Perseverance Fowler 4P 2-6-4 T chassis

[k22009]

Ok this will be a test for me as i've only dabbled with straight forward 3 coupled axles inside cylinder locos up to here. So I have a basic query right off, how best to provide some form of compensation?

 

I usually like to use horn blocks/guides on 2 of the axles and have the driven axle in fixed bearings (usually the rear). However with this i'm keen to compensate the 2 driving axles but would also like to have the bogie compensated so that a reasonable proportion of the loco weight is distributed to more than just 2 axles. The leading pony truck will have some sort of simple springing with side control.

 

The destructions provided with the chassis kit describe the set up for Flexi chas for 4-6-2 and 2-6-4 locos as being identical and 4-6-0 or 0-6-4 being a simplified version. They suggest that of the three driving axles the one furthest away from the bogie is mounted in bearings, fixed in position and it is this axle that should be driven by the gearbox/motor. The other two axles run in horn blocks and guides and are joined with a centrally mounted link beam (supplied on the etch at 8'-6 centres). The main compensating beam (a rod soldered between the frames with the normal pivoting tube sleeved over it and a rod soldered to it bears down on both the link beam and the bogie. 

Ok so whilst i can't think of a good reason why the front axle can't be driven it may cause some problems with the cylinders and motion bracket assembly. I would much prefer to have the front two axles mounted in horn blocks/guides and pivoted from a compensating beam with the rear as fixed with the gearbox/motor combo, but this would then mean the bogie will be compensated/sprung independently and most likely will not take a proportionate percentage of the model weight onto its axles it will just float up and down sitting behind the fixed axle.

 

What have others done in this situation?

 

I'm not aversed to having all axles in horn blocks/guides driving the centre or rear axle and providing a torsion arm for the motor if that would help.

 

Dave

 

[hayfield]

Dave

 

I have looked at the Mike Sharman Flexichassis instruction book and as you say the driven axle is the rear one, but via a motor mount via a subframe/motor mount(with its own pivot point) pivoting with the rear pony truck

 

I think things may have moved on a bit now, I think I would treat it as an 0-6-0, with both the bogie and pony trucks indpendantly pivoting from the chassis

[Dave Holt]

Dave.

I have two 2-6-4 tanks - a Fairburn (DJH) and a Stanier (Gibson) in P4. The Fairburn, one of my first locos has a fixed, driven (Portescap) front axle and a single compound rocking beam arrangement for the rear two coupled axles and the centre of the rear bogie. The Stanier has a better, and in my view, simpler arrangement of twin beams for the front and centre (driven (Portescap)) axle and a single beam for the rear coupled axle and the bogie centre. In both locos, the front truck is sprung.

If I were to make another 2-6-4, I would definitely use the same arrangement as the Stanier tank although, to be fair, they both hold the track as well as each other. The fixed axle on the Fairburn does make it lurch on bad rail joints, whereas the fully floating Stanier glides over.

Hope this helps.

Dave.

[Barclay]

I have one of these kits, and a modified Hornby body, stashed away.

 

The fully floating system, with twin beams on the front 2 axles and a single one between rear coupled axle and the bogie sounds like the 'purest' flexichas approach, as advocated by Mike Sharman and Iain Rice. Mr. Rice details how to apply compensation to a bogie in his chassis book, and also how to compensate the bogie itself for the full effect. I, too, would consider cheating and just springing the bogie. If you go for full compensation though you can vary the weight distribution by moving the pivot point of the beam which is very useful.

Careful to limit how much the front axle can rock because clearances are very limited behind cylinders and Walschaerts.

 

It's an interesting set of choices - I hope you'll keep us posted with developments?

[k22009]

Thanks very much Gents for the input, it's much appreciated. 

 

I think i will make up the cylinder/motion bracket assembly first, i can then see what room i have to play with.  As it will be built in EM and not P4 i'm hoping there is a little to play with.

My gut feeling is to go full monty with the twin beams on the front 2 axles with the centre driven and as Dave suggests linking the rear bogie and rear axle with a single pivoted beam. I will take inspiration from seeing Dave's Black 5 in his blog which if i remember had a similar arrangement just reversed.

 

I'll add photos etc once i make a start.

 

Dave

[k22009]

This is what came with the chassis kit, along with a few lengths of tube and rod. There a 2 sets of some items dependent on which variation you choose to build and or whether its for the Fowler or Stanier version. 

 

 

Dave

[k22009]

Well a start has been made, I formed and soldered the wrappers around the cylinder etch,  sweated the 2 halves of both the slide bar bracket and slide bars together. I drilled out the white metal castings on the cylinders and added an internal tube for the piston rod to slide in. The cross heads are from Comet rather than the etched ones with the kit. 

 

 

Dave

[k22009]

I've got most of the parts ready for assembling the basic chassis.

