CR 900 class 4-4-0 (Dunalastair III)

[Caley Jim]

With the arrival of my latest sheet of etches from PPD construction proper can start on my latest loco, a CR 900 class 4-4-0, also known as Dunalastair III.  The wheels gears etc came from Jon at Shop 3 a couple of weeks ago and have been prepared.  First job has been to work on the motor mount and tender chassis.  The motor will be at the front of the tender with  the stay-alive capacitors alongside it and the decoder and circuitry behind.  The drive layout will be as in this drawing:

 

The motor, Tramfabreik 0816, has been fitted into its mount along with the gears and the chassis 'frames' and bogie mounts fitted.

The leads are just temporary to let me check the gear meshing with a 9v battery.

 

 

The rear bogie mount (to the right above) has a 12BA nut soldered above it to take the length of 12 BA stud which will form the pivot.  There isn't room for this above the front bogie as the drive shaft will be just above the mount, so there is an extra layer on the bottom there which has been tapped to take the pivot.

 

Jim

Edited November 23, 2023 by Caley Jim
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[Caley Jim]

The last week has been something of a 2 steps forward and one, or more, back.  The assembly carrying the motor etc. will be electrically ‘dead’ with current being collected via the bogie inner frames.  To get the current to the motor there are a pair of thin double-sided PCB strips soldered either side of the rear bogie pivot.  On these are two short transverse lengths of copper wire which both take current from the top of the bogie and will also stop the tender from rocking, while allowing the bogie to rock fore and aft.   Current from the front bogie will come via the two long finger springs, allowing the weight of the front of the tender to transfer to the loco via the drag beam.  To collect the current from the loco another pair of thin PCB pads are soldered either side of the front frame sections, each carrying one of the little tubes I make by wrapping fine wire round a No.80 drill and then flooding it with solder.  A thin wire then runs from these pads to those on the rear bogie support.  The finger springs need a bit of re-shaping at their outer end.

The first iteration used decoder wire to link the pads, but when I tried the bogies on this was too thick and resulted in the wheels hitting it and pretty much stopping the bogies pivoting.  It has been replaced with some very fine varnished and cotton covered multi-strand wire which has been tucked into and cyano glued in the angle of the frame and base.  The leads to the motor are attached to the back of the bogie mount pads and go through two holes in the base.  Another of the issues I had was eliminating shorts between the pads/wiring and the chassis.  It took several unsoldering/re-soldering attempts to eliminate them!

 

On the top side I wanted to be able to disconnect the motor and decoder without having to resort to the soldering iron.  First thoughts were to use one of the small plugs and sockets I had used to connect up the wiring to the lights in my signal box, but that was going to be rather bulky.  Some of the decoders came with an 8 pin plug on them. So I cut a section off the end with 2 pins on it and made a ‘socket’ again using tubes made as before using a suitable drill (took a few attempts to get the right size drill).  These tubes were soldered to a suitably gapped piece of thin PCB and two wires added.  This was then soldered to the inside of the side of the motor cradle and the wires led down through holes as described above.  The decoder track leads have the plug attached and the motor leads have a second socket made in the same way, but this time backed by a piece of 20thou styrene with the tubes embedded in 5 minute epoxy, the leads from the motor having another plug on them.

The socket with the track leads.

With the decoder (CT DCX75) and the leads all plugged in.

Alongside the motor is the bank of 4 220uf capacitors which have still to be wired to the decoder.   This came from my 2-4-0 which has had the configuration of the decoder and capacitors rearranged to get more weight to the front of the tender.   The capacitors are not connected up as I’ve still to source the components for the circuitry.  This arrangement also means that if I want to run the loco on a DC layout, all I have to do is unplug the decoder from the track socket and replace it with the plug from the motor.

 

The bogies have also been assembled.

 The side frames and stretcher were etched as one piece with two half etched lines along which they could be separated once soldered to the PCB spacer.  LH one is right side up, the RH one upside down.  The (cosmetic) outside frames will be added once everything is up and running.

 

The whole assembly sitting on the bogies.

