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How to prevent bridging on separate objects

Posted by ghostling 
How to prevent bridging on separate objects
March 31, 2012 09:07PM
i was printing several objects on the same plate, but as the print head moves from object to object it leaves a bridge between the objects every layer that i have to cut away with exacto knife aftewards.

I've seen youtube videos of people printing several vertexes for a prusa on the same print without having any bridging between them... so how do they do it?
Re: How to prevent bridging on separate objects
March 31, 2012 11:30PM
You didn't say what software you are using, the parameter you are looking for is usually called retraction. If you're using Slic3r, definitely check out richraps excellent write-up on tuning and using it on his blog - the first article is at [richrap.blogspot.com]
Re: How to prevent bridging on separate objects
April 01, 2012 07:16AM
What temp are you printing with? It could be oozing from too high of a temperature. This will also change from plastic to plastic, so you'll have to get an idea of how different color filaments respond to different temps. Also echoing MKouri's thoughts on retraction.

JW


Josh

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Re: How to prevent bridging on separate objects
April 01, 2012 04:12PM
I was printing ABS @ 266C. file was sliced with skeinforge and fed to the printer with repsnapper.

Edited 1 time(s). Last edit at 04/01/2012 04:13PM by ghostling.
Re: How to prevent bridging on separate objects
April 02, 2012 02:17PM
266C!? That may be part of your problem right there - why are you using such a high temperature?

I'm printing ABS @ 205C 50mm/s 0.3mm layer height. Albeit that's lower than most (lovin my hot end design), but 266 is crazy high and will result in additional drooling/oozing. Have you tried lower temperatures?

Retraction in Skeinforge is controlled under the "Dimension" tab. The two settings you'll need to play with are "Retraction Distance" and "Restart Extra Distance". Typical retraction distances are around 1.0-1.5mm. Restart is anywhere from 0 to about 0.5. Increase retract distance until you get no strings, then increase restart until you eliminate a starting gap.
Re: How to prevent bridging on separate objects
April 02, 2012 03:33PM
Be careful when talking about print temperatures. Most people do not have calibrated thermistors, and the actual temperature could be tens of degrees (or more) away from indicated temperature.

But that does sound like you need retraction turned on. If you have to use restart then you have another issue, it should never really be necessary unless you are oozing, in which case either temperature needs to be reduced or retract distance needs to be increased.


Cameron

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Re: How to prevent bridging on separate objects
April 02, 2012 09:08PM
That's true, but my original question stands regardless of "actual" temp - has he tried lower temperatures during printing? Is he using such a high temperature (or whatever it truely is) because it's the bare minimum it would print or is he using it just to print faster? To me - the description of the print sounds like it's running too hot and/or retraction isn't on at all.

Additional settings could also be informative (print speed, layer height, nozzle diameter, firmware, hot-end design?).

Edited 1 time(s). Last edit at 04/02/2012 09:10PM by JazzyMT.
Re: How to prevent bridging on separate objects
April 03, 2012 05:12PM
initially i started printing at 200C.. but no matter how many times i level the heated bed, and gap it with a piece of paper under the nozzle the damned extrusion just wouldn't stick onto the bed and curls around at the nozzle. so after i raised the temperature some how it started sticking and i was able to print with it.. so that's how i came to print at 266C

i've ran out of ABS and switched to PLA now. i'm printing at 180C, 32mm/s, 0.4mm layer height. i'll try out the retraction settings and report back..
Re: How to prevent bridging on separate objects
April 05, 2012 04:48AM
so today i cleaned out my hot end using the torch method, upgraded firmware from FiveD to Sprinter on the gen6 electronics. recalibrated and sliced with slic3r 0.7.1. then started printing with PLA @ 170C. the bridging problem is pretty much eliminated.. but now there's new problems. but i guess that's a topic for another thread...

thx to those who helped.
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