Talpadk’s Blog

January 4, 2015

Printing in PolyProlylene

Filed under: 3D Printing — talpadk @ 6:43 pm
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Bowl printed in PP

PP bowl printed on a piece of cutting board

I recently purchased a small sample of white polypropylene (PP) plastic from a shop in China.

While it was relatively expensive at ~$11 for 200g worth of plastic it allowed me to try out printing in PP without buying an entire spool of filament.
And since it isn’t supposed to be the easiest thing to print due to a thermal contraction that should make it more warp prone than ABS and additionally is slightly slippery and doesn’t stick that well to other materials.

You may then ask why I would want to attempt to print in PP then, after all PLA prints just fine… well sort of anyway.

Polypropylene is/has the following features:

  • Relatively heat resistant, plastic handles on dishwasher safe cutlery are for instance often made of it.
  • Good chemical resistance.
  • Handles bending and flexing relatively well, living hinges can be made of it.
  • Is relatively soft, not always a good thing.

Well back to the printing business…

For the experiments I used my trusty RepRapPro Huxley with a smaller 0.3mm nozzle more on that later.
Yes I really should get that Mendle90 build, that would have allowed me to borrow some 3mm PP welding rod from work.

Anyway I’m by far not the first to print in polypropylene, but as with NinjaFlex I though it could use another post on the internet about the material.(Some links to “prior art”: RapMan wiki and a forum post)

While it seemed that PP and especially HDPE are good candidates for the print bed I had to try out polyimide and some generic blue masking tape as well.
As I expected they didn’t seem to work too well for me. But didn’t experiment too much with them.

I there for proceeded and bought some cheap plastic cutting boards from Biltema.
They don’t specify the type of plastic but they don’t feel very much like PP so I assume they are made of HDPE.

Once cut to size I actually managed to print unheated onto the 5mm thick sheet of plastic!
Some of the prints actually stuck too good to the print bed and got damaged while being removed.

I also encountered some problems with jams/the plastic coiling up inside extruder.
This led me to increasing the extrusion temperature to 235C and reduce the speed down to 15/20 mm/s for the perimeter/infill.
In an attempt to reduce the print bed adhesion I used a lower 225C for the first layer.

In hindsight increasing the temperature might not have been necessary, at least when manually pushing PP@235C and PLA@215C the pressure seems to be in the same range.
The extruder problems may simply be caused by the PP filament being softer than PLA.
Reducing the speed print might have been enough.

As some of the prints had left thin layers of PP on the print bed surface and new prints stuck annoyingly well to those spots I decided to try to sand the surface.
This removed both the PP residue and the grid of ridges in the plastic due to it’s cutting board origin.After this the surface seemed to be less problematic with regard to local over sticking.

I have yet to attempt to heat up this print surface, as I have previous had bad a experience with an experiment using a SAN sheet that warped badly when heated.
Besides it actually looks quite promising to use the print bed unheated.

While the chopping board isn’t that bad or expensive it is 5mm thick which is too much for my bulldog clips to handle.
I therefore looked for alternative sources of PP and PE.

The next experiment involved plastic wrap.
Here in Denmark PVC based warps have fallen out of favour and been replaced by PE based products (Assumed to be LDPE as it is soft).

The wrap was applied to a mirror surface and clamped onto the regular print bed.
The first unheated print had way too much warping.
I then cleaned the wrap using rubbing alcohol (which visually roughened the surface a little) and may have heated the bed to 90C.This resulted in a slightly better print but not quite as good as the chopping board.
Plastic wrap may be promising but I quickly stopped playing with it as it would probably have to be glued to the glass which would complicate the process.

PP printed on tape

PP printed on tape

Next up was packaging tape.
At least some of it are made of PP, biltema has some brown tape that is I did however just use some clear stuff I had laying in the drawer.

The first unheated on glass attempt had too little adhesion.
I then roughed the surface using a scouring pad and heated the bed to 70C which made the part stick relatively well to the tape.

Thoughts and notes:

  • Running the extruder at 235C might be too warm (stringing in the bowl print)
  • Maybe the glass surface conducts too much heat away too fast, might be why the cutting board sticks so well unheated?
    Perhaps experiment with a more insulating/lower heat capacity base material.
  • For flexible/soft materials I expect it is better with a thicker filament as it is harder to curl up inside the extruder
    (Note to self: Find time to build that mendel90)
  • Also for softer materials I probably ought to switch to my 0.5mm nozzle.
  • Tape based print bed materials have an advantage over solid ones, if the print is really stuck pealing the tape off might help to remove the part without damaging it.
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April 20, 2014

Measuring printbed tempeartures on a RepRapPro Huxley

Filed under: 3D Printing — talpadk @ 4:13 pm
Tags: ,

I have finally gotten around to measuring the surface temperature of my Huxley.

