North London 4-4-0T 3D Build in P4

[Jeff Smith]

Moving on with the build.  This picture shows the back to back shaping of the beams.  I might try to clean up the spring detail but it will be largely hidden behind the wheels.

 

 

The two beams with top hat bearings and the central pivot tubes fitted - superglue.

 

 

Trial installation of the beams and axles from both sides.  Note the opened up axle holes in the 3D chassis to allow approximately 2mm of total up and down axle movement.

 

 

The beams on their own to show the principle. 

 

 

Next up is to file the pivot bearing tubes to give the correct beam spacing and decide on the sprung pickup locations.

[Jeff Smith]

Sticking with the main beams these pictures show the bodies of the sprung pick ups installed and the clearance holes in the 3D chassis.  The forward one was a bit high, I thought to clear the lower horizontal chassis spacer, but for strength felt I needed to add an additional strengthener.

 

 

Now for the bogie.  First an as-is picture with the wheels and axles installed.  I cut off the side frames and superglued to a new styrene centre.  I could have packed out the frames but wanted to have a central pivot hole rather than slot.  The front of the bogie is very visible under the buffer bar.  The front axle will just run in the 3D sideframe holes, the rear will have a central rocking support and slotted sideframes.  Second picture shows the new assembly with the old centre to accentuate the change in gauge.

 

[Jeff Smith]

Having now drilled the re-built bogie with clearance holes for the 2mm axles for free running and test fitted the wheels I have decided to not have the rear axle rocking.  It is square and several test runs through some P4 points suggests no need.  This will be a relatively easy addition if I find it necessary later.

 

[Jeff Smith]

A quick test assembly indicates that the bogie pivot needs to be lowered about 2mm.  Note that the main drivers are both on the mat even though the front is high thanks to the beams - there is about the same amount of travel the other way.  Coming back to P4 from O-16.5 I had forgotten how fine the P4 flanges and tolerances are! 

 

Unfortunately IPhone camera distortion doesn't produce the best picture.

 

[Jeff Smith]

Here are the beams seen from both sides with the sprung pick-up plungers installed.  This batch seemed to have rather brittle wire ends as two or three broke when trying to bend for retention.

 

[Jeff Smith]

This picture taken earlier shows the 3D printed brass sprue with coupling rods, connecting rods and slider blocks (cross pieces?) as it comes.

 

 

I spent a considerable time cutting them off, cleaning them up and drilling for Gibson crank pins.  The blocks and connecting rod small ends are printed with about 0,25mm holes.  These seemed very small and I had some 0,55mm brass pins I intended to use to connect them.  I used a 0,58mm drill (probably an imperial size) which proved to be just right.  I was actually amazed to be able to drill the small ends successfully as the width was only 0,85mm leaving a very thin wall but the print was so accurate that they were perfect!  Praise for the designer to incorporate pilot holes!  Also the nice bosses and lube nipple details.

 

You'll notice that the slider blocks only have short piston rods which were actually the sprue.  I'm toying with the idea of somehow fitting longer rods.... 

 

 

Now for a conundrum.  Pictures show the connecting rods mounted inside the coupling rods - I don't think I have seen this arrangement before.  Maybe a spacer on the rear driver crank pins is required?

 

[DLT]

 

Now for a conundrum.  Pictures show the connecting rods mounted inside the coupling rods - I don't think I have seen this arrangement before.  Maybe a spacer on the rear driver crank pins is required?

 

IMG_0375.JPG

 

That's a fairly common arrangement on an outside-cylinder 4-4-0, and yes, a simple spacer on the rear crankpin will do the trick.

 

Looking really good,

Dave.

[Compound2632]

That's a fairly common arrangement on an outside-cylinder 4-4-0, 

 

I presume as a consequence of wanting to keep the reciprocating masses as close to the engine's centre line as possible, to avoid waddle - a reason why inside cylinders were preferred once crank axles could be manufactured reliably, despite the tight squeeze of fitting all the motion between the frames. Another point may be getting the cylinders within the loading gauge.

[Jeff Smith]

The latter seems a likely reason. It may help my model as well!

Edited November 11, 2018 by Jeff Smith

[Jeff Smith]

I presume as a consequence of wanting to keep the reciprocating masses as close to the engine's centre line as possible, to avoid waddle - a reason why inside cylinders were preferred once crank axles could be manufactured reliably, despite the tight squeeze of fitting all the motion between the frames. Another point may be getting the cylinders within the loading gauge.

 

 

The latter seems a likely reason. It may help my model as well!

