Finney7 - 4200G Group Std Tender Build - Scale7

[adrian]

Having spent the couple of weeks before Christmas finishing off a few projects I now have a little room in my erecting shop to start a new project and new projects are always much more fun.

The New Year heralds a new start and the new build started is as per the title a Finney7 4200G Std Tender. Now given the number of LNER builds on WT I was sure I could find a 4200G build but I have to admit I couldn't find any. If someone knows of one then please point me in the right direction.

I'll pose the first question for people. I was intending just to cover the details where I deviated from the instructions but given my inability to find another build then I'm happy to cover a complete blow by blow account of the build - what would you like to see - just the off off piste stuff or all the gory details?

Lets get onto the build. The first thing to mention is that if you speak to them nicely the Finney7 mob are willing to supply their kits in nickel-silver for a small markup. The small increase in price over the brass version is well worth the cost for the ease of construction. Nickel-silver is far superior to brass for soldering, painting and construction etc. it really isn't worth opting for etched brass.

I started with the wheels - these are Mark Wood's castings. I build in Scale7 so if I bought Slaters wheels I'd still have to skim them and reprofile them so it was just as easy to go with the cast wheels. I also wanted to explore what could be done with insulated hornblocks and split axles.

So previous efforts with split axles used @Steph Dale 's published solution with 2mm fibreglass rodding for insulation. This worked well for tender axles but I felt it was slightly lacking in torsional rigidity. The fibres in the glass fibre rod are all aligned longitudinally and so it was possible to twist them a little, as I say not a problem on a tender but on a loco with coupling rods I was looking for something a little stiffer. Using the castings allowed me to use 4mm diameter steel axles (for reasons covered later), with a steel telescopic section (7/64" as that was the reamer I had!). The insulated side was also drilled 7/64" and a length of tufnol rod turned to be a friction fit.



A spot of loctite on the tufnol and then popped in the lathe and with a thin parting tool an insulating groove cut in the axle.



Then pressed on the axles and then drilled for a taper pin to lock them together.



Now onto the first deviation - the tender chassis. As usual I tend to go my own way! As supplied the kit is designed to build a compensated chassis and it will do that very well. However I'm not a great fan of compensation as there is always a rigid connection between axle and tender (or loco). I much prefer a sprung chassis but in this scale the usual miniature coil springs are fiddly to setup and balance. So my preference is the "continuous springy beam" (CSB) suspension which to my view is the best of both worlds - a compensated sprung chassis. Yes this is a CSB conversion - I used the existing chassis frames to mark out the cutouts so that I replace the fixed axle and compensated bearings with the Finney7 hornguides.


Using the Scale7 spacers supplied in the kit. The photo above also provides a clue as to why I went for the 4mm axle diameter.

The hornblocks are actually 3D printed items - printed in a nylon for insulation they include a vertical tab for the CSB arrangement and crucially with a 7mm bore so that I can fit a ball race within the hornblock. 7mm ball races having a 4mm id hence the axle diameter. Hopefully my cunning plan becomes more apparent as the build progresses.



Once the hornguides had been soldered in I could assemble the chassis on a glass flat plate to build it flat and square.



The other light-bulb moment was trying to arrange the fulcrum points for the CSB on the chassis. On my previous builds I've soldered on L shaped brass angle with a hole drilled in them for the spring wire. I realised that this was unnecessary - all that was required was a fixed fulcrum for the spring wire to act against. So to keep it simple I have just used a length of 1mm n-s wire across the chassis to act as the fixed fulcrum points - these are the two rods that can be seen between the horn guides in the photo below.







Hopefully the arrangement will work and become clear in later posts as the chassis is assembled.

So full gory detail of the build or just the off piste diversions?

 

[warren haywood]

Adrian,
Probably no help at all but I’ve just completed the painting of a Finney V2 so here’s a close up of the tender.

 

[adrian]

Probably no help at all but I’ve just completed the painting of a Finney V2 so here’s a close up of the tender.

Cheers - the problem I've been having is finding good photos of the front of the tender. I can find cab photos of the V2's but the tender fronts is an elusive item.

 

[warren haywood]

I will take a picture tomorrow for you if it helps. I’m assuming it will be pretty much correct.

 

[mickoo]

 

[simond]

Never tried CSB, though I suppose my Garratt is sort-of. Neither have I tried ballraced hornblocks, so this is all very interesting. A vote for “all the gory details” please.

Atb
Simon

 

[simond]

And a question. Are you planning to pass the traction current through the ball bearings? I know it’s likely to be all of 500mA in extremis, but I recall that it’s potentially damaging to the bearing races due to spark erosion.

Is it a case of “at a few quid, my great-grandchildren can replace the bearings if they feel they have worn enough that they need to?”

Atb
Simon

 

[richard carr]

Adrian

Can we have the full gory details please.

Thanks

Richard

 

[Mike Garwood]

I'm glad to see someone else try ball races. Years ago justin Newitt and myself did some etches to trap these and use them. Justin went the full hog and decided to use these on a Bradwell 9f! I left mine in the box to see how this went first!

It all went dead when we couldn't get wheels of the right type. That was before 3D printing (that's how long ago this was). Now that there is someone skilled enough to print the wheels, perhaps it's time this was brought back to life and finished.

I love ideas that push boundaries and Spannish customs, well done Adrian!



Stay safe

Mike

 

[Dave Holt]

You've kept that one quiet, Mike. I think something in your work bench thread is called for.
Dave.

 

[JimG]

And a question. Are you planning to pass the traction current through the ball bearings? I know it’s likely to be all of 500mA in extremis, but I recall that it’s potentially damaging to the bearing races due to spark erosion.

