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Author Topic: Lumps in work.  (Read 2045 times)

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Lumps in work.
« on: August 22, 2014, 06:14:02 PM »
I am having problems with lumps in my work.  Most of the piece will be correct however there are places where the lines have what appear to be correction jogs.
Please look at the attachment and give me some good suggestion as to what the problem is and how to fix it.
Thank you.

Offline ger21

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Re: Lumps in work.
« Reply #1 on: August 22, 2014, 07:22:00 PM »
You have considerable backlash in one axis. I think it's the axis moving left to right in the first pic.

What material are you cutting? 20ipm is incredibly slow.

Why did you replace the G540. The G540 should easily outperform the Wantai drives, unless they are digital drives.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Lumps in work.
« Reply #2 on: August 22, 2014, 08:58:55 PM »
The G 540 stopped working.  I  decided to try the Wantais because they are so much less money.  I  was pleasantly surprised  when they performed better than the Gecko.  If the problem is backlash I  should be able to feel it.  I  have  dial indicators permanently attached to each axis.  How does the machine so consistently and precisely find zero.  Why doesn't the problem wander around on the the piece.  I ran the program three times at different places on the table and the lumps occurred in the same places.  When  I  switched the wires on the x and y axes the problem still occurred in the same place on the pattern.
Re: Lumps in work.
« Reply #3 on: August 22, 2014, 09:00:51 PM »
By the way.  Thanks for your input.  I  hope/wish  you are correct.  That would be an easy fix.
Re: Lumps in work.
« Reply #4 on: August 23, 2014, 01:44:22 AM »
I  cut mostly brass.  Some of the mills  I  use  are .015"  diameter.  With those I  take a depth of .004"  per pass at 8 inches per minute.  Usually 6 or 7 passes for a total depth of .028".  The  run  with  that tool would take 5 to 8 hours.

Offline ger21

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Re: Lumps in work.
« Reply #5 on: August 23, 2014, 07:24:32 AM »
If it's not backlash, then you have a loose coupling or something similar. Notice that your "lumps" occur shortly after the machine changes direction, and are always on the same axis. Usually, that's backlash, but backlash would tend to be closer to the direction change. You have a "delayed" backlash, like it takes a few seconds for the backlash to occur. Like something mechanically is slipping a small amount, but takes a certain amount of force before it slips. It's definitely a mechanical issue.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Lumps in work.
« Reply #6 on: August 23, 2014, 01:59:20 PM »
That thought crossed my mind too.  So  far  I  have not found it.  I  hope you are correct about it being mechanical.  This is the first table  I  ever built  and it has a few thousand hours on it.  People who see the machine then look at the work  I  have produced with it can not believe it.   I  am in the process of building a new machine.
I will probably retire this machine and rob the components off of it.  It has paid for it self many times over.