In Cab Items

This chapter will cover miscellaneous items in the cab which are not covered elsewhere.

I’ll make a start with the reversing stand. The reverser is a vertical stand with a screw thread operating the bell crank to the reach rod that goes to the expansion link lifting lever. It also has an indicator to show the amount of cut off.

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The basic reversing stand assembled.

The two holes at the top take bearing inserts for the bearing head holding the reversing handle. This allows the head to rock taking up the radial movement of the bell crank that attaches to the bottom of the reversing handle screw sheath connecting to the shaft that goes through the three holes at the bottom.

The reversing handle screw is drawn as a left hand 1/4″ whitworth thread. This is 20 tpi and I decided to increase the “gearing” by using 0 BA which is 26 tpi and only a few thou smaller on diameter. The length of the screw to be threaded is 1 5/8″ and no taps are usually that long. So to tap the sheath that screws onto the handle I had to grind down the shanks to allow the taps to go to the full depth. I learnt that when grinding down the shank the top thread of the tap has to be as square as possible otherwise it takes the profile away from the the thread already cut.

Tapping the sheath which is 7/16″ square BMS with CS taps (HSS cost a bomb left hand) was difficult and I had to use all three taps, taper, number two and plug, to do a couple of turns a time and when the taps were half depth it was more a millimetre or less at a time. Eventually the full depth was achieved and no broken tap!

I have realised that the brake valve plate silver soldered onto the side is on the wrong side! blow! Fortunately it is not important and does note interfere with anything. A new plate can be bolted on the correct side later as the stand is now all painted.

The connecting lever to the pin which drives the reversing rod lever is made and as the drawing showed no means of securing it the pin I have used a split collet arrangement to bolt it up tight. This can be seen in photo below with the head of the clamp bolt showing

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The reverser indicator is a slide bolted to the side of the stand as can be seen above. It is driven by a lever screwed into the reversing sheath.screw inside the stand and thus goes up and down. This lever connects to a slide  which shows a pointer in a cut out window.

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The two photos show the assembly before the indicator is cleaned up and given a bit of a polish.

There were a couple of minoe niggles to resolve in assembly, the pointer is shown screwed to a standoff fixed to the slide. This standoff obviously fits in the window but of course the slide cannot be assembled in its runners as the stand off then fouls the assembly. The solution was simply to make the pointer and standoff as one unit and bolt that to the slide once the slide was in position. The other was that fortunately I had checked the distance between the slide link pins before making the link only to find it did not match the as drawn dimension. Only a 1/16″ out but that was enough to make the pointer off centre when the reversing screw was halfway on its travel.

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The finished (almost) stand in its rough position on the cab floor. It will not be fixed until the reach rod is made and trial fitted so it can be positioned accurately. The reach rod lever has yet to be made and also the drivers brake valve which is fitted to the right hand side of the stand has to be made and fitted.

Looking at the full size A1 (Tornado in particular) it is clear that the cab arrangement on the Breeze design as can be seen above is not large enough as there is no room for the drivers seat behind the reversing stand. I do not know if this is an error in the boiler design or the frame length. This is a dissapointment as if the boiler is too long then the cab will not look right in respect of the window arrangement. Not much I can do about it at this stage.

The other thing that is noticeable is the height of the fire hole door. It is much lower on the full size. I think the boiler design is at fault here.

Back to positive thoughts ……… the blowdown hole in the boiler behind the reversing stand will have to have a banjo coupling designed with an exit through the cab floor to a blow down valve beneath the running board. Just another little thing to keep the grey cells active.

Update ….. Found some works drawing which shows the cab very similar to the as drawn design. So the full size A1 Tornado must be to a different specification. The drivers seat is shown on a slim pedestal positioned right at the back of the cab floor, level with the rear edge of the cab side wall. So that seems to resolve that worry. Cannot find anything about the backhead and firehole door position though.

Drivers brake

The drivers brake is the classic model engineers design of a disc rotating inside a housing that connects two ports out of three in each of two positions, so in one position steam is admitted to the brake cylinder and in the other position the brake cylinder is vented to atmosphere with the steam supply cut off. The body is a GM casting and the dsic and cover made from GM bar.

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The photo above shows all the parts to be assembled (apart from the handle)

The pin the casing body locates in the smaler of the two slots and sets the amount of movement of the handle/disc between the two positions open and closed.

The pipe connections have to be silver soldered in position. The outer body which seals the cavity is screwed onto the base from the rear with c/s 7 BA screws.

To esnure a good seal the disc is lapped to the outer body. It is held against the face by steam pressure alone.

The whole assembly is bolted to the reversing stand with 6 BA set screws.

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The assembled and fitted brake valve.

The handle is fitted to the shaft on a 3/32″ square and held in place with and 8BA washer and nut.