Setting z zero

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Setting z zero

Postby JMD2 » Sun Jan 07, 2018 11:28 am

Don't know if this has been covered or not.
I would like to setup a job, with the "Z ZERO" set to the spoil board and the cut starting at the top of the part. Every time I try this, the machine, CNC SHARK PRO, moves to zero, on the spoil board, then tries to starting cutting. This berries the cutter in the job and is not a pretty thing to see. Is there a work around for this? I am using the latest Vectric V-Carve Pro 9 program.
Thank you for any help.
John
JMD2
 
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Re: Setting z zero

Postby Rando » Sun Jan 07, 2018 12:59 pm

JMD2 wrote:Don't know if this has been covered or not.
I would like to setup a job, with the "Z ZERO" set to the spoil board and the cut starting at the top of the part. Every time I try this, the machine, CNC SHARK PRO, moves to zero, on the spoil board, then tries to starting cutting. This berries the cutter in the job and is not a pretty thing to see. Is there a work around for this? I am using the latest Vectric V-Carve Pro 9 program.
Thank you for any help.
John



When you set the origin (X0Y0Z0) at the bottom of the material, all your toolpaths have to then "start" cutting--that is, the TOP of the cut--from a value equal to the total thickness of your stock, then down to that height minus the cut depth.

As example, say you're cutting into a 3.25" thick piece of wood, and you want to cut a hole 0.7" deep. When the Z0 is at the bottom, that means the top is at +3.25, and the bottom of your hole is +3.25 - 0.70" = +2.55". So, your start of cut would be up at 3.25. If the software asks for "bottom", you give it the 2.55 number. If it asks for "total cut depth", you'd just use the 0.70".

But, there's also another aspect here. It might not be your toolpath at all, but the initialization positions (home position, heights) set in the control panel preferences, or in the software. Always make sure your home position and safe heights will result in the bit at the proper height. So in the example above, to keep 0.25" room above the stock (and to account for stock height variations), you'd set the start position / height as 3.50" (3.25 stock + 0.25 safe). As for the control panel, if you consistently use the spoil board for Z0, then make sure the control panel's safe height is above the thickest stock you use.

But, in the end, there's no substitute for VERIFICATION. I'm talking examining exactly where that toolpath will go, long before it hits a machine. For that, you want a "GCode Backplotter". It's somewhat like the Vectric Preview and Simulation facilities, but because it's working from the GCode, you can inspect things like starting heights, positions, etc. Likewise, because it's independently produced (not from Vectric), I know it's not going to be using the same algorithmic fiction that Vectric might have used. I use the one by CNCCookbook (https://www.cnccookbook.com), their G-Wizard Editor. Fantastic, and more than worth the price*. When you load a toolpath into it, it will display a 3D rendering of where the tool tip goes. By simply clicking on the "Front" view, you can tell exactly where that bit is going to enter the cut, and ever part about it. Independent verification of toolpath output, to me, is crucial. I don't run ANY toolpath anymore unless I've first verified a whole bunch of things.

Hope that helps. The intricacies of machine, part and tool datums can get confusing sometimes, and tool entry is something the normal simulators don't do well at representing.

Regards,

Thom

* Lots of people whine...yes, WHINE...that GWizard costs money. Yeah, well 5 pcs of a good quality 0.25"D, 2flute extended-reach, 0.020" radiused endmill that can cut a 2" deep hole in a block of aluminum costs well nearly $500. Not running that 12mm D x 52mm deep bore through major validation will burn through those 5 endmills long before the bottom of the first hole is reached. The cnccookbook F&S and editor paid for themselves in literally the first major bore I passed through them. Feeds and Speeds, and toolpath verification need to become your best buddy if you want great quality, safe cuts, and most importantly: getting all the cutter life you paid for.
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)
Rando
 
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Location: Hoquiam, WA

Re: Setting z zero

Postby Rando » Sun Jan 07, 2018 1:27 pm

John:

Okay, there IS one error condition in which this can occur, and that's if the post processor somehow tells the bit to go to the X0Y0Z0 location. This would be unexpected, and I'm thinking unlikely. But, if true, it would call for a post-processor file change to remove that statement; it's a simple text file, but if you're unfamiliar with them they can be mystifying at first.

Regards,

Thom
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)
Rando
 
Posts: 576
Joined: Tue Jan 06, 2015 3:24 pm
Location: Hoquiam, WA

Re: Setting z zero

Postby JMD2 » Sun Jan 07, 2018 2:02 pm

Rando wrote:
JMD2 wrote:Don't know if this has been covered or not.
I would like to setup a job, with the "Z ZERO" set to the spoil board and the cut starting at the top of the part. Every time I try this, the machine, CNC SHARK PRO, moves to zero, on the spoil board, then tries to starting cutting. This berries the cutter in the job and is not a pretty thing to see. Is there a work around for this? I am using the latest Vectric V-Carve Pro 9 program.
Thank you for any help.
John



When you set the origin (X0Y0Z0) at the bottom of the material, all your toolpaths have to then "start" cutting--that is, the TOP of the cut--from a value equal to the total thickness of your stock, then down to that height minus the cut depth.

