Does alternating between PLA and ABS feed clog the nozzle?

The last time I had a clogged nozzle was over a year ago on my first printer (Mendel). After printing strictly with ABS, I have not had a clogged nozzle since then on this printer after printing over 40 lbs of ABS. This weekend, my second printer (Prusa i2) 0.35 mm nozzle became partially clogged. It was skipping steps at speeds that it was able to do earlier and the extruded ABS filament diameter was reduced from around 0.40 to around 0.35 mm or less in air. When I manually push on the feed, it required a lot more force to extrude.

Since I had some leftover and some sample PLA from Ultimachine, I had been alternating it with ABS. I've noticed that PLA gets very sticky when printed at very thin layer on the PET taped heated bed. This is very hard to remove even with acetone. I wonder if mixing PLA with ABS in the nozzle is also causing residues to build up in the nozzle eventually decreasing the hole diameter. Has anyone else experienced this? Is anyone here succesful in alternating PLA and ABS feed on the same nozzle without clogging?

... really short answer - yes!

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Viktor
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I don't switch anymore, different extruders for different materials. One of the reasons I made the quick fit x carriage.

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[richrap.blogspot.com]

I think it depends on you hot end, to some extent. If you have a chamber in the heater block like the mendel-parts V6 (not a good idea, I think), you'll never get all the ABS out. I have a mendel-parts v9, which is brass straight through with a small PEEK heat break, and I have swapped from ABS to PLA with that successfully. I also have a Reifsnyder Mk4, which uses a PTFE liner, but haven't tried swapping on that - I think the ABS could adhere between/around the joint between the PTFE liner and the brass.

On the m-p v9, to clean out the ABS, I set the temperature to 230C (the temperature I usually extrude ABS at) with PLA in the extruder, then as soon as it gets to temperature I extrude to push out any remaining ABS, then extrude a fair amount of PLA (like 50mm) before reducing the temperature to a more normal 190C. PLA doesn't like sitting at 230C temperature! My unproved assumption is that this should melt any ABS and take it out with the PLA. However, I do have a 0.5mm nozzle, which probably helps. Also, this hot end generally allows me to extract the filament down to the nozzle; if I drop the nozzle temperature to 130C for ABS and 80C for PLA, I can generally pull it back out from the extruder. I haven't found this as easy to do with the Reifsnyder and PLA (don't use ABS in that).

... AFAIK the problem starts when switching from PLA to ABS, as the residues of PLA will create some hard/crystallized structures around the output and block the stream with the higher temperatures used for ABS.

Changing from ABS to PLA shouldn't be a problem ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Are there suitable solvents for PLA that can be used to clear the extruder head prior to swapping filament (ie, acetone is to ABS, as ??? is to PLA)?

... AFAIK dichloromethane, but it's toxic and should be avoided

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

loverly. I had contemplated using the same nozzle for both, but based on that, I think I'll maybe just buy a second nozzle when the time comes. Not adverse to the use of methyl chloride under certain circumstances, but it seems more prudent long term to use a "pristine" nozzle for each if I have the option.

thanks for the info

VDX Wrote:
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> ... AFAIK dichloromethane, but it's toxic and
> should be avoided


This would also be quite inconvenient without removing the hot end.

I don't think solvents would dissolve PLA residues that have formed from the decomposition of the polymer that has been overheated. It probably need to be removed physically using a drill bit or by burning it completely with a torch.

droftarts Wrote:
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> Also, this hot end generally
> allows me to extract the filament down to the
> nozzle; if I drop the nozzle temperature to 130C
> for ABS and 80C for PLA, I can generally pull it
> back out from the extruder. I haven't found this
> as easy to do with the Reifsnyder and PLA (don't
> use ABS in that).