 

Apologies for the long post.  Hope it's understandable.

 

Jim

Edited December 1, 2023 by Caley Jim
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[Hendreladis]

Amazing. There wasn't a suitable reaction icon and 'like' didn't really seem good enough. 

[Caley Jim]

Attention has now turned to the loco frames.  The gearbox was assembled first and the meshing checked by having a long shaft on the worm which could be rotated with a pin chuck. The gears were then removed prior to soldering on the thin PCB pads which will retain it in the frames, after which the worm was refitted on its proper shaft, as it will be extremely difficult to fit when the gearbox is in the frames.

 

the two frames are etched in one piece with a couple of cross-members below the coupled axles.  These allow the frames to remain square when they are bent up and will be filed away now that the spacers and gearbox are all in.

 

 

In this top view you can see all the sacrificial lugs which ensure the spacers and gearbox are accurately located.  Also the two trunnions with holes at the top which, by passing the length of axle steel through them and the gearbox, ensure the bearings for the lay gear are at exactly the correct spacing from the driven axle.  They too are sacrificial.

 

 

In order to give the bogie wheels a bit more clearance from the frames, the latter are joggled in 10thou each side at the front, the bends being re-enforced with generous fillets of solder.

 

Removing the sacrificial parts and then cleaning up are the next job.

 

Jim 

[VRBroadgauge]

On 02/12/2023 at 10:00, Caley Jim said:

 

 

the two frames are etched in one piece with a couple of cross-members below the coupled axles.  These allow the frames to remain square when they are bent up and will be filed away now that the spacers and gearbox are all in.

 

 

I'm doing a similar thing with a VR locomotive I'm designing. I've put a 0.4mm half etch across the centre line of the etches where they need to be seperated. I'll cut these with a razor saw.

 

I like the idea of making the chassis rails integral and then separating them after the spacers have been installed.

[Caley Jim]

After removing the sacrificial tabs etc., adding the springs carrying current from loco frames to tender and masking off the gearbox with tape, the chassis was given a quick blast with rattle can black.  The wheels were then fitted along with the gears.

 

At this point there was one of those 'b****r it!' moments when I found I only had a set of layers for one coupling rod when I was absolutely certain I had put two on the sheet!  Close examination of the artwork showed that I hadn't put any tags on the second set attaching it to the parts around it so there was a glaring hole in the sheet where that set should have been!   See this C-Nile virus?  Does it never stop raising it's ugly head?  Guess what will be going on the next sheet I do!

 

Only solution in the short term was to use the made up rod as  template to make a temporary one and, while it's not as neat as the etched one and not fluted, it seems to do the job as the wheels turn in unison when powered.  The photo has the good one on this side.  The crankpins on the other side have been left long to make it easier to eventually replace the rod.

 

 

Running is somewhat erratic as the lack of weight causes both chassis to shake about a bit resulting in poor current collection, so no video of it, but if the tender is held steady, the wheels turn reasonably smoothly.  Hopefully the weight of the tender and loco bodies will cure that.  You can just see the drive shaft running behind the spring.

 

I won't be making the front bogie until the loco body is well on the way as the body fixing screw will only be accessible with the bogie off.

 

Jim

[A. Bastow]

Jim! 

 

I'm watching this thread with interest as I am planning a 4-4-0 in future (L&Y outline of course). 

 

Is there any particular reason that your motor and gearbox is arranged below the footplate? I am curious as to the design choice. 

 

Cheers,

 

Adam

[Caley Jim]

Hi Adam. It's just that I have a'thing'about not wanting to have a drive shaft flailing about between the low tender and relatively open cab of my tender locos. I've no objection to other folk doing it, that's their choice. It does make things a bit more complicated with the extra gears on the tender and the need for a lay gear in the loco, but for me it's worth it to get the drive shaft out of sight. Purely a personal thing and not something I would necessarily encourage folk to do unless they are similarly minded. 

