Z Axis inconstancy in depth

Home › Forums › TinyG › TinyG Support › Z Axis inconstancy in depth

Viewing 12 posts - 1 through 12 (of 12 total)
  • Author
    Posts
  • March 6, 2018 at 5:37 pm #10893
    dustin davis
    Member

    I am cutting a vacuum table top. It is just a grid of lines 1 inch apart. .25 ball end mill supposed to cut .20 depth. Board is level I have checked it several times. But the cut keeps gets deeper with each line.

    I have no idea why but I had to set my travel distance for my z axis to 1.27″ to get it accurate movement. I have T8 lead screws on all axis. The other axis travel are .316″. The first line is at .233″ second line is .271″ third is .309″ chilipeper stated it was at the .200″ depth. I have no idea why it would keep cutting deeper on each line. Please help.

    March 6, 2018 at 7:12 pm #10894
    cmcgrath5035
    Moderator

    It would help to see your tinyG parameter set, a $$ DUMP.
    copy the results to a cloud drive and post a URL.

    Perhaps explain a bit more about what you mean when you say board is level.
    Do you mean that the board is absolutely of uniform thickness across the area of interest and that your machine is absolutely equidistant from the work surface to a reference point on the Z axis across the X,Y surface to be milled?
    Something does sound strange about your settings (need for $_tr=1.27″).

    March 6, 2018 at 8:00 pm #10895
    dustin davis
    Member

    I will try to get the settings posted tomorrow. When I say that the work is level I checked the z zero in 4 different corners of the work. The depth of cut is consistent throughout a 15 inch cut. They just get deeper with each different cut. I had an issue a month ago where the z axis went nuts. I told it go down by 1” and it maxed out. That is when I had to set the ZTR to 1.27”.

    I am not sure how to put the settings on a cloud. I will do the best I can. I am new to CNC machining. I built this machine from research on the internet. So it is not like any out there I think. Thanks for the help.

    March 6, 2018 at 10:06 pm #10896
    yawstick
    Member

    Sounds like your Z axis might be too heavy.

    March 8, 2018 at 12:55 pm #10899
    mristau
    Member

    Might your chucked bit need tightening? And is your bit sharp?

    Cutting MDF or Partical Board with dull bit can pull the bit out of the chuck. Z-axis not perfectly perpendicular to cutting compounds this problem.

    March 8, 2018 at 3:58 pm #10900
    dustin davis
    Member

    Ok so here is what I came up with. The ball nose end mill was digging in so it was pulling the axis down an extra .030 each time it plunged. I have added some tension springs to it and I am going to try to use ramp to stop this. Thanks for all of the help.

    March 8, 2018 at 9:58 pm #10901
    cmcgrath5035
    Moderator

    When you say “pulling the axis down”, do you mean the bit is slipping out of the chuck, or is the whole spindle mechanism being pulled down due to additional rotation of the Leadscrew?
    If latter, your Z stepper is undersized or needs more holding current.
    Perhaps reduce the microstepping from 8 to 4 or 2, if it is currently at 8.

    March 9, 2018 at 12:18 am #10902
    mristau
    Member

    “I am new to CNC machining.”
    This isn’t your CNC’s first job?
    You’ve run other jobs cutting similar sized material with no problem?
    What kind of spindle are you using?
    Spoil board has been leveled?

    March 9, 2018 at 8:44 am #10903
    dustin davis
    Member

    I believe the bit is being pulled out of the collet. I have a nema23 187oz stepper. I am using a 400w dc spindle er11 collet. I have not run any jobs with this spindle. I was using a Dremel before. I noticed the z axis stepper is choppy sounding when it moves compared to the other axis so I ordered a new stepper it should be here today. I really only get to use this on the weekends so hopefully I will get to try again this weekend.

    March 11, 2018 at 10:49 am #10904
    cmcgrath5035
    Moderator

    Hmmmm, of course anything is possible but I would chase “choppy sounding” as a possible mechanical issue with the lead screw setup overloading the stepper, i.e. more torque is needed to move the spindle than is available.
    A NEMA 23 should be able to manage the typical 400W DC spindles, I still use a NEMA 17 on my SO2 machine.

    March 12, 2018 at 3:05 pm #10905
    dustin davis
    Member

    OK I am not sure what I did but the stepper is sounding as smooth as the other axis now. I played with all the settings and now it sounds good. I did try running a few things this weekend. I think it was the collet. I was using a 6.5mm because the 6mm was slightly small. Well that must have been enough to let the bit get pulled out. I changed to the 6mm and it is cutting right.

    March 12, 2018 at 9:42 pm #10906
    cmcgrath5035
    Moderator

    A bit slipping in a collett would likely sound pretty bad too.

    Good luck with your on-going tests

  • Author
    Posts
Viewing 12 posts - 1 through 12 (of 12 total)
  • You must be logged in to reply to this topic.