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Re: Buck Jumping on Mass

Posted: Wed Sep 07, 2016 9:13 pm
by Jol Wilkinson

thanks for sorting the link to the LRM website. I had copied the address from the header which usually works.

I've tried again with the etch outline.

HBA PR dwg.pdf
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Re: Buck Jumping on Mass

Posted: Thu Sep 08, 2016 7:04 am
by billbedford
You can also use handrail knobs of the anchors on the horn blocks.

But a much better solution is to use hooks for fixed anchors and a fulcrum point, for instance a piece of thickish wire, fixed to the top of the bearings, and parallel to the axles. If you arrange the relative height of the hooks and the the tops of the horn guides correctly the spring wires will just clip into place, instead of having to be threaded through a series of impossible find small holes.

Of course this arrangement will need working keepers, but that should not be a problem.

CSB anchor arrangement.gif
CSB anchor arrangement.gif (5.02 KiB) Viewed 3446 times

Re: Buck Jumping on Mass

Posted: Thu Sep 08, 2016 3:51 pm
by Will L
billbedford wrote:Of course this arrangement will need working keepers, but that should not be a problem.

I agree this is a perfectly good arrangement that some may well prefer. I happen to like the handrail knobs rout because, ones you have everything is properly lined up I don't find it difficult to thread the wire. I rather like the fact that the wheel are always captive with no keeper plate is required and I don't think you need to thread the wire all that often anyway, but it's a personal preference sort of thing. If I was building one of Bills chassis that work as he suggest, I certainly wouldn't modify it.

Re: Buck Jumping on Mass

Posted: Thu Feb 15, 2018 11:34 pm
by Will L
Buck Jumping on Mass - The Build Phase
Part 8 A rolling chassis

To get to the rolling chassis, all that is left is fitting the frames around the frame spacers, but of course nothing is quite that strait forward. Both chassis kits came with 00 and EM spacers but nothing for P4. I suppose I could have gone with the EM spacers, but these were a full 1mm narrower than I felt I wanted so I had no choice but to make my own. The frame width of the prototypes, as far as I can tell, is a whisper under 4’0” so I decide to go with 15.5mm over the frames so I have a little clearance behind the wheels. This had knock on implication when we consider the footplate. Given the material the frames were etched out of, I was going to need frame spacers with a width in the region of 14.2mm. So taking some stock brass sheet (15 thou as that is what I’d got) I cut a strip about 14.5mm wide and filed it down until it was strait edged and was just 14.2mm wide. The necessary spacers were marked out on this in order down the strip just in case it isn’t perfectly parallel.
The spacers I used are shown in the next illustration, the picture is the J65 frames, the position of the spaces is shown in the drawing.
Buck Frame space.jpg

The end spacers is as the kit designer intended, but I’ve went my own way with the middle one. Both kits provided frame spacers that had tabs which fitted into slots in the frames. Generating the taps on the edge of my hand cut frame spacers was much too much like hard work so I didn’t bother, but at least the slots in the frames gave you a good clue as to where the fame spacers should go. Both kits had L spacers at both ends which I reproduced more or less exactly. The rear spacer on the J65 and the front spacer on the J69 had a hole on the centre line through which the bolt that attached chassis to body should go. I drilled this small so I could open it out to match the exact location of the captive nut on the body, when I knew where that was.

On both chassis I was planning to fit pickups bearing on the top of the wheels. This, taken together with the increased width of the frames, had consequences for the footplate which we shall go into when we get there, shortly. It also meant I wanted a horizontal spacer at the top of chassis above the centre axle to which I could bolt the pick up assembly. At this stage the design of this was yet to come so two holes tapped 12BA were provided on the centre line of this horizontal spacer so I had choices when it comes to deciding where to put the bolt. The centre spacer on the J65 is just this horizontal plate. On the J69 it is part of an L shaped spacer and I can’t now remember why there was this difference, beyond that was how the original chassis kits were designed, although I have moved the location of this frame spacer in both cases.

The Chassis Pro jig has the short axle pins removed and the long ones substituted so the chassis can now be built up in the jig. There is also a “fence” fitting for the jig which gives you a vertical surface to build the chassis against to keep it square. One frame side is put in the jig, fit the frame spacers, then put on the second frame solder up the spacers and there you are. Unfortunately I failed to photo this process but I have got a shot of the Chassis Pro set up for the job.
buck jig 4.jpg
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Time now to assemble and quarter the wheels with the axle bearing blocks and the gearbox in place. I’ve done the wheel assembly bit to death further back up this thread here and here so I won’t labour it any further beyond reminding you that these are Exactoscale wheels and thus just a bit different. Nor will I bother you with the gearbox assembly which is well decried in the instructions that Highlevel provide, beyond recapping that both locos have Highlevel 54:1 Simliners with a Drivestecher extension, so I can drive the rear axle under the cab floor and not intrude into the cab.

Once the chassis is all wheeled up it’s time to do the traditional plate glass test. By standing the chassis on a sheet of plate glass you can see in an instant if any of the wheels isn’t in contact with the floor. That is the chassis side frame aren’t perfectly square to each other, which, with horn blocks fitted all round, is perfectly possible to achieve even with the jig. There is another alternative, that you got the fixed fulcrum points in the wrong place on one or both chassis side but you had plenty of opportunity to check that earlier and you really can’t legislate for total incompetence. It is true that a sprung chassis is at least a little tolerant of mini alignment errors and you might wonder why, given the springs, it is even detectable in this way. Remember that I fitted very stiff CSB wires and the chassis is, at this stage, very light, so the wire should not deflect and any significant error should show.

After that it is on with the coupling rods and see how well it runs. With a modicum of easing of the crankpin holes in the rods you should have a decent running chassis. The following picture shows the two chassis built to this stage and attached to the footplates to prove the fit, the J65 above and the J69 below.. The next instalment will begin the body construction, starting with these footplates
buck B+S 1.jpg
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