Temperature as function of set-point

Temperature as function of set-point

Method and instruments used

For measuring the temperature a Agilent U1233A with a U11186A (k type thermocouple) has used.

The ambient temperature has measured by waiting for the display to settle and the taking a readout.

The heat bed temperatures has measured on top of the aluminium print surface with the polyarmide tape left in place.
The thermocouple was held in place by another piece of polyarmide tape.

The thermocouple was left on the print bed for 1 minute for the temperature to stabilize, the temperature was then measured on  the multimeter using the “avg” function after a 2 minute sampling period.

Measurements

The temperatures were measured at the centre and approximately 1cm from the edge.
The center temperature was measured an additional time at the end of the measurement cycle.
The print bed was in its forward position with the print head to the left at the end stop (cooling fan running)

The ambient temperature was measured as 22.1C at start of the surface scan, and 24.4C at the end.
The heat bed has maintained at 85C using the 3d printer firmware.

NA 71.2C 75.8C
77.6C 71.1C
76.1C
75.2C
 75.6C  77.1C  72.8C

After this the thermocouple was reapplied using a fresh piece of polyarmide tape at the centre of the print bed and left there.
The print bed set point was then reduced and the surface temperature measured.

Set point [C] Measured [C] Percentage
85 76.2 90
70 63.1 90
55 50.2 91
40 37.8 95

Notes

Some of the variances in the measurements across the bed might be related probe mounting relative to the surface and cooling to ambient.
Using a piece of foam or another insulator might improve this.
The lower measurement points may simply be caused by a bad thermal contact to the print bed.
Heat sink compound could perhaps have alliviated some of this as well (and made a lot of mess).

Also even though the measurements was taken as a 2 minute average, the temperature swings of the heat bed regulation may have contributed with some noise.

Also a thermal camera would have made this much easier and quicker, too bad they are so expensive.
(And that Fluke VT02/VT04 visual thermometers has such a bad resolution)

Conclusion

I would consider the bed temperature constant across the print bed within the uncertainty of my measurements.

At “higher” temperatures the surface temperature seems to be roughly 90% of the set point.

February 21, 2014

Antialiased openscad rendering

Filed under: 3D Printing — talpadk @ 10:48 am
Tags: , , , ,

OpenSCAD rendering

Std. 512x512 OpenSCAD rendering

Std. 512×512 OpenSCAD rendering

Recent versions of OpenSCAD is capable of rendering objects/assemblies to images.
To the right there is an example of the default 512×512 image quality produced by the command:

openscad -o render.png assembly.scad

Below it is an anti-aliased version of the same scad file.
I used the common trick of generating an oversized image and downscaling it.
It was created with the following two commands:

openscad -o render.png  --imgsize=2048,2048 assembly.scad
convert render.png -resize 512x512 render.png

If you update your project renderings using a makefile/script I don’t consider it much of a hassle considering the improvement in image quality.
Also at least on my laptop with the currently relativity simple scad file rendering is still fast.

2048x2048 OpenSCAD render downscaled to 512x512

2048×2048 OpenSCAD render downscaled to 512×512

In case you are wondering the assembly is a new CNC mill I’m designing.
Which hopefully is an improvement over the last design.

The old design is available HERE
The new design is being created HERE

Unlike the old design the new one is being pre-assembled in openscad, hopefully preventing having to print parts that only fitted together in my head, saving both time and plastic.

Both designs are hosted on Cubehero, my favourite site for sharing designs on.
It comes with build in version control though git (it also has a web interface for “kittens”)
Wil that runs the site is a friendly and helpful guy, and it is not bogged down with stupid End User License Agreements like another site…
I highly recommend it…

October 10, 2013

3D printing using Ninja Flex filament

Filed under: 3D Printing — talpadk @ 7:53 pm
Tags: , ,

Yesterday I received some of the relatively new “Ninja Flex” filament sold by http://www.fennerdrives.com/ 

As the internet doesn’t seem to overflow with print reviews / settings for it yet I decided to post some words about it.

NinjaFlex Sapphire 1.75mm

NinjaFlex Sapphire 1.75mm

The Filament

It is always difficult to measure a soft material but using my caliber I measured the diameter to be 1.75mm as it is supposed to.
The filament also seems to be nice and round.

I ordered the “sapphire” version of the filament, and it has a nice (mat) blue color  which turns glossy when printed.
It is also slightly translucent when printed thinly.

