[pratclMachinist]

Hi All,

I've been looking into using an anti-backlash gear as part of my z-axis drive assembly for my small CNC machine.

After some digging around, I cannot any examples of it actually being used for this purpose which got me thinking. Is there a reason why people avoid anti-backlash gears for this type of application? I found a few examples of helix gears being used, which I imagine would be for smooth operation but there would be some inherent backlash (which is what I am trying to eliminate, hence the anti-backlash gear).

Can anyone shed some light on this?

[RICHARD ZASTROW]

Not enough info.

DickZ

[pratclMachinist]

Not enough info.

DickZ

I find your 3 word response rather ironic... What other information would you like?

Anti-backlash spur gear design is pretty common and nothing new... Just imagine one being on the end of a leadscrew and being paired with a gear on the end of a motor shaft.

Mainly, I'm just looking to see if anyone knows of any glaring reasons why this should not be done (since I cannot seem to find examples of it). Or if someone knows of a better way of offsetting a leadscrew from a drive motor.

[RICHARD ZASTROW]

Is this machines Z axis vertical like on a mill or router? Or horizontal like on a lathe?

As an off-set for a motor, it should be no problem. If vertical Z axis, I hope you have a brake to prevent free-fall in the event of a power off condition. Gears are pretty efficient as are ballscrews, permitting backdrive. Most often the off-set is accomplished with timing belt & pulleys.

You didn't mention ballscrew in you first post so I didn't know if this was a rack & pinion application which is often mentioned in anti-backlash gear questions.

Ref. helical gears: The helical gears will include some axial thrust depending on weight on Z axis if vertical, helix angle, power applied and rotation direction. You did say small machine so that may be negligable.

Dick Z

[holbieone]

I find your 3 word response rather ironic... What other information would you like?

Anti-backlash spur gear design is pretty common and nothing new... Just imagine one being on the end of a leadscrew and being paired with a gear on the end of a motor shaft.

Mainly, I'm just looking to see if anyone knows of any glaring reasons why this should not be done (since I cannot seem to find examples of it). Or if someone knows of a better way of offsetting a leadscrew from a drive motor.

there is no anti-backlash gear ,
not in what you are trying to do,
the anti-backlash gears should be called noise reduction gears ,
the anti-backlash gear part just takes up the gap to keep the gear theeth from bouncing around making noise
to much pressure on the "anti-backlash gear part" will open up the gap in between the teeth

[pratclMachinist]

Is this machines Z axis vertical like on a mill or router? Or horizontal like on a lathe?

I hope you have a brake to prevent free-fall in the event of a power off condition.

Dick Z

It is a vertical z-axis for a desktop size CNC. Also, I will have a hard stop for when the power is off.

there is no anti-backlash gear ,
not in what you are trying to do,
the anti-backlash gears should be called noise reduction gears ,
the anti-backlash gear part just takes up the gap to keep the gear theeth from bouncing around making noise
to much pressure on the "anti-backlash gear part" will open up the gap in between the teeth

Interesting, do you happen to know the relative pressure/torque required to open the gap? The motors I plan on using are only 287 oz-in. I believe I have read articles about anti-backlash gears being designed such that the load path goes around the springs that open and close the gap so I didn't think that would be a problem.

Do you/anyone know of a better solution for powering an offset leadscrew without backlash?

[RICHARD ZASTROW]

Timing belt/pulleys. Been used for many years. The newer belts don't stretch after initial run-in. You can add a tensioning device if you're worried about stretching. Check out Gates' carbon fiber belts.

Dick Z