Submitted by Tim89 on Mon, 04/08/2019 - 22:30
Forums: 
CNC machines

First time posting

so hello et all

Replacing a china 6040Z machine leadscrews, and it didn't seem to improve the y-axis backlash at all

Already searched for a solution without clear progress

Any ideas?

 

Submitted by mlampert on Tue, 04/09/2019 - 09:01

Hard to tell without know how your current and previous setup are/were. Given the type of machine I presume you have a regular lead screw with some sort of nut.

Do you have a spring loaded double nut assembly?

What type of screw do you have?

A picture would be great to have a look at it.

Joel's picture
Submitted by Joel on Tue, 04/09/2019 - 11:58

Welcome to the forum, and I hope the following helps:

  1. China is notorious for proprietary lead-screw threads of every quality level with the same model labels, and you should always avoid mixing tolerance/manufacturing-sources for precision parts. There are many who suffer by mixing ground-parts with roll-formed hardened parts, and I agree replacing both the nut and screw at the same time is excellent advice.
  2. Mounting lead-screws is usually done with matched angular-contact bearing-blocks made by company's like Barden, Timken, NSK, and FAG. These bearing-blocks alone probably cost more than one would guess, but it is worth noting the professional bearings (also used in spindles) usually are rated DIN P4 / JIS Class 4 / ABEC 7 with a radial-runout under 0.00003".  Note regular roller bearings are not meant to handle much axial loading, and most larger mills can't realistically get away using them.
  3. "Cheap and Inexpensive" have two distinctly different meanings like Tormach (similar problems) or Haas (relatively good value for same price point). You may want to check youtube to learn about your machine, as other owners seem to have encountered similar tolerance problems:
    https://www.youtube.com/watch?v=DeRuMZKCiy8
  4. Note, the Y-axis racking "issues" seem especially noticeable when trying to cut materials like aluminum plate:
    https://www.youtube.com/watch?v=6a57KtmIu-4
  5. Given 4 and 5, I am not sure if backlash-compensation in software will help much in this situation, but both LinuxCNC and Mach have the setting. In my opinion, backlash is probably not the root cause of your tolerance issues given the ball-screw or axial bearing loads. YMMV with this setting. ;-)

Photos would help as mlampert suggested, given there are about a dozen variations of the 6040Z being sold.  However, these machines look like they are mostly intended for engraving wood and plastics.

Cheers,

J

Submitted by Tim89 on Tue, 04/09/2019 - 23:23

Machine is like this video, but posted solution seems will only work part way

.5 mm y-axis error is still very disappointing

https://www.youtube.com/watch?v=ABLXVCkXmpg

Is there anyway to fix issue?

 

Joel's picture
Submitted by Joel on Wed, 04/10/2019 - 21:51

Much like other antique or high-service-hour machines... You must assume there is a severe  oblique metal cutting configuration where the cutter is not 90' deg perpendicular to the surfaces. The bad news is running a large diameter fly-cutter for surfacing a truly flat-work-area may be nearly impossible.  One can usually tell the head needs adjusted when chips from the oblique cutter tend to form long curled helical shapes at regular spindle RPM speeds.

For contouring, you should probably start using Conventional-Milling paths only, smaller diameter ball-nose cutters, and drop your feed rates very low.

This means you will have to tell the CAM software to only cut in one direction per axis... so that it will twist the head in the same direction for each pass. Thus, the machine must lift the Z-axis to return to the initial side before restarting each cutting pass, and takes much more time to complete a part. Note, the cutter blades should only be cutting against the material for the direction of travel, and should be less likely to have the cutter pull the spindle off the intended path.

To answer if there is an easy fix... it is probably not practical based on what I have seen so far (some photos would really help). I am not  sure whether the 6040Z is mechanically rigid enough to handle much additional weight. This means adding a wide box-channel with a machined surface for supported X-axis rails is probably going to require rebuilding your Y-axis too.  At that point, you would have rebuilt 2/3 of the machine from scratch.

Best of luck,

J