 6 5/1

2 off 8BA bolts

2

5/8

r1/8 1/4 x 16 SWG strip x 2 1/32 long similar strip on underside of ash pan to stiffen edge

line

2 off 8BA bolts

1/2

2 17/3

1

3/8

Bend

3/32 7/32

17/3

1 9/32

3

7/32

3 1/2

Ashpan – main side view.

314

Model Engineer 23 February 2024

LNER B1

5°

2 13/3 7/16

9/16

Ø5/32

1 1 1

Safety catch

Ø1/8

Lever to drop fire grate 7/16

7/64 sq. on end of shaft 2 1/8

Fig 150

2 7/16 4 3/8

shpan side view with fire grate.

Fig 152

Fig 151

Heat shield

5/16 13/32

15/16

1 13/32

17/32

5/16

3/16

5/16

1/8

5/32

7/16

2 9/16 wide door

Ashpan – rear view.

2 7/16

Front View Of Ash Pan

Fig 153

Ashpan – front view.

o

o

2 9/16 wide door 2 7/16

1/16

1/4

1/16

pieces, you ought to be able to arrange some blocks to clamp the together and then silver solder these all together.

There are five separate pieces although you may be able to reduce that number to four by bending the piece which fits between the two bottom openings. This was all drawn to a works drawing which ddy ibbons kindly lent me. Without that I wouldn’t have known where to start! If you have cut

15/16

clamp the inch piece to a plate. I thought that it might just help a little. If you have a look at the side elevation, I have shown another bend line on the drawing to show where the sort of rectangular box begins.

Once you have mastered the two sides you should be able to silver solder that part of the box together.

The bottom of the box is uite a complicated shape so if you make the individual

5/8

>>

Ashpan – part rear view.

315

1 11/16

1/4

17/32

5/16

2 7/32

1/8

Fig 154

All 18 SWG s/steel plate 1 1/16

1 17/32

5/8

7/16 Loco frame plate

16 SWG reinforcing plate riveted inside hopper

3 7/8

Rear door

2 5/8

3/16

Front door

2 11/32 inside hopper

Damper control rod

18 SWG plates silver soldered to underside of hopper

4 7/8 8 15/16

Ashpan – plan view.

281

Damper ap on the ash pan.

Model Engineer 23 February 2024

LNER B1

282

Ash pan door.

283

Ash pan dump handle. the sides precisely it will help enormously as you can then clamp the bottom plates to the sides of the cutouts with some little degree clamps and then you can silver solder a little at a time, then remove the clamps and carry on. hoto ph 1 shows damper flap on the ash pan and

o

o

behind that there is the front of the front door. ote on the left of the picture is part of the operating mechanism for the front ash pan door. This will all be detailed in part . hoto ph - make of this what you will! It appears to be the door of the ash pan but not as I have drawn it. Anyway,

there is a good photo of the brake adjuster! hoto ph - now, there is all sorts you can pick up from this photograph. irst is one of the ash pan dump handles and the fabrication which is attached to the bottom edge of the locomotive frames which has the adjuster pin through

it. Also, just behind that is the linkage which we will come to later. It is also worth noting that in the end of the brake beam is retained by the flat cotter in the end. on’t forget the inch x swg reinforcing plate across the front of the door and the one across the underside of the ash pan door opening.

There is also a ⅛ inch rod silver soldered midway across the door on top of another similar reinforcing plate but the strip stops before the bell crank for the operating rod. On the second drawing fig there is a safety catch on the side of the ash pan which I have added to hold the seven fire bars up which should be hinged from the rear pivot of the sloping bars. I would also suggest that the rear section of the grate is made as a three-piece set so that it can be lifted out though the fire hole door. If you make the grate sections from x ⅛ inch stainless steel bars they will last a long while provided that you empty the ash pan regularly - on shed may I say! It will certainly last a good shift provided that you don’t go raking the fire to death.

One more thing it is advisable to do is to make the heat shield to protect the rear axle of the engine. This is simply a piece of 8swg steel plate to go over the curve of the axle with a straight part about . inch long x inches wide which is rolled around the top of the axle and bolted to the back of the ash pan with four spacers, which you can cut from stubs of copper tube ⅛ inch long. A couple more things you can do before we leave this session is to make the damper control rod. This consists of a length of mild steel rod 1/16 x inch wide with a fork joint on each end which need to measure 15/16 inches between the centres of the eyes.

To be continued.

NEXT TIME The ashpan continued.

1934 McDonald Tractor A working one-fourth scale model

PART 4

George Punter is drawn to another tractor project.

Continued from p.291 M.E.4736 February 9

318

he front wheel structure is similar to the rear wheel except the hub and this part was a major headache to design and make.

The shape was difficult to reproduce and, at first, I did consider fabricating them but, in the end, decided to follow the full-size practice of casting them. As can be seen from photo 31, the problem was the wavy shape and the angles that formed the attachment points for the spokes. The problem was solved by using the 3D printer to produce parts of the structure and then gluing other pieces to fill in where needed (photo 32). The mould preparation was unorthodox in that I had to use a cardboard collar in part of the packing

T

procedure to prevent the sand from going where it was not needed (easier to do than explain…).