As example, say you're cutting into a 3.25" thick piece of wood, and you want to cut a hole 0.7" deep. When the Z0 is at the bottom, that means the top is at +3.25, and the bottom of your hole is +3.25 - 0.70" = +2.55". So, your start of cut would be up at 3.25. If the software asks for "bottom", you give it the 2.55 number. If it asks for "total cut depth", you'd just use the 0.70".

But, there's also another aspect here. It might not be your toolpath at all, but the initialization positions (home position, heights) set in the control panel preferences, or in the software. Always make sure your home position and safe heights will result in the bit at the proper height. So in the example above, to keep 0.25" room above the stock (and to account for stock height variations), you'd set the start position / height as 3.50" (3.25 stock + 0.25 safe). As for the control panel, if you consistently use the spoil board for Z0, then make sure the control panel's safe height is above the thickest stock you use.

But, in the end, there's no substitute for VERIFICATION. I'm talking examining exactly where that toolpath will go, long before it hits a machine. For that, you want a "GCode Backplotter". It's somewhat like the Vectric Preview and Simulation facilities, but because it's working from the GCode, you can inspect things like starting heights, positions, etc. Likewise, because it's independently produced (not from Vectric), I know it's not going to be using the same algorithmic fiction that Vectric might have used. I use the one by CNCCookbook (https://www.cnccookbook.com), their G-Wizard Editor. Fantastic, and more than worth the price*. When you load a toolpath into it, it will display a 3D rendering of where the tool tip goes. By simply clicking on the "Front" view, you can tell exactly where that bit is going to enter the cut, and ever part about it. Independent verification of toolpath output, to me, is crucial. I don't run ANY toolpath anymore unless I've first verified a whole bunch of things.

Hope that helps. The intricacies of machine, part and tool datums can get confusing sometimes, and tool entry is something the normal simulators don't do well at representing.

Regards,

Thom

* Lots of people whine...yes, WHINE...that GWizard costs money. Yeah, well 5 pcs of a good quality 0.25"D, 2flute extended-reach, 0.020" radiused endmill that can cut a 2" deep hole in a block of aluminum costs well nearly $500. Not running that 12mm D x 52mm deep bore through major validation will burn through those 5 endmills long before the bottom of the first hole is reached. The cnccookbook F&S and editor paid for themselves in literally the first major bore I passed through them. Feeds and Speeds, and toolpath verification need to become your best buddy if you want great quality, safe cuts, and most importantly: getting all the cutter life you paid for.


Thank you for the information. I will take a look at the " CNCCookbook" and give it a try.
I have had the machine for a long time, but still have a lot to learn.
Thank you very much.
JMD2
 
Posts: 4
Joined: Mon Nov 13, 2017 9:41 am

Re: Setting z zero

Postby JMD2 » Sun Jan 07, 2018 2:06 pm

Rando wrote:John:

Okay, there IS one error condition in which this can occur, and that's if the post processor somehow tells the bit to go to the X0Y0Z0 location. This would be unexpected, and I'm thinking unlikely. But, if true, it would call for a post-processor file change to remove that statement; it's a simple text file, but if you're unfamiliar with them they can be mystifying at first.

Regards,

Thom

Thank you. not too sure that something like this something I can handle, but will take a look and see.
Thanks again,
John
JMD2
 
Posts: 4
Joined: Mon Nov 13, 2017 9:41 am

Re: Setting z zero

Postby TAW » Mon Jan 08, 2018 11:55 am

Hopefully you have this worked out. When you say "I would like to setup a job, with the "Z ZERO" set to the spoil board and the cut starting at the top of the part."........
Are you talking about when you design the project and setting start points a bit/ depths or are you talking about the actual part set up and zeroing the part on the machine?
If the later if using virtual zero or manually setting the Z (top of work pc) will need to be zero. If you are trying to cut thru the work piece with tabs to the spoil board - you will be setting your final cut depth just slightly deeper then the work pc(like .002)
hope this helps or you have figured it out. good luck
TAW
 
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Re: Setting z zero

Postby JMD2 » Mon Jan 08, 2018 5:53 pm

TAW wrote:Hopefully you have this worked out. When you say "I would like to setup a job, with the "Z ZERO" set to the spoil board and the cut starting at the top of the part."........
Are you talking about when you design the project and setting start points a bit/ depths or are you talking about the actual part set up and zeroing the part on the machine?
If the later if using virtual zero or manually setting the Z (top of work pc) will need to be zero. If you are trying to cut thru the work piece with tabs to the spoil board - you will be setting your final cut depth just slightly deeper then the work pc(like .002)
hope this helps or you have figured it out. good luck


Guess I wasn't too clear. I have the program from VECTRIC, (The Chess Set) and it calls for the second side to be setup with the Z-Zero on the spoil board. I think I have seen this talked about before and if I remember, the CNC SHARK POAST will not let you set it up that way. Just wondering if that was correct or if there was a way to do it.
Thank you for your reply. I will get something figured out.
John
JMD2
 
Posts: 4
Joined: Mon Nov 13, 2017 9:41 am


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