PLA printing & clunks

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Misterc
Posts: 3
Joined: Fri Jul 31, 2015 2:34 pm

PLA printing & clunks

Post by Misterc » Sat Aug 08, 2015 11:34 am

I know there is a thread about clunking but I;m not sure if this is the same thing.

I thought I would try some PLA in my printer, I have read things on the forums about extruders getting hot and clunking etc and keeping doors and lids open and a small fan on too and opening the fan redirector switch.

so I withdrew my ABS that came with the printer and then put some new PLA in, it extruded ok. Then I set a simple job to run with a raft for a few cubes of varying sizes to see the outcome.

The print started and the clunking began, nothing came out of the nozzle. So I followed the instructions in the thread below this (after withdrawing the PLA). I had a look in the gear area etc, no dust or powder. I then treid the print job with no material in, no clunking.

I then extruded the PLA again, it started coming out the nozzle and then set the print job to run, again nothing coming out the nozzle and clunking again.

So nozzle heating and not blocked when it extrudes ok just nothing on printing, I then withdrew material again and thought I'd set the print job running again with no material and try and feed it in as it did the rafts. this worked and obviously apart from missing a bit of one of the rafts it took the material and printed with it.

There was some clunking when doing the bottom layers, nothing when doing the sides and infill and then clunking again when doing the top of the cubes. also there are small sections with no material. see picture attached.
pla-cubes2.jpg
cubes
pla-cubes2.jpg (67.19 KiB) Viewed 4063 times

Once finished I thought I would try the same job again calibrated the platform a little lower, I wanted to see if a)it was just nozzle too close and b)if it would clunk clunk on starting again.

started the print job - clunk clunk clunk wouldn't print. stopped, withdrew material, started print job again and manually fed the material in and off it went same as last time. Any clues what is causing this please ? surely I don't have to withdraw & manually feed the PLA each time I start a print ? all tips welcome.

As for the print this time with the platform calibrated one click lower there was no clunking during the prints and no omitted pla on the surface of the cube.

roller
Posts: 1622
Joined: Sat Oct 06, 2012 9:09 pm
Location: Brisbane, Australia

Re: PLA printing & clunks

Post by roller » Wed Aug 19, 2015 1:17 pm

First, have a search on the forum but use google instead of the inbuilt search because the forum search will ignore terms that are common or only 3 characters like PLA... kinda useless huh. I say that because it's been discussed a million times.

In brief ... the extruder designed is flawed for PLA. Too much heat gets into the assembly, softens the PLA too early, it buckles and jams. Then you hear the clicking.

The second problem is PLA is more brittle. When ABS jams you get a few clicks and the print continues. When PLA jams for a few clicks it shreds some of the PLA into a fine slippery dust which makes the feed more likely to fail. This jamming usually occurs on the first layer so with PLA start your first layer with a little more space and be more picky about your bed being flat.

There are mods to solve the issue. Some extruders run hotter than others and need more drastic measures. I have one of the slightly hotter ones and found Drew's air pumping mod one of the most successful but there are some simpler printed ducting mods which are easier. You might want to try them first.

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