Extruding - Non-sticking PLA- a bundle of questions

Hi,

My Mendel progress is plodding forward but I've reached a stage where I can't quite work out what my main hurdle(s) are.

My extruder works (when I'm not jamming it) and extrudes PLA. However, it's not sticking to the print bed at all. I've a few thoughts on possible causes and related questions. Any help very much appreciated. I feel I'm soooooo close!

BTW - My print bed in heated (seemed to be running at about 50 deg C, so I probably need to turn that up a bit?)

1) How close should the nozzle head be to the print bed when it starts to print?
I imagine very close (e.g. 1 layer thickness?)

Also, If the nozzle was quite high (e.g. 0.5-1cm from the bed) and I extruding some PLA onto the bed, should I expect that to stick or would it have cooled so much by the time it hits the bed that it's too solid to stick?

2) Could PLA not sticking to the bed (when extruded right onto it) be a sign that my extrusion temperature is too low (even though it is liquid enough to be successfully extruded). I think I'm extruding at about 185 deg C though I'm being cautious after several burned filiments jamming the nozzle (maybe too cautious)

3) When I extrude the extruded PLA often curls round and sticks to the nozzle (instead of falling vertically downwards). Could be a sign that my extrusion temperature is too low (or just junk inside the nozzle)?

4) I'm using RepSnapper. In the 'Print Options' tab (not 'Print' tab) there's a slider to change the "Extrusion Multiplier". Does increasing this value cause more or less filament to be extruded?
Any thoughts on good/standard settings?
(I measured my extruders rate for drawing in filament and calculated the extruded rate from that. I then modified the EE_STEPS_PER_MM by a suitable ratio, so that should be right (17.2))

5) In the 'Print' tab (not 'Print Options' tab) there's a slider to change the "Downstream Speed Multiplier". What is this?
There's also "Downstream Extrusion Multiplier". What is this? Does increasing this value cause more or less filament to be extruded?
If I extrude 'manually' from RepSnapper I can set the "extrusion length". What is that measured in? Motor steps, perhaps?? (it's turn much to be mm)

As always, that's for all 'bleedin' obvious (and otherwise) answers

Thanks

Pete

Hi,

Sadly I haven't time to go through each of your questions right now - but regarding #1 the nozzle should be almost touching the platform - as you say approximately 1 layer high. So I presume that your next sentence contains a typo and you don't mean "0.5-1cm", but rather 0.5-1mm. The former is waaay too high.

And re: #3 - I found that gunk in the nozzle will cause the extrusions going in every direction but down. I personally use a thin wire to make sure there are no blockages.

For what it's worth, i'm printing PLA at ~195°C without a heated bed and it usually sticks fine when the nozzle is the correct height above the bed. A trick that can help (if you're using Skeinforge) is to set the Bottom and Raft modules on, but set the layer height of the raft to zero. This makes no raft but the first layer goes on slower which can help it stick.

Hope this helps.

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net

Gary,

Cheers for that. I did really mean cm (not mm). I'm interested to know if general expectation is that 'falling' 0.5 cm will cause it enough to solidify. I imagine so, but want to check my assumptions. But 'waaay too high' answers that I guess.

So, my hieght (right on bed) is OK - good!
Gunk in nozzle is probably a problem - will give it a scrub (and that wire is a god idea)
Sounds like I should try higher temp (and mentally prepare for some Jamage

I haven't tried Skienforge yet. I plan too but wanted to work with a simple interface (RepSnapper) first.

Cheers

Pete

Flackster Wrote:
-------------------------------------------------------

> BTW - My print bed in heated (seemed to be running
> at about 50 deg C, so I probably need to turn that
> up a bit?)

Try 55 deg C and make sure you are extruding onto something not just bare Aluminium?

>
> 1) How close should the nozzle head be to the
> print bed when it starts to print?
> I imagine very close (e.g. 1 layer thickness?)

With a 0.5mm nozzle you want to be about 0.2 to 0.3mm max from the bed, you can use sheets of office paper to 'feel for the gap' or use a gauge / blade etc.

>
> Also, If the nozzle was quite high (e.g. 0.5-1cm
> from the bed) and I extruding some PLA onto the
> bed, should I expect that to stick or would it
> have cooled so much by the time it hits the bed
> that it's too solid to stick?

No, it will not stick, but the heated bed will heat it back up and start to bond the blob poorly. It will cool very quickly in free air.

>
> 2) Could PLA not sticking to the bed (when
> extruded right onto it) be a sign that my
> extrusion temperature is too low (even though it
> is liquid enough to be successfully extruded). I
> think I'm extruding at about 185 deg C though I'm
> being cautious after several burned filiments
> jamming the nozzle (maybe too cautious)

Yes, check what real temperature you have inside the extruder hot-end, your thermistor will be reporting something, but you need to calibrate what it's reporting with what you actually have at the hot-end. the temperature is quite important with PLA, I'm extruding at 193 deg C.

>
> 3) When I extrude the extruded PLA often curls
> round and sticks to the nozzle (instead of falling
> vertically downwards). Could be a sign that my
> extrusion temperature is too low (or just junk
> inside the nozzle)?
>

That's normal, depending on how fast you are running the extruder you will get little loops, curls and general madness of the extruded filament when being done in free-air, usually if you pull it down so a blob is hanging then you will get a nice extruded straight line of filament all at a nice even thickness (if your extruder is running well).

> 4) I'm using RepSnapper. In the 'Print Options'
> tab (not 'Print' tab) there's a slider to change
> the "Extrusion Multiplier". Does increasing this
> value cause more or less filament to be extruded?
> Any thoughts on good/standard settings?
> (I measured my extruders rate for drawing in
> filament and calculated the extruded rate from
> that. I then modified the EE_STEPS_PER_MM by a
> suitable ratio, so that should be right (17.2))
>
> 5) In the 'Print' tab (not 'Print Options' tab)
> there's a slider to change the "Downstream Speed
> Multiplier". What is this?
> There's also "Downstream Extrusion Multiplier".
> What is this? Does increasing this value cause
> more or less filament to be extruded?
> If I extrude 'manually' from RepSnapper I can set
> the "extrusion length". What is that measured in?
> Motor steps, perhaps?? (it's turn much to be mm)
>
> As always, that's for all 'bleedin' obvious (and
> otherwise) answers
>
> Thanks
>
> Pete

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[richrap.blogspot.com]

Ideal surfaces for a heated bed are Glass, Kapton Tape, and Blue Painters Tape, in that order.

Bare Aluminum will not stick, hot or cold. It robs the extruded filament of heat immediately on contact due to its high thermal conductivity.

I have only recently begun extruding directly on glass (aka Pyrex, or BoroSilicate Glass), and it sticks better than Kapton when heated, and releases easier when cold.