S2 offsets cut in either X or Y axis.

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sectorix
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S2 offsets cut in either X or Y axis.

Post by sectorix » Tue Aug 26, 2014 12:49 am

I have a problem that I'm not sure how to approach.
I ran a program today, after running the same program yesterday without any problem, but now it seems like the S2 hangs for a sec on X or Y at some point of the program (tried like 5 times) and then offsets the cut.

here is an example: Green is the good cut, and Red is the bad offset one.

Image

I have tightened the belts, and cleaned the wheels. I am running at 30IPM on plywood with 1/4" upcut spiral bit, at 1/8" pass each time (per suggestions in this forum).

What can the problem be? (please be very detailed, as I am learning this as I go)

Barry

secretspy711
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Re: S2 offsets cut in either X or Y axis.

Post by secretspy711 » Tue Aug 26, 2014 1:04 am

Hi Barry,

Your machine is losing steps. Looks like only 1 axis is doing it though. Try turning up the potentiometer for that axis a little more. Were the feedrate suggestions you obtained from this forum for your setup or something different? (stock motors and spindle?)
Shapeoko 2 #5510: 1200 x 500 mm, Makita RT0701

sectorix
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Re: S2 offsets cut in either X or Y axis.

Post by sectorix » Tue Aug 26, 2014 1:23 am

secretspy711 wrote:Hi Barry,

Your machine is losing steps. Looks like only 1 axis is doing it though. Try turning up the potentiometer for that axis a little more. Were the feedrate suggestions you obtained from this forum for your setup or something different? (stock motors and spindle?)
Stock motors, Makita RT0701c. here are the parameter suggestions : http://www.shapeoko.com/forum/viewtopic.php?f=8&t=4058

questions in order:
  • what is losing steps? no chance that the machine gets stuck because of torque or something ? I mean, look at the offset, its nearly half an inch.
  • what is turning up the potentiometer does ?
  • how much should I turn it up ?
  • should I do both X and Y ? (this picture shown an X offset, but I also had a Y offset on a different cut).
Barry.

secretspy711
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Re: S2 offsets cut in either X or Y axis.

Post by secretspy711 » Tue Aug 26, 2014 2:57 am

what is losing steps? no chance that the machine gets stuck because of torque or something ? I mean, look at the offset, its nearly half an inch.
Losing steps means that the motors are not turning as much as the controller is commanding. They have no position feedback, so the controller expects them to "step" the number of steps commanded. It's losing steps as it cuts,
what is turning up the potentiometer does ?
That will drive the motors with higher current (amps). It makes them stronger.
how much should I turn it up ?
If you turn it up too much, the motors will get hot and the controller will go into thermal shutdown, and they will make a strange noise. The goal is to turn it up as much as you can for reliable operation, without going into thermal shutdown. This will give you the most strength to push the bit through materials. Your motors should be warm after they have been running for a while, but not hot.
should I do both X and Y ? (this picture shown an X offset, but I also had a Y offset on a different cut).
Wouldn't hurt.

Are you using the same type of cutter as in the link? That could also make a difference.
I assume you set up your GRBL parameters also, such as steps/mm and accelerations, right?
Shapeoko 2 #5510: 1200 x 500 mm, Makita RT0701

sectorix
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Re: S2 offsets cut in either X or Y axis.

Post by sectorix » Tue Aug 26, 2014 3:02 am

I am using that same cutter yes. grbl works fine thus far.
I would try to turn the motors a bit higher. how many degrees should I go from default ?

WillAdams
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Re: S2 offsets cut in either X or Y axis.

Post by WillAdams » Tue Aug 26, 2014 3:34 am

Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

sectorix
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Re: S2 offsets cut in either X or Y axis.

Post by sectorix » Tue Aug 26, 2014 4:22 am

Sorry for my weird questions but I dont understand the calculations on will1384's post. I have no Idea how to measure the current. I have no electronics experience and would appreciate laymans terms explanation with perhaps a visual aid.

TheAmusingMe
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Re: S2 offsets cut in either X or Y axis.

Post by TheAmusingMe » Wed Aug 27, 2014 6:30 pm

Hi Barry, I recently had to tune the current on my grblShield too, and I think the reason the answer on the wiki is complex is because there are a few different variables that differ for each user based on total set up. I personally got a Shapeoko 2 full kit from Inventables, but other may have their own brand of steppers, power supply, controller board, etc., but the process to get the correct current is the same.

I'll explain what I did on my grblShield, and if you're using the same controller set up then hopefully you can do the same to help resolve your problem.

First off, here's a picture of the arduino compatible grblShield by Synthetos:
Image
(image from: https://github.com/synthetos/grblShield ... grblShield)

The potentiometers (off-white cubes with little + screw driver slots) are the part that need adjusting, each one corresponds to an axis on the mill and is psychically closest to the silk screening on the board (in the picture, left to right, is Z, Y, X). First off I get the mill turned on and powered up and connected to some software with jog functions (I used UGS), then I turn each pot counter-clockwise until I feel even the slightest resistance, this is the '0' position. I then start issuing jog commands on the first axis, I don't expect the machine to move, as there is virtually no current going to the motor. I then start turning the potentiometer clockwise slowly while continuing to issue jog commands -- when it starts moving I stop and mark the potentiometer with a marker, this is my minimum. Next I tried to find a maximum current, under no load, that was as close to thermal shutdown as possible. This step isn't entirely useful as that maximum becomes useless when running actual jobs, but I like having it marked on my potentiometer. I did this by turning the potentiometer clockwise until I heard a whine coming from the motor, I backed it off a little and monitored the controller chip for that axis with an IR laser thermometer. If the chip's temperature didn't run away (my line in the sand was breaking 120F) then I'd turn the potentiometer a little higher and wait another minute or so and test again. This found me my upper limits.

Next step for me was to find a practical setting, so I started in the middle of my range and began air milling a simple test, monitoring the temperatures of the chips. I would even apply opposing force with my hand to simulate material resistance, I found I could apply a pretty good amount of force to the axis without missing a step once I homed in on the best current settings. After getting the current settings to a place I liked I ran a long air mill job and monitored the chip temperatures again, none got higher than 116F (without cooling) so I felt my current settings were in a good place, and if I find missing steps on a job I can always turn up the pot again. I've also since added a fan and heatsinks to the IC chips that control current.

Hope this helps, it was just the process I did, others may have better way to get to the same result and I'm nothing more than a hobbyist myself.

MarlynSofia
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Re: S2 offsets cut in either X or Y axis.

Post by MarlynSofia » Fri Jan 09, 2015 8:25 pm

Thanks to TheamusingMe for the thorough explanation.

I am calibrating my shapeoko 2; the cuts are looking much better but there are still not perfect.

-The bit cuts too much away in the spot where it ends and start a new path.
-The straight lines are a bit wavy but were not wavy when running Hello world or drawing straight lines with a pen.

I am looking at the current and adjusting the frame as it was not as straight as I thought it was (though it is not really terrible).

Anything else I should look into? I am using grbl 8.c and UGCS.

Thanks
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twforeman
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Re: S2 offsets cut in either X or Y axis.

Post by twforeman » Fri Jan 09, 2015 9:09 pm

Wavy is probably deflection. Something is loose (v-wheels, bolts, etc.) or flexing.

Do you have a fan blowing on the Gshield? If not you could be losing steps due to overheating of the drivers.
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