Indexer stepdown ratio

[brian_harnett]

Does anybody know the stepdown gear ratio of the indexer?
I am thinking of making my own.
I made a regular lathe setup for it already and it would be real easy to incorporate it.

[Brady Watson]

For a PRT you could get a 3.6:1, 7.2:1 & special order --> 10:1, 25:1 & 50:1

Standard Alpha is 10:1 with 25:1 & 50:1 special order (I believe...)

-Brady

[brian_harnett]

Thank you Brady now I have a starting point.

Brian

[gerald_d]

Brian, what diameter can your lathe swing? My gut feel says use inches as the ratio. Eg. 6" swing diameter, go for 6:1 indexer.

(This isn't totally a thumbsuck - it gives you the equivalent of a 1" pinion on a linear rack - same feed speeds & forces as for flat work with direct-drive pinions. If you want to emulate geared pinions, go to higher ratios, maybe as high as 4x swing diameter.)

[earld]

Wouldn't the amount of divisions in a circle be a main concern for ratios?
Earl

[scott_smith]

Earl, the VU (unit value) command will compensate for that. I think they are concerned more with the torque of the steppers.

[earld]

Brady-
What is the angular resolution of the PRT indexer?
Earl

[Brady Watson]

Earl,
That depends on what ratio the stepper gearbox is....

[gerald_d]

Earl, the angular resolution is probably not the critical factor. You want to know the resolution on the curved surface of the object that you are cutting. If that surface is at a very large radius/diam. then the angular resolution needs to be much higher than for small diameter work. That's why you need high ratios for big diameters. But, if you pick an indexer with a fixed high ratio, it may turn too slowly for small diameter work. You have to try and match the ratio to the diameter of the stuff that you turn.

[earld]

Ah. The machinist in me is getting in the way.
My concern for an indexing operation is to accurately divide the circle. But, the ShopBot Indexer also has to perform as a lathe as well as a cylindrical "y" axis.
Thank you
Earl