Today I will talk about the CNC Backlash which is found in cnc machine axis.
I will explain
- what is cnc backlash,
- cnc backlash causes,
- when to worry about cnc backlash,
- how to measure backlash,
- how to resolve and compensate cnc backlash through hardware and cnc control software.
What is CNC Backlash?
CNC Backlash is any kind of play which is found in cnc machine axis.
or you might say,
CNC Backlash is non-movement of the cnc axis which occurs on axis reversal.
Causes of CNC Backlash?
This play (backlash) might be due to
- Clearance which is kept in mechanical parts to reduce friction.
- As mechanical parts get loose with time.
- As with time mechanical parts keep moving and rubbing each other and after long time they lose their actual shape and size.
CNC Backlash Is already there
A cnc machine axis move due to their Lead Screw and Lead Screw Nut. There is always kept a very minor backlash in the lead screw and lead screw nut to reduce damage and wear.
CNC Backlash When to Worry
It is good if your cnc machine axis backlash is near 0.0001″ but not always possible, so 0.0003″ to 0.0004″ is acceptable. But if the amount of play in the lead screw and nut crosses this limit then there is the time to worry, and call up you mechanical maintenance guys.
CNC Backlash How to Measure?
CNC machine backlash can be measure with a Dial Indicator attached to an Adjustable Stand.
Put the stand on the cnc bed and direct the needle (plunger) of the dial indicator towards the axis which you want to measure.
- Set the dial needle to 0.0mm (zero).
- Now move the axis in one direction 0.5mm. Dial indicator should show 0.5mm travel.
- Now reverse the same axis 0.5mm.
If your dial indicator now goes back to 0.0mm, then everything is okay. But otherwise, if on reversal the dial lags behind, then the amount the dial lags behind is the backlash.
CNC Backlash How to Resolve? ( Backlash Compensation )
Now you have two choices the hardware way and software way to resolve cnc backlash.
You first better choose the hardware way, because normally backlash is due to lead screw or lead screw nut wear, so better resolve the issue by tightening them a bit if they are loose than required, there are plenty of other hardware ways to cope with backlash.
CNC controls also give us the ability to control (compensate) cnc backlash through their parameters.
CNC Backlash Compensation through CNC Control Parameters How Much Successful?
The better advice is that you resolve the issue by changing the lead screw (if possible) or lead screw nut, or just tightening them if they are loose might work, but otherwise
CNC control parameters can be changed to compensate backlash, the cnc lathe machine I work on with fanuc control has the 0.012mm set in its parameters as the backlash compensation for x-axis and z-axis.
So such values can be changed to resolve the backlash issue.
But such changes are not long lasting, because if the backlash is due to hardware wear, then if you don’t take any steps the hardware will keep wearing and with the passage of time the backlash will increase then you have to change the backlash parameters again with a bigger value.