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Accuracy test

Posted by cristian

cristian

Accuracy test
October 17, 2015 09:30PM

Registered: 9 years ago
Posts: 344

I wrote a small test (see hysteresis_test.scad) to check the precision of my printer. The test is thought to discover in particular some kind of hysteresis (backlash, uneven belt tension, etc.) by making the hotend go backward and forward from one side of the bed to the other. However I discovered that the overall precision of my printer is so low that hysteresis is the least of my problems:

precision.jpg

(0.2mm layer height)

How precise is your printer instead?

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imqqmi

Re: Accuracy test
October 18, 2015 04:20AM

Registered: 8 years ago
Posts: 752

Looks like some wobble in the xy plane, on prusa i3 this usually is related to the z threaded rods not being straight.

I've printed this yesterday and got rid of the wobble in my prints:
http://www.thingiverse.com/thing:141479

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cristian

Re: Accuracy test
October 18, 2015 05:39AM

Registered: 9 years ago
Posts: 344

In my case I think the wobble comes from the weakness of the structure. The printer is a smartrap of the first generation, with cantilevers everywhere. I got rid of Z wobble by using spectra line instead of a threaded rod, which seems to work very well but clearly it is not the only issue.

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the_digital_dentist

Re: Accuracy test
October 18, 2015 06:53AM

Registered: 11 years ago
Posts: 5,764

How fast did you print it? If it is the frame wobbling, a lower print speed may help keep it under control.

Edited 1 time(s). Last edit at 10/18/2015 06:55AM by the_digital_dentist.

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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cristian

Re: Accuracy test
October 18, 2015 07:07AM

Registered: 9 years ago
Posts: 344

Quote
the_digital_dentist
How fast did you print it? If it is the frame wobbling, a lower print speed may help keep it under control.

30mm/s. No hope I think smiling smiley

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the_digital_dentist

Re: Accuracy test
October 18, 2015 07:52AM

Registered: 11 years ago
Posts: 5,764

Post a picture of the printer...

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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cristian

Re: Accuracy test
October 18, 2015 08:24AM

Registered: 9 years ago
Posts: 344

In this thread there are several pictures, with the last improvements at the end of the thread. My printer is probably the perfect heap of all the things that should not be done for a reliable 3d printer design: structure made of plastic parts and wood, cantilevered bed and Y axis, loose linear bearings, loose belts (I cannot stretch them too much or the structure bends)... What else?
My next printer will be much more in line with the philosophy of the son of MegaMax. winking smiley

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the_digital_dentist

Re: Accuracy test
October 18, 2015 09:46AM

Registered: 11 years ago
Posts: 5,764

Oh my!

I like the improvement when you switched to the fishing line. I see a lot of the quadrap machines are doing that. Hmmmm....

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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cristian

Re: Accuracy test
October 18, 2015 12:05PM

Registered: 9 years ago
Posts: 344

I forgot: the bed is bent. grinning smiley

But I have a great hotend that never jams no matter how much I overextrude or overheat, so I can squeeze it on the bed with no consequences. With a raft I manage to print pieces about 10x18 cm.

The fishing line is one of the most successful improvements to my printer, however it supposedly works only if Z bearings can slide very smoothly.