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Tangential Cutting issue, need advise
« on: February 21, 2013, 12:34:15 AM »
I am using mach's tangential cutting feature, my problem is the blade rotation starts to spin before the Z axis is up, destroying my material everytime, I have tried everything to solve this issue, including pulling most of my remaining hair out, and I cannot get mach3 to stop this,

I have read some similar posts, of this exact issue in this forum back from 2009, and the issue still remains today in the newest version of mach,  :(

I ask is there anything I can do to fix this myself,  to allow the Z to clear the work, before the knife spins to it's next position.

Offline Tweakie.CNC

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Re: Tangential Cutting issue, need advise
« Reply #1 on: February 21, 2013, 01:49:19 AM »
Hi Jaydem,

The easiest solution with cutting holes is to create a lead-in /  lead-out (from the CAD/CAM program being used to create the tool-path) which has exactly the same radius as the hole being cut. This positions the cutter into the correct direction before it enters the work.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Tangential Cutting issue, need advise
« Reply #2 on: February 21, 2013, 02:39:04 AM »
Thanks, Tweakie that's a good solution,  that should work for most of my parts, that I discard the scrap, I will give it a try in the morning,

I still need to find some solution for the parts that have no room for a leadout, but at least I think I can run good parts, to get thru this first order, even with the wasted material

the issue is only with the exit of the knife, after the cut, the A axis rotates and raises the Z at the same time, the start is fine, as the knife is already moved to the correct position
« Last Edit: February 21, 2013, 02:40:45 AM by jaydem »

Offline Tweakie.CNC

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Re: Tangential Cutting issue, need advise
« Reply #3 on: February 21, 2013, 03:00:24 AM »
Hi Jaydem,

My apologies if I am unable to describe it correctly. The lead-in / lead-out has the same radius as the circle being cut and is placed exactly over the path of the circle - this way there is no wastage and the cutter will be clear of the work surface before any rotation occurs.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Tangential Cutting issue, need advise
« Reply #4 on: February 21, 2013, 09:46:10 AM »
Hi  Tweakie


it's always hard to descibe with text,

Yes, I understand,  leadin/out with overlap, on the same radius, in line with the cut, but it still does the same, the knife blade is still deep into the material, when it starts to rotate, and move up, which rips the material.

My knife is powered / rotated with a stepper motor Axis A

I am having the exact same issue as this guy back in 2009 see ,  http://www.machsupport.com/forum/index.php/topic,12637.0.html

Jay

Offline Chaoticone

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Re: Tangential Cutting issue, need advise
« Reply #5 on: February 21, 2013, 10:22:00 AM »
Jay, I have a friend who uses tangential and the best way he has found to prevent this is for the z to lift with the knife at the same angle as it will begin its next cut. In other words, try to finish a cut going -x and make sure the next cut starts with the x going -. Is that doable?

Brett 
;D If you could see the things I have in my head, you would be laughing too. ;D

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Re: Tangential Cutting issue, need advise
« Reply #6 on: February 21, 2013, 12:00:22 PM »
Hi Brett
yes, I have used that method on drag knife cutting in the past, but what I am doing is different I am using Mach's Tangential cutting feature, which controls the knife angle on it's own, I have very little control

please see video of the issue, as the knife exits the material, mach starts the rotation before the knife is clear of the material,


http://www.youtube.com/watch?v=rJ34d0e09oo&feature=youtu.be

Offline Chaoticone

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Re: Tangential Cutting issue, need advise
« Reply #7 on: February 21, 2013, 12:10:52 PM »
Jay, I know exactly what your saying. I watched the video too.  When the tool lifted up the knife was already rotateing to the angle it started the next cut.  Careful tool path generation is the best fix I have seen so far.  I will see if I can find out more for you though. 

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!

Offline Chaoticone

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Re: Tangential Cutting issue, need advise
« Reply #8 on: February 21, 2013, 01:24:24 PM »
Jay, can you add a z positive move just before any posotive moves the z has already to clear the work?  Maybe just above the wrok but below the Z positive where you are adding this line.  I would like to know if that works.

Brett

;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: Tangential Cutting issue, need advise
« Reply #9 on: February 21, 2013, 03:27:11 PM »
Brett, Tweakie, Chaoticone
Yes,  I was able to solve my issue,  once you guys got me pointed in to the direction of the gcode, , it works, I used a combination of three things, add lead in and out for circular shapes and for straight moves I edit the Z moves with a G01 instead of G00, , which seems to work,  thanks for all the great info,
Jay