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brian_harnett
04-17-2006, 10:05 PM
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
04-18-2006, 04:36 PM
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
04-18-2006, 05:58 PM
Thank you Brady now I have a starting point.

Brian

gerald_d
04-19-2006, 01:03 PM
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
04-20-2006, 09:31 AM
Wouldn't the amount of divisions in a circle be a main concern for ratios?
Earl

scott_smith
04-20-2006, 04:41 PM
Earl, the VU (unit value) command will compensate for that. I think they are concerned more with the torque of the steppers.

earld
04-20-2006, 05:41 PM
Brady-
What is the angular resolution of the PRT indexer?
Earl

Brady Watson
04-20-2006, 11:43 PM
Earl,
That depends on what ratio the stepper gearbox is....

gerald_d
04-21-2006, 01:12 AM
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
04-21-2006, 11:51 AM
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