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Author Topic: Belstone's Scratchbodge Studies  (Read 4999 times)

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Offline belstone

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Belstone's Scratchbodge Studies
« on: May 04, 2016, 11:38:35 am »
With the J27 nearly finished and running beautifully I am thinking about what to do next.  I have three more old Poole locos to play with - 4F, 9400 Pannier and this Compound.



It's a bad model and a bad runner, but I wondered about using it as the basis for a D34 "Glen". So I took the body off...



Just as I feared.  A whopping great huge motor, mounted high up and just where you want lots of weight for traction. 4-4-0s are tricky beasts to motorise in any scale: if I tried to build a "Glen" out of this the body would be so oversize it would be close to TT gauge. So I had a rummage around and came up with another J39 motor.  It worked well in the J27, so why not try and fit it to this?

I managed to get some brass tube 1.5mm outside diameter.  The Poole wormwheel is 1.5mm bore, J39 motor 1.0mm shaft.  So I pulled the worms off the two motors (the J39 one is very tight), pressed a length of tube into the Poole worm, ran a drill bit (0.93mm, presumably an Imperial size) down the centre and pressed it onto the J39 motor in a vise, taking great care to support the rear motor bearing as otherwise it would probably have popped straight out of the backplate. The worm went on nice and true with no measurable runout.  Good start.

First attempt at fitting the motor was a failure.  There isn't really enough space between the driving wheels to clear the motor casing, and although it would just about fit inside a D34 boiler that still didn't leave any space for weight.  Plan B - stick the motor in the smokebox!  Why not, it weighs almost nothing, so having it over the bogie wheels won't make too much difference to the balance and means I can fill the firebox and most of the boiler with lead.  This called for some extreme brutality with the cutting disc: I Araldited a brass channel to the front end of the chassis, carefully filed it to get the gear mesh right and then glued the motor to the channel.  I really need to find a better way to mount these motors, but I was in a hurry and wasn't sure if it would work.



Whole load of teething problems.  The chassis is quite badly worn, with so much vertical play on the front axle that the gear dropped out of mesh when I took the weight off the loco wheels.  I filed the bottom of the chassis to tighten things up.  I also had problems with slipped quartering (possibly due to the extreme force needed to remove the front crankpins so I could take the connecting rods off) and one flange catching on the corner of the motor casing under load (those worn axle slots again, the axles move back and forth as well as up and down.  Basically it's worn out.)

But I finally got it running, with tender pickups on one side. The other side kept shorting on the chassis and I had to take off the pickup strip for now. I think someone has been here before me: the tender chassis was "live" the opposite polarity to the loco chassis, which isn't too clever with a metal drawbar between the two.  Helps explain why it ran like a pig in original form. I lashed up some weights to take it up to 45 grams - not ideal weight distribution with most of it over the back axle - and found it would comfortably handle two bogie coaches and 11 wagons which is plenty.  Nice slow speed control as well, at least for a passenger loco on big wheels.



Next stage is to Dremel the inside of the Compound body, fill it with lead and put it back on.  I'll leave the outside cylinders off as I have Dremelled the attachment point. With a smaller boiler and firebox it would make a 2P, sort of. 2P and 4F share the same boiler and I have a 4F body surplus to requirements. Hmm.  Then sort the tender pickups properly and see how it stands up to extended running.  The motor position is still not ideal as it sits in the space where there would be daylight under the boiler on a D34.  If I were really clever I'd fit a spur gear between the worm and drive gear and raise the motor so it sits entirely inside the smokebox, but at that point it would be easier to make a new chassis from brass.  It's not impossible - having seen how well these things run with massive amounts of slop in the gears, axles and coupling rods I don't think we are dealing with precision engineering here.

The driving wheels are deep flanged pizza cutters and won't like finescale track much.  So by the time I've changed them for later ones (if I can find any) there won't be much left of the Compound apart from the pickups, coupling rods and gears.  Still, it's fun.  Next up is the 9400 chassis which will be going into an N15 0-6-2T.  That's tricky - high motor and small boiler.  Looking at the 9400 chassis I reckon I can drop the motor at least 2mm at the back, chamfer the pole pieces and just squeeze it in.  Plenty of room in the side tanks for ballast, so I only need a fag paper clearance above the motor on that one.

If anyone has any non-running later Poole / early Chinese steam locos or chassis bits, with the finer flanged wheels, I'm interested in acquiring some and happy to pay a sensible price.

Richard

Offline belstone

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Re: Belstone's Scratchbodge Studies
« Reply #1 on: May 04, 2016, 11:48:07 am »
Looking at the photos again I have realised why the tender pickups seemed to be the wrong way round.  Somehow I managed to get the chassis facing backwards! On the Compound the rear axle is driven, on my reworked version it is at the front.  In my defence the attachments for the bogie and drawbar are identical, and with the cylinders off the chassis is pretty much symmetrical. LOL as they say.