The outer rim was rolled in the same way as the rear wheels. A ring of mild steel fits over the outside of the rim to help give the steering direction and in the manufacture, this helped to keep the wheel circular in shape and concentric. Rivets were used on the rim to spoke joints but the hub to spoke joint was screwed with the heads being filled to make them look like round headed rivets. Bronze bushes were made and pressed in from each side and a brass hub cap made and fitted.

Having made the front wheels, it was now time to make the front axle and steering gear. On the full-size tractor, the axle is cast but when scaled down I felt that some of the sections would have been too thin and not strong enough. My choice was to fabricate this part from laminations of laser cut mild steel silver soldered together.

Jigs had to be made up to

hold the king pins in place and at the correct angle for silver soldering. As can be seen in the photographs (photos 33 and 34), the steering gear is made up of many convoluted pieces of metal that all join to form a functioning unit. These parts were all fabricated from steel and then connected to the steering box.

The steering box uses a worm drive to move the arm and a search in my spare gears box revealed that I had both a worm and wheel of just the right size and ratio; how lucky can you be?! The joy of finding this rapidly disappeared, however, when I discovered the helix was the wrong way! Now we can’t have a steering system where you turn the wheel to the right and the tractor goes left. There was no easy way around this dilemma so I had to make cutters to cut the gears but achieved success in the end. A casting is used for the steering box and patterns were duly made and used (photo 35).

With the casting machined up it was offered up to its

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Front hub and wheel.

Model Engineer 23 February 2024

TRACTOR

position on the side of the main gearbox and a steering rod connected it to the front of the tractor.

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Steering wheel The steering wheel was the next interesting part to make and use was again made of the 3D printer to produce a pattern and support piece (photo 36 . I did think of fabricating this part but opted for casting. The 3D printer uses a support network to hold up parts that need it in the printing process and this would be used when the sand was packed around the pattern, also to give it the support if required. A solid was included between the spokes of the steering wheel to help the flow of the metal during the pour and this would later be cut out with a piercing saw and cleaned up with files.

I had now reached the stage where the model was able to stand on its own wheels and could be moved. The picture in my mind was slowly coming to fruition but there was still a long way to go and so many problems to overcome.

Parts for fabricating the front axle.

Pattern for the front hub and castings.

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Patterns for the steering box.

Completed front axle.

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Platform and seat The platform at the rear of the tractor, where the operator stands, is supported by a framework attached to the gearbox and includes the sprung tow bar and support for the mudguards (photo 37). The floor on the full-size tractor is covered with a tread pattern sheet metal and I was able to buy a sheet of the correct scale from a supplier in London.

There are two floor mounted boxes that are used for housing tools and the blow lamp for heating the hot bulb when starting the engine. These boxes were fabricated from thin sheet steel and bolted to the floorboard platform (photo 38).

The seat was beaten out of mild steel sheet. A pattern was made in paper and then transferred to the metal. The shape was roughly cut out and then the slots were cut using a piercing saw. A wooden sinking block and mallet were used to create the shape (photo 39).

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Rear platform of the full-sized tractor.

Steering wheel patterns.

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Rear platform of the model, showing the tool boxes and seat.

A small bending jig was used to turn down the outside edge once it had been cut to its final shape. This whole process took about one day - time flies by when you are having fun! The seat is supported on a small cast bracket that has compound angles of

The seat and associated parts with the sinking block used to beat it into shape.

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The seat assembly.

Winding the seat spring.

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The lubricator. attachment and has a conical spring to make life a little easier for the driver (photo ).

More jigs had to be made for the spring winding process and an example can be seen in photo 41.

Mudguards The mudguards are made from sheet steel with the curved parts being 1.6mm thick and the vertical parts 2.0mm thick.

Both parts are fusion welded at the joint and the added raised ribs are made from D-shaped brass riveted (1/32 inch rivets) and soft soldered in place. The raised ribs also

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The lubricator installed on the model. appear on the vertical parts of the mudguards and radiate out from the axle axis. On the full-size tractor, I think these ribs are to help dampen out the vibration and prevent fatigue.

Some of the tractors had a brace bar that bridged the two mudguards placed in front of the lubricator box.

Injection pump housing and fuel tank As I mentioned at the beginning, the engine is equipped with an oil injection system which is housed above the cylinder head and this would be the next part to be constructed.

It consists of a small, rectangular brass tank housing a double piston pump with the outlets directing the oil to where it is needed (photo 42). A series of cams, check valves, ratchets and clutches all fit inside the box and a sight glass is built into one corner. The amount of oil pumped is controlled by the length of the drive arm and clutch/ratchet and is adjustable (photo 43).

The fuel tank is elliptical in shape, is made from mild steel and is mounted on brackets above the engine, with the fuel being gravity fed to the injector pump (photo ). The bonnet

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The fuel tank. is made from rolled sheet steel and is the last part to be made in this section before work began on the major task of building the engine and we will make a start on that next time.

To be continued.

Model Engineer 23 February 2024