I haven't done ABS on a J-Head, but I find I can get all traces of PLA out by letting it sit for a while at 65C before yanking the filament out. Some baked-on crud usually comes along with it as a bonus.

i tried ABS for the 1st time last week with my .35 j-head

after having hassel i decided to just go back with PLA for many reasons

thinking this may happen what i did was leave the hotend at 230c and run like 2 M of PLA hoping it would clear out the ABS

WRONG

so far after 2 weeks iv had around 3 jams now

you will find your steps just plummit and extruding it just rubbish.

what i have been doing to clear is set hotend at 230C then push hard as possible down with PLA

you will get a lot of black old burnt up ABS pop out then will run clear with ABS

other then this (which i wil do next time i clear out my hotend)

take your j-head apart and leave the hotend brass part in aceton for a night or two

if i ever try ABS again will 100% be using a seperate hotend !

Quote
Enlightx
take your j-head apart and leave the hotend brass part in aceton for a night or two

This probably won't get rid of burned PLA or ABS since they're insoluble. A blow torch worked well for me in the past.

haha, just don't use mapp gas... I learned my lesson!

I switch between PLA and ABS on a daily basis without incident. I think problems people are having are more to do with bad nozzle temperature regulation than anything else.

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www.Fablicator.com

I don't think my J-head has any temperature regulation issue. I do notice that under normal operating temperature (230 for ABS and 210-215 for PLA), plastic that gets stuck on the outside surface of the nozzle/heating block will eventually turn black. If I don't clean the plastic off the surface of the hot end, bits of black stuff tend to be deposited in the print. This suggests that even at these temperature, the plastic is slowly decomposing.Thus, I don't think that it's necessary to overheat the nozzle to clog it. In fact, I once left my nozzle at operating temperature overnight with ABS overnight without printing and it was partially clogged the next day. Luckily, I was able to clear it with a syringe needle.

I can switch back and forth no problem, ever.

Just make sure you use the higher of the two melting point until all traces of the previous plastic are gone.

I always clean my nozzle out, ABS or PLA, by first making sure most of the plastic is removed from the inside and then dipping a coffee filter in acetone and scrubbing it out. Acetone does soften PLA up to a point but you have to be aggressive.

After cleaning the nozzle with a propane torch and isopropanol, it's still behaving the same. I looked through the nozzle after cleaning it and it looked clear to me although I didn't have a drill or anything that measures 0.35 mm to stick to it to verify. So for now, it seems that I didn't clog this nozzle by switching back and forth between PLA and ABS many times. The extruded filament size is still the same. So, now I'm not sure what has changed.

There was a little bit of PLA that had leaked past the seal between the PTFE and j-head, but it was very little and it didn't look like it would have affect performance. When I first put it together after cleaning, I looked at the feed after extruding some plastic by hand and pulling it out an noticed a little bit getting into the gap in the PTFE. So, I tightened it some more (while hot) and did the same thing until there were no signs of it. At that point, the feed can still slide in all the way to the nozzle freely.

We really need to quantify the force needed to extrude to make it easier to diagnose problems with the hot end and cold end.

The hot end is functioning again. It turned out to be the teflon tubing inner lining.I stuck the opposite end of closest fitting drill bit and found that it didn't go all the way through the tubing, It was tighter in the part that overlaps with the hot end. So, after removing the teflon tubing, I used the drill bit to enlarge the hole again. This did the trick.

So, in conclusion, switching PLA and ABS did not clog up my nozzle after all. It seems to have resulted from the teflon lining deforming over time resulting in the hole getting smaller near the hot end.

I’ve sliced the end of the tubing insert into 4 slits on the bottom 2mm of tubing that goes into barrel. this seems to increase life of tubing, otherwise it eventually molds to the shape of the inside of the nozzle, and shrinks its hole size below 3mm. this way when the end shrinks it is pushed apart by the feedstock. since I started the slits I've only had to change the nozzle 1 time on that machine, and it was because of some tiny rock or dirt that jammed it. Also that reminds me use a sponge filter before feedstock enters extruder. If anything color will remain consistent