Thread Form

I saw this online and wondered if anyone on here recognises the thread form? Apologies that it’s woodwork related! I just wondered if it’s an existing thread that been used (Tap & Dies) or whether specific wood cutting tooling has been made to produce it. It’s a nice looking thread.

Taps and die boxes are easily available for wood screws such as these

they don’t conform to and metal working taps AFAIA

Whilst it doesn’t exactly answer your question … This is the standard style of tooling for wood:

**LINK**

https://www.craft-supplies.co.uk/products/itm/sbt-screw-box-and-tap/

MichaelG.

Looks like it could be a modified form of Acme thread with rounded off corners to stop chipping.

But this article makes it seem that guys working with the brown stuff just make up their own threads as they go along to suit themselves. LINK

It may have rounded off bottoms as well in which case it looks suspiciously like a 'knuckle' thread.

Ian P

I’m well aware of the thread making tools available for wood but I’ve never seen anything that produces a rounded thread like that in the picture. I’ve passed the picture on to another wood turner and he’s also interested as he’s never seen anything like this either. The items in the picture were made in Eastern Europe so perhaps the tooling is unique to the area?

Thanks for that, an interesting resource.

We have the screw of a walnut oil press (circa 1860). It's about 1.5m long and 170mm diameter, pitch 60mm. They were hand carved from a log of lime wood.

First a suitable log was sawn, square, then made octagonal by planing off the corners by 45 degrees, then made 16 sided and eventually round (Similar to sailing mast making).

It was then mounted on a couple of stands, one end with a stub and the other with a handle.

As one operator turned the handle, the other walked from one end to the other, scribing a pencil line along the length thus marking a spiral. These guys were real artisans !

Once they had the spiral line, they would cut a saw cut to the depth of the thread along the spiral. Once that was done, they used a chisel to form the thread profile - thread angle approx 90 degrees!

The final cleaning up was with a wooden moulding plane with a 90degree dagger blade.

I have yet to find out how they made the nut !

Bob

It's difficult to see from the photo, but it could possibly be a knuckle thread. This thread form has rounded crests and roots.

Neil

Just noticed that I have been beaten to it!

Edited By Neil A on 23/02/2023 16:32:29

Yes, I’ve just found this.

**LINK**

Interesting. Well spotted.

And it turns out there are standards for Knuckle threads. LINK Apparently they are also used on railway couplings and brake rods and fire department fittings owing to their high tolerance for dirt etc on the threads.

So surely there must exist a standard for BSSB threads. (British Standard Sweeping Brush)

🥴

The answer may be in "One Good Turn: a Natural History of the Screwdriver and the Screw" by Witold Rybcznski. He describes how the Romans cut male threads in a similar way to your description, but the nuts didn't have a thread, instead wooden pegs were inserted radially to bear against the flank of the thread. This was much weaker than a proper female thread and could only be used for light loads.

The book states that the female thread was invented (or at least first described) by Vitruvius, who used it to replace the weighted lever of earlier olive presses with a screw. He temporarily fitted one of these nuts to the crossbeam of his press (in which a tapping diameter had been bored) and attached a metal cutter to an extension of of the screw, so that by repeatedly turning the screw and advancing the cutter, a helical thread was cut in the beam.

Brian G

Don't know about BSSB, but there is British Standard Bottle Top thread

Brian G,

The nut looks like it had some sort of tap to make the thread. I bet it would have taken a very big wrench to turn it.

Looking at the top of the screw, you can see thread rounding where it has worn away and where the rats used to chew at the animal fat that was used to lubricate the thread.

Bob

Edited By Speedy Builder5 on 24/02/2023 06:48:58

I suppose it depends hoe "Handmade" the products are, it would not be difficult to make a suitable form cutter and threadmill both parts on a CNC. Seems there are other nut crackers with teh same rounded profile thread rather than the more common 90deg Vee form that most of the tap and die box sets available produce

Also doable on a Routerlathe or a toolpost mounted spindle on a screwcutting lathe if you also use those to make your tap.

Edited By JasonB on 24/02/2023 07:55:52