Offline belstone

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Re: Belstone's Scratchbodge Studies
« Reply #2 on: May 05, 2016, 03:34:25 pm »
A bit of R&D...



I really don't need a 2P but the old Hornby model was a present from my grandfather when I was eight.  It has done so much running that the plating has worn off the wheels. It's not exactly a scale model, but I like it.  I don't have scale drawings for a 2P or Compound, but I found good side-on shots of both.  Coupled wheelbase looks the same (and a good bit shorter than the Farish model), Compound boiler is a touch longer (between dome and smokebox) and the front footplate is higher to clear the outside cylinders.  Cab looks a bit shorter on the Compound but not much.

The Farish boiler is too large in diameter for a 2P, or a Compound I suspect.  The extra body length for the oversize wheelbase is all in the firebox. So it's never going to be a scale model, but I found that dropping the front footplate actually makes the boiler diameter look a bit smaller.  I have room to take a slice out of the boiler just behind the smokebox, which handily is a plug-in plastic item.  The first cut is always the deepest:



New front footplate from brass, shallower front bufferbeam, and build up the smokebox saddle in Plastikard.  This might actually work. Of course there is also the tender, which is I think on a Black Five chassis and resembles the Fowler tender in the same way as a beagle resembles a bulldog. But how far do you go with something that is only supposed to be a mechanical test bed for the model you actually want to build?

Offline belstone

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Re: Belstone's Scratchbodge Studies
« Reply #3 on: May 06, 2016, 01:20:23 pm »


so... does this look anything like a 2P? Front footplate lowered, boiler shortened just behind the smokebox, and black marker pen to hide the shiny bits and give me an idea of the outline.  I'm not convinced yet.  The cab is too short. I'll put a new thick front on it which will help with the over-length firebox. Proper front bogie wheels will make a big difference as well.  I need to finish off the base of the smokebox, and I'll try and find a way to make a solid front extension for the chassis, to support the motor a bit better and give the body something to attach to.  It's propped up with tissue paper inside the boiler for the photo.

The brass strip I used for the new footplate was rubbish.  Too thick (my fault) and stamped rather than cut, so it had rounded edges and a bow in the middle (not my fault).  Filing brass strip flat feels like a punishment.

Offline Bealman

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Re: Belstone's Scratchbodge Studies
« Reply #4 on: May 06, 2016, 01:55:34 pm »
Looking great! But isn't that old Farish front skateboard awful  :-\
Vision over visibility. Bono, U2.

Offline belstone

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Re: Belstone's Scratchbodge Studies
« Reply #5 on: May 06, 2016, 02:19:15 pm »
Looking great! But isn't that old Farish front skateboard awful  :-\

I reckon it would make a good basis for a permanent way trolley.  The wheels are the right size.

Offline jrb

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Re: Belstone's Scratchbodge Studies
« Reply #6 on: May 06, 2016, 03:03:26 pm »
I reckon it would make a good basis for a permanent way trolley.  The wheels are the right size.

But the flanges definitely aren't! :P
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Offline Dorsetmike

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Re: Belstone's Scratchbodge Studies
« Reply #7 on: May 06, 2016, 04:15:31 pm »
Another use for a Compound is one of the SECR/SR 4-4-0s, D1, E1 or L1. I'd also be inclined to ditch the Farish motor and use a UM tender drive. Some years ago I hacked one into an ex LSWR D15.
Cheers MIKE


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Offline belstone

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Re: Belstone's Scratchbodge Studies
« Reply #8 on: May 06, 2016, 05:08:57 pm »
Another use for a Compound is one of the SECR/SR 4-4-0s, D1, E1 or L1. I'd also be inclined to ditch the Farish motor and use a UM tender drive. Some years ago I hacked one into an ex LSWR D15.

The UM tender drives are a bit bulky for a little North British tender (remember this is a mechanical test bed for the D34).  I wanted to see if the smokebox mounted motor works, otherwise I'll be looking at a can motor in the tender and a shaft drive which brings its own problems and doesn't look pretty on Victorian locos with low sided tenders and smallish cabs. Not sure I'll be able to live with the lack of daylight under the boiler.  One other option might be to mount the motor very high up in the smokebox, turn the chassis round so the driven axle is at the back, and run a thin shaft down to that, which still leaves some space for lead weight where it is needed.  But by that stage I'd be better off binning the whole thing and building a chassis from scratch, which rather defeats the object of finding good uses for old Poole mechanisms.

