Intermittant diagonal layer shift, how to diagnose? June 13, 2020 01:43PM |
Registered: 7 years ago Posts: 619 |
Re: Intermittant diagonal layer shift, how to diagnose? June 13, 2020 07:16PM |
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Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 11:23AM |
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Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 11:28AM |
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Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 02:49PM |
Registered: 7 years ago Posts: 619 |
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the_digital_dentist
Can you post a few pix of the printer and prints?
It sounds like a mechanical problem...
Are you using steel core belts?
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 02:57PM |
Registered: 7 years ago Posts: 619 |
Quote
ruggb
I also have a scratch built coreXY. The layer shift I was experiencing on mine was a result of missing steps. That was caused by two issues. One was flyback voltage on the steppers that was eliminated with diode blocks obtained from AliExpress. They are cheap and come in different configs. One is a simple plugin under your driver.
The other was a Marlin issue that produced minor shifts that made the walls look rough. It appears to have been solved late last year. If you have not updated to at least 2.0.5 released or a bugfix, you should.
However, with the noise your printer is making and not homing properly, a mechanical issue is a high probability.
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 03:37PM |
Registered: 10 years ago Posts: 294 |
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 03:48PM |
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ruggb
Just a reminder:
NOTE; the stepper motors on a coreXY are NOT XY. Technically, they should be referred to as AB. It takes BOTH motors to move the head in a straight X or Y direction. One motor running will only move it on the diagonal.
That shift does appear to be a diagonal shift, so it is likely a drive issue on one motor. If I run mine too fast, even though I have 180° wrap on the belt/motor pulley is will skip and my belts are tight.
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 03:59PM |
Registered: 12 years ago Posts: 5,796 |
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 05:01PM |
Registered: 7 years ago Posts: 619 |
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the_digital_dentist
I see pulleys held in place with screws. Is there something that stops the screws from squeezing the pulleys too tight so they don't jam? There are usually two tiny ball bearings in the top and bottom of the pulleys. If the mounting screw is too tight, it can squeeze the inner rings of the two bearings towards each other. That puts a huge load on the balls and races and will quickly destroy them. If the suppliers of those pulleys were smart, there would be a metal spacer between the pulley's inner rings that would prevent that problem. This is one reason why I prefer to use flanged ball bearings for pulleys. You can stack them up and put all the pressure you want on the inner rings- they're already butted up against each other so there's no stress on the balls and races.
Another thing to be careful of is that the outer ring of the bearing doesn't rub against the screw head or washer that is holding the pulley in place. With the tiny bearings in 3D printer pulleys you have to be very careful of that, too.
If you pull the belts off and move the mechanism does it move smoothly and easily? Do the pulleys turn smoothly and easily?
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 05:34PM |
Registered: 12 years ago Posts: 5,796 |
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 05:50PM |
Registered: 7 years ago Posts: 619 |
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the_digital_dentist
Those are pretty small steppers. I think I used 64 oz-in steppers, 400 steps/rev, in the XY stage in UMMD. I recently tested some servomotors in the sand table and really liked them, so I'm going to pull them from the sand table and try installing them in UMMD to see how it behaves. The servos are rated for 26 oz-in, but you can't compare that to stepper torque. Servos can deliver much higher peak torque on demand (if your power supply is beefy enough!), and they maintain that torque right up to 3k rpm. In a corexy mechanism, there are a lot of mechanical losses so it's better to oversize the motors than to go too small.
I'm not sure about the belt teeth contacting smooth pulleys- those pulleys are very small diameter so very few teeth will be in contact over a 90 degree wrap. You could twist the belts, if there's a long enough span, so the smooth back sides of the belts ride on the pulleys. With the F608 bearings I used in UMMD, there's no issue of print artifacts from the belt teeth hitting the smooth pulleys. On my sand table I was hearing a lot of zip zip noise from the belts/pulleys but I run that mechanism at 500-1500 mm/sec. Twists in the belts made that noise go away completely.
The pulleys don't have to match the diameter of the drive pulleys, but you do have to keep the belts parallel to the guide rails, so careful lateral placement of pulleys and motors is necessary.
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 06:52PM |
Registered: 7 years ago Posts: 619 |
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 07:10PM |
Registered: 10 years ago Posts: 294 |
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 07:17PM |
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Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 09:34PM |
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the_digital_dentist
The behavior that occurs when you hit "pause" depends on the contents of the pause.g configuration file. Likewise if you then hit "cancel", the next behavior will depend on what's in the cancel.g file (if it exists- it might not). If there's no cancel.g, the tools are deselected and heaters turned off.
