Linear Screw ID.

[The Gresley Luthier]

Hi All.

I have inherited what look like 8mm diameter, 12 t.p.i. ACME Threaded, 4 Start Linear screws, but of course I cannot be certain, but I do not have the Ball Nuts.

My question is this, does anyone know of a supplier near me where I can go and try a few samples out to get the correct one for this rod??

I live I Church Gresley, near Swadlincote, Derbyshire.

Can anyone advise?

[JohnHaine]

If acme, not ball nuts.

[Muzzer]

A four start 12tpi acme thread sounds like a real minority sport and I don't imagine there would be (m)any suppliers who have mating female parts for them sitting on a shelf somewhere. At best you might find a tap that would create one for you but that would be an expensive purchase, assuming they even exist, considering that you'd probably only use it once if at all.

Are you sure about the spec? 4 starts with 12tpi suggests the adjacent threads will be around 0.5mm apart (48tpi), which doesn't sound likely. You might mean 3tpi with 4 starts, I suspect (~2mm between threads). 3tpi means you turn the shaft 3 turns and the nut advances an inch, regardless of how many starts it has.

You'd probably be better off throwing them in the parts bin and getting yourself some Chinesium ballscrew/ballnut replacements, perhaps SFK08025 (8mm dia, 2.5mm pitch). I doubt you will find an 8mm ballscrew with an 8mm thread but I may be wrong.