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Progress with Tablet Instruments (Part 5)

Here are the quick links to the former articles:

Part 1 dated 7th December 2020 can be viewed HERE,
Part 2 dated 26th January 2021 HERE,
Part 3 dated 13th March 2021 HERE, and
Part 4 dated 21st June 2021 HERE.


Tablet Instruments – Continued

Malcolm Kitchen has submitted another report on his work to recreate Tyer’s No.6 Tablet Instruments needed for use on our extended railway.

Repair of Tablet Instrument Case

The Exmoor climate can be very unforgiving – especially when it comes to wood. A repaired tablet instrument was put into store a few years ago in good condition. The deterioration in the wooden case over the period since has been depressingly rapid. Variations in temperature and humidity caused the veneer to split and grow a crop of mould; glue to dissolve; and ugly black stains to appear where steel screws and pins had corroded beneath the surface.

Fig 1 - Tablet instrument case with portions of veneer already removed.

The case was dismantled into all of its component parts – all except for the front ‘A’ frame. Almost all of the heads of the steel screws used to assemble the carcass broke off at the top of the threaded portion, despite the use of penetrating oil to try and ease their withdrawal. The screw remnants then had to be dug out; the screw holes bored out and sections of dowel inserted to take replacement screws which are now brass throughout.

A Google search suggested oxalic acid to remove the black rust stains, and this worked almost miraculously. Once applied though, it is difficult to call a halt to the action of the acid, and a side effect was a bleaching of the surrounding mahogany. This then had to be corrected using stain to match back in.

Once the carcass had been reassembled, including the 16 individually shaped mahogany segments forming the arched top, the outside surface of the case was covered with new mahogany veneer. Unfortunately, I got a large bubble in the veneer on one of the sides, so had to cut it out and let in a new section. Tyer’s had originally veneered the inside surface of the case as well, but in oak. This veneer was also beyond repair, but since it is invisible when the instrument is fully assembled and in use, it was simply removed and not replaced.

Figs 2 & 3 - The repaired case (front and rear views). 

Hopefully, modern glues and improved storage conditions will mean a slower rate of deterioration going forward.

 Another Block Bell

Some more spare parts from the S&T store have been used to make up another block bell, this time complete with a telegraph key or ‘tapper’. A new mahogany case, electromagnets, bracket mounting for the tapper pivot, and other miscellaneous parts were made up. The bell dome itself came from an old fire alarm. Almost inevitably, just after completion, the original bell and its pillar mount came to light at Woody Bay. These will now be incorporated into a subsequent build.

 

Figs 4 & 5 - The new block bell (interior and complete views}.

New Tablet Instrument Side Panels 

At least one tablet instrument is missing its side panels. These are lockable hatches that keep dust out of the mechanism and prevent any tampering with its operation, but can be removed for routine inspection and lubrication. Rather than just use a simple piece of board, Tyer’s (or their sub-contractors) made elaborate panels out of 5 pieces of mahogany. The S&T spares include several spare lock and handle sets, which not only avoided the need to source replacements, but give the new panels a more authentic look. The two main differences between new and old are down to my inability to do tenon joints, and the lack of a suitable piece of mahogany for the centre of the panel (which had to be veneered instead).

 

Fig 6 - A new side panel at the to. The Tyer's original below. 

 

Fig 7 – A further side panel under construction. 

About 98% of the mahogany used in this work is recycled - either donated to the L&B, or recovered from local tips.

If you have any parts we could use, please email us.

Malcolm Kitchen

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