the biggest problem for me is....

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Johncoffee
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the biggest problem for me is....

Post by Johncoffee »

..to start the actual print. I'm currently running with ABS, did the two fan shrouds successfully, but still I have issues..

Often during heat up some material comes out of the nozzle which I keep removing until the nozzle is clean again (I usually du this using my fingers)
When print starts and the head moves down to the bed, nothing seems to come out of the nozzle for a couple of seconds. The head already starts to draw the models outer line.
When material finally comes out, it doesn't adhere on the bed instantly but starts to curl around the head a little. But at some point sticking starts but then the head somehow destroys its print by
removing material again with some remaining 'curly material'. Not sure how to describe this.

Question: how long should it take until material finally flows out when the head is on the bed? Instantly?

Thanks for any hint.
A video for a print start would be helpful a lot. Can anyone post something?

Thanks a lot in advance!

*John*

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Captain Starfish
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Re: the biggest problem for me is....

Post by Captain Starfish »

The behaviour you're describing is quite normal, but if the head striking a curl is knocking the first loop loose then you need to improve your bed adhesion.

I usually find that re-levelling the bed and making sure I have some ABS juice down sorts it out, that normally it happens because the nozzle is too high off the bed. I also run my first layer at 0.25mm thick, about 50-70% of the normal speed, and 130% extrusion rate which I think all help get the first layer well bonded to the bed so the nozzle can push aside the curl without taking everything with it.

When the hot end is preheated to temperature I'll extrude in 10mm increments until I get a solid line of filament coming out, leave it a couple seconds to do its ooze then break it off.

It usually takes a few seconds for a good filament to start coming out at the start of a print. So set up to print a skirt/brim of maybe 5-10 loops. If you make it 0 distance from the part it will also help with the bed adhesion.

Johncoffee
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Re: the biggest problem for me is....

Post by Johncoffee »

Thanks a lot Captain Starfish - I'll take your advises and will try them out!

Awesome :-)

Best regards
*John*

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thedoble
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Re: the biggest problem for me is....

Post by thedoble »

Hey John

I suggest wearing a glove if you're going to use your fingers to remove filament from the hot end - eventually you'll slip and it's a nasty burn!

A couple of things you can do to reduce the filament flowing before you're ready:
- Wind back the extruder by a half-turn or more. This will reduce the pressure.
- Depending on your controller software, you may be able to heat the bed first, then heat the hot end once it's ready. The hot end is pretty quick to heat up, and less time at operating temp means less time for plastic to ooze out.
- Use a Skirt. A skirt will 'prime' the nozzle, ready for printing. It draws outlines around the print, you can usually set a distance or a 'number of loops' setting in your slicer software, and also a 'distance from model' - I use 3-4mm as it means that any blobs or bits of plastic are some distance from the model itself and don't get 'baked in'.

If you wind back the extruder and use a skirt, the nozzle should arrive at the print bed with no ooze. It will then draw 1 or 2 outlines, extruding nothing while the filament moves to the hot end. Then when the print proper starts, the nozzle is nicely primed.

EDIT: oops, starfish covered this, oh well now it's in stereo!
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Re: the biggest problem for me is....

Post by IMBoring25 »

Since you're removing extrudate anyway there's also the option of manually priming just before you do so. Shouldn't matter, but if you have a short (length) skirt or a tall skirt (more than one layer) for any reason, it would make things more stable.

The hot-end burns aren't as bad as the soldering iron ones, but I still pull off my ooze with needlenose pliers (don't touch any wiring or a turning fan).

Johncoffee
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Re: the biggest problem for me is....

Post by Johncoffee »

short Feedback - awesome Captain Starfish & thedoble . Thanks to your both help with the suggestions I managed a almost perfect start sequence. Not sure where I can set the 130% extrusion rate for the first layer. Or is 130% for the skirt?

my conclusion:
- increase number of skirt loops
- good to know that it can run 1-2 loops without extruding
- also good is the idea to heat the extruder after the bed
- use gloves in order not to burn fingers ;-)

*John* now a happy camper :-)

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Re: the biggest problem for me is....

Post by geneb »

I bought a number of rough washcloths that I use both to protect the bed while I'm working on the hot end and to wipe off the nozzle before a print. They work great. :)

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Captain Starfish
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Re: the biggest problem for me is....

Post by Captain Starfish »

Johncoffee, I'm on the other side of the country from my machine for work at the moment or I'd tell you which page the first layer % setting was on. Have a good dig around in the settings, it's there I promise!

Glad to hear you're up and running a bit happier.

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Span24
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Re: the biggest problem for me is....

Post by Span24 »

Green Scotch-Brite pads with the green pad on one side and yellow sponge on the other, such as can be found at Wal-Mart, work great to 'swipe off' that glob of ooze which can form just before printing starts. It also helps keep the nozzle shiny and bright!
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Johncoffee
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Re: the biggest problem for me is....

Post by Johncoffee »

Thanks for the nice tip Span24!

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