 

This got me thinking about whether the cylinders and slidebars had been narrowed for OO usage.  It seems they may have been.  According to a drawing Ian Kirk posted in another NLR thread the cylinders should be 24.5mm apart.  The model is slightly less but I think will still be OK in P4.

[Jeff Smith]

A little more progress.  The 3D print includes guard irons front and rear projecting down from the buffer beams, spaced for OO of course.  I took these off.  The prototype front irons were actually mounted on the front of the bogie so I made some from brass tube and strip as in the photo.  Superglued to the front.

 

 

This photo just shows some items painted black.  Some strengtheners had to be added across the chassis as the clearance holes for the sprung pick ups made the chassis very thin.  Brake hanger supports have been added - 0,55mm brass pins from the inside of the beams.  The sawn off hangers have been drilled for later fitment.  Main driver weights have been added from 10 thou styrene.

 

 

I am reminded now why I model in P4, particularly when following the thread about the new EMGS/Peco track and turnouts and all the discussions about just moving OO wheels out to suit EM.  The wheel flanges just look so right in P4, and from an earlier picture of the bogie on my 30 year old P4 track, the turnouts look right too.

Edited November 13, 2018 by Jeff Smith

[Jeff Smith]

Back to the model bench after a three week trip around Europe.

 

I finally bit the bullet and assembled the chassis; I try to this only once as I don't like removing Gibson wheels once installed.  0,25mm spacers were installed between the wheels and the bearings.  There is enough end float in the axles to allow for some slight twisting of the axles and rocking frames relative to each other.  The chassis is actually quite flexible.  Wheels were quartered and coupling rods check fitted.  The crank pins are a very tight fit between the tank sides and will need to shortened.  The front sits a bit high so the bogie pivot shoulders will need to be filed maybe as much as 1mm.

 

[Jeff Smith]

A few more hours work.  Connecting and coupling rod bosses thinned down to fit onto the Gibson crank pin sleeves.  Note connecting rods inside coupling rods as per the prototype - these line up almost perfectly with the cylinders although no actual piston rods are fitted.  Rear end of coupling rods fitted with spacers per discussion earlier in this thread.

 

The bogie ride height has been adjusted and is approximately correct now.  The model runs freely when pushed but the motor has yet to be hooked up.

 

[DLT]

Looking great Jeff, lovely job.

Cheers, Dave.

[Jeff Smith]

Dave, I'm reluctant to say you told me so, but you told me so......the sprung pickups did not work out satisfactorily and have been removed.  They seemed ok until I soldered on some fine wires.  I've used these before but maybe my iron was too hot or I paused too long but three out of four lost spring force, and the one that survived was not quite running on the metal wheel rim!

 

After some thought and reassembling the chassis I plan to use top wipers running on the tyres - these will be well hidden inside the side tanks.  A search in my supplies cupboard only turned up a couple of inches of phosphor bronze strip.  I seems unbelievable but pick-up strip just does not seem to be available in the US.  You can buy 5"x 7" sheets of thin PB but no strip.  An eBay search only turned up availability in the UK - I settled for a pack of ten from Slaters which has been posted to me today.

 

Test running of the chassis under power with flying wires to the motor indicated a tendency for one of the front wheels to lift however there was no weight on the chassis.  Nevertheless by attaching the wipers to the 3D chassis - one on each side bridging across the wheels - they will introduce downward spring forces which I think will help.

[Jeff Smith]

So, whilst awaiting the PB strips I have turned my attention to some 3D body improvements.  Some of which are due to 3D printing limitations, I believe 1mm is the thinnest section possible, and some due to it being an OO model.

 

 

Most noticeable at the front are the frame extensions which are both too narrow (OO) and too thick.  In the prototype they are just inside the bolted on cylinder end and are quite thin.  They also extend below the front footplate (as they do in the model).  On the model there is also a curved fillet between them, joining the smoke box front to the footplate.  All the lamp irons and destination board brackets will have to be replaced too.  Not sure about the smoke box door hinge but will add the handle, darts and hand rail.  I think I will retain the buffers.  The heads are just 1mm thick and flat so I have filed them thinner and with a convex front - I'll see how they look when painted.

 

The clack valve pipes need to be thinner - the valves are a bit oversize but most likely will be retained.  The top pipe that goes to the smoke box (don't know what its function is) is too thick.  Another obvious addition will be the footplate curved valance below the sand boxes.

 

I hasten to add that the designer of the 3D model did a magnificent job and these changes are to enhance it and convert to P4.  I would not have attempted a scratch build.