Offline belstone

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Re: Belstone's Scratchbodge Studies
« Reply #9 on: May 09, 2016, 11:40:14 am »
I think I am having a modelling midlife crisis.  Three weeks ago I decided to have a go at scratchbuilding a loco body to fit a Farish chassis.  Then I tried to rework a Farish compound chassis as the basis for a scratchbuilt "Glen" 4-4-0.  And now this:



Basically the Compound chassis was worn out, and my first attempt at mounting the motor was a bit rubbish.  So as it is a nice simple chassis, inside cylinders and only four wheels to worry about, I thought I would have a go at building a better chassis for it.  Frames are two pieces of brass channel soldered back to back to form an H section, which isn't how most people build a chassis.  The wheels drop into slots filed in the lower edge and are secured by a brass keeper plate.  It has two-stage gearing, with a small spur gear (ex Farish diesel bogie) between the worm and axle gear, so I can raise the motor and get some daylight under the boiler.  Top-acting pickups, phosphor bronze strip bearing on the wheel rims.

The biggest problem was filing those axle slots.  They need to be exactly 1mm wide, square to the chassis and the correct depth, with no room for error.  Mine weren't, and the driven axle waggled all over the place.  After a lot of thought I bent 0.7mm brass wire round a 1.5mm steel shaft, used a steel coupler spring to hold the U shaped wires hard against the inside of the frames, and soldered them up.  I then spent about an hour very gently easing them with a file so the wheels would still go round when I refitted the keeper plate.  I've only done the driven axle for now.



Like all my projects this one kept escalating.  The wheels were rubbish - quartering out on one axle, and nicks in the flanges.  At this point my own personal modelling demon took over.  "Turn them down to RP25 profile" said the demon.  "But I haven't got a lathe" I replied.  The demon pointed to the box of baseboard building tools.  "Yes you have" he said.  "Just do it."

So.... wheels removed from axles, attached to a mandrel (12BA steel bolt and an old Atlas diesel wheel as a spacer), mounted in a pin vice in the chuck of a Black and Decker power drill, and filed down to a profile which matched a current production Farish wheelset.  Then refitted to plain ended axles (ex Farish diesel, I have dozens of these with split gears) with a dab of industrial thread locker, quartered by eye and back to back set in my home-made gauge, and finally checked for wobble by mounting each set in the chassis and running it up and down the track while watching carefully.  Bonkers I know. I had an old wheelset from a Black Five which I did first to see if the idea would work before I wrecked the Compound wheels, and that is the one in the photos. I need better thread locker, mine I think has "gone off" as it sets far too quickly and the resulting bond isn't strong enough.  I need something that takes 30 minutes to cure, not 15 seconds, so I can make final adjustments to quartering and squareness after I have done all the wheelsets.





Front bogie is the old Farish "skateboard" with the axle holes drilled out by hand from 1.0 to 1.6mm in 0.1mm steps, fitted with a set of Farish wagon wheels with the pinpoints filed off the axles, and thin spacing washers between wheels and bogie cut from Plastikard.  The loco body was packed with lead, also a couple of strips of lead inside the H section chassis wherever I could get it to fit. Keeper plate is nice thick brass, with a single securing screw (which also attaches the pickups) and a locating tongue to stop it moving sideways. Yes, I drilled the hole for the screw off-centre. No, I don't care.



So does it work?  Yes, in that it runs in both directions, controllable down to a crawl, and will pull about the same load as the J27 - 2 coaches and 18 wagons without too much slipping, and with a more typical "2P" load of three coaches and four vans it will belt along quite happily at a scale 60 mph or so.  It doesn't seem inclined to stall, at least on plain track, despite only having two wheels picking up on one side at the moment. So the concept of a smokebox-mounted motor on a 4-4-0 is good.  But there is quite a lot wrong with it.

The main problem is those axle slots.  The axles need to be at exactly 90 degrees to the chassis, with the spacing exactly matching the length of the coupling rods. Mine are nearly right, but nearly isn't good enough and there is a noticeable wobble as the rods try to pull the rear axle backwards and forwards.  Those U shaped wire bearings might be the answer: file the slots oversize and fit the bearings using steel rods turned down at the ends to the diameter of the coupling rod journals, so the spacing is spot on.  It's fiddly, but the only alternative is to buy a milling machine, and they are not cheap.

The other problem is the transmission.  The spur gear I used is tiny and (being Poole Farish) not perfectly central on the shaft.  Gear meshing is super critical and took a lot of fiddling to get right.  Even now the loco is a bit rough and noisy going forwards, incredibly smooth and sweet in reverse.  I could live with that more easily if it was the other way round. I think what is happening is that the spur gear is slightly offset - if you imagine a line from the axle centre to the point where the gear contacts the worm, the centre of the spur gear is slightly back from that line.  So in one direction it tries to "dig in" to the worm and drive gear.  It doesn't help that the bearings for the spur gear are sloppy - it is mounted in a cut-down Farish diesel bogie frame, with brass wires soldered to the frames above the shaft to stop it jumping up and down. But there is still some fore and aft movement.  Not fit for purpose as they say.

