9. Bed

Degrease the bed

Aluminum bed
IPA degreaser, soap water, etc.

Action

Remove any possible machining oil, stains stayed on the surface of aluminum bed before pasting the heater pad and magnetic rubber pad.

Attach AC-powered Silicone Rubber Heater

Aluminum bed
Magnetic rubber of PEI plate (optional)
AC-powered silicone rubber heater

Exam

No bubble is allowed!

Action

Repeat step 1 to 3 as shown in the picture below and attach the silicone rubber heater to the bottom side of aluminum bed. If you have ordered a PEI sheet, attach the magnetic rubber to the top side of aluminum bed.

Paste the magnetic rubber to the top side first, because the components on the heater will flip-flop the bed when you push the magnetic rubber.

Make sure no air bubble between heater and bed. If air bubble exists, heat will accumulate at that point due to no metal to conduct heat. Glue on the heater will vaporize and bubble will continue growing until you notice the awful smell. Then you’ll have to peel the whole heater off, clean the glue and re-install it.

Connect Thermal Fuse

Ceramic thermal fuse 150°C
Ceramic terminal block, or butt connectors
High temperature RTV (room-temperature-vulcanizing) silicone

Thank Cube owner Brad Stinson for sharing the ceramic terminal block method.

Exam

Measure the resistance with a multimeter at the 2 connectors to AC power source. The resistance should be:

About 35 ohm for a 110V heater
About 138 ohm for a 220V heater.

Action

There are some different ways to attach the fuse. The fuse reacts faster to over heating if being pasted to the heater pad. Fastening the fuse to the aluminum bed is mechanically stronger. Either one works.

There is another repeatable 150°C thermal switch buried under the rubber patch.

Stripe the sheath so 5~8mm wire is exposed for the ceramic terminal block.
Connect the wires to the block first before pasting them to the heater pad.

Alternatively connect the fuse to using butt connectors:

Alternatively secure the fuse to the corner hole in the bed:

Optionally apply high temperature RTV to to prevent the edges from separation over time. (Image courtesy: SK-Tank owner Michael K Johnson)

Connect Thermal Fuse

(11/08/2022) This method has been deprecated. Use the components in the previous page.

Thermal fuse 130°C
RH bolts M4 x 10 (2)
Nut M4 (x2)

Polyimide tape (a.k.a. Kapton tape, heat-resistant tape. Self-sourcing.)
Thermal paste (optional, self-sourcing.)
High temperature RTV (room-temperature-vulcanizing) silicone (optional, self-sourcing.)

Exam

Both exposed connectors are well covered to prevent electric shock.
The white cylindrical body is fully contacted with the heater so heat can be conducted to the fuse inside faster. Applying some thermal paste around the fuse helps heat conduction.

Measure the resistance with a multimeter at the 2 connectors to AC power source. The resistance should be around 35 ohm for a 110V heater, or 138 ohm for a 220V heater.

Action

Make a small circle at both ends of wires of the thermal fuse. Connect the fuse with the 2 exposed Y connectors, and attached the fuse firmly onto heater with polyimide tape. Multiple layers of tape are recommended.

Optionally apply high temperature RTV to to prevent the edges from separation over time.

P.S. There is another repeatable 150°C thermal switch buried under the rubber patch. Bypass the one-shot 130°C thermal fuse if you think a repeatable thermal switch is safe enough.

Optionally apply high temperature RTV to to prevent the edges from separation over time. (Image courtesy: SK-Tank owner Michael K Johnson)

Kinematic Coupler

Bolt m3 x 15 (2) (front legs)
Bolt m3 x 20 (1) (rear leg)
Nut m3 (4)
Steel ball 8mm with hole (3)
Cable tie or string
Magnetic rubber pad (optional)

Background knowledge

To deal with thermal expansion and to prevent the bed from wobbling, a Kelvin kinematic coupler is used in the bed:

The left-front point is fixed in the front bracket
The right-front point floats in a slot, allowing the bed to thermally expand in X direction but restrict rotation.
The rear point floats on the surface of rear bracket, allowing the bed to thermally expand freely.

Actions

Use two m3 x 15 bolts as two front bed legs, and one m3 x 20 bolt as the rear leg.

For the rear leg only, optionally use an m3 nut as a spacer so the bolt head of the m3 bolt is higher than the printing surface and is used as a stopper of the PEI sheet.

Attach 3 steel balls to the 3 legs of bed as shown in the picture. If you use a magnetic PEI sheet, cut a gap at the corners of magnetic rubber for the bolts.

After ABL sensor fine tuning, secure the bed with a cable tie or a string to prevent from falling in case that bed brackets are not at the same height or faulty Z movement.

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