Sunday, 24 April 2016

Dreaming of Reaming.....

We achieved good progress during the last week - largely focused on reaming the bolt holes for the new LH Driving Hornblock. This involves using an expanding reamer - a hand tool that gradually increases the diameter of a hole by shaving material away a few thousands of an inch at a time. The holes in the horn block casting and their partners in the frames have to align perfectly and have to be exactly the same diameter. (This is so that the fitted bolts that clamp the horn block to the frames have a proper chance to prevent any relative movement between the parts.) It's quite hard work and carries the continual risk of getting needle-like shards of steel embedded in the operator's hands. It took four full working days to get 18 of the 22 holes to an acceptable condition. The remaining four holes are being used by the temporary bolts that are holding the horn block in position on the frames. They'll be reamed once the horn block is permanently in place. During week commencing 25/04 the horn block will be transferred to the machine shop so that we can machine a true landing surface on the back of the casting and give the correct seating for the fitted bolt nuts.

Thanks to Brian Thomson we now have the new castings for the hornclips (or tie-bars) that provide the essential closure to the open end of the horns underneath the axleboxes. Brian collected these from Blantyre Castings and brought them up to Aviemore a few days ago. They will be measured up and machined to a good fit on their respective sides of the loco.

During the week we had three additional Volunteers working on the loco - grateful thanks therefore to Martin McLeod, Nick Thomson and Dave Butler. 

Away from hornblocks we made some progress with trying to true up the eccentric sheaves. As a result of kind cooperation by the SRPS at Bo'ness Brian Thomson produced the basis of a mandrel for mounting the sheaves in our big lathe. Brian finished manufacture of the tool at Aviemore and it was duly mounted in the lathe. The first set of sheaves was clamped around it and the lathe given a spin at low speed . Unfortunately it was immediately obvious that Mr MacIntosh's eccentrics need a bigger lathe than we possess. There was an audible clunk from the lathe gearbox / headstock assembly at every revolution and the operation was suspended. There are a couple of options - we know that the RPSI at Whitehead in Northern Ireland have suitable capacity for handling this job. They have been asked to give us a price and delivery proposal. The alternative is to dress the sheaves by hand at Aviemore and machine the eccentric straps to fit the sheaves in their worn condition. More on this next week. In the meantime Alan French has come up with an excellent proposal for ensuring a good bond between the cast iron of the eccentric straps and the white metal lining.

Still on the subject of eccentric straps Calum Titley has carried out a very impressive controlled temperature weld repair to a crack in one of the straps. Taking infinite pains he has very slowly built up the damaged casting using a procedure that ensures that the parent metal temperature never increases above a required maximum temperature. This ensures that the cast iron grain structure is unaltered and the repair should have the required integrity.



The new hornclip castings with a boot to give an idea of scale..

Different view of the new castings; same boot.

Martin McLeod demonstrates the use of an adjustable expanding reamer (and sensibly wears gloves to avoid a handful of steel skelfs)

The reamer, driven by Martin, makes it way slowly out of the frames..the steel shavings can be seen in the adjacent holes.
Brian Thomson grinds the embryonic eccentric mandrel; Nathan keeps things steady.

Brian machine the newly manufactured mandrel to a precise 8" diameter. 828's crankaxle lurks in the background..

Nathan and the arm of Nick Thomson getting close to giving the LH eccentric set a spin in the lathe..

Nick Thomson steadies things in the big lathe..

Slight concern about the welfare of the lathe....Mr MacIntosh didn't skimp on the size of his eccentric sheaves (or pulleys, as the Caley called them.)

Dave Butler took on the task of stripping the gauge glass fittings for overhaul and here he is with one of the water-side fittings.

After stripping all the fittings Dave then started cleaning them up. They should be bright and shiny but their working environment tends not to help this...
Calum Titley working on his controlled temperature weld repair to one of the eccentric strap halves..

A pause for the camera..



CR828 draws admirers from far afield - she had a visit from this young couple who are Volunteers on the West Somerset Railway and were very impressed with a blue locomotive - a change from Brunswick Green and copper capped chimneys ...


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