So for the Mk2 version I will see if I can mount the worm driving the axle on its own shaft, with a spur gear drive to the motor.  That will be much better from an engineering point of view: anyway I'm not entirely happy with the idea of hanging worm gears on these little Chinese motors, as I'm not sure the bearings can handle the resulting thrust loads. 

But it's a promising start, and I may yet prove that it is possible to build an N gauge chassis on the dining room table without any expensive machine shop equipment.  That would be quite cool.

A couple of photos of the 2P, still looking rather rough and ready. I need to tidy up the under-boiler area, possibly with some false lower boiler sides glued to the motor.  The proportions are naff and always will be, thanks to the too long wheelbase and over-large boiler.  I don't think I will bother with the wire handrails, reworked cab and other stuff that I had planned for it, on the grounds that a pig in lipstick is still a pig. But I'm getting quite fond of it.





Richard

Offline Bealman

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Re: Belstone's Scratchbodge Studies
« Reply #10 on: May 09, 2016, 12:08:05 pm »
That is brilliant work. Love the fine profile of the new wheels!  :thumbsup: :thumbsup:
Vision over visibility. Bono, U2.

Offline maridunian

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Re: Belstone's Scratchbodge Studies
« Reply #11 on: May 09, 2016, 03:18:13 pm »
Brave man - but getting excellent results!!

WRT to getting perpendicular slots for the axles, (not that I've ever done this) could you sandwich the axles between layers of brass strip, sort of
____________________
[___________________]
[____]o[_____]o[_____]
[___________________]

if you see what I mean? If the transverse strips were kept well overlength until it's all soldered/glued, a wooden jig could give you quite good control of their right-angleness. Been thinking about doing something like that for a high-mileage Minitrix dock tank that staggers a bit in reverse ...

Mike

Offline belstone

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Re: Belstone's Scratchbodge Studies
« Reply #12 on: May 09, 2016, 03:42:59 pm »
Brave man - but getting excellent results!!

WRT to getting perpendicular slots for the axles, (not that I've ever done this) could you sandwich the axles between layers of brass strip, sort of
____________________
[___________________]
[____]o[_____]o[_____]
[___________________]

if you see what I mean? If the transverse strips were kept well overlength until it's all soldered/glued, a wooden jig could give you quite good control of their right-angleness. Been thinking about doing something like that for a high-mileage Minitrix dock tank that staggers a bit in reverse ...

Mike

That is very ingenious and I like it, a lot. So much so that if I can find any 1.5mm square section brass this evening I'll try it.  The axle journals will be square rather than round, but so are the Farish ones.  Being a masochist I also fancy drilling out the silly plastic crankpins on my Black Five wheels, then tapping them to take 14BA screws.  That will need a jig, but just a 1.5mm length of rod soldered to a plate with a hole drilled in it.  Cut off crankpin, poke rod through hole in wheel, position and drill.  I can shorten the crank throw a bit as well.  Cool. Now I just need to find a four-coupled loco that uses Black Five sized wheels (model Black Five, not real, those wheels are well undersize for the real thing).

Offline maridunian

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Re: Belstone's Scratchbodge Studies
« Reply #13 on: May 09, 2016, 04:54:14 pm »
That is very ingenious and I like it, a lot.

Thank you!

if I can find any 1.5mm square section brass this evening I'll try it.  The axle journals will be square rather than round, but so are the Farish ones. 

I'm guessing a little bit of up/down play would be tolerable, whilst fore/aft won't be..

Mike
« Last Edit: May 09, 2016, 04:57:38 pm by maridunian »

Offline belstone

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Re: Belstone's Scratchbodge Studies
« Reply #14 on: May 09, 2016, 09:49:59 pm »
Quick bit of investigation on the 2P.  I dismantled it and checked the wheels: with no rods attached it rolls dead smooth without wobbling about.  First good surprise: the coupling rod journals are HUGE. 1.5mm (plus a bit of wear) so I didn't need shouldered dummy axles, just plain ones.  Second good surprise: the axle spacing is spot on, which I wasn't expecting given how I filed the axle slots.  The bad news is that both axles are about 1.5 degrees out of square to the chassis.  I don't think that explains the wobbling or gear noise, so I guess I'll have to bin this one and start again.  Mk 2 version will feature better gears and "Maridunian bearings" (see above).  I have some square brass tube - actually 1.6mm rather than 1.5 so I will have to tickle it with a file to tighten everything up. The brass rod in the second photo looks bent but that's just camera lens distortion.  The rod is straight: the chassis isn't :(




 

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