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Dean 044 Tank Loco No 34/35

No 34 Dean GWR Helston.044 tank




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#26 bertiedog

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Posted 17 April 2018 - 20:11

 The wheels are here, aren't they small!   The castings look good, starting the machining before weekend and in meantime making the counter weights and crankpins etc.

 

Machine by griping the tyre, running as true as the casting allows, then drilling and boring the centre, reversing on a mandrill, and fixing with superglue and pressure from a live centre with a cup.

 

The tyre is turned flat.and the root radius machined in one op,, then the wheel is removed after machining the flange and front face, a spot of heat breaks the glue.

 

Each wheel in turn, and then grip on flat tyre to machine the back, with recess to expose the spokes.

 

Then all are re-mounted one by one on the mandrill and the taper is cut on locked settings for all four,

Then all are cleaned around the back of the spokes. Whilst on the mandrill the tyre can be polished to high finish, and by gripping on the flange the boss can be finished with a satin surface.

 

The back of the wheel is not flat, a raised central boss is know left to prevent running on the frames. Axles are made to just the bored holes and pressed on with loctite.....

 

As the wheels are cast iron, slow lathe speed should be used with carbide tools or inserts.

 

 

i do not turn between centres, it requires pre fitted drop in bearings and this method with care gives great accuracy. and ease of assembly and quartering by a simple jig.

 

The vital point is that all wheels must be identical diameter. no tolerances. the same or the wheels will not pull.

 

Stephen


Edited by bertiedog, 18 April 2018 - 22:02 .

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#27 bertiedog

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Posted 18 April 2018 - 20:23

The main outer frames are all cut ot and reduced on belt sander to size as a pair, and the final details will be filed to shape.

 

The axle holes are drilled to size, 3/16th, 4.7625, but then opened up to allow for the floating action of the axles at 2mm bigger at 6.7625, in practice the drill was 3/16th and 6.7mm

 

The inner frame is drilled 6.7 and the bearing inserted after drilling just under 3/16 and teaming to 3/26th size. The outer diameter of the bearing is 8mm, non critical, and it has a step machined on one end to insert into the 6.7 hole, leaving the outside flush and the rest inside the frame. This leaves a gap for the gearbox.

 

All sizes are nominal only critical one are reamed, and I use both mm and imperial to give a bigger choice of drills.

 

Whilst on the bench the coupling rod blanks, (as a pair) are spot drilled with the 3/16tth drill to allow further drilling later to crank pin size, usually I use 3mm in O gauge..

 

3mm crankpins can be drilled and tapped 6Ba and take a washer and nut to retain the rods. The bolts used can be reduced in size across the head to 8Ba size. It gives a strong reliable crankpin assembly.

The washers are made in the lathe from brass bar.

 

The side coupling rods are made from nickel silver., or mild steel. tinned with pure tin solder and wiped away whilst hot, leaving a rust proof and corrosion proof, finish.

 

 

Next issue is the bogie, plain box and bolster type, with axleboxes and springs. Each profile milled out on a bar and separated into four blanks in the lathe.

 

The outer axle box face and the springs are silver soldered together for strength.

the springs are turned grooves on a plate, and cut into four, with the spare spring ends filed away. the top spring has its end split to take a hanger rod, again soldered on solid.

 

The axles boxes will be kept slim to aid clearances. A bronze bearing for the axle stub will be drilled in the lathe and soldered into the back of the axle box 2mm axle stub on 3/16th axles.

 

The box of the bogie has a stout bolster bar added across the frames. in 1.2 mm hard brass. This can be drilled and tapped to take centering springs and the bogie pivot hole The hole will slotted to allow side movement and pivoting. the amount measured on assembly and test on curves.

 

Stephen



#28 N15class

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Posted 18 April 2018 - 20:53

6BA is a bit large even for 7mm. 12 is fine but most use 10.

 

6BA would only leave you just over 0.1mm wall with using a 3mm crank pin.

 

any pictures of progress?


Edited by N15class, 18 April 2018 - 20:53 .


#29 bertiedog

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Posted 18 April 2018 - 21:43

The 6ba crankpin bolts are not normal head dimensions, but milled on a rotary table across the flats to reduce the head to just be able to fit on the washer. Or it can be milled to leave a washer formed from the head in Bugatti style.

Commercially hex headed bolts in the BA series are available from Model Engineers suppliers in one head down sizes as well, ie a 6 BA with an 8 BA head, but by milling away you can get 9BA head on a 6BA bolt.

If the Bugatti method is used the head can be as small as 12BA

 

BOLT HEADS.jpg

 

In the Bugatti style the edge is rounded in the lathe after milling the flats The Bugatti was design not to just reduce size and weight, but to eliminate the washer and make all sizes have just one spanner to fit them all.

 

‚ÄčI usually use the Bugatti on steam engines for boats, but they look good on connecting rods as well. You may have to make a spanner or use a quality adjustable spanner to fit. Also the best tighteners are tool makers clamps

 

The crankpins are 1/8th stock or 3.1750mm and leaves thick enouth wall, and the thread goes in 3mm depth. The crank pin is stainless steel, the bolt is mild steel, the washer if fitted, is made in stainless steel.

 

Stephen.


Edited by bertiedog, 18 April 2018 - 21:51 .

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#30 bertiedog

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Posted 18 April 2018 - 21:57

Awaiting arrival of new camera, I can use a phone camera but results are awful. They use flash but it blurs due to camera movement unlike a real true flash. Just not sharp enouth, and I am not buying an Apple just to take better pictures, Phones make calls, cameras make pictures.


Edited by bertiedog, 18 April 2018 - 21:58 .

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#31 bertiedog

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Posted 19 April 2018 - 08:39

After a rethink, the PC etched pickup mount will not be needed, with the inner frames bottom filled with a machined block of sheet bakelite, 6mm thick, fixed with countersunk 8Ba screws

The block will have the spring bolted to it direct, and power taken from one of the bolts via an electric washer.

It will need a bit at the rear cut way to fit over the gearbox. The 6mm thick plastic will add to the strength pf the frames.



#32 bertiedog

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Posted 19 April 2018 - 08:57

pickup2.jpg

 

The arrangement of the bakelite block within the inner frame to support the third rail pickups. The suppressor circuit can be added to the other bolt for connections, and earthed to the chassis.

Stephen


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#33 bertiedog

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Posted 20 April 2018 - 15:12

The build coming along faster than thought, a few templates in card to check fits and the bodywork soldering will be underway over the week end.

 

Got in supplies of 145c solder and 6-/40 solder paste from Cupalloy.

 

The chassis main frames are complete and drilled for frames pacers, also used to take bolts for the body retaining.

 

The inner sub frame is also complete with ends but no spacers except the Bakelite bottom block to take the pickups.

 

Still to decide whether brass or copper pipe is best for the boiler barrel. Copper can be awkward to solder to as it soaks up heat, and risks spreading heat to other joints that could melt.

 

The gears need no modification at all apart from a covering gear case. It will need a small brass cradle made to take the motor to fit the sub frame.

Stephen.














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