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axis drift?

Posted by jimmyclarke 
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jimmyclarke
axis drift?
July 24, 2015 04:09AM
I'm currently struggling with my hobbed bolt, so I am switching to a direct feed.

Woke up this morning to find my new extruder has printed, but twice there has been a shift causing it to print crooked,
(it should of looked like: [www.thingiverse.com])



As my hobbed bolt eats my filament, my prints are failing more often than not, so I don't have many examples, but the failed 3DBenchy to the left also shows this drift
This has happened with the printer in different positions in the house, so if it is interference it must be self inflicted.

I would guess that ferrite cores on the motor wires would be welcome, but what else can I do to eliminate this?

Thanks!
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o_lampe
Re: axis drift?
July 24, 2015 04:27AM
That´s called "skipping steps".

You can raise the Vref of the stepper, ( if possible without over heating )
or reduce acceleration in firmware. ( in my case from 9000 to 8000mm/s^2 helped )

Make sure, the nozzle isn´t scratching across the last layer from over extruding/ wrong e-steps.
-Olaf
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elwood127
Re: axis drift?
July 24, 2015 10:34PM
Just went through the same thing. I raised my voltage from .5 to .7. I have the Melzi board. Hasn't printed a sloped object since. They say that anything above .7 starts getting dangerous. Just a note, when trying to touch the "single" leg of the trim pot to measure voltage (which is tough because you can barely see it much less get a multimeter lead on it), it turned out that touching the adjustment screw gave the same reading and easy to touch.
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madmike8
Re: axis drift?
July 25, 2015 02:48AM
Tip I learned. Take a small screw driver and strip some wire then wrap it around the screwdriver. Use heat shrink to secure the wire and cover all but the tip. Install alligator clip on other end of wire. Then clip the alligator lead the positive test lead of your multimeter. Touch the negative lead to ground, and then use the screwdriver to get the reading as your adjusting.
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o_lampe
Re: axis drift?
July 25, 2015 03:05AM
Quote
madmike8
Tip I learned. Take a small screw driver and strip some wire then wrap it around the screwdriver. Use heat shrink to secure the wire and cover all but the tip. Install alligator clip on other end of wire. Then clip the alligator lead the positive test lead of your multimeter. Touch the negative lead to ground, and then use the screwdriver to get the reading as your adjusting.

I´ve heard you must not use a conductive screwdriver? Only ceramic or plastic tips are allowed...
-Olaf
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jimmyclarke
Re: axis drift?
July 25, 2015 05:26PM
Ah that makes sense, I had turned that pot down to reduce noise!
Thanks I will get it sorted.

In terms of using a non conductive screwdriver, I can confirm the importance as I blew a driver up with a metal screwdriver! winking smiley
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madmike8
Re: axis drift?
July 25, 2015 06:31PM
That's why you cover all but the tip with heat shrink. To reduce chances of a short. Question for you folks... Are you setting the vref with the motor power supply turned on?
You can set vref with just the Mega's USB port plugged in.
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o_lampe
Re: axis drift?
July 26, 2015 03:38AM
5V only...
the risk of turning the potmeter to much and kill driver/stepper is high.
-Olaf
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sarf2k4
Re: axis drift?
July 26, 2015 08:40AM
I don't use the vref method, I do it the most safest yet troublesome way. Turn everything off including usb port, turn the pot by about 1/8, then test, if it will introduce motor skip, also touch the motor if it is hot or not by roughly around 30'c I think it's okay
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madmike8
Re: axis drift?
July 26, 2015 12:07PM
Lol... Well do what you feel safest in doing... But if you have a semi steady hand, and you've freed yourself from dealing with the multimeter leads. It really is a pretty simple process to set vref for 5 drivers in a few seconds. I actually got a second set of test leads and made a set just for this with the screwdriver on the positive lead and a female molex on the negative lead. Plug the molex onto a ground pin, and adjust vref with the screw driver on the pot. building these things is my hobby, so I do a bunch of them.
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sarf2k4
Re: axis drift?
July 26, 2015 08:31PM
hahaha... nope, I don't have proper equipment nor "engineering done right" methods. I followed Tom's guide to adjust them smiling smiley
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jimmyclarke
Re: axis drift?
July 28, 2015 10:45AM
Well I adjusted the pot a smidgen to the right and now no axis drift and printer is still quieter than when I started, so very happy

Now though I ended up with this, (think it still fits the thread topic)


All settings are the same from when I printed the first piece that drifted, so I don't think it's the temperature?

What do you think?
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sarf2k4
Re: axis drift?
July 28, 2015 11:26PM
From the looks of it under extrusion, try increase the pot current a bit too, probably the extruder motor does a lot of retraction on that layer, making it skipping steps
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o_lampe
Re: axis drift?
July 29, 2015 03:04AM
Quote

I'm currently struggling with my hobbed bolt, so I am switching to a direct feed.

Did you adjust the e-steps to match the new extruder gear diameter?
-Olaf
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jimmyclarke
Re: axis drift?
July 29, 2015 09:09AM
Yes my esteps are correct, this is me printing a mount for direct feed so I am still running the hobbed bolt
and there was no retraction on, and no noticeable skipping (which doesn't say much I know)

Cleaned nozzle to no avail, now all my prints look like the worst part of my previous picture, the annoying part is you can see when it just stops working nicely, it's like I've taken a month step back of getting this printer functioning

It has managed to print a very ugly looking, but dimensionally correct mount, so I will now try the direct feed to see if it helps matters

will report back, cheers
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sarf2k4
Re: axis drift?
July 29, 2015 08:11PM
Might be your filament or your flow rate though. Is there by any chance that you've turned on the hot end at around 230-250'c (abs) even though not printing?
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madmike8
Re: axis drift?
July 29, 2015 09:44PM
If your hotend uses a ptfe sleeve and you've printed at more than 230 degrees, you've probably damaged the sleeve and need to replace it.
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sarf2k4
Re: axis drift?
July 30, 2015 01:14AM
With teflon tube inside heatbreak are fine as long as you don't exceed 250'c
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