Twin start thread?

[Raymond AndersonParticipant @raymondanderson34407]

Hello all,

I have a thread in front of me that is Trapezoidal, 22mmØ it measures a pitch of 2.5mm is this a standard or twin start ? [ 1 rev of a matching nut moves exactly 2.5mm ]

Regards,

Raymond.

[Raymond AndersonParticipant @raymondanderson34407]

[Les Jones 1Participant @lesjones1]

Hi Ramond,
It is a single start. The pitch in my opinion is ALLWAYS the amount the nut moves for one revolution. You need to know how many starts there are to know HOW to measure the pitch with verniers / rule / thread gauge. For a two start thread you need to measure the distance between alternate peaks. You should be able to count the number of starts if you can see the end of the thread.

Les.

[Raymond AndersonParticipant @raymondanderson34407]

Thanks Les, It does measure 2.5mm pitch, but it appears to be non standard for a trapezioidal screw as the measured pitch is the same as an M22 thread but I cannot find anything of that pitch at 22mmØ in trapezoidal form.

Regards,

Raymond.

[Keith LongParticipant @keithlong89920]

Raymond

Quick and easy way to verify the number of starts if you can't easily see or get to the end of the thread – wrap a bit of thin string into the thread groove carefully following the groove you're in. After a couple of turns you'll see if the sting is in all grooved – singlr start; every other – two start; every third groove – three start and so on.

Another thought – are you sure that it is a trapezoidal thread and not just a standard metric that has been "topped" a bit enthusiastically?

Keith

[KWILParticipant @kwil]

My supplier's catalogue clearly shows a 2.5mm trapezoidal threading insert is part of the normal range

[Keith LongParticipant @keithlong89920]

According to my understanding the "pitch" of a thread is the distance between adjacent crests while the distance that the thread "moves" axially along the bar for one turn (and also the nut moves in one revolution) is the "lead".

So a single start thread will have lead and pitch equal, but a two start with a pitch of 2.5mm will have a lead of 5mm.

Raymonds example is a single start thread.

Keith

Edited By Keith Long on 01/12/2012 15:42:00

[Raymond AndersonParticipant @raymondanderson34407]

Thanks guys. I am aware that 2.5mm Trapezoidal inserts are standard, but when looking through various catalogues from Eichelberger, Nook and Marchant Dice the standard Trap leadscrew for 22mm Ø is 5mm pitch. It is this that has me thinking that the screw in question is non standard. So it would appear to be standard single start of 2.5mm pitch, but non standard pitch for a leadscrew of 22mm Ø. The screw in question is the x axis of my Chester lux milling machine, the y axis is also the same Ø and pitch. only shorter.

Regards,

Raymond.

[Les Jones 1Participant @lesjones1]

Hi Ramond,
I've just had a look on the web an found that my understanding of the terminology is wrong. Keith's understanding is correct.

Les.

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