The filament is very flexible (I can tie a tight knot on it without it breaking)
The filament is also elastic but not as much a a regular rubber band… perhaps 5-8 times harder if I should make a guess.

The material is not known to me, but I strongly suspect it to be polyurethane (PUR) with a surface coating/treatment to make it less sticky.
Fennerdrives already produces PUR belting  which have been used in 3D printing prior to this material appearing and due to the mat to glossy change.
(Update: it has been confirmed that it is polyurethane)

The Fennerdrives recommended settings are:

Recommended extruder temperature: 210 – 225°C
Recommended platform temperature: 30 – 40°C

The filament isn’t exactly cheap I would say roughly 3x the cost of PLA/ABS including shipping compared to the cheap PLA/ABS I normally buy.
Then again soft/specialty filaments doesn’t seem to come cheaply normally.
(Actually a lot of the cost comes from the somewhat expensive USP shipping)

Fennerdrives does ship both from the US and the UK, living in Denmark (inside the EU) this is a big plus for me.

3D model for the rubber feet

3D model for the rubber feet

The test prints

As I’m currently designing and building a tabletop CNC mill I thought that I might as well print some rubber feet for it.

The print isn’t necessarily the simplest one to print due to the outwards sloping unsupported  walls.
However the angle is quite close to vertical and wouldn’t normally be causing problems.

The 3D model was created using FreeCAD which is my preferred open source CAD package.

I used Slic3r for generating the G-code.

And my printer is a RepRapPro Huxly which has a bowden extruder which might actually not be ideal for extruding a soft and springy filament.

Print 1

Was done using my regular PLA/ABS profile.

I had to abort the very first attempt as the filament wasn’t printed continually.

  • I increased the extrude temperature from the low temp that felt right while manually extruding the filament
  • Reduced the speed using the M220 command
  • And upped the heat bed temperature to 85 deg C

Much to my amazement the rubber foot actually printed sort of  okay.
It was however sticking so hard to the “Kapton” tape that removing it actually pulled the tape off the print bed!

Prints 1 though 4

Prints 1 though 4

Print 2

I then tried to create a specific profile for printing the rubber filament.

  • Reduced the printing speeds to avoid having to scale them using the M220 command
  • Removed the “Kapton” tape as it had become wrinkled any way
  • Printed without having heat on the bare aluminium print bed.

It printed with roughly the same quality at the first print but was very very easy to remove.

Print 3

I noticed that the hot end seemed quite “laggy” probably caused by the flexible nature of the filament and i therefore made some additional changes.

  • All print speeds were set to 15 mm/s to avoid having the extruder changing speed
  • Retract was disabled, again to keep a constant pressure in the hot end
  • “Skirt loops” was increased to 4, to give the hot end more time to build up a constant pressure.
  • Infill was reduced from 50% to 0% to see if the vibrations caused the surface defects
  • The hot bed was set to 40 deg C

Just after starting the print I realized that setting infill to 0% would cause some parts to be printed in mid air with nothing supporting them from below.
Out of curiosity I did however allow the print to continue.

The printer managed to print the part despite the fact that is was “unprintable”…
Also the surface finish was very satisfying.

Due to the 0% infill the part was slightly softer as was to be expected

Print 4

I don’t like printing the impossible as it may or may not succeed I made one small change

  •  I changed the infill back to 50%

I’m pleased to report that the surface finish seems to be just as good as before.

Printer settings

Please keep in mind that  printer settings varies from printer to printer and that the one described here may not be optimal even for my own printer.

The following list is semi sorted by what “I think is probably the most important settings”

  • No retract
  • Uniform print speed (of 15 mm/s)
  • Multi loop skrit (4 loops)
  • Hot end temperature 240 deg C
  • Print bed temperature 40 deg C
  • Travel speed 100 mm/s
  • Extrusion width 0.5 mm with a 0.5 mm nozzle
  • First layer 50% (might actually be a bad idea)
  • Layer height 0.3 mm

Again while reading this keep in mind that I haven’t played very much with the temperatures.

I had some undocumented failures after print 1 where the extruder/hot end seemed to jam and I haven’t dared reducing the temperature again as I needed/wanted some functional prints.
The problems may however be related to too fast extrusions, filament loading and or the filament being deformed by the retracts.

My prints was stringing slightly internally lowering the temp may be able to reduce this…

 

Edits

  • It has been confirmed by the friendly customer support at Fennerdrives that the material is actually polyurethane.
  • Even without any heat on the hotbed it still sticks very very well to “Kapton”

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