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 09:53PM |
Registered: 10 years ago Posts: 294 |
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 10:13PM |
Registered: 7 years ago Posts: 619 |
Mechanical endstops.Quote
ruggb
does it have mechanical endstops?
do you have pullup or pulldowns?
Possibility of noise if the stop point is random
But not homing can't be the same issue that is causing the missing steps.
If it missed steps on a home it should continue till it hit the endstop.
Or do you have some other form of endstop?
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 10:57PM |
Registered: 10 years ago Posts: 294 |
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 11:20PM |
Registered: 12 years ago Posts: 5,796 |
Re: Intermittant diagonal layer shift, how to diagnose? June 14, 2020 11:41PM |
Registered: 7 years ago Posts: 619 |
Worth a shot. I am out of ideas.
Re: Intermittant diagonal layer shift, how to diagnose? June 15, 2020 07:39AM |
Registered: 7 years ago Posts: 61 |
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dlc60
This isn't a big printer, so the 37oz-in steppers _seemed_ to be adequate...
Re: Intermittant diagonal layer shift, how to diagnose? June 15, 2020 11:05AM |
Registered: 7 years ago Posts: 619 |
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mcdanlj
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dlc60
This isn't a big printer, so the 37oz-in steppers _seemed_ to be adequate...
The size of the printer isn't highly relevant to how much torque is needed for XY/AB steppers in your corexy.
One more thought: Have you tried swapping stepper motors between stations and see if the problem follows the stepper or the station? If you swapped X and Y (or A andand the problem changed direction, you probably have a bad or fouled stepper. You might swap either of them with Z? Or if you have extras lying around, just swap with another one?
Re: Intermittant diagonal layer shift, how to diagnose? June 15, 2020 12:25PM |
Registered: 10 years ago Posts: 294 |
Re: Intermittant diagonal layer shift, how to diagnose? June 15, 2020 12:44PM |
Registered: 7 years ago Posts: 619 |
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ruggb
noise is going to produce random results.
It is going to affect higher Z circuits like thermistors and endstops not stepper motors.
It will come from stepper motors and fans.
Stepper motor noise can be reduced using flyback diodes, which in my case stopped the layer shift I was having.
Most all boards have filter caps on higher Z circuits, but that didn't help my thermistors when the wires were bundles with the fan wires.
Re: Intermittant diagonal layer shift, how to diagnose? June 15, 2020 06:12PM |
Registered: 7 years ago Posts: 61 |
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dlc60
I will consider that. In looking back, I think that my problems started when I dressed the cables and mounted the Maestro in this enclosure.
...
I wonder if some of you have been correct and the problem might be electrical interference since cables go every which way in an enclosure and cable isolation just doesn't happen...
Re: Intermittant diagonal layer shift, how to diagnose? June 15, 2020 07:10PM |
Registered: 10 years ago Posts: 294 |
Re: Intermittant diagonal layer shift, how to diagnose? June 15, 2020 11:42PM |
Registered: 7 years ago Posts: 619 |
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ruggb
the solution is simpler now than it was when I implemented it. It is also very cheap.
For reference when DC is applied or removed from a coil a significant reverse voltage spike is prduced. That spike can fry components, produce extra steps in stepper motors or cause them to miss steps, as it did on my printer. Look at any commercial product driving a relay or other type of coil. There is a diode across the coil. Why it isn't standard for stepper motor, I do not know. Another thing the diodes did was to significantly quiet the steppers.
This is what I used;
[www.aliexpress.com]
This is even simpler; but I didn't find it till after I installed the above.
[www.aliexpress.com]
It mounts under the driver if you have one of these, TMC2100 A4988 Drv8825
I can't vouch for this as I did not order any.
Re: Intermittant diagonal layer shift, how to diagnose? June 15, 2020 11:44PM |
Registered: 7 years ago Posts: 619 |
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mcdanlj
Like ruggb, I can't come up for a mental model by which noise would account for precisely this symptom.
Quote
dlc60
I will consider that. In looking back, I think that my problems started when I dressed the cables and mounted the Maestro in this enclosure.
...
I wonder if some of you have been correct and the problem might be electrical interference since cables go every which way in an enclosure and cable isolation just doesn't happen...
I suggest it's just as likely that in bundling everything together, you ended up with an intermittent connection. Connector not quite firmly seated. Wire broken at crimp and only most of the time connecting. Something like that.
Re: Intermittant diagonal layer shift, how to diagnose? June 16, 2020 02:02AM |
Registered: 11 years ago Posts: 14,685 |