 

Jim 

[A. Bastow]

4 minutes ago, Caley Jim said:

Hi Adam. It's just that I have a'thing'about not wanting to have a drive shaft flailing about between the low tender and relatively open cab of my tender locos. I've no objection to other folk doing it, that's their choice. It does make things a bit more complicated with the extra gears on the tender and the need for a lay gear in the loco, but for me it's worth it to get the drive shaft out of sight. Purely a personal thing and not something I would necessarily encourage folk to do unless they are similarly minded. 

 

Jim 

 

Massive thanks for the reply. It does allow you to model a cab interior properly if you so wish!

[Caley Jim]

tender body coming along slowly.  The openings in the footplate and tank top needed a wee bit of fettling to clear the motor etc, but otherwise most bits fitted rather well.

 

This side has the 'temporary' coupling rod.  the extra weight is keeping the tender a bit steadier, but there is a slight stiff spot which causes it to wobble slightly.  I think that's in the gears somewhere and will hopefully 'run out' once it gets a bit of lubrication.  It's already been run with some toothpaste to polish the gears.

 

Front plates/cab doors and toolboxes next, then I'll start on the bogie outside frames.

 

Jim

[Caley Jim]

"The best-laid schemes o' mice and men gang aft agley'' (To a mouse; Robert Burns).  Sometimes because the schemes weren't as well laid as you thought!

Such was the case with the outside frames for the tender bogies.  These were designed to be in one piece with the stretcher running under, and bolted onto, the pcb spacer, keeping them electrically isolated from the frames carrying the wheels.  What I omitted to account for was that they had to pass through the relatively narrow gap between the wheels.  This meant the stretcher had to undergo a bit of surgery with a carbo disc, as can be seen in this photo with the underside of the completed front bogie on the left and the etch for the rear one on the right.

 

 

The axleboxes have two prominent ribs on either side and this was the next idea that didn't quite work as intended.  The plan was that the little half etched triangles on the etch would be folded out, with the etch including the axleboxes having fine slots in the axlebox back plates through which these would pass, thus both forming the ribs and locating the axlebox unit on the frames.  Hmmm!  Bending up the eight ribs to the same angle and passing them all through the slots simultaneously proved all but impossible!  The previously non-existent plan B had then to be devised.  This involved cutting away the triangles and using some of the longer half etched tags, with the end cut at an angle, passed through the side from behind.  Two were used at first to locate the axlebox unit, and then the others added.

 

This is the completed front bogie.  The inner end stretchers on both bogies had to be cranked towards the bogie centres in order to keep them clear of the lower gear.

The axlebox  unit is a multilayer etch incorporating the axleboxes, the large inverted leaf spring between them, which was pivoted on the frame, and the compensating beam between their tops.

This is the rear bogie (which also has guard irons on it).  The axlebox unit layers are on the left, with the other unit fitted to the stretcher unit on the right.  The little slots in the end stretchers are to locate the brake blocks.

 

Here we have the tender with the front plates + cab doors and tool boxes added and sitting on its bogies.  I suspect the cab doors will have to be angled out slightly to allow the loco to go round curves.

 

The half etched areas on the bottom of the tender frames were put there as I was unsure how much clearance would be needed to allow the bogies to swing on curves without the compensating beams fouling the tender frames, however their short wheelbase and the close bogie centres mean that the tender will go round an 18" radius curve with hardly any swing of the bogies, so I may attempt to fill these in.

 

I can now start on the loco body, however work on that can only go so far until Squires get 10mm thin walled brass tube, for the boiler, back in stock! ☹️

 

Jim

[queensquare]

18 hours ago, Caley Jim said:

"The best-laid schemes o' mice and men gang aft agley'' (To a mouse; Robert Burns).  Sometimes because the schemes weren't as well laid as you thought!

Such was the case with the outside frames for the tender bogies.  These were designed to be in one piece with the stretcher running under, and bolted onto, the pcb spacer, keeping them electrically isolated from the frames carrying the wheels.  What I omitted to account for was that they had to pass through the relatively narrow gap between the wheels.  This meant the stretcher had to undergo a bit of surgery with a carbo disc, as can be seen in this photo with the underside of the completed front bogie on the left and the etch for the rear one on the right.

