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


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This thread will describe the build of the NLR 1-10 Class 4-4-0T using the 3D body designed by L49 (Jim Connor, CDC Design) and available on his Shapeways page in both early narrow cab and later wide cab versions. See http://www.rmweb.co.uk/community/index.php?/topic/77233-north-london-railway/

 

Having built the Branchlines/Gem NLR 0-6-0T and the Peter K NLR 51 Class 4-4-0T I needed this one to complete my NLR motive power set.

 

I had completely forgotten the discussion in the link above about providing a P4 chassis and ordered the existing OO version. I originally ordered the wide cab version in Fine Ultra Detail (FUD) together with the brass printed coupling and connecting rods, however Shapeways refused the order, perhaps due to dimensional conflict. When I tried ordering the narrow cab version in FUD the order was completed ok......having got the narrow cab version I had to search for a suitable candidate for 1920s service as most by this time had been modified with the wider cab. No.24 was apparently never modified and saw LMS service as No. 6493 before being scrapped in 1928 (ref Locomotives Illustrated 129 - NLR Tank Locomotives), a picture of No.24 in 1919 is on page 25. The LMS lettering style will have to be a guess as several versions were recorded.

 

Here are some pictures I took for a 3D discussion thread dealing with surface finish so does not really show the chassis well. The print comes in five pieces, the body, chassis including smoke box, cab roof, bogie and bogie retaining stud.

 

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Having received the parts I was able to make some decisions on the motor g/b combination. A scale drawing suggested a Branchlines Multibox (53:1) with Mashima 10/20 and flywheel. Wheels are Gibson P4 (4S62 and 4S31).

 

Even with the multibox sides cut down to the gear profiles there was still some conflict with chassis and body structure. Photos below show a test fitting of the assembled g/b and motor. The rear driver chassis holes have been reamed out to 1/8" to accept the axle for trial installation. The vertical part of the rear chassis spacer had to be removed and part of the firebox/backhead (shown in pencil). The g/b width is 8mm with the chassis 10mm between frames. This will give adequate space for movement of the proposed twin beam compensation but the beams will have to be outside the chassis.

 

The chassis outer faces have been smoothed by removing the brake shoes (retained for later fitment) and using an emery board. The working on the FUD is a bit like resin, it cuts and files cleanly but is fragile - the front l/h spring has already broken off.

 

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My proposal is to make new side frames (1mm styrene?) with the same profile (with dummy springs and compensation beams) with a central pivot. The existing chassis will just have the axle holes opened up to allow for axle movement. The bogie will be load bearing. The side frame beams will be fairly rigid so I believe I will have to install the top hat axle bearings with some allowance for up and down angular movement - with thin beams some twisting can take care of this.

 

More as I progress....

Edited by Jeff Smith
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Joseph, I can't see a problem with making it a rigid chassis but think that brass top-hat bearings would be advisable. With 3D, resin, polystyrene and brass models, added weight is a necessity. Tank locos luckily have plenty of space for extra weight as well as for wider EM/P4 wheels.

 

This particular design incorporates the front and smokebox as part of the chassis but most designs have stand alone bodies and chassis.

Edited by Jeff Smith
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From an engineering standpoint I find it remarkeable the anyone would consider using modelling plastic as a bearing surface. Fitting brass top hat bearings (1/8" ID, 4mm OD) isn't rocket science.

Well keyser's did for their motor bearings.............Which worked well!!!!!

And as for rocket science, I never could under stand that comment! Don't around 15 million of us in the UK launch rockets every year for around a week in November! Hardly difficult!

Light blue touch paper and retires........simply rocket science

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If I remember my engineering theory, bearings are usually comprised of one hard surface and one relatively soft surface and a lubricant. The axle is the hard surface, the bearing is the soft surface, could be brass or plastic depending on the expected wear life and the lubricant.

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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.

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Bearing material is usually softer than the material running on it as it is usually easier and cheaper to replace. White metal shell bearings in vehicle engines, bronze bearings in boat prop shafts, etc.

