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Problem with tool changes and errors in z heights
« on: October 11, 2015, 07:44:28 AM »
Hi folks

I have a simple chinese 6040 router table and I use small manually interchangeable bits - as I mainly cut small scale wood pieces.  I design the work in Fusion 360 and spit out the code from the CAM section.

Im having a problem with changing tools -  and getting errors in z heights in the cut. 

I typically split my code into per tool blocks. My basic process is as follows:

With the bit back at x-0, y=0, I change the bit manually - and then Set the z height of the bit - using the slipping a sheet of paper under the bit end method ...

I then click ref all home to zero the new z value - and check that z value is 0 as I toggle the machine coords button.  If either isn't I use the zero z button. .. I then region the tool path .. and then I continue the cut ..

Trouble is something is going wrong and Im getting errors of in the overall z value  - sometimes as much as 4-5 mm out.  Whilst I set the dimenesions of my tools in Fusion 360 Im assuming that it thinks every tool gets zeroed before use - i.e. that the error is in how Im using Mach 3 - not the CAM package.

Any ideas what Im doing wrong?  Would much appreciate your assistance.

Cheers

Keith







Offline ger21

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Re: Problem with tool changes and errors in z heights
« Reply #1 on: October 11, 2015, 02:41:38 PM »
Quote
With the bit back at x-0, y=0, I change the bit manually - and then Set the z height of the bit - using the slipping a sheet of paper under the bit end method ...

I then click ref all home to zero the new z value

When you ref all home, it's changing thew Z zero that you set with your paper. You do NOT home the Z axis after setting zero.
Gerry

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Re: Problem with tool changes and errors in z heights
« Reply #2 on: October 12, 2015, 10:34:45 AM »
As ger21 said, the ref home is resetting your values.

Touch off the paper, zero the Z axis work coordinates.  jog up and out of the way if need be and start your code. 
Re: Problem with tool changes and errors in z heights
« Reply #3 on: October 12, 2015, 04:50:38 PM »
Thanks heaps guys for your information  .. Could I also ask .. Is it necessary to hit the zero z button at touch off with machine coordinate button both active/on and inactive/off .. I can't zero out both without hitting ref all home ..

Offline ger21

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Re: Problem with tool changes and errors in z heights
« Reply #4 on: October 12, 2015, 04:57:00 PM »
Machine coordinates should be off when zeroing the Z axis.

The only way to zero the Machine Coordinates is to Ref All Home. This is typically done when first starting the machine, and provides a reference position for things like Softlimits, and tool change positions.

When you zero the Z axis, you are setting a Z axis offset relative to the machine coordinates. Once you zero the Z axis, you don't want to change the Machine Coordinates, as they will then change your Z zero.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Problem with tool changes and errors in z heights
« Reply #5 on: October 14, 2015, 12:37:58 AM »
Ok - that seems to work :) - my understanding with the regen tollbooth function is that it it is only necessary for visual accuracy - i.e. after loading a new program or doing the tool change we are discussing I dont need to regen the tool path before starting with this subsequent cut ?
Re: Problem with tool changes and errors in z heights
« Reply #6 on: October 14, 2015, 07:33:42 AM »
your correct, regen toolpath only updates the toolpath to the current tool position.  say you load your gcode and your machine is way off in left field.  sending the machine to X 0 y 0 and then regen the toolpath will show the toolpath from that location, instead of a small toolpath with a long line to where the tool was way off in left field.