 

 

The axleboxes have two prominent ribs on either side and this was the next idea that didn't quite work as intended.  The plan was that the little half etched triangles on the etch would be folded out, with the etch including the axleboxes having fine slots in the axlebox back plates through which these would pass, thus both forming the ribs and locating the axlebox unit on the frames.  Hmmm!  Bending up the eight ribs to the same angle and passing them all through the slots simultaneously proved all but impossible!  The previously non-existent plan B had then to be devised.  This involved cutting away the triangles and using some of the longer half etched tags, with the end cut at an angle, passed through the side from behind.  Two were used at first to locate the axlebox unit, and then the others added.

 

This is the completed front bogie.  The inner end stretchers on both bogies had to be cranked towards the bogie centres in order to keep them clear of the lower gear.

The axlebox  unit is a multilayer etch incorporating the axleboxes, the large inverted leaf spring between them, which was pivoted on the frame, and the compensating beam between their tops.

This is the rear bogie (which also has guard irons on it).  The axlebox unit layers are on the left, with the other unit fitted to the stretcher unit on the right.  The little slots in the end stretchers are to locate the brake blocks.

 

Here we have the tender with the front plates + cab doors and tool boxes added and sitting on its bogies.  I suspect the cab doors will have to be angled out slightly to allow the loco to go round curves.

 

The half etched areas on the bottom of the tender frames were put there as I was unsure how much clearance would be needed to allow the bogies to swing on curves without the compensating beams fouling the tender frames, however their short wheelbase and the close bogie centres mean that the tender will go round an 18" radius curve with hardly any swing of the bogies, so I may attempt to fill these in.

 

I can now start on the loco body, however work on that can only go so far until Squires get 10mm thin walled brass tube, for the boiler, back in stock! ☹️

 

Jim

Great progress Jim, I’ve sent you an email.

 

Jerry

[CF MRC]

That’s a very impressive water cart, Jim. 
 

Tim

[Ian Lilley]

Hi,Jim,I've noted your use of tooth paste to polish a geartrain and wondered (a)will any toothpaste work (the one I use on my teeth is a gel and does'nt appear to be particularly abrasive)(b)how much-presumably just a small dab(c) how long do you run it for(d)How do you remove it afterwards-I would be reluctant to use water so close to the motor.Keep up the great modelling !

Ian Lilley

[Simon D.]

A lot of people recommend Pearl Drops

[Caley Jim]

3 hours ago, Ian Lilley said:

Hi,Jim,I've noted your use of tooth paste to polish a geartrain and wondered (a)will any toothpaste work (the one I use on my teeth is a gel and does'nt appear to be particularly abrasive)(b)how much-presumably just a small dab(c) how long do you run it for(d)How do you remove it afterwards-I would be reluctant to use water so close to the motor.Keep up the great modelling !

Ian Lilley

Thanks, Lilley.  It is done on the advice of fellow dental professional @CF MRC.  All toothpastes contain a very mild polishing agent.  A small dab on each gear pair is all you need and I run it jut for a few minutes to smooth off any tiny roughness.  In the case of a tender loco there's no issue about washing it off as the motor is in the tender.   For a tank loco with the motor in the loco, I simply remove the motor before washing.  be sure to give everything a good scrub with an old toothbrush to remove any small traces and dry the chassis over a radiator or in the airing cupboard.

HTH

 

Jim

[burgundy]

50 minutes ago, Caley Jim said:

......  be sure to give everything a good scrub with an old toothbrush to remove any small traces and dry the chassis over a radiator or in the airing cupboard.

 

The perfect answer to how to remove toothpaste from a set of gears: use a toothbrush. Surely the ultimate BGO! 

Best wishes 

Eric 

[Caley Jim]

Progress has been slow over the past couple of weeks, what with the festivities etc.  A fellow member of our group kindly gave me some more components for stay alive circuitry which let me finish of re-motoring my Drummond 171 class 0-4-4T which now has a Tramfabreik 0615 motor with a Zemo MX615 decoder along one side and a flat wide 470uf capacitor and the circuit along the other.  It took a bit of tuning in Decoder Pro to tame the motor a bit, but it's now reasonably under control.

