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Author Topic: Best Practice for Zeroing and Tool Changing on CNC Router?  (Read 12608 times)

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Best Practice for Zeroing and Tool Changing on CNC Router?
« on: February 03, 2014, 02:55:24 PM »
Hi,

I'm quite new to CNC Routering - I've built my own machine but I'm now trying to get a handle on the use of it.  Could anyone shed some light on the best practice for zeroing and then tool changing on a CNC Router please?

To zero XYZ initially I was planning on using a script and some metal plates connected through the breakout board - I first found Mr Cockrums macro but since then I've found and added to airnocker's auto tool zero macro.  My version of the code first asks the user for the diameter of the probe/cutting tool and then uses the radius of this probe/tool to calculate the offset for zero (I've not tried it yet!).  I thought it sounded fine in principle...

But then I'm wondering... say I use an end mill to machine a flat shaped area into which I want to then V-Carve (for example to make a sign)...  If I zero XYZ using the mill (which as a cylinder should be fine), then cut, then want to swap the tool for the V-Carve cutter I just swap it out and zero the Z axis again (because the centre of the tool will be the same) - is my theory.  The assumption I'm making is that XY shouldn't need re-zeroing, but is this bad-form considering I've just been un-tightening/tightening the spindle in-situ - am I safe to assume it won't have moved?  If not, how would you zero a V-Carve cutter with only 2 straight flutes?

I've tried looking up information on tool tables (which I don't think would work because the cutter height won't always be the same in the spindle if she shanks aren't long enough to stop at the end of the collet) and offsets in Mach3 but I'm still not understanding something - I think I might be over-complicating it all!

Regards,

Matthew

Offline ger21

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Re: Best Practice for Zeroing and Tool Changing on CNC Router?
« Reply #1 on: February 03, 2014, 04:58:31 PM »
You only need to zero the X and Y once. Most people do this separately from the Z axis.

For the Z axis, my 2010 Screenset includes macros to automatically zero tools during toolchanges. Everyone using it will tell you its hands down the best way to zero tools without an ATC.
It requires two plates, one movable, and one permanently mounted to the machine.

Before you start cutting, you zero the tool to the workpiece with the movable plate, and the macro measures the location of the fixed plate relative to Z zero. It then automatically zeroes subsequent tools to the fixed plate.

The Big Tex screenset also uses two plates, but doesn't zero the tools automatically.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Best Practice for Zeroing and Tool Changing on CNC Router?
« Reply #2 on: February 05, 2014, 09:06:46 AM »
Hi Gerry, thanks for your reply - your auto-zeroing looks really good but on this (my first) machine I've built I don't think I've left enough flexibility in the design to have a fixed plate to reference too - can you choose negative coordinates (e.g. x-50 y300 after zeroing XY) for the position of the fixed plate?  I think I might be able to push the cutter outwards further in that axis...

Also, would I output just 1 Gcode file from the CAM with the tool changes programmed in there (rather than generating a separate Gcode file for each tool change as I was originally going to do) and does it need to be output to the Mach3 post-processor or the Mach3 ATC post-processor in order to generate those onscreen prompts you show in the first video on your 2010 screenset webpage?

Regards,

Matthew

Offline ger21

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Re: Best Practice for Zeroing and Tool Changing on CNC Router?
« Reply #3 on: February 05, 2014, 10:44:44 AM »
Yes, the plate on my machine has a negative Y position. Just keep in mind that the location is specified in machine coordinates.

Sounds like you're using Vectric software. You want to use the ATC post. There's a 2010 Screenset thread at cnc zone that contains a modified post I did specifically for this screenset. I don't have a link right now, but I can dig it out later. I need to post it on my site.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Best Practice for Zeroing and Tool Changing on CNC Router?
« Reply #4 on: February 05, 2014, 03:05:19 PM »
That would be great if you could - I think I've found the thread ( http://www.cnczone.com/forums/screen_layouts_post_processors_misc/108401-mach3_2010_screen_set.html ) but I'm not sure what/where the modified post-processor is you refer to.

Offline ger21

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Re: Best Practice for Zeroing and Tool Changing on CNC Router?
« Reply #5 on: February 05, 2014, 07:02:03 PM »
I had to dig through 300 posts to find it.
I just added both inch and metric Vectric posts to my website, at the bottom of the page. Refresh the browser if you don't see them.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Best Practice for Zeroing and Tool Changing on CNC Router?
« Reply #6 on: February 06, 2014, 10:19:52 AM »
Thanks Gerry, I've downloaded the pp files to take a look at.  Regards,  Matthew