Introduction: How to Make a Heated Build Platform for a Makerbot Cupcake

By www.allartburns.org
About: designer, fabricator, hacker Carnegie Mellon Master of Tangible Interaction Design 2009

A heated build platform is an essential component of a production Makerbot Cupcake or other Reprap-based printer using ABS media. Large prints often "warp" because the bottom of the print cools while the top of the print is still being created. The solution is simple -- keep the base of the part relatively warm until the entire print is finished and can cool at the same rate.

These instructions will show you how I made my platform, if you make an improvement please share it with the rest of the Reprap/Makerbot community so they can give it a try.

Note that there are actually two sets of instructions here. The first set requires you to have access to metalworking tools and some basic metalworking skills. If you have a friend who can help you with this (like maybe someone in Robotics Club or who is a welder), that's just as good. The second set gives suggestions on how you can work around not having fancy/expensive tools.

Obligatory Warnings

This project requires a number of tools that can seriously injure you or a bystander. Wear your safety glasses and be careful.

A heated build platform uses Nichrome wire and can easily reach 220F/105C without any change in physical appearance.

Never leave a Makerbot unattended while the build platform or extruder are at temperature.

Step 1: Collect Materials and Tools

Components

- Piece of aluminum plate approximately 100mm x 100mm x 5mm. If it's only 4mm or 6mm thick, or 105 x 105, that's not the end of the world. There are a number of online metal suppliers who deal in small lots/sizes, look around before you go to your default Big Online Superstore, you might be able to save some money.
- Approximately 35 cm of insulated nichrome wire. I use the same wire that people use for the extruder, 31 gauge double-glass silicone nichrome wire.
- a thermistor, I used the 100K ohm EPCOS thermistor available from online resellers like Mouser electronics.
- a 4.7k resistor
- a 10uF capacitor
- a 3 pin, .100 header socket
- Kapton (equiv) tape, the roll that comes with a Makerbot kit works just fine.
- 3mm round magnets
- cyanoacrylate glue
- 2 different colors of 18ga stranded wire for connecting everything together

Optional components:
- a 4-pin connector pair to make a quick-release attachment for the platform
- high-temperature epoxy for gluing things to the platform
- heat-shrink tubing

Tools

First you'll need most of the stuff you needed for making a Makerbot or Reprap: soldering iron, solder, wire cutters, wire strippers, etc. Then you'll need one of two sets of tools:

Machine shop tools:
- basic metalworking tools like a drill press, transfer punches, clamps, etc and know how to use them safetly.

Hacker: you're making it up as you go :-)
- masking tape
- a sharp pencil or mechanical pencil with a long lead
- metric ruler
- small t-square
- electric drill and appropriately sized drill bits (we'll figure it out later)
- center punch and small hammer. if you don't have a center punch, buy one to keep with your drill, you won't be sorry
- flat metal file
- round metal file (not the end of the world if you don't have this)

If you can borrow/use any of the following for free, it will make this project much easier:
- Good multimeter (ex: Fluke) with a temperature probe
- Metal mill with drill chuck or a x/y table and drill press
- Band saw: buy a longer piece of aluminum plate than you need, cut it into sections, then have a group building party with other Makerbot owners!

Step 2: Lay Out the Holes to Be Drilled

There are a several different ways to lay out the holes on the aluminum plate, the easiest is to transfer the holes from your current build platform. This also takes into account any minor variations in your build platform (the hole layout has changed since the early platforms) and reduces the chance of a measuring error.

If you (or your friend) has access to machine shop tools:

Clamp the aluminum plate to the build platform making sure to leave room around the holes you are going to transfer.  Next, using the transfer punches, transfer the 3mm magnet holes and 5mm alignment holes. (This is the sort of thing you should have learned in "Machine Shop 101" :-)

Hacker tools:

1. Cover one side of the plate aluminum plate with tape, this is where we will make our transfer marks.

2. Firmly tape the build platform to the tape side of the plate. Use both horizontal and vertical strips and wrap them around the back. You want as little movement as possible while you make marks.