 

I also assembled the stay alive for this loco, but, for some reason which my consulting electronic engineers are unable to determine, both the circuit and the decoder get very hot very quickly as soon as it is put on the track.  Hopefully they will be able to solve the issue at our next group meeting.

 

Meanwhile some work has been done on the loco body, attaching the cab/splasher sides and tops and crankpin splashers to the footplate along with the cab front.  Handrails etc were fitted to the sides before assembly as was the beading around the spectacles (brass wire).

The two strips of 40x40thou styrene either side of the gearbox are temporarily there to centralise the body at the rear.  That job will be done by the firebox sides when the boiler is fitted.  The front boiler support is not at nearly as much of an angle as it appears here and the two lugs on the cab front are to locate the rear end of the boiler.   As far as the boiler is concerned, the 10mm diameter brass tube being OoS at Squires, @CFMRC  has kindly sent me a 'manufactured' length and work has started preparing that to be fitted.  There will be a slight lull in progress again, however, as I have promised to give a talk on the Quintinshill Disaster to my local PROBUS club next month, so preparation for that will need to take priority for the next few days.

 

Jim

[Wolseley]

Very nice work.  I have tackled an etched kit for a brake van and, as a result, have the utmost respect for anyone who tackles an etched kit for a locomotive.  I wouldn't mind trying myself, but life is too short for me to take on something like that while I still have unmade whitemetal kits.

 

It looks a lot more accurate than the 60 class I recently put together by marrying an old DJH kit with a Tri-ang Hall......

[Ian Lilley]

Many thanks for the information Jim, pretty much what I expected but I thought it advisable to get the answers direct from the dentists mouth!Unfortunately the motor is fixed in the chassis but I'm sure I can clean any residue with due care,

Ian

[Caley Jim]

Slowly progressing.  With the boiler, smokebox front and cab roof fitted it's starting to take shape.

 

I've learnt that it's best to leave the handrail knobs and cab-side lamp brackets until late in the build, otherwise they tend to suffer damage through handling.

 

I've still to try it under power as we didn't manage to diagnose the problem with the stay alive.  Suspect a problem with the caps.

 

Washout plugs and smoke box door next, then, with the fitting of the boiler making the footplate rigid, the buffer beam and valences can go on.

 

Jim

[CF MRC]

Will you make a Cardean, Jim? I always thought the old GEM kit looked very impressive. 

 

Tim

[Caley Jim]

Don't know that I can justify a Cardean.  I'm only justifying the Dunallastair and the G & E Direct set on the basis that there has been an 'incident' somewhere on the Shotts line, so services are diverted.  I suppose I could say something had happened around Law Junction, so WCML services were similarly diverted.  Then I would need to build a rake of WCJS coaches.  To be honest, I always fancied doing a WCJS sleeping composite, just to see what punters reactions would be!

Has the definite look of a 'cut & shut' job!

 

Jim

Edited January 18 by Caley Jim
Typo

[CF MRC]

Interesting carriage that, Jim. I do like the WCJS carriages. We could justify a LNWR Birmingham businessman’s train  on the NLR to Broad St, hauled by a Jubilee (not Nick’s type). I did procure etches for some of the coaches but unfortunately they went AWOL with a former member of the group. I think we have more than enough other projects on the list though…

 

Tim

[2mm Andy]

20 hours ago, Caley Jim said:

Don't know that I can justify a Cardean.  I'm only justifying the Dunallastair and the G & E Direct set on the basis that there has been an 'incident' somewhere on the Shotts line, so services are diverted.  I suppose I could say something had happened around Law Junction, so WCML services were similarly diverted.  Then I would need to build a rake of WCJS coaches.  To be honest, I always fancied doing a WCJS sleeping composite, just to see what punters reactions would be!

Has the definite look of a 'cut & shut' job!

 

Jim

I'm sure I have seen an article/drawing of the WCJS sleeping composite coach recently - possibly in a LNWRS or HMRS journal?

 

Andy