If I wanted some of these I would probably make them from an M20 bolt if I could not buy them at a suitable price or in a suitable amount of time. Do you have a lathe that can do this? If not someone near you may be able to help.

Martin C

Cannot find threaded fastener using 11/16 thread size in either AS/UN or BS standard series (Machinerys Handbook#17). BS fasteners have A/F sizes as a fixed proportion of the thread size so come out as random decimal sizes. AS and UN fasteners use round fractional A/F sizes and 11/16 A/F corresponds to 7/16 thread or 3/8 thread in heavy series fasteners.

Hi, plenty of charts showing 11/16″ BSF, but it maybe a non-preferred size though, which maybe why it isn’t always shown.

Regards Nick.

Vic,

£10 + postage (assuming the postage isn’t excessive) might be the best option if you can’t find “off the shelf” bolts.  £10 for a relatively large die seems more than reasonable.  Assuming of course, you have a suitable die stock.

On 10 December 2024 at 18:26 Martin Connelly Said:

…  but since the hex on an M20 bolt is similar to the one for 3/4″ BSW/BSF I felt it would be suited to an 11/16″ BSF bolt.

Martin C

I thought this was the best way of getting a ‘proper’ bolt – skim down to ¹¹⁄₁₆” then thread 14TPI 55° in a lathe.

Availability of BSF has been fading since the system was deprecated in 1949 in favour of UN, and it took another beating after metrication.   Judging by the way my engineering references don’t list it, ¹¹⁄₁₆” BSF was never popular, and may have disappeared as an off-the-shelf size before 1940.    Maybe because it’s an odd size sitting awkwardly between ⅝” and ¾”.  The metric standard also features many rarely used sizes and pitches that are difficult to source.

¹¹⁄₁₆” BSF isn’t a problem for anyone with a screw-cutting lathe who has learned how to set it up and drive it.  Not difficult once it’s been done a few times, but intimidating on day one.

Unless the lathe has an idiot-proof gearbox, the owner has to decode a table of gears and mount them correctly on the banjo.  Then, if he insists on grinding HSS, he has to make a 55° thread cutter, and worry about mounting it on the tool-post at 27½°.  That sussed, he discovers that looking the thread up in a reference results in a heavy shower of difficult maths, hard to grasp parameters, and no obvious clue as to which are important, or how they might be measured on the job.   With the job and change wheels set up on the lathe, and a rough idea how deep the cutter has to go in, he finds a new mystery – the TDI (Thread Dial Indicator).   Threads are never cut in one pass so misunderstanding the TDI or failing to engage the half-nut at the right time ruins the thread – don’t dither!

Good news:

• Once the change gear table has been decoded once, and the gears successfully arranged on the banjo, it’s much easier next time, and it gets progressively easier.  What once seemed hard becomes routine.
• Not necessary to grind HSS or fret about 27½° angles of attack.   Instead buy a carbide threading insert and go straight in.   Inserts can be either ‘Full-Profile’ or ‘V form’; the full-profile type produce a properly finished thread – angle and form, but only on one size.   V form cut an imperfect form, but can be used to make a range of threads, usually “good-enough”.
• The important parameters are TPI/pitch, outer diameter of the bolt, and depth of cut.
  • Pitch and outer diameter are straightforward.
  • Depth of cut is harder, but I mostly avoid the sums with this rule of thumb method.   With an insert, I generally go straight in for about 70% of the pitch, and then start gauging the thread against an existing nut or bolt.  At 70% deep, the gauge won’t even try to engage, so try going in a little further, say, another 10% of pitch, then 5%, 2% and finer cuts as necessary to finish.  The gauge can be felt to engage, and the further it turns, the closer the match.  Don’t hack the thread out as quickly as possible, because that risks removing too much metal!  Also, remember to lightly de-burr the outside thread with an old file or coarse-ish sandpaper, so that  burrs don’t create the illusion that the thread needs more depth.    Once the thread fits by feel to your satisfaction, stop.  Can be as tight or as loose as you want, without having to measure it.    The disadvantage of rule-of-thumb compared with doing the sums and measuring scientifically is that rule of thumb is slower.  Good for making a few, but not if scores are needed:  when speed matters, do the maths, so the lathe can go straight to the required depth of cut by watching the dials.
• The TDI can be ignored by not disengaging the half-nuts.  Instead, stop the lathe at end of cut, retract the cutter, and reverse the lathe to get the tool-post back to the start position.  Then wind the cutter in enough for the next pass, set the lathe to ‘forward’, and repeat.  Preferred method on metric lathes many of which don’t have a TDI.

If I happen to have a die of the right size, my preferred method for larger threads is to lathe cut threads to about 70% of pitch, and finish them with the die.  The lathe does all the hard cutting and creates an accurate helix for the die to follow without wandering.  Then the dies finishes the thread to the proper profile and size without fuss.

Ought to mention too that I usually cut threads with the lathe in reverse, so that the cutter powers away from the headstock, not into it!  Makes it possible to cut at high speed because there’s plenty of room before the saddle hits the tailstock.   How practical this is depends on the lathe.  Not clever on lathes with a screw-on chuck!

I took a couple of weekends to learn basic threading, well worth the effort.   There is a booby trap:  don’t learn to thread on a lathe in 2014 and then wait until 2017 before over-confidently trying to apply those skills.  Skills need to be practised, and it’s amazing how quickly small important details are forgotten. You can guess how I know!

Vic’s collars are fine for a temporary solution and might even be plenty “good enough” in the long run.  The problem with protruding bolts/collars is they tend to get in the way or snag.   Annoying to keep catching a sleeve in one, serious if something hefty snags and bends the bolt.   If that’s likely, I’d buy a few M20 bolts and convert them to BSF.

I’m extremely jealous of Vic:  he owns a Pittler!  They’re very versatile. I believe Cherry Hill relied heavily on one.

Dave