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What's going on here?

Posted by Shibboleth 
What's going on here?
November 09, 2011 10:09PM
I've got a strange effect happening at the moment with my prints:



That's the vertical view of a 'reprap shot glass' The outer shell of the print is not in contact with the inner shell. This artifact seems to be happening in most of my prints, in one form or another. With some, the lower layers are offset up from upper layers. With others, holes aren't symmetrical on both sides of the print. It's just clearest here.

For this print, I just used a fresh re-install of SFact, with no setting changes at all. I believe it's not a printing artifact.

Vertically, the print comes out beautifully, it's looks like it's getting some strange instructions. Is SF not skeining correctly?



Any suggestions would be appreciated.
Re: What's going on here?
November 10, 2011 01:41AM
Have you confirmed that the toolpath generated from the g-code has the same problem before suspecting SF or SFACT?
Re: What's going on here?
November 10, 2011 02:00AM
Quote
brnd
Have you confirmed that the toolpath generated from the g-code has the same problem before suspecting SF or SFACT?

What he is saying is you should look at the skeinlayer output to see if this is really being set to the printer or if you have some other problem such as loose belts, missing tooth on pulley, loose pulley, or something else mechanical that could cause the problem.


Bob Morrison
W├Ârth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse
Re: What's going on here?
November 10, 2011 02:59AM
Re: What's going on here?
November 10, 2011 03:53AM
Thanks for the suggestion. I'm not totally sure how to go about checking the toolpath, but here's the screen output in Pronterface:



As to the other suggestions:
Missing Teeth - I use Aluminium pulleys.
Loose Belts - Both X and Y makes a nice 'twang' sound when plucked.
Slipping Pulleys - Unlikely. I have flats on my motors, and the grub screws are wound down.

I can't see where the problem is, but it does seem (judging from the screenshot above) that it must be mechanical. Thanks for the suggestions!
Re: What's going on here?
November 10, 2011 04:48AM
Looks like severe backlash to me. Did you get the aluminium pulleys on eBay from Hong Kong? If so the teeth are too thin and allow the belt to slip when it changes direction.

Is this a Prusa or a Mendel?


[www.hydraraptor.blogspot.com]
Re: What's going on here?
November 10, 2011 06:46AM
Hi Shibboleth, Sadly I can't help work out what's happening with your print but I would like to ask that when you find the cause, and you have the time, would you consider adding a photo and short description to the 3D print failure Flickr pool? http://www.flickr.com/groups/3d-print-failures It might help others with the same problem in the future.


------------------------------------------
garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net
Re: What's going on here?
November 10, 2011 04:33PM
I had something like that at one point but not quite as extreme. Think my issue was a loose x axis - the bushings on the z axis had worn down a bit and that was allowing the x axis to move to and fro a bit on some moves.
Re: What's going on here?
November 11, 2011 03:30AM
It looks like Nophead was right. The Al pulleys were too narrow. As soon as I took them off and replaced them with the original RP pulleys, great improvements occured:



As you can see, this has fixed up the problem 99%Thanks for all the help!
Re: What's going on here?
November 11, 2011 09:47AM
What feed rate are you using? You should try the Marlin firmware. Those wiggles in the loops would probably go away if you do.
Re: What's going on here?
November 11, 2011 08:47PM
brnrd Wrote:
-------------------------------------------------------
> What feed rate are you using? You should try the
> Marlin firmware. Those wiggles in the loops would
> probably go away if you do.


+1
Re: What's going on here?
November 12, 2011 12:54AM
I'm using 60 mm/sec feed rate, which I know is fairly high for a new printer.

I think the wiggles are caused by 'stickiness' of the bushings. Hopefully, they'll go away as the printer wears in, or I'll just change to linear bearings.

I must admit, I haven't heard of the Marlin firmware before, I'll have a look into it.
Re: What's going on here?
November 12, 2011 07:00AM
It's due to the Sprinter firmware. Marlin configuration.h file is very close to Sprinter so it would be easy to change.

You can get it here:
Gen 6
Non-Gen 6
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