Reply To: GKN ‘Speedread’ micrometer

[peak4Participant @peak4]

Posted by Rolster on 24/08/2023 12:13:26:

Bill many thanks for the detailed explanation and link to the drawing.

BR Roland

Bear in mind that the drawing relates to the original patent from 1916 (not 1956 as per my typo) and the production models of the GKN-Shardlow do differ.

Both my 1" & 25mm ones, which came in the leather cases, were stiff when they arrived here off eBay.

I didn't need to risk dismantling them, and I'd avoid it if possible, particularly as the tiny spindle in the gearbox is made of plastic.
I'd try and keep any lubricant away from there, but the main spindle thread can be oiled as normal.
Unwind the thimble almost as far as it will go, I don't think it will come all the way out without removing Nut No10, but do be careful; this should expose the adjustment collar.

edit- just checked my 1" version, and unwinding the thimble doesn't expose the adjusting collar in the way it did on my 25-50mm, so it looks like you need to remove the thimble from its taper to alter the backlash; I must have just added a couple of drips of oil down the gap without removing the thimble.
The exposed nut is Nut No10, not the backlash adjustment, so don't remove that unless you need to

As regards oil, I've taken to using Balistol Universal oil as an instrument lubricant. It's strange stuff with an odd aroma, and originates from Germany; I have ½ litre bottles as well as a spray can.
https://ballistol.co.uk/products/ballistol-universal-oil?variant=39852136366262
It claims to be OK with metal, wood, leather and plastic, so you can even use it for cleaning wooden micrometer boxes and leather cases.
I'd try and keep it away from the display end though in case it mists the windows, or strips the paint off the dials.

I did pick up a Borlotti direct reading micrometer a while ago, but by the time it arrived here, the vibration in transport meant that most of the paint had vibrated off the plastic wheels, so whilst they turned and counted OK, the display didn't show many numbers.

Bill

Edited By peak4 on 24/08/2023 12:44:22