the tool coordinate system of a 6 DOF robot

Hello everyone.
Now, I model my robot with DH parameter and it seem to be right, but I have a question that I don't know how to set the tool coordinate system.
As I did, the origin of G54 is at the origin of the first joint of my robot and position and attitude in cartesian space which show by XYZABC when I run the linuxcnc, that is the sixth joint's position and attitude relative to the first joint‘s origin(also the G54 origin). Now when I install a tool, I want the position and attitude in cartesian space is the origin of tool(not the sixth joint). It seems that the command in Gcode, for instance G10 L2 Pn ... and the command touch off in linuxcnc is just to set the coordinate system of working, right? So how can I set the tool coordinate system which is handled just like the joint coordinate of robot?

Maybe you will think it is just not a question, but I am a starter, everything I don't know I want to figure out, if someone know the answers,please tell me. thank you

Hello andypugh, you are really a nice and warm-hearted person.
My kinematics module is just the genserkins and my tool is not vertical around Z axis and has some declination to xyz. It seems that this kinematics module does not have any other pins for tools. I don't understand your meaning, you really mean that I should treat the tool as another joint and configure it when set DH parameter?

Thanks again, andypugh.
I seem to understand some about what you say, now, what I should do to deal with this question is to set the tool table correctly, using the command "G10 L1" and so on, right?
Thanks

Hello andypugh
Thank you very much. I am so grateful that you help a student new with Linuxcnc like me,
this question about the tool system is handled. I am not a intelligent boy and maybe there are some more questions to be asked by me.
thank you all.

Sorry for disturbing you again!
It is also the tool question. I edit the tool lable following the manual. but in real movement, I found that the tool list in tool table just keep unchanging. because I use the genserkins, it just has 6 joint, when I set the tool table, I found that it didn't calculate using parameters in tool table and just made a subtraction and it is not correct, I don't know how to set the tool coordinate system which make the reference point to be the tip of tools. Thanks..