B1 61159

[Dave Holt]

Whilst waiting for some custom detailing parts for the Ivatt tank, I've made a start on a Dave Bradwell chassis for a B1 loco.
So far, I've prepared some etched parts and folded up the inner chassis and positioned the outer frames, as shown below.

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Construction will basically follow Dave's instructions but one deviation so far has been to double up the material thickness where holes have to be tapped 10BA. Not sure why such massive screws are used, 14BA would be more than adequate and less intrusive.
Dave.

[Dave Holt]

The main frame assembly is now completed.

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According to the instructions, it's the cylinders and valve gear bracket next.
Dave.

[Dave Holt]

Cylinder frame and valvegear bracket formed and fixed.

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Coupling rods and horns/axleboxes next.
Dave.

[Dave Holt]

Horn guides fitted using the coupling rods on extended axles.

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Dave.

[Will L]

Horn guides fitted using the coupling rods on extended axles.
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Dave.

Swazzle in "That then way to do it!"

[davebradwell]

Dave, it' nice to watch it all apparently going well but it seems wise for me to pop up as you approach the axleboxes. The springs are connected to these by little wire bridges, which aren't great, but the key point is that the spring wire should be held very close to the bottom of the axlebox. I've had a few grumbles from folk who have formed loops in the wire causing the model to sit too low and there's not a lot can be done about it by then.

Will also throw-in that this is the mk1 kit and when I wanted to build another B1 I completely re-drew it on cad incorporating my usual fixed hornguide fronts as I've developed an aversion to jigging these from the rods. I introduced the mk2 around 2015. It has tab and slot frame construction to cater better for EM but the details are much the same as seen in Dave's build. Spring fixing to axlebox much improved.

DaveB

[Dave Holt]

Thanks, Dave. I'll make sure the spring wire is close to the axleboxes.
I'm a bit concerned over the slotting the horn guides to accommodate the springs. Are the two existing holes in about the right place for the slot, and how deep should the slots be? You mention "filing" but I was thinking a slitting disc might do the job easier.
Dave.

[davebradwell]

Just had a look at mine, Dave, and I used a thin wedged Swiss file (knife file?) to cut the notches - I didn't have the luxury of a Dremel until recently. Still haven't really got the hang of it though so I can't give valid advice here. For position, look at how the spring lies at a slight angle to the frame between adjusting screw and wire support where it should be close to said frame. My slots are quite wide and v close to the backing plate for the horns so can accommodate the angle. Narrower slots may have to be offset.

Slots should be "deep enough"! I think the ride height of the axleboxes is marked somewhere on the frames so judge or even measure depth to give a bit more than 1/2mm rise above this. It's a significant job and, yes, I did eliminate it in the re-design. Ignore existing holes in hornguides. Hope there's no danger of slitting disc generating enough heat to unsolder guides.

DaveB

[Julian Roberts]

Horn guides fitted using the coupling rods on extended axles.
Dave.

No fancy chassis jig for you Dave?

[davebradwell]

No julian, all my kits from the N2 onwards put all important bits in the right place - with a bit of care during construction, of course. I can't understand why no-one has caught up with this, although Bill Bedford was there before me, I believe. It's a no-brainer with everything drawn on cad - if I draw 2 holes in a coupling rod 32.00000mm apart then the photoplotter is going to have a good go at 32.00, as long as it's maintained in good calibration, of course. Once the rods are accurate, you just need a similar trick with the frames.

DaveB

[Julian Roberts]

Right, DaveB. However is there not a catch, that the axleboxes may not be so precisely made and identical with each other, and the hole may not be exactly in the centre? - depending on the manufacturing process?

[davebradwell]

I've checked them, Julian, and the error in the axleboxes I use is tiny - hole is less than half a thou' off centre. The standard 5mm type I've checked are still very good, anyway, especially if you put all the errors going the same way so you're only concerned with the difference and not the sum.

I was pleased to see in the new MRJ that the late Dick Petter machined his hornblock openings so presumably did it to a dimension to get spacing right. It seems he was well known for the smooth running of his locos.

DaveB

[Jeremy Suter]

I was pleased to see in the new MRJ that the late Dick Petter machined his hornblock openings so presumably did it to a dimension to get spacing right. It seems he was well known for the smooth running of his locos.

DaveB

He certainly was a good modeller
Everything he did was well thought out before he started. The bearings he made are excellent I copied his Jig to make them and his horn guides are just cut out of the 32thou frames the bearings slotted in neatly . with a 3.2mm hole rather than 1/8 inch he never had a problem with tight fitting bearings either in the hole or the slot.

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[Dave Holt]

The front bogie has been assembled to near completion and trial fitted under (or above, when upside down!) the frames.

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The bogie work has allowed me to put off a couple of tricky aspects of the frames - the axlebox spring locators (fiddly) and slotting the horns to take the driving wheel spring wires (terrifying with the risk of wrecking the whole chassis). Won't be able to avoid these indefinitely if the loco is ever to run.
Dave.