 

I believe PTFE and other specially developed non metallic bearings are used successfully for bearings. In this case, is there any research or experience that 3D printed plastic of the type used for the chassis print has good wear characteristics?

 

Although etched brass and n/s chassis would seem to provide a suitable bearing surface material, even these are invariably fitted with brass bearings to give sufficient bearing surface area to minimise wear.

 

It would seem sensible to fit brass top hat axle bearings in the first place, rather than possibly find out later that the plastic isn't sufficiently hard.

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FUD (or whatever they're calling it this week) is weak and crumbly. It's not what you need for a bearing. "Versatile plastic" (previously WSF) is a nylon and some kinds of nylon have been shown to make good, low-force bearings. It's how some RTR rolling-stock is made. Nylon pinpoints in nylon bearings seem to work, but metal axles are reported to wear out nylon bearings quite quickly.

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I wonder if the OP is going to compensate this chassis? Although I agree with the comment that top hat bearings are essential, compensating will provide more headaches!

 

I have a FUD kit for an 0-4-0T which I am planning to complete as a P4 model, I shall be looking avidly at this thread for ideas, but I'm unlikely to compensate it.

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Yes, it will be compensated with twin beams but because it is an OO chassis the beams will have to be on the outside. The beams will actually be the same profile as the existing chassis. For an 0-4-0 the usual method is one fixed axle with the other tilting on a central pivot.

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Yes, it will be compensated with twin beams but because it is an OO chassis the beams will have to be on the outside. The beams will actually be the same profile as the existing chassis. For an 0-4-0 the usual method is one fixed axle with the other tilting on a central pivot.

All true but there is a need to secure horn blocks and guides to the chassis. Not necessarily easy when the design isn’t intended for them.

 

I’m looking forward to the build.

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Guest Lyonesse

From an engineering standpoint I find it remarkeable the anyone would consider using modelling plastic as a bearing surface. Fitting brass top hat bearings (1/8" ID, 4mm OD) isn't rocket science.

Plastics can make excellent bearing surfaces.  The arrangement looks OK to me, especially for a loco that's only going to trundle a few yards up and down a shunting plank.  There might be an issue with parallelism of the axles, but drilling out the holes to 4mm and fitting brass top hats is hardly going to solve that.  If you want to take an engineering viewpoint then how about questioning the obsession with 1/8in axle bearings.  How about 2mm or 1mm od bearings, to reduce friction?

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Plastics can make excellent bearing surfaces.  The arrangement looks OK to me, especially for a loco that's only going to trundle a few yards up and down a shunting plank.  There might be an issue with parallelism of the axles, but drilling out the holes to 4mm and fitting brass top hats is hardly going to solve that.  If you want to take an engineering viewpoint then how about questioning the obsession with 1/8in axle bearings.  How about 2mm or 1mm od bearings, to reduce friction?

This could devolve into a discussion about engineering an d material practises. Increased bearing diameter and width reduces (if my recollection from my engineering training many years ago is correct) in reduced bearing surface area load. Larger diameter increases bearing interface speed, so a compromise is required.

 

There isn't an obsession with 1/8" axles for loco driving wheels, it is what was practical in the early days and has simply become a generally accepted standard for wheel manufacturers and kit designers.

 

Surely one of the claimed benefits of 3D printing is accuracy of dimensional control, so providing a 4mm ID beaing hole shouldn't be a problem. If it is, how do you guarantee an accurate 1/8" bearing hole in the plastic?

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All true but there is a need to secure horn blocks and guides to the chassis. Not necessarily easy when the design isn’t intended for them.

I’m looking forward to the build.

There are a couple of ways of doing twin beams. If you have traditional Flexichass type hornblocks then the sideplay and wheelbase is controlled by those. The beams just control vertical movement and overall height is fixed by the location of the central beam pivots. However two previous 4-4-0s I've built had the bearings in the beams. The chassis really just supplied the location of the beam pivots. More on this when I find a suitable illustration.

