new pla calibration

I have just taken delivery of a new batch of pla and am struggling to get a decent print from it.
Is there a recommended sequence of steps I would benefit from to get it calibrated?
Parameters I've been changing.
Temperature, old pla was 220 new seems about 180!
Does not stick to glass as well, increased bed temp from 45 to 55
Seems to ooze a lot so increased feed rate and reduced flow rate

> Parameters I've been changing.
> Temperature, old pla was 220 new seems about 180!

Is it a different brand / color?

> Seems to ooze a lot so increased feed rate and
> reduced flow rate

This makes no sense. You should never change them separately unless you want more/less plastic.

What speed are you printing at?

What kind of hotend?

Do you purge all the air / molten plastic from the hotend before starting to print?

Are you sure the first stuff was PLA?

The only settings you should ever have to change when changing filament are: filament diameter and temperature. Some times you may need different bridge settings, but that is not your current issue.

I am sure you have read this a lot but you should really try slic3r. It is far easier than Skeinforge and as of 0.7.0 it makes better parts IMHO.

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If it oozing a lot it might need drying. PLA absorbs moisture in a humid environment. Did it come in a sealed bag?

If the temperature is too high it comes out like syrup and oozes under gravity.

To get it to stick to glass you could try a higher bed temperature for the first layer. I use 90C. And / or you might use a higher nozzle temperature for the first layer.

Edited 1 time(s). Last edit at 03/07/2012 06:13PM by nophead.

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For PLA, 70'C-80'C works better on glass. At least that has been my experience with PLA from Ultimachine.

your feed and flow rates should always be the same, you should re-calibrate your e-steps/mm and or change the filament packing density to 1.

My hotbed temp for pla is 80ºC for the first layer then 60º for the rest of the print.

Thanks for comments
I think the main problem was the first metre or so was inconsistent it seems to have settled down now.
This batch does seem reluctant to stick to the glass so I am having to increase the bed temp substantially.
A few questions though
Can you have the bed too hot? Obviously not so it melts the PLA but will it hinder rather than help if it gets too hot.

Quote

Are you sure the first stuff was PLA?

How can you tell? I've only used PLA and a very small amount at that.
I can't see any settings in skeinforge or slic3r to alter the bed temp after the first layer so my solution would be

M190 S63 ; set bed temp & wait
M140 S70 ; set final bed temp
M104 S200 ; set extruder temp
M116 ; wait for both temps to be reached
M140 S40 ; set bed temp for rest of print (assume the 70deg will only drop slowly so ok for the 1st layers.)

Yes the bed can be too hot, but the first layer is different from the rest.

PLA has has a high melting point, around 160C (where it becomes a viscous liquid) but it also has a low glass transition at about 55C where it becomes like rubber and a when a bit hotter; jelly.

I find a high temperature (90C) for the first layer makes it stick well but after that it has to be just below the glass transition, otherwise the base remains like jelly and gets distorted by the contraction of the layers above until it peels. I use 60C, measured under the bed, so the top is likely below 55C.

The higher the first layer temperature is the better it sticks, but it obviously has to be less than the melting point. Also extruding the plastic a little hotter on the first layer helps. For subsequent layers, the closer it is to the glass transition the bigger the object you can make without it warping, but it has to be below Tg.

Edited 1 time(s). Last edit at 03/11/2012 10:52AM by nophead.

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Still having problems with the first layer.
Perimeters go down ok (but are they too squashed?)
When the infill is being done the head will sometimes plough through the layers and distort/move the print.
See attached image which I hope may help someone diagnose my problem(s).
Thanks.

P.S. if the first layer is successful then the rest of the print is fine.

http://www.thingiverse.com/thing:19468

Edited 1 time(s). Last edit at 03/19/2012 03:13PM by glyn.

If you think you are extruding too much material, you can fudge it and increase the filament diameter by 0.1 mm or the filament packing density by 0.05 (5%). This will result in less material extruded.

Well I think I have solved it.
I think it was just a case of the head being too close to the bed on the first layer. I follow the standard procedure for bed levelling but the skeinforge default bottom setting seems too low so I now have settings of :-
Additional Height over Layer Thickness = 1.5
Altitude = 0
which works a lot better.