Category Archives: Design

Design tips for creating 3D digital models for printing on a MakerBot

Thing idea: Crayon mold

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Crayon Mold v0

Crayon Mold v0

Problem: Broken crayons, useless crayon bits, or crayon shavings.  Crayola has their own crayon making system – a cross between an easy-bake-oven and little molds.  However, I don’t think it is quite versatile enough.  Plus, why pay $20 for what could be accomplished easily for $0.20 worth of plastic parts?

Solution: A printed crayon mold!

Description: Crayons melt at about 128 – 147 degrees Fahrenheit, or up to about 66 degrees Celsius.  ABS won’t melt until around 88-125 degrees Celsius, so there’s a wide margin for melting the paraffin wax crayons without distorting the mold.1

I would want at least three different molds – the normal crayon size, the fat crayon size, and then a triangular non-rolling crayon size.  I’m picturing a two part mold for each, with the seam of the two parts running along the crayon lengthwise and a half funnel for pouring.

In addition to the half-mold, I’d also design a snug fitting square block for fitting the assembled mold into.  That way you could stand it up and pour crayon wax into it.

Another potential use for this would be to place the pieces of crayon inside the mold, close it up, then heat.  This would allow you to mend a broken crayon.

Usage: I can think of several different ways to use this mold.  Frankly, I’m not sure which is easiest/most advisable/least advisable.  There are easily several considerations:

  1. Assembly:
    1. The mold could be assembled with crayon inside to be melted and repaired.
    2. Crayon pieces could be melted and then poured into the assembled mold.
    3. Crayon pieces could be placed in the funnel at the top of the mold, the entire system heated and crayon allowed to melt down into the mold.
  2. Melting:
    1. Crayon could be melted in a test tube or similar container in the oven, microwave, hot water bath (such as on the stove) or perhaps even open flame and poured into the mold.
    2. Crayon could be melted while inside the mold by placing the mold in a heat source (oven, microwave, hot water bath).
    3. Crayon could be placed in the funnel and allowed to melt down into the mold with the application of a heat source (oven, microwave, hot water bath, open flame?, or sunlight plus magnifying lens!)
  3. Cooling:
    1. Allowing to naturally cool to ambient room temperature.
    2. Placing in fridge.
    3. Placing in freezer.
    4. Placing in cold water bath.

I’m not sure which method of heating and cooling are optimal.  Though I’d suspect it is preferable to apply the least amount of heat over the shortest period possible.

Variations: It would be interesting to create these molds in different shapes besides cylinders.  You could top each one with a geometric shape, the head (or tail!) of some kind of animal or character, or something else entirely.  You could mold crayons into spheres, blocks, chips, or little figurines.  While not particularly sturdy, you could even mold them into building blocks or components of some larger device.  A clever person could use some left over nichrome wire to build a heated metallic funnel.

  1. That said, my extruder isn’t pumping out plastic until it hits 200 degrees Celsius at least. [↩]

How to Raise Your MakerBot from the Dead

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Happy Zombie Day

Happy Zombie Day!!!

… or Happy Zombie Day!

My extruder is back online! Huzzah!  Since I had it disassembled I made a few minor modifications.

