MakerBot Safety Cutoff Kit 1.0 Rev. D

The MakerBot Safety Cutoff Kit is a small kit designed to cut power to the heater in case of a catastrophic failure.

Contents of the Kit

• 1 x Green Printed Circuit Board (PCB) with white printing on top (“Rev D” indicated)
• 2 x 1K Ω resistor, 1/6W (small, brown-black-red-gold bands) [R1] [R5]
• 1 x 10K Ω resistor, 1/6W (small, brown-black-orange-gold bands) [R2]
• 1 x 6.8K Ω resistor, 1/6W (small, blue-gray-red-gold bands) [R3]
• 1 x 120 Ω resistor, 2W (large, brown-red-brown-gold bands) [R4]
• 1 x black relay with 8 pins
• 3 x green, 2 pin terminal blocks
• 1 x red LED
• 1 x green LED
• 1 x black, SL type 4 pin connector
• 1 x MakerBot Endstop Cable
• 1 x Large Diode

Assembly Instructions

Remove the tape from the ends of the components. Orient the board with the white printing on top and two large corner holes toward you.

You should see a a pair of circles in the top middle of the board, one labeled FAULT and the other labeled NORMAL. Place the red LED in the FAULT position and the green LED in the NORMAL position, with the longer lead in the hole toward the edge of the board and the shorter lead in the hole on the flat side of the circle. Confirm that the flat side of the LED matches up with the flat side of the circle printed on the PCB. Bend the leads out at 45º angles to hold in place.

Place the large 120 Ω resistor (brown-red-brown-gold bands) in the square on the lower left hand side of the board labeled [R4]. Bend the leads out to hold in place, with a bit of space between the resistor and the board.

Likewise find the two squares marked [R1] and [R5] on either side of the pair of LEDs. Insert a 1K Ω resistor (brown-black-red-gold bands) into each square. Bend the leads out to hold in place.

Find the square marked [R2] between the pair of LEDs and insert the 10K Ω resistor (brown-black-orange-gold bands). Bend the leads out to hold in place.

Find the square marked [R3] to the left of the [R1] square and insert 6.8K Ω resistor (blue-gray-red-gold bands). Bend the leads out to hold in place.

Solder the resistors and LED in place. Clip the tails from the soldered components.

Place the three green terminal blocks, FET 12V IN, HTR 12V OUT, and TEMP CUTOFF in position. Make sure that the openings are facing out! Then flip the board over so it rests on the three terminal blocks and solder them all in place.

Then it should rest on the terminal blocks so you can solder nicely while it’s upside-down…

Place the black SL type connector in the positon labeled ALERT. Make sure the connector lock faces inward as in the diagram and solder in place.

Then flip over again and solder. Once again, it should stay in place while upside-down.

After the terminals are in place, add the relay and solder that as well.

Now for the tricky part.

The Rev. D version of this kit includes a large diode — this is the big thing that looks like a transistor or voltage regulator.  We need to not only solder this through a couple of holes, but we also need to attach its heat sink to a large heat sink pad.

It’s just a bit difficult because we’re actually soldering a heat sink — which by definition can soak up a lot of heat.  This means that we’ll be keeping our soldering irons in contact with the parts for much longer than we’re used to.  Don’t worry — we’ll walk you through it.

First, we’ll tin the pad.  Hold your iron with one side in good contact with the pad; after a few seconds try to add some solder.  At first, a few jagged blobs might stick to the pad.  That’s not good enough; we need the solder to flow on the pad.  Continue holding the iron on the pad until the entire pad flows.  When it gets to the melting temperature, the solder will suddenly get shinier and flatten out, spreading all over the pad.  When it does that, it’s well-tinned; it should look like the picture below (or even smoother.)

Next, we’ll put the diode in place, and then bend the leads so it makes contact with the pad.

Next, I’d recommend bending the diode leads opposite each other to hold it in place better.

And now the trickiest part: actually soldering the heat sink down to the pad.  Basically, all you have to do is hold the tip of your soldering iron through the hole in the diode’s heat sink.  Slowly feed in some solder as it’s heating to make sure there’s enough flux.  Eventually, all the solder will flow nicely; you’ll see it get shiny again, and suck down into the gap between the heat sink and pad.  When this happens, add enough solder to also cover the top side of the heat sink.

Last, use another tool to hold the diode in place as the solder cools.  Angled snippers are good for this task.  Make sure you’re already holding the diode down as you remove the soldering iron so the contact is good as the solder cools and solidifies.  When you’re done, the solder will smoothly cover the hole over so it’s not even visible.

Now, flip the board over and solder the leads down.  Use something from the workshop to prop up the diode if you need to.

And now you’re all done with soldering.  Phew!

Install it in place on your bot!

Now that your board is soldered together, it’s time to mount it in place. One good place is the right side of the Z-stage.

There aren’t any holes, so we’ll have to drill them. Hold the board in place and use a pencil to make the position of the holes.

Then drill (carefully) with an electric drill. You’ll use a 3mm bolt, so a 1/8″ bit will work well. Vacuum up the sawdust before you continue!

Now just bolt it in place with some 1/8″ spacers and M3x16mm bolts and nuts.

And now (very important) install the thermostat. You might have already done this when you built your hot end, but if not, this it how it’s installed on a MK6+ hot end.

Then move down the nut to hold the thermostat against the retainer plate.

Connect it up!

Ok, now let’s wire things together.

First, take a length of red/black wire to go to the extruder controller’s heater port. Insert it into the cutoff kit’s “IN” terminal (marked “FET/12V”). Make sure that you line up the ground and 12v inputs correctly. If you haven’t installed your electronics yet, just leave enough wire to make it down to the electronics cavity.

Next, connect the thermostat to the “SENSOR” port — this one doesn’t have any polarity.

Take the wire leads that go to your hot end heater and connect those to the “OUT” terminal (marked HTR+/HTR-). The heater doesn’t have any polarity either.

Last, plug the 4-pin cable into the header, and snake it down into the electronics cavity.

The other end should connect to the port labeled “E-STOP” on the motherboard.

Note that the 4-pin Endstop Cable must be patched into your Motherboard for proper functionality.

OK, now you’re done. If you’ve wired everything up correctly, the red FAULT LED will not be lit. If anything goes wrong, you’ll see that light go on and your heater will be stopped automatically.

Testing!

To test that you’ve assembled everything right, open up the ReplicatorG control panel and start heating your extruder hot end. The green LED should be on, but not the red.

Next, disconnect one thermostat wire from the SAFETY CUTOFF terminal. You should hear the relay click, and the red LED should go on. You should also see the temperature of the hot end start to drop. If the green LED is still glowing that’s OK, but it should be dim in comparison to the red LED.

If this is what you see, you’re good to go. If you see any other behavior (especially if the relay does not cut power to the heating element!) remove the safety cutoff, check your work and all connections, and resolve the issues before going forward with your build.