3. Using a sharp pencil (or a .3mm mechanical pencil) carefully make marks through the platform holes on to the tape below. You can either attempt to make a dot in the exact center of the hole or "color in" the hole, either way, make it as exact as possible.
Note: the magnets used by Makerbot are square but we're using circular magnets of approximately the same size. You'll be drilling into the center of the square you transferred

Either set of tools:

If you're using a bolt-on acrylic plate, transfer holes for this as well (probably 4mm, but verify with your specific platform). Note the orientation of the acrylic plate relative to the alignment holes -- you want the plate holes on the left and right side of the platform as you're looking at the Cupcake from the front. If the holes are on the front and back they will interfere with the x-travel of the build platform.

Step 3: Drill the Various Holes

If you're in the US, you probably don't have any metric drill bits lying around, but that's ok. There are decimal drill sizes close enough that we can use those instead. Remember that we're making holes for bolts and to hold glued-in magnets, we just want the smallest hole that works. It's better to err on the small side and finish the hole to size with a file than drill to big of a hole.

The equivalents are:
- 4mm alignment holes: 15/64" or 1/4" bit
- 3mm magnet holes: 7/64"
- acrylic print surface holes: 1/8" (might vary depending on who made your surface)

Machine shop tools:

Center punch the transfer marks and drill the holes using the appropriate drills.


Hacker tools:

The trick here is that you need to drill the holes in the exact center of the marks you made. One way of doing this is taking a ruler and measuring to the center of the hole and making a mark there. Use the center punch to make a mark at the true center then get set up to drill the holes.

Mount the platform in something solid like a vice. If you don't have that, clamp it to a table or workbench with a piece of "sacrificial wood" under it. When you drill through the plate you don't want to drill into your table... If your electric drill has speed selection, set it as high as possible then slowly drill each hole. Take your time, don't push the drill, just focus on keeping it as perpendicular to the plate as possible.

Both sets of tools:

After you've drilled all the holes, hold the plate and the build platform together and look at the holes with a bright light on the other side. If there are any differences use the file to make the hole larger. Do not try to use the drill like a mill and cut sideways with the drill bit. If you think the holes are correct then try mounting it in your Makerbot Cupcake to see how the alignment looks.

Once you're happy with the holes use a flat file or belt sander to clean up the edges of the drilled holes so that they are perfectly smooth with the top and bottom of the plate.

Step 4: Attach the Magnets

Using your x/y carraige as a guide for magnet polarity, glue the magnets into their holes.

What I do is use the tiniest amount of glue possible, let that set up, then gently removed the platform and added more glue on each side of the magnets. While the platform is on the carraige, use a felt-tip marker to write a big "T" on the top side.  This will prevent you from accidentally putting the nichrome wire on the wrong side of the platform because you forgot which side was "up".

Don't ask how I know this.

Step 5: Stuff to Think About While the Glue Dries

While the glue is setting up is a good time to think about usage and safety, and how you plan on laying out and routing the wire.

Usage and Safety Notes

While we're waiting on the glue to dry, let's talk a bit about how the completed platform will work and how it's different than the extruder heater.

The software for controlling a Makerbot, ReplicatorG, is now capable of driving a heated platform and collecting data from the thermistor to control the temperature. (You'll need to tweak it for your particular thermistor and setup, but we'll deal with that later.)

Like the extruder, the heated plate uses approximately 30cm of nichrome wire to heat a piece of metal to a specific temperature. However, the heated platform is a much larger volume of metal than the extruder head and requires much longer to heat up and more importantly for safety reasons, takes longer to cool down. You'll want to keep an eye on the temperature readings in the control panel and wait until it's cool enough to touch.

On my Makerbot Cupcake, it takes only 17 seconds to heat the extruder from 25C (room temperature) to 60C, the operating temperature many of us use on our heated platforms. To heat my platform from 25C to 60C takes a full 10 minutes.