 

 

Edited December 18, 2018 by Jeff Smith

[PenrithBeacon]

So far, so brilliant! Really enthralled by your thread.

As you get to doing the body I’d be most interested in how you prepare the model to remove the stepping and layering which seems to be inherent in the 3D printing process.

[Jeff Smith]

The stepping looks worse than it is. The apparent variable translucency enhances the stepping effect. This material is a bit like resin to work on - it chips rather than curling like styrene. It was FUD (Fine Ultra Detail) but is currently available in Smooth Fine Detail Plastic. I've no idea how different this replacement material is.

[Guy Rixon]

FUD and FXD and Smooth Fine Detail Plastic and Smoothest Fine Detail Plastic are all UV-cured resins produced by the SLS process. Only the step size of the printing varies.

[Dave Holt]

Jeff.

 

It's coming along nicely.

For piston rods, I find nickel-silver rod [0,8 to 1 mm diameter, to suit the prototype] represents hem well. I turn down the wire to about 0,5 mm for the last 1 mm or so. This way, you only have to drill a small hole in the front of the cross head [think you called it the slider?] casting. Not having a lathe, I do the tuning by holding the n/s wire in a pin chuck and using a combined rubbing and twisting action along a fine file. As long as you progressively turn the pin chuck as you file, you end up with an acceptably round and central reduced shank, which can be carefully soldered [but could be glued] to the cross head. In my locos, the slide bars are far enough apart to do this assembly with the parts in situ, to ensure proper alignment. However, on your model, it looks like you would have to do it as a separate item, aligned by eye, and then carefully adjusted by trial fits until satisfied that a smooth fit has been achieved.

 

Dave.

Edited December 17, 2018 by Dave Holt

[Jeff Smith]

Dave, I appreciate your suggestion to add piston rods - I may yet consider this but would require drilling the cylinders from the cross head end as holes are not provisioned in the 3D print. Probably have to take the wheels off to do that!

 

As a suggestion to the designer, Jim Connor, it would have been nice to have had the cross heads printed with integral full length piston rods. However this may have introduced an assembly problem in getting the connecting rod big-end onto the crank pin....

[Jeff Smith]

Got to grips with the front footplate and removed the lamp irons, destination board supports and, most difficult of all, the OO thick frame extensions and fillet.  Unfortunately I only have side views of the front footplate but I suspect there was actually a gap between it and the smoke box - however I cannot be sure and it would have been difficult to produce anyway so it remains solid.  I stuck 40 thou styrene on the outside of the frames below the footplate and then cut and fitted one piece 20 thou frames above and below, this fitted snugly against the inner rim of the cylinder end covers.  I also thinned the edges of the footplate to make it look thinner.  The pictures show unpainted and then painted.  I also used engineers dividers to scribe the edge of the smoke box door using the dart mounting hole.

 

[peterfgf]

The Ffestiniog and Welsh Highland Railway have started to replace brass/bronze (some with white metal) bearings in coupling and connecting rods and valve gear rods with a plastic material. They claim it is easier to machine and is better wearing and requires less lubrication than the metallic bearings traditionally used. Apparently, the material is well established on steam locos in South Africa.

I expect it's quite a special grade of plastic but it does show that even bearings don't have to be metal.

Hope your chassis goes well.

Dave.

Plastic and resin impregnated fibre bushes have been used in ships' stern-tube bearings for many years.  Typically, the internal diameters can be up to about 900mm with wall thicknesses of 50-60mm.  The material may be easier (softer) to cut but setting up in a lathe to machine is not- the internal and external diameters still have to be machined to similar tolerances as white metal lined bushes.  The application was not always successful at sea: the compressive strength is not high which led to failures at the after edge under high propeller loads and the thermal conductivity is poor which can lead to local overheating and consequent failure.  I understand that resin impregnated fibre (Railko) was used for the bearing pads on BR class 40/44/45s (and possibly others).

Peterfgf

[Jeff Smith]

Fitted some lamp irons and destination board brackets made from brass bar/strip.  Not sure when the lower central lamp would be used but presumably without a destination board in place!

 

[Jeff Smith]

Fitted the lamp brackets and destination board brackets to the back of the cab.  They look a bit overscale but will be ok when painted.  The destination board brackets are shorter on the back on prototype too.

 

 

The Slaters phosphor bronze strips arrived from the UK so two pick-up strips were cut to length, the ends bent to create edge contact and then soldered onto the PCB support.  With the body adding a tad more weight the chassis runs well once I had cleaned an old piece of P4 track.