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  #1  
Old Wed 22 January 2020, 15:04
ChuckS
Just call me: Chuck #125
 
Mt Clemens, MI
United States of America
Very abrupt stops in -X direction only?

Hi All,

My MM has been running faithfully for a few years. It's been idle since August (life!), and I ran her a bit today. She is not happy. I warmed her up a bit, jogging around the table, all seemed happy.

Mostly, I make custom kayak paddles. Basically the same shape as an airplane propellor, but without the twist. These get cut with a parallel toolpath that mostly runs in the X axis. Back & forth, back & forth....

Two problems today, possibly related, possibly not.

1. When cutting a test paddle my machine Estopped at X43, at line #300. I reset the machine, and it again Estopped at X43.1, but at about line 500. I checked my rails for anything that might lift the Y carriage, and found nothing. The y carriage does seem to move smoothly by hand. Next, I remembered to actually look at the diagnostic screen in Mach3. When Estopped, all 3 limit circuits were angry. Sounded like a bad ground, so I checked all connections in my limit switch circuits. I did find a couple of not quite tight enough terminal screws. The machine has not Estopped since, so maybe I fixed something.

2. I run my machine at about 500 ips, with an acceleration setting of 25 in/sec/sec. It has worked well for years, in a variety of materials. Today, it seems to be accelerating at the normal rate, and if moving in the +X direction, it decelerates normally. If moving in the -X direction, the deceleration (only) is VERY abrupt- enough to apparently rebound a little.

The video shows the trouble. This is an air cut. There is no bit in the spindle.

Any ideas?

Thanks!

https://www.youtube.com/watch?v=Ju-IpLF1v4s
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  #2  
Old Thu 23 January 2020, 17:07
lonestaral
Just call me: Al #114
 
Isarn
Thailand
Send a message via Skype™ to lonestaral
Try checking the acceleration / deceleration settings.

Are you using Mach 3?
I changed to Linux, very much superior.
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  #3  
Old Fri 24 January 2020, 10:37
ChuckS
Just call me: Chuck #125
 
Mt Clemens, MI
United States of America
Thanks!

I'm about to head out & see what I can find. Yup, Mach3. I have a complete, ready to go brain box which based on UCCNC ready to go. I just really, really don't want to change with a big deadline looming.

I'll start by changing the acceleration settings.
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  #4  
Old Fri 24 January 2020, 16:34
lonestaral
Just call me: Al #114
 
Isarn
Thailand
Send a message via Skype™ to lonestaral
You could try pushing the X axis around by hand with the power off.
See if it runs smoothly.
If you have separate axis drives see if the are any indicator. warning lights.
Best of luck with the deadline.
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  #5  
Old Mon 27 January 2020, 15:25
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
That definitely looks like trying to accel too fast on the way back the left to me - you exceed the torque available to the motor, and things get funny from there.

The simplest and most obvious thing to me is that maybe the gantry is slightly out of alignment? Do you have twin hard stops at the end of the run that you can manually pull the gantry to with the motors off? If not, if you drop one motor out of the rack by pushing it down, does the gantry move and try to realign itself? This one bit me.

Next question that comes to mind is if one of the two X motors has a bad connection, and is basically following along until torque limit is exceeded. With motors on, can you push either end of the gantry either direction?
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  #6  
Old Fri 31 January 2020, 20:20
ChuckS
Just call me: Chuck #125
 
Mt Clemens, MI
United States of America
Thanks all!

And the answer is..... the gear that drives on the rack was just a bit loose on the shaft of my belt drive. The gears were also significantly worn, so I replaced all of them on the x & Y axis. With a reasonable push, I couldn't move either end of the gantry. With a BIG push, the loose gear showed itself. The Z axis drive gear was replaced last summer.

After about 1000 hours of use, I can't begrudge it some much needed love & maintenance. At the first chance I get, I want to give everything a thorough inspection & repair.

My Z axis plate is on borrowed time. I flipped it end for end last summer as it is showing wear. I have the steel to build a replacement, but time is lacking, and my usual machinist buddy took a different job....
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  #7  
Old Sat 01 February 2020, 17:13
lonestaral
Just call me: Al #114
 
Isarn
Thailand
Send a message via Skype™ to lonestaral
Happy o hear that you got it sorted.
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