RE: [CAD_CAM_EDM_DRO] CNC Positioning

Hi Ruan

Not a stupid question at all.

The router control will have a known point of reference
thet is created by a homing procedure. Many ways are used
to do this...detect a switch closure or particular encoder
encoder pulse, lightly drive into a stop, etc.

In my router 0,0,0 is the center of travel of all axes.
This is defined in the machine control.

Now there are G-codes hand programmed or generated by CAM
software that define the motions. This is read by the control
to create the motion. There are g-codes for offsetting as well.

I try to keep things very simple and straightforward to avoid
crashes and unintended cuts. I will explain the steps to engrave
and cut out a single carved plaque:

The shapes and carving are are created on a CAM system in the office.
This creates a file which is copied on to the machine controller hard disk.
All single (custom) parts have their center defined as x=0 and y=0.
The surface to be cut is made Z=0 with cuts into the wood a negative
number. Again this is all done by the CAM program before the file
goes out to the machine.

Now on the machine the plaque blank is placed with it's center roughly
at the default x=0 y=0 of the machine and clamped.

The blanks vary in thickness from job to job so now the MACHINE CONTROL
is used to set the point where z=0 (the plaque surface). This is done
by manually jogging the tool down quite close to the surface. The remaining
small gap is measured (I use a small spark plug gap gage) and the control
is put in to MANUAL DATA ENTRY mode. This simply allows one to execute
typed in G-gode commands without running a g-code program. I then type in:

G92Zn

where n is the gap I measured with the gage. Now the control will
consider the work surface as z=0.

The cam program is then run. Tool changes for carving and cutting out
are in the program as well as things like pauses to flip the work
to do two sides. Locating pins or other devices are helpful with
two sided work.

Les





Leslie M.Watts
L M Watts Furniture
Tiger Georgia USA
(706) 212-0242
http://www.lmwatts.com
Engineering page:
http://www.lmwatts.com/shop.html
CNC surplus for sale:
http://www.lmwatts.com/forsale.html
CNC carved signs:
http://www.lmwatts.com/signwp.html




-----Original Message-----
From: ruanb1 [mailto:ruanb1@...]
Sent: Tuesday, April 13, 2004 11:23 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] CNC Positioning


Hi

Please don't $#@$ me for the stupid question I am going to ask now!!!!

I want to try my hand at building a CNC router. Got all the parts etc.

I would just like to know how do you tell the router where to start
the cut? Say for instance I have an irregular shape mounted to the
table, do I zero the controller or at the software???? Especially
after say changing cutters or routing on both sides of the object.

Sorry, extreme stupid, but never seen one of these in action, just
dreaming of trying my hand it.

Your answers will be greatly appreciated.

Regards
Ruan




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