Mini-Kossel-Heatbed

Heatbed design for mini kossels. It is slightly elevated above the base extrusions in order to keep the motors underneath as cool as possible. For the same reason, there's a 3mm cork mat sandwiched between the heater and base aluminum plate. Quick and dirty steady-state thermal simulations have shown that the bottom alu plate will be about 60°C with a bed heated to 110°C.

Experiences after 18 months or so of operation

• It works very well in general, heatup times are below 1 minute
• 1 mm aluminum is on the lower end in terms of stiffness. If I redid this, I'd increase the metal to a least 2 mm

Features

• Fits kossel mini
• Solid construction using lasered 1mm aluminum sheets
• thermal isolation towards the frame using ptfe tubing and PE washers for minimized heat loss and faster heatup times.
• Cork isolation under the heater to protect motors underneath

Required materials

• Cut alu_base, alu_fixture, alu_ring from 1 mm aluminum sheet
• cork, circular, diameter around 180mm
• kapton bed heater, 160mm diameter
• 3 pieces of ptfe tubing 6mm od, ideally 3mm id, 6mm long
• 3x M3x20 and nuts to fix the whole thing to your kossel, as well as three compression springs, approx. 6-9mm in height.
• Your choice of build platform, i.e. boro, regular glass, carbon. Diameter 170 mm

Putting it all together

Check the exploded view and the pics to get a better idea.

1. Align alu_fixture and alu_ring, mark the cutout of alu_ring on the fixture. It helps to stack alu_fixture and alu_ring using M6 screws in the holes while doing this.
2. Glue your kapton heater on the marked alu_fixture
3. Resolder the wires on the heater so that they point towards the heater's center. This way they'll go out nicely in the center hole of alu_base
4. Prepare cork circle, cut out a hole big enough to get the cables of the heater and thermistor through
5. Prepare the screws and ptfe-tubing (see pics for washer detail), put everything together.
6. alu_fixture with glued-on kapton heater
7. alu_ring
8. cork circle
9. alu_base
10. Screw setup from top to bottom:
11. M3 washer
12. Plastic washer
13. Into ptfe tube and through heatbed sandwich
14. Plastic washer
15. Spring
16. Plastic washer
17. Nut in extrusion