  1. I’ve added binder clips to the front and back edges of the build platform.  I found that my acrylic build base is slightly deformed and probably getting more so with each build.  This is a temporary fix while I get around to picking up a new build base.
  2. You’ll notice I’ve also added pieces of rubber band.  I cut a long rubber band into two pieces about an inch long, tied them off to make small loops, and put them around the handles to the binder clips.  I don’t want to take the handles out of the binder clips because then they’ll be difficult to move/remove/replace.  But, as I printed they tended to vibrate creating unnecessary noise.
  3. When ABS oozed down my PTFE threads and around the barrel, I sliced off about 1mm to use as a washer between the nut and large washer.  The reason I’ve heard suggested for the PTFE washer is that it keeps the large metal washer from acting as a heat sink.  The nut is right on the barrel and is able to heat right up along with the rest of the barrel.  When the large washer is pressed on the nut (as it is supposed to) it is able to absorb heat through the nut as well as it’s contacts to the barrel.  The thin surface area contact between interior hole in the large washer and the barrel probably doesn’t allow for much heat to be transferred to the large washer.
  4. I’ve read it mentioned that wrapping an extruder with nichrome is a two person or three handed job.  I’ve found it to be fairly easy with just my two hands.
    1. I use a small piece of kapton to tape the nichrome to the extruder head/nozzle oriented so that it is lined up parallel to the barrel. 1
    2. From the point where I can see the nozzle touch the barrel I leave about 2-3cm of nichrome hanging off the edge, with the rest of the nichrome pointed up towards the barrel.
    3. Then I wrap the nichrome up the barrel in a single layer keeping a tight contact with the threads until there’s about 2cm or so left.
    4. Then I tape down all of the nichrome on the barrel, except the last 2cm.
    5. I untape the part of the nichrome on the nozzle.
    6. As I was out of those little metal connectors provided by MakerBot, I had to improvise a little.
      1. I stripped the leads on the nichrome so that about 3mm was exposed and used needle nose pliers to put it into a hook shape.
      2. Then I stripped the leads to the insulated wires so that about 15mm was exposed, used my fingers to twist the leads, doubled it back along itself, twisted it again so that there was a little loop.
      3. I hooked the nichrome into the loops of braided copper leads and crimped it down using the needle nosed pliers.
      4. Solder and done.
    7. I then liberally applied kapton to wrap the barrel and nichrome so that it would be unlikely the wire or leads would ever have to bear any of the stress should I move the extruder around.
  5. With my last two extruder assemblies I’ve taken a slightly different approach to attaching the thermistor.  This method makes it easier to pull the thermistor out, but slightly more difficult to install it in the first place.  Here’s what I do:
    1. I laminate the thermistor between two layers of kapton tape just past where it meets the insulated wires.  Only the very tip of the thermistor is exposed.
    2. I wrap the barrel in nichrome as above, then ceramic tape, then wrap that in kapton – without the thermistor inside.
    3. Once the entire barrel is wrapped up just as I want it, I use a utility knife to make a vertical slice up the ceramic tape starting at the edge of the nozzle until I reach the point where the nozzle meets the barrel.
    4. I then peel back the ceramic tape and kapton, exposing a V shaped portion of the nozzle.
    5. I put the tip of the thermistor down into the V, replace the ceramic tape and kapton over it, and tape it down.
    6. I then re-wrap the barrel in kapton again.
    7. The first time I disassembled my extruder I screwed up my thermistor when unwrapping the barrel.  While this makes it more difficult to get the thermistor into the assembly, it also makes it so much easier to pull it out and reuse it.
  6. At the top left of the above photo you can see a small black box with green and white wires coming out of it.  That’s where I added an ethernet jack connector to the extruder assembly to make it easier to connect/disconnect the extruder.
    1. When I assembled my MakerBot I used insulated wire out of an ethernet cable.  Since I only needed a few sets of insulated wire, I ended up with one piece of ethernet cable that still had the ethernet jack on it with four wires sticking out.  I also had two ethernet ports left over from my opto-endstop kits.
    2. I plugged the ethernet jack into the ethernet port and tested the leads on the wires against the leads on the port.  Once isolated I soldered wires to the four leads that lead to the four wires from the jack.
    3. I then soldered the four wires from the ethernet jack to the thermistor and nichrome.
    4. I took the wires I soldered to the ethernet port and ran them through the hole on the right side of the MakerBot in the back on the top.  Then connected those leads to the appropriate ports on the extruder board.
    5. Once the wires were soldered up and extruder assembled I plugged the ethernet jack into the ethernet port and checked ReplicatorG to see if I could get a thermistor reading (yes) and heat the barrel (yes).