Planning Your Connections

Before going on to your next step, you need to decide how you want to use your heated platform and where you want the wires to go. My first experiments had the wires existing to the side, but I was also trying to make a quick-release using a Molex connector. Makerbot routes their wires out the back and that's what I'll do in this example. If you decide to try making a quick-release, you might want to rotate everything 90 degrees first.

Step 6: Lay Out the Nichrome Wire

We want the platform to heat evenly without any cool zones, so we need to run the wire through a path that covers as much of the platform as possible. If we just ran the wire around the edge or up and down the middle we'd have one area that is very hot and other areas that were cool. We have to find a path for the wire that doesn't go between the x/y table and the platform and we also want to position the thermistor so that it reports a good temperature for the platform.

For example, let's say we put all the wire on one side and the thermistor on the other side. By the time the thermistor was at 60C, the side of the plate with the wire might be at 70C, or even 90C. (Someone who remembers heat equations can probably tell me the exact temperatures. :-)

What's worked best for me is a loose U-shape as shown in the photo with the thermistor in the open part of the U as shown in the photo.

Make a path using Kapton tape where you will put the wire. While the wire is insulated, this helps prevent a short if the insulation cracks or gets worn over time.

Cut a bunch of 25mm pieces of Kapton tape then an inch at a time, lay out the nichrome wire and tape it down.

Do a test fit on the x/y carriage. Put the plate down as if you were going to use it, then feel under the plate and make sure the nichrome wire isn't touching the carriage or worse, trapped between the carriage and the platform.

Step 7: Attach the Thermistor

This is similar to attaching the nichrome -- put down a base of Kapton tape then tape the thermistor on top of that. One thing to be careful about is making sure the thermistor leads don't touch each other and short the connection. After you've taped it down, use your multimeter to measure the resistance. If the value you get is 0 or only a few ohms, then you've gone and messed it all up.

Step 8: Wire It All Together

The only thing remaining to do on the platform is solder lead wires to the board and tin the other ends of the wires.   If you were considering making a quick-release clip on the platform, now is a good time to do this.  In the example photo, I've used high-temperature epoxy to mount a molex connector to the side of the platform.

Now you'll need to modify the extruder controller to properly read the thermistor using the A6 pins.  When Eberhard Rensch came up with this technique, he soldered everything to a header. I didn't have a header like his, but I've had luck both with making Molex clips and with soldering the leads to a 3-pin header connector. Going from top to bottom on A6, here are the connections:

1) one thermistor wire, the leg of the capacitor with the stripe above it (negative side)
2) one leg of the resistor
3) other leg of the resistor, other leg of the capacitor, other thermistor lead

The wires for the nichrome go in the screw terminals marked A-/A+, order is unimportant.

A few of things to keep in mind while doing all this.

- The thermistor leads are uninsulated, so you'll need to insulate them from the board to the solder joint, this is where the heat-shrink tubing is useful
- The nichrome is insulated, strip it before you try soldering things
- It wouldn't hurt to have a layer (or three) of Kapton tape over the exposed nichrome wire, even the insulated sections.
- Consider some form of strain relief at the platform, even if it's just bunding up the wires and using kapton tape to secure them to the side of the platform
- Either braid the wires together or use heat-shrink tubing every few inches to keep things tidy

Step 9: FIRE IN THE HOLE!

Now it's time to test things. Load up the latest version of ReplicatorG and follow the instructions for activating the heated platform.

Start with a very low value for your heated platform, say 10 degrees above room temperature.  Once the readout says it's at the desired temperature, use a thermometer or temp probe on a multimeter to verify the temperature.    If you don't have any way of verifying the temperature, don't touch it to find out if it's hot!  Using the back of your fingers, hold your hand very close to the platform and see if you feel unusual amounts of heat.

In units of 10 degrees or so, work your way up to 60C, which is a little too hot for most people to touch.  You should be able to feel the heat coming from the platform with the back of your hand.

Once you think it's the right temperature, get to printing!