Drawing robot supplies shopping list

Going Shopping

Going Shopping

Sometimes it can be difficult to figure out where to get started on a project.1 Once you’ve read through the build instructions, you’re going to need to get your hands on some parts.  I’ve provided a “shopping list” of sorts below:2

I’ve got more to say about each of these fantastic suppliers, but that is another post in and of itself.  Feel free to shoot me an email or leave a comment if you just can’t wait.

  1. Photo courtesy of polycart []
  2. No kickbacks, just a happy customer from each of these suppliers []

Vertical Pen Test by Jens Clarholm

Vertical Pen Test by Jens Clarholm

Vertical Pen Test by Jens Clarholm

Jens Clarholm has been hard at work to find the best pen for his Circlon1 drawing machine.  The Circlon holds pens vertically as it draws, which necessitates pens that draw quickly and smoothly.  

You should definitely check out Jens’ detailed and thoughtful review.  For the sake of posterity, the winners were Pentel Energel Deluxe RTX and the Pilot G-2 07.

If you need to find the best horizontal pen for a drawing robot, you may find my review from last year helpful.

  1. Spirograph-style []

Designing with Injection Molding in Mind

Injection molded parts

Injection molded parts 

I had always assumed injection molding was a pretty straightforward process.1 You send your digital files to the injection molder, you pay a bunch of money, and plastic parts show up.  While looking into the process of injection molding, I discovered there are all kinds of design requirements.

  • Uniform Thickness.  Apparently having a non-uniform thickness to plastic injection molded parts causes lots of problem.  The plastic can flow into the mold unevenly and cause bubbles or voids.  The thinner parts would cool quicker and the thicker parts would stay warm longer, causing the part to warp as it cools.
  • Draft.  Apparently all parts that are injection molded require some amount of “draft.”  This means that a part should be tapered outward slightly – so that it can slide easier out of the mold and incur less friction as the mold parts slide together and apart.  The various resources I’ve found suggest a minimum draft angle of 0.5 degrees to as much as 5 degrees for parts with lots of surface texture elements.
  • Part Radiusing.  Since the plastic shot into a mold is basically a viscous liquid, it flows better around curved corners and has a difficult time flowing around sharp angles.  The guides online suggest that internal curves should have an internal radius of 0.5 times the wall thickness and an external radius of 1.5 times the wall thickness.  Plus, proper radiusing means consistent wall thickness, even around part corners.
  • Coring Out.  The process of removing excess material, leaving the bare minimum uniform wall thickness in walls and ribs for strength.  This allows the finished part to be of uniform thickness to prevent uneven shrinking and internal part stress.
  • Radiused Corners.  As a part’s geometry is carved by a CNC mill out of the metal mold the CNC can only carve with a minimum diameter equal to the CNC’s bit.  This means corners won’t ever be true corners, but rather small curved internal corners.

Interestingly, these design requirements also explain why so many plastic parts are basically shells.  I had always assumed this was done to reduce plastic and cost.

  1. Photo courtesy of Creative Tools []

What is the best paper to use with a PlotterBot?

This is not the paper you're looking for.  Move along.

This is not the paper you’re looking for. Move along.

The choice of paper in a PlotterBot is nearly as important as the choice of pen or marker.1 Some of these considerations are:

  • Quality.  Is the paper archival quality?  Will it yellow or discolor over time or when exposed to light?
  • Expense.  Is it expensive?  Sometimes things happen during a drawing and you end up with a diagonal line going across the entire sheet of paper.  It’s annoying when you’re using cheap banner paper, because you might have lost a few hours of work.  It’s really painful when you’ve bought 10 sheets of super nice paper for $50 and it’s totally wasted.
  • Finish.  What is the finish?  Smoother/glossier papers will tend to bleed less, but they will also tend to smudge more and possibly take the ink less well.  Papers with a flat/matte finish will tend to smudge less, but be more absorbent and bleed more.  Paper with a grain or tooth to it will also wear down on your felt tip marker or accumulate paper fuzz on the tip of your pen.
  • Portability.  Will it roll?  If you’re selling or transporting drawings, you don’t want a stiff board that would crack rather than roll into a hard mailing tube.  Thinner papers that roll better will also accidentally wrinkle or crease more easily.
Cheap banner paper roll of choice

Cheap banner paper roll of choice

Cheap Banner Paper

So far my favorite paper, as crazy as this sounds, has been the cheap banner paper rolls I buy from the local Staples office supply store.  These rolls are about $5 each for a 30″ wide roll that’s 52 feet long.  Since each of my drawings tend to be about 2-3 feet in height, I can get more than a dozen drawings out of each roll.  This paper has a mild gloss to it, very little tooth, rolls and unrolls easily2 , takes Sharpie ink well, and doesn’t bleed or smudge much.  I’m pretty confident that this paper isn’t archival quality, but given that each drawing is about $0.40 worth of paper, it’s a trade off I’m willing to accept.

There is always an informative discussion on paper choices over at Sandy Noble’s Polargraph forum.  Although I haven’t tried these other papers, here’s a short list of some of those recommendations.

Strathmore 300 Series Bristol Board used by Sandy Noble

Strathmore 300 Series Bristol Board used by Sandy Noble

Bristol Board

Sandy Noble uses Bristol Board as it is smooth (so it doesn’t gum up the pen tip) and easy to roll.  He found that it tended to hold the curl of a roll once it had been held that way.

The largest sheets of 300 Series Bristol Board Strathmore makes is 22.5″ x 28.5″.  You have your choice of vellum or smooth.  I can only seem to find these listed as 23″x29″ and sold by the sheet starting from $1.50/sheet.  However, they also sell rolls that are 42″ wide and 10 yards long which seem to go for about $50/roll.  ((My robot was specifically built to accommodate a 30″ roll of paper, but could be adjusted without too much modification to draw on an even larger scale and accommodate larger rolls.))

Tango Advantage Digital 10pt C1S used by Kongorilla

Tango Advantage Digital 10pt C1S used by Kongorilla

Tango Advantage Digital 10pt C1S Paper

Kongorilla recommends using Sharpie Ultra Fine tip markers on Tango Advantage Digital paper.

The largest sheets of Tango Advantage Paper I can find online are 19″ x 13″ – which is on the small side, given my robot’s capabilities.  A pack of 450 goes for about $80, which brings the price to around $0.18/sheet.

Borden & Riley Paris Paper used by Gensior

Borden & Riley Paris Paper used by Gensior

Borden & Riley Paris Paper

Gensior recommends Borden & Riley Paris Paper as he finds it smooth, flexible, strong, semi-gloss finish, and seems to not bleed with the Pigma Micron pens he uses.  He does note that it only comes in white.

I was able to locate some of this art paper online in sizes up to 19″x24″ for $40 for 40 sheets (basically, $1/sheet) and 36″x10 yard rolls for $29.

  1. Photo courtesy of Kristina Alexanderson []
  2. But does wrinkle and crease easily too []

What are the best pens to use with a PlotterBot?

The Pen Plotter is Mightier Than The Sword

The Pen Plotter is Mightier Than The Sword

One of the most common questions from Maker Faire was whether I used any special pens.1

There are a few issues to consider when selecting a pen to use with your drawing robot.  First and foremost, the pen needs to be able to write consistently when it is positioned perpendicular to a vertical surface.  Secondly, it shouldn’t dry out too fast – since a single large drawing could take as much as 6-8 hours.  Third, it should have a large enough supply of ink enough to drawing of choice.

I’ve tried out lots of different kinds of pens – from normal office supply style gel pens, to permanent markers, to expensive art markers.  Overall, my favorite pen to use was the art markers, but for most purposes I would probably go with a Fine Point Sharpie.

Prismacolor Premier art markers

Prismacolor Premier art markers

Art Markers

Art markers, the kind you’d find at an art supply store, are really great.  They come in a variety of colors and the ones I prefer, the Prismacolor Premier Chisel Double Ended markers have a wide and fine tip end to choose from.  These particular pens seemed to last a really long time.  I was able to draw three or four hour drawings with a single marker.  The only downside to these markers are the cost.   Amazon only sells these pens in large sets (12, 24, and 72 markers) that average out to about $2-3/marker.  While you can buy them individually from your local art supply store, they will end up being about $3-5/pen.  That said, if you just had to have a drawing with a particular color marker, you probably can’t beat the color sections from a Prismacolor set.

Sharpies

Sharpies

Sharpie Markers

Sharpies are ubiquitous, come in lots of colors, and are fairly cheap.  A pack of assorted colors of Sharpies would probably average out to about $1-$1.5/pen.  Chances are your local office supply store runs a deal on these every few weeks.  I picked up a pack of 12 colors for about $5 just before Maker Faire this year.  In my experience, a Sharpie Marker Fine Point would be good for about two big drawings.  Sharpie also sells pens – which might work even better since they have a smaller surface area and may not dry out as quickly.  I’ve experimented with trying to “revive” a dried out Sharpie by soaking the pen tip in rubbing alcohol (as I had read somewhere on the internet), but it didn’t seem to do much.

Pilot Precise V5 / V7

Pilot Precise V5 / V7

Pilot Gel Pens

One of my favorite pens for paper work/office use is the Pilot Gel series of pens.  Of these, I prefer their “Precise” line of pens.  They only come in a very few colors (red, black, blue, and green), but they are reasonably cheap (less than $1/pen when bought by the box).  When used in a drawing robot, you’ll want to make sure they’re mounted at a slight downward tilt.  They only come in either Fine Point or Extra Fine Point.  For this reason they’re okay for small or medium sized drawings, but not very good for large pictures – as the lines would be too thin and the drawing would take too long.

Pen Reviews on Polargraph.co.uk

Sandy Noble’s website (Sandy is the creator of the Polargraph board and software I use for my own robot) has a great forum with lots of resources including several reviews and recommendations for pens.  There’s a review and guide for Sharpies, one user recommended a “KOH-I-NOOR Fiber professional,” and Sandy expressed a preference for a Kuretake Zig Millennium.

UPDATE:

Two Polargraph users, Lanthan and Kongorilla, have posted the results of their tests using various pens, including ball point pens.

Also, be sure to check out the Egg-Bot documentation over at Evil Mad Scientist Labs for suggestions on pens and markers (and other things!) to use with their pen plotter.  (Thanks Lenore!)  I would point out that those pens were tested using the Egg-Bot, which holds the pen nearly vertically, versus a wall-hanging pen plotter which holds the pen nearly horizontal.

  1. Photo courtesy of Brian []