 

Spacers are all cut out and numbered, horn blocks and guides also numbered and made up into units, coupling rods sweated together (just need to rivet them together to form an articulated pair). I've cut out the frames along the guides where the horn blocks will be soldered and also cut off the springs underneath. My aim is to try to make the wheel sets removable with a keeper plate, so the springs and brake assembly will be attached to this too. I've cut out a couple of beams for the front 2 sets of drivers which will hopefully miss the spacers and also the slide bar bracket which slots into the top of the frames. There are a plethora of holes already in the frames for plunger pickups, brakes hangers etc some of which won't be used but fortunately the pivot points for both the twin beams and the rear axle/bogie pivot are clear, i'll drill for those before i solder the spacers in place. I've been trying to plan out the best way of hinging the beams and getting them sitting on top of the horn blocks. Not having used twin beams before i presume they are mounted to just rest on top of the horn blocks when the axles are in there nominal position.

 

 

Dave

[Dave Holt]

Dave.

Yes, you're right. The twin beams rest on top of the axle-boxes when they are in their mid position. I would reduce the parts of the beams which rest on the boxes to slightly less width than the axle box and radius the bearing faces so that the beams do not try to tilt the axle-boxes in their horn guides when the beams tilt.

You may need to put a slight set in the beams so that they just clear the inside face of the horn guides and do not rub on them. Use a spacer tube to hold the beams apart and close to the frames. You need a very small amount of clearance to minimise friction, but not so much slop that the ends of the beams can come off the top of the axle-boxes.

I hope this doesn't sound too complicated because you'll find it fairly straight forward in practice.

Dave.

[k22009]

7 hours ago, Dave Holt said:

Dave.

Yes, you're right. The twin beams rest on top of the axle-boxes when they are in their mid position. I would reduce the parts of the beams which rest on the boxes to slightly less width than the axle box and radius the bearing faces so that the beams do not try to tilt the axle-boxes in their horn guides when the beams tilt.

You may need to put a slight set in the beams so that they just clear the inside face of the horn guides and do not rub on them. Use a spacer tube to hold the beams apart and close to the frames. You need a very small amount of clearance to minimise friction, but not so much slop that the ends of the beams can come off the top of the axle-boxes.

I hope this doesn't sound too complicated because you'll find it fairly straight forward in practice.

Dave.

 

Thanks for the guidance Dave, yes what you have said all makes perfect engineering sense. There are so many little things that do make even a small difference and are not always plain and obvious until you sit back and visualise what actually happens. There are so many books for guidance but most do not include the little intricacies that actually make you think how it all functions and that do make quite a difference to the model that's being built.

 

Dave

[k22009]

I managed to get the spacers all soldered in to place along with the horn block guides. All looks nice and square, using sprung axle jigs and coupling rods to determine the correct positions.

 

 

Next i added the rear pivot point for the bogie rear axle beam and thanks to Dave's guidance i modified the twin beams to sit within the horn block guide flats and radiused the bottoms. I soldered a washer onto the side between the beam and frame and cut a tube into two pieces which was soldered to each inner face of the beams so that each side would operate individually. A rod was then threaded through everything and soldered on the outside to the main frames. Thankfully it all pivots very freely and without any distinguishable sideways movement.

As a note to stop various parts getting soldered up at the same time i usually dab a spot of Brass black onto the part i don't want soldered as it doesn't bond to it at all and makes for an easy soldering operation then.

 

The frames with the cylinder assembly and slide bar bracket loosely in position.

 

 

You can just see the washer between beams and the main frames this will ensure the beams miss the horn block guide.

 

The frame spacer under the pivot beams was modified before soldering in so that the beams rotate freely, the pivot beams also misses the slide bar bracket just above. 

 

 

Dave

[k22009]

Assembled the compensated bogie and added the pivot beam from the rear driving axle which also bears on the centre of the bogie, a sprung wire between bogie and chassis acts to give some side control. Pony truck also assembled along with another sprung wire. A 1/2" wide strip of brass worked perfectly as the keeper plate with a cut out for the high level gearbox. This is held down to the spacers with a few 14BA screws. The brakes and pull rods are removable. I've used Romford crankpins on the Gibson wheels.

 

 

 

Just need to add the springs i cut off the chassis at the start to the keeper plate along with sand pipes etc.

 

Quick push test on a length of EM track and it all runs along very smoothly. Amazing, phew.

 

Dave 

[k22009]

Cosmetic springs, sand boxes, pipes and supports added.

 

Donor body resting on top of the chassis here, i've had to thin down the buffer beams on the inside both ends to get the chassis to even come close to fitting.

 

 

Valve gear to assemble next and after that i need to arrange to modify the body/chassis fixing points so it sits correctly, the rear one is quite high in the coal bunker so that will need to be lowered. 

 

Dave

 

 

 

 

 

[k22009]

After a brief bout of time off for a holiday in the Alps it's been back to the Fowler.

 

I've started the valve gear and got it all together, but there's a sticky spot that i need to rectify to get it running freely. The body mounting points have been built up from plasticard and fixed in place, at the same time i cut out the coal load in the bunker and glued a false platform for something a little better to sit on. The cab floor has been reinstated as there was a space in the moulded cab interior, which i think was probably for the chip. 

 

 

I've to add some lamp brackets, paint the cylinder covers and line the cylinder wrappers, add the coal and that's about it.

 

Dave