English vintage saw split nuts

[RogerP]

Anyone know what threads these most often had? I've examined several and tried matching to thread charts and digging in my tap collection but haven't really come to a conclusion. I've also done a web trawl but again no firm answer. I suppose they could be unique on some of the oldest ones but the later saws were mass produced so must have used some standard.

Roger

 

[AndyT]

I doubt if they were standardised at all. Back when they were freely available, you'd buy the two parts as a pair, so all that mattered was that the nut fitted the screw it came with. There would have been no need to make a nut fit a separately sourced screw.

In Simon Barley's magnum opus on saws, there is a whole chapter on handle fasteners. He says that the screw threads were rudimentary and would have been made with a tap and a screw plate.

I've got a couple of screw plates and could not match their threads to any standard sizes - but they would also have originally been sold with their own matching taps.

Looking at the one separated saw screw in my possession, it measures 1/8" in diameter and has about 28 TPI - which does not match any standard as far as I can see.

In this recent thread, I wrote that I bought a small Whitworth tap, to make some crude replacement nuts, but having looked in my box of taps I think I must have remembered that wrong. When you get down to 1/8" diameter, most standard forms are quite fine threads, but as far as I can see from my own very small sample, coarse threads were used on saw screws. I think the tap that I bought and used must have been one marked 6 UNC 32 which has a relatively coarse 32 tpi - I would have just picked it out as being the closest available.

 

[RogerP]

Thanks Andy. That's the same conclusion I came to.

So, not wanting to get bogged down in making a non-standard course tap and die, I compromised and went modern with M4.

They'll do the job.

 

[AndyT]

I reckon they will! You might get some customers too... did you make the whole thing or is the screw part a standard brass screw with the head filed/turned down?

 

[spanner48]

I've checked a fair number of the split-nut screws. They seem to be 5/32" x 24 tpi. Similar to 5/32" Whitworth, but with the coarser thread of a 3/16". But they seem to be fairly standard; so I guess there might have been one or two Sheffield firms specialising in sawscrews and nuts, and supplying the saw manufacturers themselves.

But no: I can't find a tap or die for that thread.

spanner48

 

[IWW]

Yep, what Any sez matches my experience. None of the saw bolts I've had to deal with matched any Whitworth or Standard American threads in equivalent sizes by a long shot. My impression is that the older the saw, the coarser the threads, too, but that could be just because I've had a skewed sample.

I've made numerous replacements over the last 10 years for various saws both for myself & others. It's easy enough to match the visible parts, be they the older type with split nuts & flush-set heads or the domed heads & sleeve nuts, but not the threads, of course, so it's always a matter of making a matched pair (bolt plus nut) if a bolt is stripped or nut missing. I just use a metric thread, too, either M3 or M4 depending on the size of the originals - some of those cast bolts on pre-20th C saws are really skinny, barely 3mm. These have 4mm shanks. I leave a collar under the head & file it square so it will be a tight fit in teh original hole - matching the ribs on cast bolts is too much bother for too little return:


Easy to spot the odd man out in this line-up:



But once on the saw (& the other heads polished up, it's not so easy:



My worry is that someone in the future may take the handle off a saw like this without noticing that one bolt is different & try to force the wrong nut on the wrong bolt when reassembling. They may figure it out before doing permanent damage, or they mat not....

Cheers,
Ian