Informal Measures at MHR Loco Shed

Steam locomotives are chunky great things made of chunky great components. Most replacement parts are unobtainable and have to be made and 'fitted' in nineteenth-century engineering fashion. This involves not only precision machining by Bubs and his protêgés, but persuading interference-fit parts take their right place and coaxing heavy castings or plates into precise position, or floppy big sheets of steel to line up their holes for bolting-up.

This often needs several people, some holding and positioning (with podgers* or sledge-hammers) and some checking of alignments and giving of directions:

"It wants to go to your right a bit"
"How much?"
"Just a tad"
"How's that?"
"Back a smidgeon"
"OK?"
"Another gnat's"

The informal measures used are evidently essential or they would have died out, but MPD* volunteers new to engineering would find it helpful to have them ranked. Guidance is required.

Our mentors give articulate explanations. They talk of 'being assertive without being aggressive' (an important sledge-hammer technique) or ensuring that 'everything is in repose' before bolting-up. But when pressed further, they lapse into those special engineering words which are so helpful in persuading reluctant and perverse components to align or separate.

We must go further afield and ask for your assistance. Please help us rank the following in order of size, or better still offer a precise measure:

TAD
WHISKER
GNAT'S
SMIDGEON
BIT
JUST A TOUCH

Estimates in thousandths of an inch would be excellent. Regional variations, or additions to the list would be most welcome

Contributions to: tonywood@watercressline.co.uk

Thank you

*Glossary:

Podger - blunt-pointed small crowbar inserted and manipulated to align two or more holes
MPD - motive power depot

Subj: Re: Precision adjustments
Date: 06/04/2001 21:49:39 GMT Daylight Time
From: Ian Kirby
Tony
We missed out "Just a touch". But everybody knows that's 25 thou. (now added, TYVM Ian)

BIT = 100 thou.
SMIDGEON = 50 thou.
TAD = 20 thou.
WHISKER = 10 thou.
GNAT'S = 5 thou
And don't forget, "Oh! F**k" is any number of thou. too far.

>>Are we talking aircraft thou or loco thou here?

Tony, please don't show your ignorance. EU standards, Dimensions Convention, Article 9, Section 63, Subsection c(2), Clause 39, Subclause 3(f), where and if Imperial measure is allowed clearly states, as everybody knows and has at their finger tips, the following:-

" 1 aircraft thou = 1 loco thou (in distance) (But loco thous are heavier and aircraft thous are LOUDER!) "

Date: 07/04/2001 04:29:41 GMT Daylight Time
From: A Crespin

Gnats
Whisker
Smidgeon
Bit

Does this make me as nuts as you lot ?
Andy

Subj: Definitions
Date: 11/04/2001 20:17:23 GMT Daylight Time
From: Malcolm Lawrence

Dear Tony
Translated from the subtle and precision practice of Orthopaedic Surgery, I understand the following from your list of definitions:

BIT - it's not quite right, put it where I want it.
TAD - close, but not quite right.
SMIDGEON - a bit closer, still not quite right.
GNATS - even closer, but don't excite the gnat or we'll be back at square one.
WHISKER - all but right.

We also use a final measure - the "that'll do" which means it's not quite right but it should work, it might fit and in any case there's nothing any normal human being can do to improve it. Such a state is often achieved by use of the fine adjustment device, otherwise known as the Birmingham or Irish screwdriver, depending on which part of the world you trained.
Exact measures are all in the eye of experience and closely adhere to Murphy's Laws
Cheers
Malcolm Lawrence

Loco Shed Page

Index of Archived Loco Shed Pages