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How Do These Touchoff Sensors Work

Discussion in 'CNC IN THE HOME SHOP' started by Metal, Nov 8, 2016.

  1. Metal

    Metal United States Active Member Active Member

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    So, Ideally I've seen in youtube videos, you zero a tool (somehow) then zero the part with something or other, then when you switch tools it can touch the sensor to zero again and continue on without missing a beat. I'm assuming I need good home switches to get coordinates off of, then setup some sort of touchoff location or script which is called after each tool change.

    Anyone have any suggested reading on how to set all this up? Currently I'm edgefinding manually and then putting paper under the cutter and slowly moving the knee up until the paper gets snagged and calling it home, which is five flavors of pain in the butt.
     
  2. Boswell

    Boswell United States Hobby Machinist since 2010 H-M Supporter-Premium

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    My experience is that this is more complex than is initially evident. There are a few different ways to to set Z-Zero.
    1. using the paper method you described. The advantage is that it does not take any special equipment, batteries or understanding complex systems to work.
    2. Using an electronic version of the paper technique http://www.ctctools.biz/electronic-z-axis-pre-setter-with-led-g09/ . I use something similar to this. It is 2.000 from bottom to top. The spring loaded plunger gives me the ability to overtravel a tiny bit without damage. You place this on your part where you want to zero Z axis to. When the tool touches the top plunger an LED lights up.
    3. You can use a tool table. This is a feature of most control systems that lets you very carefully measure the relative length of your tools and store them in a tool table. Then you should be able to touch off to the Z Zero point with one tool and then switch out tools of various lengths without reseting the Z-Zero. This is a simplistic explanation and the devil is in the details including
    3a: Are you using tool holders that register the tool holder to the mill in a repeatable way to get the accuracy you are looking for?
    3b: you will still have to initially set the Z Zero anytime Z Zero changes. For production runs were you use a setup for days, weeks or years and multiple tool changes, this could pay off big time. If you are like me and most everything is a one-off, I am not sure it sames much time. I can change the tool and reset the Z Zero with the new tool in under 2 minutes and so the work to setup and maintain a tool table just does not seem like a good time trade-off. Others might have a different opinion though.
    4. I think if you are sign-making and using standard thickeness materials like say 3/4" wood and your accuracy only has to be 0.01" or so then you may have other options like a z setting tool that plugs into the control (Mach3) and works like a Probe to automatically set Z to a know height. Just remember have a know height above the table for you tool only works if you material Z Zero point is also a known height above the table.
     
  3. Groundhog

    Groundhog United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Calypso Ventures makes "MachStdMill" which is a screen set (overlay and enhancement) for Mach3. One feature of MachStdMIll is probing, touch plate, and automatic tool length measurement enhancements to Mach3. This is a link the the videos for milling. Touch plate and Automatic Tool measurement are what you are interested in. It is not necessary to have MachStdMill to set your mill up to make and use the touch plates, although I like the program (even though it hasn't been updated or anything for several years). Watch the videos to get an understanding of what you can do (with or without his program). Sometimes his use of acronyms gets confusing so you might want to look at the manual too.
    http://calypsoventures.com/machstdmill/millingvideos.html
     
  4. Metal

    Metal United States Active Member Active Member

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    Yeah I have a probe which can double as a z-zeroing point, my question was more on the programming side what is the way to do it

    Thanks groundhog, I"ll check it out, I've been using probeit largely, but I've seen the tormach and other mach3 based machines sort of do this automatically so I was wondering programically how they do it, since it does seem pretty nice once it is done.
     
  5. Groundhog

    Groundhog United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Calypso shows (in the manual) how to make the plate hardware and also electrical diagrams to have 2 plates and a probe at one time. Also has some good screens for finding edges of various shapes, centers of round objects, angles, valleys, etc. However they don't tell you how they do it!
    I don't remember what I paid for the program, but I've been happy with it.
    Seems like I saw info like you are looking for somewhere. Maybe deep in the Mach3 documentation? Don't really remember. If I think of it I'll let you know. Good luck!
     
  6. Groundhog

    Groundhog United States H-M Supporter - Premium Content H-M Supporter-Premium

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  7. TomS

    TomS Active User H-M Supporter-Premium

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    I agree with Boswell that setting up a tool table doesn't make a lot of sense for most of us hobbyists. Very rarely do I run a job that needs more than 3 or 4 tools, many jobs are 1 or 2 tools and, as he said these are usually one-off parts.

    What I use is an insulated block of aluminum that is 1" thick and connected to the breakout board. I set up the probe in Mach3 and I can auto zero a tool using script found on the internet in a matter of seconds. If this is what you are looking for I can post pictures of my setup and include the script language.

    Tom S.
     

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