As I tinker and modify my MakerBot it seems I’m moving towards a system where I try to make the extruder assembly as modular as possible.  I didn’t have this as a conscious thought when I started, but that’s where these modifications have been headed.  While it is very convenient to have a totally modular extruder only connected to the robot by four bolts and an ethernet cable, that system is most useful if you are using drastically different print heads (such as a frostruder, Paxtruder, Bowden extruder, etc).

If you’re just swapping between PLA, ABS, or other plastic filament or color variations thereof, you can reuse the vast majority of the extruder assembly – the board, the motor, and the entire acrylic plastruder.  If you had a different heater assembly you could just undo the two screws that attach the heater to the extruder, disconnect the thermistor, disconnect the nichrome, and swap in a new set.  Although I don’t have a fully assembled second heater section yet, this set up makes a lot of sense to me just for ease of maintenance and repair.

  1. While I sing Christmas carols with my friends Meryl and Cheryl. [↩]

Printing a MakerBot

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I’ve already pontificated on the idea that if you’ve purchased a MakerBot Cupcake CNC Deluxe kit, you basically get a second MakerBot for half off.  (Spoiler: it’s because you can print a ton of the most expensive parts that go into building a new one).  I don’t know why, but the idea of replacing wooden parts on my ‘bot with printed parts just fascinates me. 1

So, let’s have a list of potentially (and actually!) printable parts:

  • Electronics spacers
  • 3 large pulleys, 1 small pulley
  • Y stage, the entire thing, as a single print
  • X stage, in three large prints (there would be no need for the end caps if the three pieces were designed properly)
  • Insulating retainer ring
  • Printruder
  • Dinos
  • X stage end caps
  • Z stage captive nut guides
  • Z axis rod bearing brackets

Having more printed components for the MakerBot would reduce a lot of work in it’s assembly.  There’s a lot of tiny fiddly bits in the X and Y stages that would become obsolete.

Heck, it might even be possible to replace some of the bolts with some kind of printable fastener system.

  1. Cue Johnny Cash singin’ One Piece At A Time [↩]

Peanut Butter Jar Mousetrap Insert

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Peanut Butter Jar Mousetrap Insert

Peanut Butter Jar Mousetrap Insert

Here’s my entry in the Mouse Get! Challenge from Cathal Garvey.  I call it the “Peanut Butter Jar Mousetrap Insert.”

The idea is pretty simple.  Mice probably like peanut butter enough to squeeze into a small opening for a chance to eat it.  If the opening is difficult to wedge back open they might not be able to get back out.

So, buy a jar of peanut butter, eat most of it, leave some peanut butter at the bottom, cut out most of the top from the lid, print the “Peanut Butter Jar Mousetrap Insert“, put the insert with the pointy bits going inside, close the lid, prop it up somewhere so it doesn’t roll away, and wait for your peanut butter covered mouse!

Preparing to paint

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Here’s what I did to get ready to paint:

  • Gathered a lot of cardboard boxes, opened up and laid flat
  • Taped said cardboard into large overlapped sheets, taped up any holes
  • Bought primer, dark gray
  • Opened the garage for ventilation
  • Changed into clothes I didn’t mind getting dirty
  • Looked carefully at the various diagrams to make sure I’m going to paint certain parts the colors I want

Mission critical decisions

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Such as:  Should I paint?  What color(s)?

I’m thinking I should paint.  I figure it will help the robot body stand up to a little extra wear and tear while looking cool.

Not white or black.  That’s SOooo October 2009.  I’m liking gray/gunmetal/silver.  I’ve only seen pictures of one silver MakerBot and I rather liked it.  (Thank you to RDon Ebben/Robostang 548 for posting pics of his MakerBot 347.)  The picture is a little dark, so I don’t think I can see it to its full effect.

Just the other day a user named unrepentantgeek posted a Google Sketchup version of a MakerBot, to make it easy to test out paint/color schemes.  URG – you’re the best!  Thanks to you, I got to test out this color scheme:

Roughly a 50% gray on the outside, silver on the inside.  (I figure I can’t rightfully name the machine Bender unless it has a shiny metal assplate, right?)