584,817 active members*
4,660 visitors online*
Register for free
Login

Thread: Z axis play

Results 1 to 6 of 6
  1. #1
    Join Date
    Jul 2017
    Posts
    3

    Z axis play

    Guys, I have an OpenBuild C-Beam machine that I have modified to give me a little extra depth and I have replaced the dewalt router with a VFD spindle router.

    I have some lag between the bed moving and the spindle cut catching up with the movement. Lag is not noticeable on the X axis but on the Y axis there can be significant lag depending on cut depth.

    The origin of the Lag is on the Z axis where there is flexing of the Cross beam as the cut is being made.
    Is this normal to have some flexing and if it is can it be quantified?

    Not sure I explained this correctly.



    TIA

  2. #2
    Join Date
    Apr 2004
    Posts
    5728

    Re: Z axis play

    It sounds like you increased the leverage against your gantry beam when you increased the height, This design https://openbuildspartstore.com/open...-beam-machine/ was minimal to start with, barely rigid enough to cut soft materials. No, it's not normal for gantry beams to twist visibly, but it does happen, especially when design parameters are exceeded. You can try replacing it with a stouter piece of extrusion, but that might just make another part of that machine the weakest link.
    Andrew Werby
    Website

  3. #3
    Join Date
    Jul 2017
    Posts
    3

    Re: Z axis play

    Quote Originally Posted by awerby View Post
    It sounds like you increased the leverage against your gantry beam when you increased the height, This design https://openbuildspartstore.com/open...-beam-machine/ was minimal to start with, barely rigid enough to cut soft materials. No, it's not normal for gantry beams to twist visibly, but it does happen, especially when design parameters are exceeded. You can try replacing it with a stouter piece of extrusion, but that might just make another part of that machine the weakest link.
    Thought that about the gantry height as well but test showed that the twisting of the beam is there at what ever height the z axis is. I replaced the spindle drive today to see if the extra weight was an issue but it made no difference at all to the amount of flexibility the beam has. I guess it is a design issue. I suppose a work around would be to increase the number of passes over a design and limit depth of cut to something like 0.5mm per cut.

    Think I’ll also look for a different machine, not much choice for the hobbyist though all seem to be cheap machines from Amazon.

    Thanks for the input

  4. #4
    Join Date
    Jul 2018
    Posts
    6248

    Re: Z axis play

    Hi Lodds - you can fill the extrusion with expanding concrete. Not normal concrete. Concrete is about the same stiffness as aluminium so the fill is a good match and it will considerably stiffen the gantry in torsion which is your current issue. Your Z axis tool plate is not stiff enough as well. if you wobble the spindle with your hand you will see how the machine flexes and where you need to stiffen it. Peter

  5. #5
    Join Date
    May 2005
    Posts
    1662

    Re: Z axis play

    I'm not sure how the term "lag' is being used in in the top post.
    To measure deflection a dial indicator would be handy to narrow down the source. My guess is the v-wheels with their stand-offs are responsible for most of the flex. Ramp entries and small depth of cut will help.
    Click image for larger version. 

Name:	Magbase_dial_indicator_smaller.jpg 
Views:	0 
Size:	99.0 KB 
ID:	451060
    Anyone who says "It only goes together one way" has no imagination.

  6. #6
    Join Date
    Jul 2017
    Posts
    3

    Re: Z axis play

    Quote Originally Posted by peteeng View Post
    Hi Lodds - you can fill the extrusion with expanding concrete. Not normal concrete. Concrete is about the same stiffness as aluminium so the fill is a good match and it will considerably stiffen the gantry in torsion which is your current issue. Your Z axis tool plate is not stiff enough as well. if you wobble the spindle with your hand you will see how the machine flexes and where you need to stiffen it. Peter
    Peter, What a great idea, not even heard of expanding concrete before. I'll check it out.

    I'm also considering replacing the crossbeam with 222mm plywood but reflecting on how to attach it to the current structure not sure though how the X axis would function, still looking at all options.

    Tony

Similar Threads

  1. Removing play in Z axis
    By 5Carbides in forum Joes CNC Model 2006
    Replies: 2
    Last Post: 02-25-2020, 12:29 AM
  2. Z axis play
    By bmurph in forum Benchtop Machines
    Replies: 0
    Last Post: 01-24-2012, 07:17 PM
  3. Play in X Axis Table
    By WeTDrEaM in forum Fadal
    Replies: 4
    Last Post: 10-31-2011, 04:55 PM
  4. Play on X axis
    By Peat in forum Cincinnati CNC
    Replies: 0
    Last Post: 10-28-2011, 11:45 AM
  5. Is there a way to take play out of Z axis?
    By aadrew10 in forum Haas Mills
    Replies: 10
    Last Post: 06-10-2011, 07:16 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •