Category Archives: 3D Printing

Smoothing out 3D printed parts

3D printed parts look cool and unique, but sometimes you want them to look like something that isn’t 3D printed.  And to achieve this, you need to cover up or smooth out the ripples caused by  the FDM process.

I ran some early experiments with scratch filling primer, but it took four to five coats before getting the smooth surface I was looking for.  And this took several days between wet-sanding and waiting for the parts to dry.

Not sure why I didn’t in the first place, but I remembered using automotive Glazing Putty when I customized my Jeep’s console to fit a VGA touchscreen.

To apply the putty, make sure you wear some nitrile gloves (the purple ones are cool because you’ll be like Depp’s version of Willy Wonka!).  This stuff is petroleum based and will eat right through regular latex gloves and might do nasty stuff to your fingers.  Anyhow… get a dab on that gloved finger and rub it into the part.  Make sure to rub against the grain so that it fills in the layer gaps.  If you get a little too much on at this stage, its ok… it just means you’ll have to do a bit more sanding at the next step.

Let the glaze dry for at least 20 minutes and then hit it with some 400 grit sandpaper until you see the high points of the layers coming back.  Then I recommend using the previously mentioned scratch filling primer as a base layer and sanding that with a 400 grit before you apply the final color.

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Awesome, inexpensive 3D printer filament

I stocked up on a bunch of filament a couple years ago, but my stock is starting to run out.  In the past I’ve mainly used plastic from Ultimachine and Faberdashery – but its gotten quite expensive ($20.00 a lb) and shipping is not cheap.

So I asked a good friend what he’s been buying lately.  He’s quite happy with the filament from Hatchbox. Its almost half the price of the other guys, comes on a spool and is available via Amazon Prime!

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Link: Hatchbox filament @ amazon.com

New solution for getting PLA to stick to your print surface

I’ve been tipped to a new solution for PLA adhesion that works incredibly well. I’ve printed objects with square corners that cover nearly the entire print bed (190mm) and it works like magic. No curling or lifted edges. Compared to Kapton on “blue tape”, it is easier to apply, has a nicer finish and is infinitely less expensive.

Solution: one (1) part white glue to ten (10) parts water. Turn up the heated bed to your PLA print temp (~60-70c). Mix the solution throughly – should look like thin milky water. Dip a folded paper towel in to get it damp, then swab the printer deck. Make sure it coats the deck evenly. Yes, it will appear streaky. Wait until the heat from the bed dries up the solution – you’ll see it go from shiny to flat/opaque.

I usually run 10-20 prints before I feel the need to re-apply. If you go days between prints, its probably a good idea to re-apply to get the standing dust off the print surface.

Yes, it is true that the glass-side finish of the prints is not as smooth at bare-glass prints – but you’ll notice that its nearly impossible to remove the parts from the glass until you let them (part and glass) cool to room temperature. I’ll take a 10% reduction in surface quality any day over a lifted print.

I’m curious to see other’s results with this method.

Dropbox and Skeinforge/Printrun

If you’re like me and sometimes print from different hosts (desktop at home, laptop remotely), then you may have run into some issues in getting your settings all synced up between those machines.

I found Dropbox to be the perfect solution.  Keep all of your profiles, alterations and models in a Dropbox directory and stop worrying about copying stuff in a scramble before you pack up your stuff for the next meet-up.

If you don’t already have a Dropbox account, get one today [link] – they are free and awesome!

Note: I’m on Mac/OSX on both my desktop and laptop.  These instructions will also work for linux.  However, I’m not sure about creating shortcuts and how reliable they can be on Windows OSes.  If you know the best way, please leave a note in the comments!  The cool thing about Dropbox is that it is cross platform and should work between mixed operating system configurations as well…

I created a 3d_printing/ directory in the Dropbox root.  Under that I have my printrun/ installation directory (with skeinforge in subdirectory below that), a 3d_objects/ directory (so that I always know where my printable models are) and most importantly, a skeinforge_settings/ directory.

I’ll address the latter mention first – as it is most important.  In the skeinforge_settings/ directory, I have copied the alterations/ and profile/ directories from the .skeiforge/ directory in my home folder.  Once that was copied, I made a symlink in my home directory (replacing the original .skeinforge directory) that points to the folder in Dropbox:

ln -s ~/Dropbox/3d_printing/skeinforge_settings ~/.skeinforge

The other important symlink is the printrun/pronterface settings file.  Copy the .pronsolerc file from your home directory into the Dropbox skeinforge setting directory, and make sure to rename it (I called it _pronsolerc) so that it won’t be hidden to the GUI file manager.  Symlink that file as well (you’ll have to remove/copy/rename the original first, of course):

ln -s ~/Dropbox/3d_printing/skeinforge_settings/_pronsolerc ~/.pronsolerc

Now… repeat this for the hosts that you plan on using as your printing hosts.

Once you’ve done this – you’ll gain two advantages over your previous setup:

  1. any change you make on any host will be automatically synced between machines.
  2. (and perhaps most important) you’ll have a revision history for your profile changes – this has saved my bacon more than I care to count

Reprap calibration: Bottom, the First Layer and Z-Home

The technical details of the bottom, or first layer, on a reprap print was something that eluded my understanding when I first started working with my printer.  Here’s my best understanding of the subject, as it relates to your reprap (or repstrap or TOM) and your slicing software.  I focus on skeinforge in particular.

First off, we should focus on what the software and your controller board will think is the Home or zero position.  Most tutorials say the print head should be “the width of a piece of paper” above your print platform when to Z-home endstop is engaged. No paper being identical, I decided to use something a bit more reliable to measure the distance: a gap indicator or “feeler” gauge.  Here’s a link to an inexpensive example that conveniently has the metric measurements marked in addition to the SAE units.

In my case, with a .5 mm nozzle,  I currently print with .3mm layer height.  In my skeinforge configuration, the Bottom module is enabled and Additional Height over Layer Thickness ratio is set to 0.5 – this means that it will move the print head up .15 mm ( 0.5 ratio * .3mm layer height ) in the Z direction (from Z-Home) before it starts extruding the first layer.

So… based on these numbers, in theory, I should make sure my print head is .15mm from the platform when Z is in the Home position. BUT… we do want to make sure we are a bit closer than that, so we can get good adhesion to the print platform for that first layer.  How close you go will ultimately depend on your printer the platform surface.  I mostly print PLA on glass, with a 2.2 width over height ratio (giving me a .66 mm extrusion width), so I try to make my gap as close to that .15mm as possible  [though being: more plastic surface area = better the surface grip].

Now the actual measurements: the smallest gap I can test with my particular gauge is .006″, or .152 mm.  My platform is mounted at four corners, so I make sure to measure at the extent of each of those corners.  I also have some fairly stiff springs supporting my platform, so the way I “feel” the height may differ from yours.  I place the gauge between the print head and the platform, and adjust the platform height while slowly moving the gauge back and forth until I feel the gap is close enough to start interfering with that movement.  After that, I tighten another half turn to reduce the gap another fraction to add the extra “squish” that will help with adhesion of that first layer.  I only do this extra half-turn because I do not have a gauge that will measure past .15 mm.  I’m hoping that I’m getting somewhere between .12 mm and .14 mm as my actual gap size with this method.  This height, added to the additional height ratio that comes from the Bottom skeinforge module will have our print head starting a couple hundreds less than my .3mm layer height for that first layer (hopefully somewhere between .27 mm and .29 mm).

I try to keep that extra “squish” as minimal as possible.  If you get the head too close to the platform, the plastic needs to go somewhere – and that will be to either side making your extruded stream wider than expected.  When laying down infill on the initial layers, the extruded material will start to overlap and flow upward past the current level of the print head.  This could interfere with the movement of the head, even on the next layer…

Extra Notes:

I recently printed up some thumbwheels with trapped nut holes and added them to the bottom of the screws (with 6/32″ nylocks) that hold my platform.  That single improvement made platform height adjustments a SNAP.  Once I get up from the couch here, I hope to take some pics of my setup.  In the meantime, here’s the Thingiverse link to the parametric model that I used.  I sized my wheels to about 1″ in diameter.  Anything smaller proved to be difficult to turn for micro-adjustments.  Anything bigger and you might start limiting your X and Y extents.