I just nipped them up with a small spanner Mike, don't go barmy though.

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Britool does [previously did ?] a nice one

Rarely used, but great ‘pose value’

MichaelG.

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See Post #154 here:

https://www.garagejournal.com/forum/showthread.php?t=277755&page=8

Edited By Michael Gilligan on 01/06/2020 17:30:52

It depends how deep the threads are in the cast iron. If you can manage 4 diameters, there is very little chance of it stripping before the screw breaks.

In the "Model Engineers Handbook" by Tubal Cain (pages 152 or later editions 13.9) there is a table giving the safe load in screws and bolts covering 0-16BA and 5/8" Whitworth down to 1/8"x40.

If you are not well practiced in tightening nuts and bolts etc then making up a practice piece and testing till destruction will give you a "feel" for when a fastener is tight enough or over tight and starting to fail.

I've had over 60 years experience with small nuts and bolts starting with Meccano in the 50's and you can definitely get a feel for how tight it should be. The right tool for the job makes a difference as well.

I would think the torque is likely according to material and core diameter. Nothing more. Just get more clamping force, for the finer threads (where there is a a choice of pitch), for a given torque.

I used to give the apprentices metal to tap in different sizes for them to screw in bolts until they broke, or the thread stripped. It was a very educational task, and quite popular with the lads.

0Ba should be similar to M6, as it is same pitch and diameter.

Yep according to Tubal Cain 144 lb inches as opposed to 142 lb inches. But who will notice.

For all practical purposes steel BA and small metric can use same torque settings.

Interestingly he gives only 108 lb inches for 1/4 Whitworth. Presumably due to the core diameter being around 3/4 of 0BA. The ratio of core areas being very similar to the ratio of torque.

I guess thats further proof that the design intention is that the bolt should always fail before a good thread in the same material. Reality often being different.

That said 0 BA is not a size to keep in stock. It screws in, loosely, to 1/4 BSF, 1/4 UNF and M6 making a weak joint that is prone to undo at the slightest provocation.

I know we all know better but I've got to the stage of wondering why the spanner didn't fit before realising "Stupid, dangerous, mistake about to happen.".

Can take a few years before you finally admit just how effective "want to get this done tonight" and "this is the only one I have so I'll use it" can be at turning the rational part of your brain off.

Clive

I used to break 1/4 BSW bolts until I began to recognise the fastener going into yield, Often too late.

Strangely, many years later, I spent six months commissioning the, at the time, worlds largest yield tightening machine. It put 32 W range 1/2 UNF bolts just in to yield Only took 6 seconds, Awesome!

One of my Designer colleagues, I am sure laid out the calculations for bolt toques, but I can't find the folder, so I'll ask him if he can let me have a copy.

I have found a paper giving an "An Analysis of Bolt Torquing"; by Clement Rajendra.

Try Googling "PDHonline Course 149 (2PDH)"

Skimming through it, it appears to concentrate on UNC, but no doubt by modifying thread angles and pitches in the calculations, figures for BA can be found.

Howard

It's the same as undoing a stuck nut or bolt, when you get that springy feeling, stop pulling.

If you are feeling nervous you can calibrate your pulling finger/s by using a spring balance on the end of the spanner.

In your case I would leave it as is for now and when you finish wet the gaskets with washing up liquid, block the exhaust port, apply compressed air at running pressure and see if it blows bubbles tighten till it just stops. This way you get a margin for years in the future to get them undone.