Baja i3 Rework Heated Bed Assembly

From Roaddog Labs Docs

Introduction | Bill of Materials | Y-axis Assembly | X-axis Assembly | Connecting X-axis and Z-axis | Motor Installation | X and Y-Axis Motion | Heated Bed Assembly | Extruder Installation | Electronics and Wiring | Firmware Configuration | Validation and Testing | Working with Files and Printing

Thermistor Assembly

The thermistor reports the temperature if the bed or hot end to the printer electronics. On the kits that don't offer a completed thermistor or bed wiring you'll need to assemble the thermistor.

Thermistor Kit Parts

1 x 100k ohm NTC Thermistor


2 x PTFE sleeves

2 x short heat shirk pieces

2 x butt splice

2 x crimp socket contacts

1x 1x2 header connector housing (also called a "Dupont" connector)

Thermistor Kit Parts

Prepping the Wire and Connectors

Depending on your kit the wires may appear visually different but they install the same. Strip about 2 mm of jacket off of each end of each wire.

Crimp the socket contacts onto the wire. I don't suggest using solder for this. The clearance into the housing is small and solder will make the connection too big to slide the contact all the way into the housing. When you crimp the contact make sure you get some of the strain relief on the wire jacket. That helps hold the contact to the wire. The strain relief is the longer V-shaped part of the contact. Make sure not to crimp the small tab near the contact end. That is used to hold the contact in the housing.

When you've got the crimps good and tight, insert them into the housing. Face the contact so that the small tab is on the same side as the slot in the housing. Slide the contact in until the small tab locks into the slot on the housing. Pull gently to make sure it is locked. Repeat for the other wire. At this point you have one header connector attached to two wires.

Sliding Contacts In
Completed Connector

Prepping the Thermistor End

In this step we'll connect the thermistor to the wire assembly we made in the previous step. The way the thermistor works we can't short out the lead to each other or anything else. To insulate the thermistor leads we use the small pieces of PTFE tubing. We slide a piece over each leg of the thermistor covering all but a few mm of each leg. It's a little tricky to get the thermistor legs into such small tubing. It just takes a bit of patience.

Thermistor Insulated

Strip about 3mm of jacket from the bare end of the wire assembly from the first step. We'll be crimping the butt splice to this end. With a butt splice connector we join two wires by putting one in each end of the connector and crimping it. The wires to be joined basically meet in the middle of the butt splice. What we will do is crimp one side of each of the wires to one side of the butt splice. Slide the heat shrink pieces onto the wire matching the heat shrink to the color of the wire.

Butt Splice with Heat Shrink

Next, take the thermistor that has the PTFE insulated legs and place the bare part of the leg into one of the butt splices that has been crimped to the wire. Now crimp the side of the butt splice with the thermistor leg making sure you get some PTFE tubing down into the but splice. Repeat for the other side.

Connecting the Thermistor

Pull the heat shrink over the butt splices and shrink the tubing around the connection. You can use a hair dry, best is a heat gun. Some use open flame from a ligher but I discourage that as it can burn the material.

Shrink Wrap the Leads

You now have a completed thermistor assembly.

Completed Thermistor Assembly

Heated bed assembly

Bed Assembly Parts

  • 1 x PCB heatbed
  • 1 x glass build plate
  • 1 x thermistor assembly
  • 4 x Binder clip
  • 4 x M3x25 mm screw
  • 4 x M3 nuts
  • 12 x M3 washer
  • 4 x bed springs

Attaching the Thermistor

Take the completed thermistor assembly and place the thermistor head in the hole in the middle of the heat bed. The top of the heated bed is lthe side with the solder pads for the bed power connection. Gently bend the head of the thermistor to a 90* angle from the wire. Take care not to damage the head or short the leads. If the leads were installed as per the previous section it shouldn't be an issue. There is a hole in the center of the headed bed. You are going to place the thermistor head in that hole, entering it from the bottom of the heated bed. The bottom is the side that does not have the main solder pads.

Solder Pads are on Top of the Bed

Once the thermistor head is in the hole (it may be a bit loose, that's OK) tape the head in the hole. Run the thermistor wiring toward the solder pads, using blue painters tape or polyimide tape secure the wire to the bottom of the bed. The pic is an example but you should use more tape than that in your build. Running the wire toward the solder pads will allow you to bundle the heated bed main power and thermistor wiring and route it to your printer control board.

Attach Thermistor to Heated Bed

Soldering Heated Bed Main Connection

Start by stripping and tinning only one end of the main power wire. This will connect to the heated bed. Tinning is the process in which you prepare the wire for soldering by adding some solder to the end of the wire. The end that will connect to your RAMPS should not be tinned or soldered. That is a screw terminal and those work best with bare wire.

Run the wire up under the heated bed through the holes in the solder pads. The MK2A heated beds with the Roaddog Labs kits are single voltage and to polarity does not matter. Either wire can go into either hole. Other boards, specifically dual voltage boards, the polarity does matter. Consult the docs of those boards for details.

It's difficult to see in the pic below but the left side is poking through the hole while the right side shows what to do once you get through the hole. It's a 90* bend of the wire onto the pad and finish with solder. Do that for both sides.

Connect Power Wire to Solder Pads

Mounting Heated Bed to Print Bed

Mount the heat bed on the bed mount with four screws, bed spacers or springs, (the base kits have spacers instead of springs) washers and nuts as shown in the picture. The springs will compress a fair amount. This is normal. If your kit included bed spacers, tighten them snuggly. Make sure the screws through the bottom of the bed frame do not contact the main frame as the axis travels.

My perference is to mount the heated bed with the solder pads on the left hand side of the machine. I find that wire management is a bit easier and the potential for the wiring to become unsecure and drop into the Y axis belt path is eliminated.

Complete, assembled heated bed.

Install the Bed Glass

Place the print bed glass on the heat bed ans secure using the binder clips as shown in the picture above. Note the base kits include only one clip per end. That is typically enough but if you would like to use more the clips are small binder clips available at any office supply store.

Routing the Wire

If you've mounted your bed with the solder pads on the left side then you can run your wiring using this method. I zip tie it to the bed frame as seen in the pics. Once you get the wire management complete move the bed by hand a few times and observe how the wire reacts when the bed is moved. You may need to adjust the wire routing slightly.

Wiring Routing