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# Thread: EMC2, Xylotex and Sherline Rotary Table

1. ## EMC2, Xylotex and Sherline Rotary Table

We just recently installed a Sherline Rotary Table on our Taig CNC with Xylotex motors and drivers and EMC2 (2.2.2).

The Rotary axis seems to work fine with rapid moves "G00", so simple indexing is not a problem.

We are experiencing very slow rotary table movement during some G01 movements.

The slow rotary table movement occurs approximately 25% - 50% of the time.

It doesn't seem to matter if the "A" command is combined with XYZ (continuous 4-axis) or on a separate line by itself.

I have seen a few posts that try to address this ( and have implemented the "fixes" ), but they haven't worked.

Any ideas?

---- s. kiwols

2. Without knowing anything more, it sounds like the feedrate. If it rapids fine with G00 then it would seem logical (could be wrong) that it should move at the specified feed rate on G01.

Alan

3. I am not a Mach user, but this was a feature with TurboCNC. How does Mach do feed rates of rotary axis?

Does Mach know the center of the axis, and tool length thus being able to work out an appropriate rotational speed for a given desired surface speed (F)?

If the machine is not set up this sophisticated, then...

If F10 is 10 inches per minute on a linear axis, and also used as 10 degrees per minute on a linear axis then you can see how a linear axis seems incredibly slow. The solution with TurboCNC is to use the G93 inverse time feed rate. Here is the description:

G93 Inverse time feed rate

Function: Set feed rate unit to inverse time ratio

Syntax: none

Example:

G93 F60 ;All G01 blocks will take one second

G93 F120 ;All G01 blocks will take 1/2 second

G93 F0.5 ;All G01 blocks will take 2 minutes

Notes:

In this mode, the length of time that each block will take to execute is controlled. The unit is the reciprocal of length of time in minutes. (e.g.: 60 is 1/60th of a minute or one second).

G93/94/95 are modal to one another. Each mode will stay in effect until another is called.

This mode is useful for unusual situations where the feed rate is difficult to calculate directly, but the overall time to move is known - such as when several axis types are moving simultaneously.

As with the other feed modes, if the commanded feed rate is too fast for the machine, the motion will be performed at the fastest available speed.

With arcs, each arc segment is treated as an individual block in this mode.