printing soft PLA

A few months ago I read about a sort of PLA in the reprap forum which is more soft and less rigid.
Still PLA but polymerized in a different way and though with different physical characteristics.

Then last Friday I opened a package containing this soft PLA. And the PLA is like rubber - better than expected.
Not as elastic as rubber but comparable to any other soft plastic.
Some printing tests quickly showed: This is not like the PLA I'm used to print. You need a higher printing temperature,
you have to print much slower and it is more sticky to the NOPI tape.

After tweaking my mendel the first real usable object appeared:



And it's elasticity is incredible. You can't do things like this with rigid PLA or with ABS:



The problem was, that it glued like a chewing gum to the NOPI tape so you can't get it off without destroying the printed object.



In case of a mendel spring it is no problem, but of course I had to change to a different tape.
After testing kapton tape, textile tape, normal sticky tape and canvas film I - fortunately - forgot to change to a different tape before starting the print
and printed directly onto the glass printbed. I recognized the lack of tape but didn't abort the print - and this was the best idea :-)

Printed on glass - without headbed! - it sticks perfectly and is easy to remove.



After testing a few times how fast you can print this soft PLA I found out that there is a upper limitation of about 19 mm/s - independent of the flow rate.
Every print above this speed breaks if you squeeze it.
A good printing temperature is around 210 °C although the distributor reported a melting temperature of 270 °C.

All in all this mendel spring is an improvement to the ones printed with ABS and I'm looking forward to other things made of this soft PLA.

Greetings from the lake of constance

BonsaiBrain

P.S.: You can buy a roll of this PLA at our shop: www.2printbeta.de

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bowden-cable modification

Hi there!

I want to use two nozzles on one carriage to be able to print with support sometime in the future.
There is not enough space on a normal x-carriage for 2 extruders and our current enhanced x-carriage has the disadvantage that the two noozles are 7.8 cm away from each other. This shrinkes the space on the printbed, which is reachable with both heads, extremely.

On my mission to improve my mendel I tried a bowden-cable for separating the extruders from the x-carriage.

This makes it possible to place 2 noozles closer to each other because most of the space is used by the motors of the extruders.




The problem of this bowden-cabe is the higher friction of the filament in the cable, because it has no PTFE or teflon inside.
To be able to push the filament through the bowden cable I changed the gears on the WADE-extruder.
The former ratio was 11:39, now it is 9:47. That means I can now push with factor 1.5.



This is still not enough for printing with ABS. The wheel of the motor spins back due to the high friction in the bowden-cable.
To print with ABS you would need to insert a third gear to get more force.

But fortunately the friction of PLA is lower. The lower melting temperature makes it easier to push it through the noozle so it is possibe to print with low speed.

Next I tried to calculate fitting skeinforge settings to print with the bowden-cable installed.
The pulling-back of the filament at the end of a line is not that easy as without a bowden-cable. It makes no sense if the distance is more than 1 cm.
A little pulling-back is still needed, otherwise the flow of the filament creates very ugly bulges.

The normal problems appeared when you change from ABS to PLA. The first prints looked like modern art objects.
Very disappointed and not remembering that the strange look could be ABS relicts I almost gave up.



But then I changed the setup several times until the prints looked quite ok.

This are the first results:



Next step is the installation of the second bowden-cable made out of PTFE.
I hope that this will work with ABS, so my mendel will be finally ready to print with ABS and PLA on the whole printbed space.

Greetings from the lake of constance
BonsaiBrain

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