# Upgrading an Atlas leadscrew from 5/8" to 3/4"



## Privateer (Oct 24, 2013)

So after seeing the pictures of Ray's lead screw undertaking, I've been working towards fabricating my own. A question comes to mind in the middle of this, and that is how will TPI of the 3/4" screw affect thread cutting. For example, in a 5/8"-10 lead screw, one revolution nets you 1/10 of an inch in travel, but in the 3/4" - 8, you get the 1/8 of an inch/rev. All the threading tables I've seen haven't specified which lead screw was being used, so I am understandably curious as to whether I need to concern myself about change gear ratios after I upgrade.

Terry


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## pdentrem (Oct 24, 2013)

There are small programs to calculate the gear train on the net. Also tables etc in many books like in the Machine Practice series of books.
Isn't the Atlas 10" lathe  5/8" leadscrew a 8 tpi? The reason I ask is that I never have seen a table showing otherwise. The metal thread table, on my lathe, that was riveted on the gear cover door was original to the lathe and it had started as a 10D 5/8" lead screw but was converted to 10F spec 3/4" screw later in life. Now the 6" lathes had different tpi over the years.
Pierre


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## Privateer (Oct 25, 2013)

Ok, I apparently had a blonde moment when I was counting threads a day or two ago, I just checked again and it is indeed 8 TPI on the 5/8" lead screw. So.. nevermind because apparently I'm :nuts:.

Terry


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## Vince_O (Oct 25, 2013)

Im in need of a new lead screw for my 6 in 101. Theres a few on epay but Im scared that if I buy one it will be as worn as mine is. Mine looks good till you measure the threads. Mines worn like .015 near the head stock, so my auto feed dosnt work in that area. I guess I could get the machine shop in town to make me one.


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## wa5cab (Oct 30, 2013)

Vince_O,

0.015" doesn't sound that terrible.  Have you tried new half-nuts?

Robert D.


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