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Having designed and built over a dozen 3d printed chassis designs I'd firstly point out that dimensional accuracy in the z axis for WSF is pretty poor so you usually get oval holes. Having trialled it, even with brass bearing inserts I wouldn't trust it for a chassis.

In FUD I print the chassis with holes for brass bearings (or sealed bearing races for layshafts). It is accurate enough for bearings to be a slightly firm press fit, though I still secure them with a bit of superglue (cocktail stick, wipe the rim of the hole, be very careful it doesn't get inside the bearing). I don't think the printed material would last long at all as a bearing, then running would deteriorate quickly as the holes elongate or loosen.

I have to admit that I usually sprue off fiddly detail parts as they get in the way of smoothing and painting and get knocked off. Fortunately FUD superglues really well and with a bit of care you can make a strong, invisible joint.

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Guest Lyonesse

This could devolve into a discussion about engineering an d material practises. Increased bearing diameter and width reduces (if my recollection from my engineering training many years ago is correct) in reduced bearing surface area load. Larger diameter increases bearing interface speed, so a compromise is required.

 

There isn't an obsession with 1/8" axles for loco driving wheels, it is what was practical in the early days and has simply become a generally accepted standard for wheel manufacturers and kit designers.

 

Surely one of the claimed benefits of 3D printing is accuracy of dimensional control, so providing a 4mm ID beaing hole shouldn't be a problem. If it is, how do you guarantee an accurate 1/8" bearing hole in the plastic?

We could have that discussion.  But a better idea would be to let Jeff Smith get on and build the NLR tank and either prove or disprove the practicality of printed plastic axle bearings.

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We could have that discussion.  But a better idea would be to let Jeff Smith get on and build the NLR tank and either prove or disprove the practicality of printed plastic axle bearings.

The sense of the thread has perhaps become a little muddled. I will not be using plastic/3D bearings. I plan to use standard brass top hat bearings in the beams.

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With apologies for the second picture being out of focus, progress has been made as follows.

 

Axle holes in the 3D chassis were reamed to 1/8" and axle jigs installed.  3D brass coupling rods used to verify the axle spacing - right on as you can see.  Both sides the same so axles are parallel.

 

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3D chassis used to create a new chassis side which will be the beam on one side.  Cut outs will be made once the principle has proven satisfactory.  The profile was finalised using the 3D chassis as a guide - the ultimate in soft tooling!  Photo shows the beam in place and marked to drill the central pivot.  Work has stopped while I decide what to make the pivot from....probably a brass tube through the chassis with steel pin.  The beams will need some sort of bearing to pivot on and control the beam width.  More thought required.

 

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Also, I intend using Gibson sprung pick-ups, these will be mounted in the beams and therefore need clearance holes through the 3D chassis.

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I decided to use some telescoping brass tube, the larger one being 2.4mm OD.  The picture shows the tube pushed through the chassis in the beam centre pivot position, I had to drill through the printed chassis spacer.  Each beam pivot will have a short sleeve of tube installed and the next size down will pass through both beams and the chassis to be the pivot.  The length of the centre tube will control the beam spacing.  Once I have made the other beam and am satisfied that the axles remain true I will ream out the beam axle holes for top hat bearings.  My theory is that the 1mm styrene beams will be flexible enough to twist and cope with the slight axle lift and vertical misalignment that the beam compensation system is designed to deal with in P4.  The back to back should allow about a mm of clearance between the beams and the 3D chassis to allow for this twist......fingers crossed!

 

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All very interesting ideas Jeff, but a word of caution about plunger pickups.  Once installed the springing can't be adjusted, they're awkward to clean and have been known to seize up.  I have had these issues and I stick to conventional wipers made from nickel-silver wire or phosphor-bronze strip.

All the best, Dave.

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I appreciate the caution. I have installed them on several locos but my models don't see heavy duty. Generally once finished and tested most go on display. However for frequent use I can imagine problems can be encountered - wheels would have to be removed to repair or replace.....

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