PLA 45 problems - solved

[amont 0]

I bought a spool of PLA 45 in the hope of achieving dimensionally accurate prints on my UM2 but have had no success with it.

In fact it has produced amongst the worst prints I have ever had, greatly distorted and the bottom of the prints lifting to such an extent that the surface turns into one large curve. This in turn means that they refuse to remain attached to the glass and I find a tangled mess being dragged around the build plate.

There is nothing on the Orbi-tech website that helps.

Does anyone out there have successful experience of PLA 45 who can tell me what settings they used?

Ironically, and contrary to all advice, by far the best material I have used so far has been cheaper stuff bought on Ebay. It is harder and more brittle than the more expensive brands and because of this combined with the fact it is sold on spools with too small a diameter it breaks into 50-60mm lengths when getting towards the end of the roll.

BUT...... when it works it produces the best surface finish with no dimensional distortion that I can detect. No lifting, no partially printed layers, no 'waist' 1-4mm up from the build plate. This may have something to do with the fact that it is a harder material. If I cannot get better results with the more expensive brands I will have to revert to using it and accept that I have discard the end of the role. I doubt it will work out any more expensive (1kg v 100m, free delivery, etc). Colour is not important to me (although white or light grey is best for examining the results).

Further to the discussion started by Shurik 'Seeking advice on print settings' and the subsequent replies I would be delighted if Ultimaker or an experienced user would produce a cheat sheet. This has been raised before but seems to have come to nothing.

I realize that there is no 'one size fits all' solution but at least a starting point for the various settings for various materials, perhaps in the form of a table, would help.

Also some basic introduction as to how the various settings influence the output.

I also appreciate that for many tinkering with these machines is a major part of the enjoyment of having them but as much as I enjoy using my UM2 I need to get things made and spending hours scouring google for the odd bit of information here or there is not a good use of my time.

I hope someone can help.

Thanks for reading.

 

[gr5 2,271]

I've never used PLA45 and haven't heard much about it but it sounds like it is meant to be printed on a cold bed. I would keep the bed below 45C (I assume that's the glass temp) and maybe even keep it below 30C or just at room temperature.

This means you probably can't print on glass so I would use the roll of blue tape that comes with the UM2 (or preferably get some wider tape - I use 2" wide, illuminarti uses 6" wide blue tape).

It's important to clean the top of the blue tape with isopropyl alcohol before printing on it. This removes the wax on top and allows PLA to stick to it better.

It also sounds like it was invented before heated beds were common and it's possible that all PLAs out there are "low shrink" compared to ABS and the whole product is not any better than modern PLA formulations. But I really don't know.

I hope you get this to work.

 

[gr5 2,271]

prints lifting to such an extent that the surface turns into one large curve.

 

For regular PLA I would say the bed should be at 70C and you should add gluestick. For prints larger than 5 inches across you should use 1 part wood glue mixed with 3 parts water, mix well, paint on with a paint brush, and let dry as the bed heats up (takes about the same amount of time to dry as the bed to heat up). Also the brim needs to look perfect - squished down and with no gaps between each stripe which means you need your bed height almost perfect. Also bottom layer should be thicker than .1mm (.2mm is good) but no thicker than .3mm. If there is a gap between the brim and the part - abort. If gap is caused by extruder clicking - bed is too close to nozzle. If gap is on every line in brim, bed is to far from nozzle.

Because the glass temp of PLA is around 50-60C, having the bed at 70C means that the part would rather deform slightly than lift off the bed. Yet 70C is cool enough that you have to push/pull very very hard to get it to deform. So usually 70C gives you a very good result on the bottom layers.

But don't try to remove the part until it is below it's glass temp. So for PLA45 it needs to cool more than regular PLA.

 

[gr5 2,271]

Something just occurred to me.

Regular PLA has a relatively linear expansion coefficient at all temperatures from 0C to 250C. In other words if you graph the density versus temperature you get a mostly straight line (a few slight deflections here and there but mostly straight).

The melting point may be around 180C but the glass temp is around 60C. Room temperature (air temperature) is typically around 22C. The shrinkage from 60C to 22C is the only part that is important. When it is above glass temp shrinkage is not so much a problem because it happens so fast, it basically happens in place and the part does not shrink but instead the volume of each individual PLA strand shrinks.

But once you cool to the glass temp, everything is solid. Further cooling puts stress on the rest of the part.

Typical shrinkage from glass temp to room temp is .3%. This is the number most injection molding designers use: 3%. It's how much it shrinks those last (approx) 40 degrees from 60 to 22.

PLA90 has a glass temp around 90C so PLA45 probably has a glass temp around 45C. The cooling from 45C to 22C is only about 20 degrees C. So it should shrink half as much (about .15%). I'm guessing. This is probably how it works - they didn't change the expansion coefficient but instead lowered the glass temp.

This also means that if you can print in a heated chamber at around 45C you should get zero shrinkage until you cool the part and the whole part should cool equally.

 

[amont 0]

Thanks for the help gr5, I have now done some successful prints.

I re-calibrated the print bed - this is something I do regularly but I did again just to be sure. But I am sure what made the difference was bringing the bed temperature down to 30C.

This was going to be my first attempt of what I thought might be several, working down the temperature range, to find a solution but in the event it worked straight away - I did not really want to get involved with tape unless I absolutely had to.

The prints are good but not really any better than what I have already achieved with regular PLA, and they are slightly flexible which does not help my cause. Also, being a natural colour, it is translucent which does not make inspecting the results any easier.

I don't think I will bother with it again.