Brian McKenzie
Western Thunderer
A long time ago when I was building a large scale traction engine I screwcut a double start square thread on both brake screw and nut! Once you get your head round the technique it's not that difficult if you have the correct equipment. However having done it once I am in no hurry to repeat the exercise but it's nice to be able to say I could.
Ian.
Ian,
Some years ago, I followed Sid Stubbs article in MRJ #42, and made several two-start worms in stainless steel on 1/16" dia shafts.
The reversing gear shaft for my model is only 1.3mm in diameter. I 'might' be able to scratch a 3-start thread in it and mould a die block over the top.