I remember a discussion about this some years ago - might even have been on the Usenet UK model railway Group. But the end result was that there was no evidence of erosion on bearings, albeit we were talking about plain bearings at the time. But I suspect that the same could apply to ball or roller bearings. The area of contact on a ball is minute, but there are an awful lot of them on a six bearing chassis to distribute the current flow.

Jim.

 

[Richard Spoors]

View attachment 136453 View attachment 136454 View attachment 136455 View attachment 136456 View attachment 136457

Am I correct in saying this is the all welded tender, similar to those built by contractors to the LNER such as North British, Armstrong Whitworth and Robert Stephenson & Co. for the K3? Just a few less rivets to punch out than in the Darlington and Doncaster built tenders! Nice to have pictures of the front elevation.
Cheers

Richard

 

[simond]

I remember a discussion about this some years ago - might even have been on the Usenet UK model railway Group. But the end result was that there was no evidence of erosion on bearings, albeit we were talking about plain bearings at the time. But I suspect that the same could apply to ball or roller bearings. The area of contact on a ball is minute, but there are an awful lot of them on a six bearing chassis to distribute the current flow.

Jim.

thanks Jim,

I suspect it’s an issue in full size practice, with much higher currents & ball or roller bearings. You’ll see grounding brushes on real locos to ensure there’s no voltage across the rolling element bearings, hence no current through them.

atb
Simon

 

[mickoo]

Am I correct in saying this is the all welded tender, similar to those built by contractors to the LNER such as North British, Armstrong Whitworth and Robert Stephenson & Co. for the K3? Just a few less rivets to punch out than in the Darlington and Doncaster built tenders! Nice to have pictures of the front elevation.
Cheers

Richard

It's a welded tender currently paired to B1 61264.

 

[3 LINK]

I think Steve Fay has roller bearings fitted to one of his Castles, and went on to say it was one of the sweetest running locos he had ever owned...

Martyn.

 

[adrian]

It looks like an overwhelming vote for all the gory details so I thought I'd better review my initial post again to make sure I'd captured everything. I spotted one omission so a small update for anyone considering a similar build. On the chassis etch there is a half etch relief to represent the brake cylinders from a side view. Now in the instructions the build used to provide illustrated photos it shows a couple of short length of tubes to provide a more 3D version. So the more observant may have noticed that these half etched versions were removed prior to build the chassis.

 

[Ian@StEnochs]

thanks Jim,

I suspect it’s an issue in full size practice, with much higher currents & ball or roller bearings. You’ll see grounding brushes on real locos to ensure there’s no voltage across the rolling element bearings, hence no current through them.

atb
Simon

I had an “incident” where ball bearings were ruined by an electrical fault.

I was using my pantograph mill which is situated quite close to the wall. While concentrating on the work there was a bang, some sparks from round the back, the lights went out and the machine stopped. On investigation I found that the idler pulley had cut through the cable from the plug to the machine. As I said the machine is close to the wall and the socket is set above the machine, something had caught the wire and pulled it against the edge of the pulley.

After replacing the wires, checking the setup and resetting the trip the machine ran as before except there was a lot of noise, traced to the bearings on the idler pulley. I replaced the ball races, a standard size, silent running was restored. On examination, the damaged bearings, didn’t look different from their replacements but rotation felt rough and certainly not smooth. If the bearings were eroded by current flow it must have happened quite quickly.

Ian.

 

[simond]

Rabbit hole warning...

Prevention of electric erosion in bearings

Atb
Simon

 

[adrian]

Rabbit hole warning...

Prevention of electric erosion in bearings

As this seems to be an issue for 1Kv supplies and higher I don't think I'm going to worry too much about it. If by some remote chance it does become a problem I can always retrofit some slip rings on the axles.

Anyway the chassis mods for the CSB suspension was a lot easier than anticipated. The supplied frame spaces needed a couple of notches cut in them to clear the CSB spring wire.



Then for the end fulcrum points at the front I just cut the notch a little longer and the little fold down brackets for the wire pegs to provide the hose connections to the loco provided a useful end stop for the CSB wire.

At the rear the end fulcrum point worked out just at the end of the chassis so I used a spare bit from one of the etches - it was actually one of the compensation beams which I no longer needed - hence the hole in the middle. That was soldered across the end of the chassis and a couple of holes to feed the wire through.


So this is the running chassis - with the CSB fulcrum points highlighted and I'm pleased to say it rolls quite nicely. You may have noted that the spacing of the fulcrum points are not equidistant between the wheels. They are biased towards the front and rear wheels. This is another bonus of the CSB arrangement in that the fulcrum position can adjust the weight loading on each axle. So with the longer spring length over the centre axle it means that the centre axle loading is slightly softer than the outer axles. I can't remember the exact numbers but it's something like 35% loading on the outer axles and 30% on the centre.

One more fortuitous benefit from this is the top ledge of the horn guides stop the wire dropping down too - so the axles are held in place as they are in this photo so I don't have to mess around with all the fiddly keeper plates on the bottom of the horn guides. A bit like Kerplunk I only need to pull out the 2 wires to drop the axles out of the chassis.



So after that initial diversion I'm now back following the instructions. The next step is the frame work for the stretchers and the water scoop. These are all the components and I'll continue the build in the next instalment.

 

[Dikitriki]

Hi Adrian,

Nice to see the build coming along, and you have made the springy beam system look easy.

I just wonder whether your new rear stretcher is going to interfere with the coupling? That hole may have a use!

Richard