Lathe feed handle is strange value I think

[Reddinr]

So, I've been living with this for years but my curiosity got going about it today. My lathe (Grizzly) has 0.77 inches per apron handle turn for the long axis. I has 8 major divisions per handle turn and 7 minor lines per major line. It says that each minor line is 0.01" so 77 graduations total per turn. It all adds up.

I'm wondering how they wound up with that strange set up. I can imagine it is all about the gearing ratios to the rack and the rack teeth/inch but why wouldn't you want something like 1/2 inch per handle turn or 1 inch per turn? Is this type of thing common or is this lathe unusually designed?

Thank goodness for the DRO.

 

[Video_man]

Likely it is a 2 mm. pitch, 2 mm is 0.0787 inches. The manufacturer did that on the fine downfeed on my Grizzly AIS mill I bought in 1999. The dial was marked for 0.100 inches but the internals were 2mm leading to puzzling inaccuracies until I saw what they had done.

 

[benmychree]

To get it to come out even as you ask, would require having a rack made in circular pitch rather than diametral pitch, as most US built machines are, with the exception of the American Pacemaker lathes or possibly others, same goes for metric lathes with metric racks, I suppose.

 

[RaisedByWolves]

So, I've been living with this for years but my curiosity got going about it today. My lathe (Grizzly) has 0.77 inches per apron handle turn for the long axis. I has 8 major divisions per handle turn and 7 minor lines per major line. It says that each minor line is 0.01" so 77 graduations total per turn. It all adds up.

I'm wondering how they wound up with that strange set up. I can imagine it is all about the gearing ratios to the rack and the rack teeth/inch but why wouldn't you want something like 1/2 inch per handle turn or 1 inch per turn? Is this type of thing common or is this lathe unusually designed?

Thank goodness for the DRO.

Our Moriseiki lathe is like this, .008 per graduation.

Ive gotten good at guesstimating dimensions on it after running it for 35 yrs.

No DRO on it, but if I’m feeling sporty I have a digital 1” indicator on a mighty mag base.

 

[benmychree]

Another option is a Travadial, I have one on my Regal lathe, no electronics, and it can't fall on the floor and bend the spindle as with dial indicators.