"One Perfect Part at a Time"


4th Axis on My Taig

I did a lot of research on how to implement a forth axis on my Taig CNC mill. I had some wild ideas not to be discussed here <grin> but that is the enjoyment of thinking outside the box. In this case the box is a pretty good one so I finally dropped back into the conventional world.

The screw drive of the standard rotary table has a lot of benefits in this  4th axis application. There are a few limitations in the area of backlash (controllable) and rapid speed (not really necessary.)

With small mills like the Taig and the Sherline, weight (mass) is a required parameter to consider. Most rotary tables are designed to have a lot of weight as part of their design. It adds stability for normal machining. However for miniature CNC machining, it is undesirable to abuse your drive system with a lot inertial mass to start, stop and reverse perhaps up to a hundred times a minute.

The winner in my selection is the Sherline 3700-CNC rotary table with motor mount. At $320 it is not the least expensive of my 4th axis schemes but I think it is the best in this case.

First point is the weight. At 8 pounds it is heavy enough and when you look at it, you see it carries no extra weight in a heavy case or mounting system flanges.

Second point is it is specifically designed for CNC operation internally (Sherline says in the worm housing) as well as the included #23 motor mount and coupling.

Third big point with me is the drive is 72/1 turns. Some rotary tables are 40/1 (yuk!). At 72 turns and 1/4 stepping, each step is 0.00625 degree. (Sherline uses 1/2 stepping.) A 90/1 would have… Continue reading

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