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Initial Tool move below safe Z

Message 1 of 3
159 Views, 2 Replies

Initial Tool move below safe Z



I am having an issue when creating a simple toolpath for a CNC router. The machine is a Techno LC 4848. I have attached my file as well as my code and screen shot of the line in question. Can't seem to get my initial move to happen at the safe height.   It seems that many have had this issue in the past with machine setup being blamed. With code as it is I can't see how that would be true. Thank you for your thoughts.

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Message 2 of 3

Thats because you aren't homing the machine with Z at the very top. G28 is machine home. I recommend changing your post option to use G53 instead, or omit it entirely. 

"z0.2." is also wrong

Please click "Accept Solution" if what I wrote solved your issue!
Message 3 of 3
in reply to: ajones28RRCMD



Yes, it is certainly the machine setup that is wrong, as @programming2C78B has already stated the G28 G91 Z0 is the command that sends the CNC to it`s Z Home position, if that position is wrongly set then the CNC will go to the wrong position !!

There are two Z0 positions on your CNC, one is the Machine Z0 and the other is the Part Z0, the Machine Z0 is usually set by Homing the machine at start up, this can be done either by the use of switches at each axis or by using what is known as "soft limits", so, an easy way to get it right would be for example to jog the machine to a "safe" Z Height and set the machine Z0 to that position, say for example 4in, then if your own safe height setting in the program is say 2in then that first move that is commanded by the G28 G91 Z0 will move the machine to the Z4in position before moving down to your Z2in position, the G53 Z0 will do exactly the same, depends on the configuration of your controller, some will use both some won`t 🙂

The whole idea of the G28 G91 Z0 and the G53 Z0 commands are there for safety so if the machine is used/setup correctly then it will always be safe.


Some controllers do have a built in "safe height" setting that the user can set that the machine will always go to first so the G28 G91 Z0 or G53 Z0 command lines are not required, grbl is one that has this, if that is the case with yout controller then as @programming2C78B suggests don`t have either of those commands in your code, you will need to upload a copy of the Post Processor that you are using so someone can modify it for you if you are not able to do it yourself.

A "Safe Height" first move position can be set in the PP to whatever you require but it will always be the same, to change the value "on the fly" would need the PP tro be configured differently.

Hope this has been of some use to you by way of explanation 🙂

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