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Bruce

Are there any Creationists out there?

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AF stands for "Across (the) Flats" - the measurement from one flat face on the bolt head or nut, to the opposite parallel flat face.

 

Used to work in with another earthmoving contractor bloke name Austin (Aussie) Fulford. When we were doing repair work on the dozers (we would often work our machines together on the same job), and we were finishing up and gathering up our respective tools - sometimes there'd be a little residual doubt over ownership of a particular spanner. Aussie would always cheerfully claim any tool with AF on it, as his - because his initials were stamped on it! :cheezy grin:

Edited by onetrack
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3 hours ago, Bruce Tuncks said:

There is a letter from James Watt about how this wonderful new cylinder was only 3/8 inch wider in one diameter than another.

I guess that this is why they invented piston rings.

I think those first steam engines used greasy hemp packing.

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I have recently discovered the great advantage of the old Imperial system. When you are trying to reproduce old and damaged parts, it can be impossible to know what the original dimension was in millimetres. But in inches it is obvious. This was a one-inch board, or the rebate was 7/8 inch deep. 

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3 hours ago, pmccarthy said:

When you are trying to reproduce old and damaged parts, it can be impossible to know what the original dimension was in millimetres

Obviously when working with things made pre-metrification, you have to work in the units of the day. I've just got a heap of my Dad's  old spanners and I see that there are Whitworth ones amongst them. Whitworth and BSF spanner markings refer to the bolt diameter, rather than the distance across the flats of the hexagon (A/F) as in other standards. 

 

Whitworth is still used. The standard tripod mount on all SLR cameras and, where fitted, on compact cameras, and therefore on all tripods and monopods, is 1/4 Inch Whitworth. Larger format cameras use 5/16 inch Whitworth with tripod adaptors from 1/4 inch Whitworth if necessary. Fixings for garden gates traditionally used Whitworth carriage bolts, and these are still the standard supplied in UK and Australia. The 5⁄32 in Whitworth threads have been the standard Meccano thread for many years and it is still the thread in use by the French Meccano Company.

 

https://en.wikipedia.org/wiki/British_Standard_Whitworth

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I think the best grounding in mechanical skills is a few years building Meccano when you are quite young.

 

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Witworth is interchangeable with UNC, unified national coarse thread. I think the only difference is that the whit threads are 60 deg sides and the UNC are 55 degrees.

The yanks are not only mad to be using fraction sizes, but they also have bolt sizes in numbers. No 0 is .060" and each increase of number is an extra .013' in diameter.

Still in common use in aircraft.

Edited by Yenn
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Yenn 

Do the number drills have a correlation to those number bolt sizes ?.

If it does , it could have been a game changer.

spacesailor

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Number and letter sizes are commonly used for twist drill bits rather than other drill forms, as the range covers the common sizes from 1/16", increasing by 1/64".

 

Number drill bit gauge sizes range from size 80 (the smallest) to size 1 (the largest) followed by letter gauge size A (the smallest) to size Z (the largest). The gauge-to-diameter ratio is not defined by a formula, but is instead based on, but is not identical to, the Stubs Steel Wire Gauge, which originated in Britain during the 19th century.

 

Although the ASME B94.11M twist drill standard, for example, lists sizes as small as size 97, sizes smaller than 80 are rarely encountered in practice. When a number is used to describe a size, the larger the number, the smaller the diameter. The two sizes commonly found in aircraft maintenance are #40 and #30, which are the sizes of drills used for making the holes that nutplate rivets, as well as #21 and #11 and "F" for solid rivets, and also #27, #20, #16, #10, # 5 and "I" for Cherymax rivets. You should always consult the specifications for a rivet before drilling holes as the amount of slop in the hole determines the quality of the grip of the rivet. Needless to say, you shouldn't use drills from a set of common sizes (1/16 to 1/2") when drilling holes for rivets.

 

Another place that numbered drills are used is in carburettors to clear the galleries associated with the fuel jets.  But let's not consider playing with those.

 

The worst thing about numbered drills is trying to put them back in their correct order if you drop the box.

 

 

 

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