# Thread Dial Indicator



## Slavko (Oct 29, 2015)

Hello...

My first post here. Maybe the question is stupid but I really didn't find the answer googling the web.
So I Have mini lathe with metric lead screw with 1.5mm pitch. I have no thread dial indicator. As I need to cut some specific threads I wonder how to do that. I know how to do without releasing split nut but stopping spindle where is just little place is sometime painful. So I want to use split nut to disengage carriage.
Now the question when to engage it back. I found some table over the net that say That I can engage split nut anywhere if I have one of this pitches: 0.5mm, 0.6mm, 1.0mm, 1.5mm and 2mm. For other I need Dial indicator. Is that true?


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## jeff_g1137 (Oct 29, 2015)

Hi
Look at youtube


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## Slavko (Oct 29, 2015)

Hello...

I already look that videos. (well not all of them/not all) but as I find for now the things is different if we use imperial machine and metric. And pages that deal with metric system and dial indicator is rare. (or at least I didn't find it yet)

Slavko.


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## Slavko (Oct 30, 2015)

Found answer in other forum.


> The thread dial is much easier to understand if you study it with the lathe stopped, a very long piece being threaded, and the tool just pointing at the thread groove. The dial goes around once in a distance equal to the number of gear teeth times the leadscrew pitch, whether English or metric. If you have a 4MM pitch screw and a 12 tooth gear, the dial goes around in 48MM of travel along the leadscrew. When you disengage the half nuts and the dial goes around you have moved 48MM. If your thread pitch is evenly divisible into 48, it works because you have moved 12 whole threads on the leadscrew and also some number of whole threads on the work. That will work for 8, 6, 4, 3, 2, 1.5, 1, 0.75, 0.75, etc.. It will not work for 1.75 or 1.25 , etc.. You need a different gear for those. A 14T gear will work for 1.75MM and a 15T gear will work for 1.25MM.
> 
> There is more to it when you consider markings for part of a dial turn but you have to get a good understanding of full turns (using only one mark) first. Once you get the idea that any moves have to include whole threads on both the work and the leadscrew you can figure out the rest. As an example, cutting a 3MM thread on a 4MM leadscrew, once you disconnect the half-nuts and move the carriage, your next spot to engage both the work and leadscrew will be 12 MM away. This will move the half-nuts three full threads on the leadscrew and will move the tool 4 full threads on the work. If your dial gear has 12 teeth so that it goes around in 48MM, your engagement points (every 12MM)will be at one-fourth of a dial revolution. So if your dial has four marks you can engage at any mark.
> 
> ...


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