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  1. #1
    Join Date
    Apr 2008
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    203

    Machine precisely off.

    Just did a program that had alot of holes in the beginning and in the beginning if the cutout profile I had to stop the machine and rehome. I got coordinates of two opposing holes on furthest corners. One closest to zero was spot on and the one furthest was .09 off. I figure between steps being slightly off, and backlash it's to be expected.

    Re ran the program to see if it would be off, and it barely touched the sides of the holes.

    Anyone have a good method for doing test and tweaking.

  2. #2
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    Apr 2008
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    203
    Just checked holes are within .010". So I have a feeling it may be my steps are just slightly off. Anyone have some tips for calibrating over longer disrance than a caliper can reach.

  3. #3
    Join Date
    Apr 2013
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    1899

    Re: Machine precisely off.

    Quote Originally Posted by davy182 View Post
    Just checked holes are within .010". So I have a feeling it may be my steps are just slightly off. Anyone have some tips for calibrating over longer disrance than a caliper can reach.
    Why do you need long distance to calibrate? if you can get, or maybe already have, a good caliper then you can use that. If you can get 5" displaying 5.000" then it is as good as it gets and 100" would also be 100.000" displayed if you had a 100" caliper. Or am I missing something?

  4. #4
    Join Date
    Mar 2003
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    35538

    Re: Machine precisely off.

    Why do you need long distance to calibrate?
    If the pitch of your screws or racks are off slightly, it's better to calibrate over a long distance.

    Your large parts will be more accurate. Small parts or features may be off a few thousandths, but that's probably not critical on a large machine.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  5. #5
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    Apr 2013
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    Re: Machine precisely off.

    Quote Originally Posted by ger21 View Post
    If the pitch of your screws or racks are off slightly, it's better to calibrate over a long distance.

    Your large parts will be more accurate. Small parts or features may be off a few thousandths, but that's probably not critical on a large machine.
    I still think that if you can't measure it within 5" then it probably doesn't matter when you make something which is large. Also, if your screws are slightly off then I think that's measurable within 5" as well, unless you have some very unusual screws or racks. When you measure 5" as 5.000" on a caliper you will measure 100" as 100.000" also. I understand that if you have a long screw then maybe 5.000" at one end is not 5.000" at the other, but I think that can be identified if one takes several 5" measurements along the table, offset as it may be necessary. I don't know any other way of measuring accurately over longer distance. The other alternative is to have a long reference ruler, which is within a tolerance and extend the caliper with that ruler, but such ruler might be more expensive than a long caliper.

  6. #6
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    Apr 2013
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    1899

    Re: Machine precisely off.

    Quote Originally Posted by davy182 View Post
    Anyone have some tips for calibrating over longer disrance than a caliper can reach.
    Just had an idea... maybe you like it maybe not...

    I don't know how long or wide parts you want to make, but if you only have a normal caliper then you could mill pockets and islands in aluminium, say every 5" and measure each. That would show if you have linearity issues and where the problem is. This allows you to measure accurately over a longer distance since you just have to measure 5" at a time and add those together, and you will easily see where on the table you have problems and can adjust the steps per value to correct the issue. Of course, you need to repeat this more than once. Sort of like milling a chess board with 5" squares. You can use other material as well, as long as you are happy with something else, like acrylic, Delrin or maybe even MDF. That would save you time and tool.

  7. #7
    Join Date
    Dec 2013
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    5717

    Re: Machine precisely off.

    Maybe a centerpoint in the spindle (or any sharp cutter edge), a magnifying glass, and a Stanley tape measure. The reason I suggest a Stanley tape measure is because I checked one once and found it to be within 0.005 in 20 inches, at least compared to my mill DRO, maybe others are similar. Without sophisticated measuring instruments, that's about the best you can do.

    The good news is that your machine seems to be repeatable.
    Jim Dawson
    Sandy, Oregon, USA

  8. #8
    Join Date
    Mar 2003
    Posts
    35538

    Re: Machine precisely off.

    I was looking around a few weeks ago for an accurate tape measure, and found that there are class 1 and class 2 tape measures. The vast majority are class 2.

    https://www.thetapestore.co.uk/knowl...e_Measure.html
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  9. #9
    Join Date
    Mar 2003
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    35538

    Re: Machine precisely off.

    If your pitch is off .001" in 5", and you calibrate for a 5" part, you'll be off .02" on a 100" part.
    If you calibrate the machine at 100", a 5" part will be off .001".
    I'd prefer the latter.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  10. #10
    Join Date
    Apr 2008
    Posts
    203

    Re: Machine precisely off.

    thanks for the posts, found the devil.

    Ger as always great advice. I found for large parts a tape and the camera feature on mach with crosshair works great for calibration. But yes, i concur with if you calibrate small and cut big you may have a large error on the big parts ( i would normally be a 1/32 to 1/16 off)

    Well the last owner redid my rewire for whatever reason and used the home depot red bullet connectors on the encoder connections. Yup, not a loose but crappy connection. Must have not gotten all the copper in the crimp. I found it as i accidentally touched the wire and the machine cut that part wrong. After stopping the machine I wobbled it and the y started to move. Put my connectors back on and bingo bango no un-programmed movement.

  11. #11
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    Apr 2013
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    1899

    Re: Machine precisely off.

    Quote Originally Posted by ger21 View Post
    If your pitch is off .001" in 5", and you calibrate for a 5" part, you'll be off .02" on a 100" part.
    If you calibrate the machine at 100", a 5" part will be off .001".
    I'd prefer the latter.
    Yes, but I am talking about calibrating 5" to 5.000" and NOT to 5.001". As I said, this assumes linear inaccuracies. If your screw is perfect at one end and off somewhere in the middle and so-so the other end then you have to chose what is important. Making 5" cuts and measure the cuts over the 100" table would tell would tell you if the screw is linear or not, and where it is the worst/best. If the pitch is off then that can be adjusted by the steps per value to get accurate cuts. That's what I did with my machine, after all, a 1605 is NOT 16.000mm in diameter with 5.000 mm pitch, but a little more or less, so taking some reference measures and adjusting the steps per values are necessary. This is common practice also with 3D printer, where the differences can be even more.

  12. #12
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    Apr 2013
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    Re: Machine precisely off.

    Quote Originally Posted by davy182 View Post
    But yes, i concur with if you calibrate small and cut big you may have a large error on the big parts ( i would normally be a 1/32 to 1/16 off)
    ...but that was not what I was suggesting. Anyway, if a tape measure calibration is good enough then that's easy to do. But it's great that you actually found the source of error and fixed it.

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