ZemcikO AL table
Aluminum heated table for REPRAP sinuhed or mendel clone
Status: working (1 month tested wo problems)
Description: Originally designed for my reprap sinuhed project. It is easy to make if you have access to drill a small home milling machine. The cost of input material is low. Published documentation is for sinuhed and Mendel project. Most parts are similar. Main difference is size of alluminium plate and position of heating elements. Compared to Table from printed circuit board this table achieves greater thermal Stability. For printing on Alu u will need kapton tape applied.
Bill of materials
250x250x3 mm Alu plate (~5E)
16mm diameter clear PTFE 200-250mm long (2,5E)
100k thermistor (3E)
ABS printed parts (~10ccm) (0,5E)
Small piece of capton tape (0E)
Terminal Block (4x2) (1E)
Thermal glue 3,5ml (12E)
Compression spring 6*30mm 10N +- (2E)
8x M3*16 countersunk screw + selflock nuts (1E)
4x M4x40 hexa + 8x Wide washer +4x selflock nuts
1x M4x40 imbus + 1x self-lock nut (both less then 1E)
35x3x2000 mm Alu rod (~4E)
36x M3x8mm countersunk screw
36x M3 nuts (both less then 2E)
18x 6R8 3W resistors (6E)
Small piece of aluminium foil (0E)
Total +- 42 Euro
Standard PC power supply wiring
I suggest a power source with higher voltage than 12V. After several attempts, I came to the requirement of a minimum 120W of thermal power. It means u need 1,2ohm for 12V. This value, however, means very slow heating (up to +-30min).
5R6 resistors Preffer wired or vitreous resistors for 2 or 3W. They must be stable at 150°C. For one table u will need 20 resistors. Resistors need to be connected according to the drawing. The resulting electrical resistance is 1,12 Ohm. (If we ignore electrical resistance of wires). For 12V we get approximatelly 128.5W of electrical/thermal power.
4R7 resistors U will need less amout of these resistorsat the expense of a bigger load. (possibly shorter life of resistors). U will need only 16 resistors. Resulting electrical resistance will be 1.175 Ohm. For 12V we get approximatelly 122.5W of electrical/thermal power.
In both cases standard PC power supply with 15A on output, for whole reprap, should be enough.
Industrial power supply wiring
Its much better solution u can use 24V 350W power supply for +- 25-30Euro. This power supply can be set to a lower or higher voltage. I was able to set 21-27V. Just remember this power supply cannot maintain 350W permanently. Safe limit is +- 290W. For connecting to ramps mosfets use 12V swiching relay. It cost around 1,5Euro and works realy well. With 21V u can use 6R8 or 5R7 resistors. I suggest you use a wire type resistors Or resistors for up to 150°C. Standard metalic ones works, but after first test and reaching 130°C, they changed its value! Up to 2/3 of the initial value.
Serial wiring with Industrial power supply
After another year of service and with new experieance i have finally switched to serial wiring. Just now im using 2W 0R1 wired resistors (wired resistors instead of methal oxide ones). They are 0,5mm larger in diameter and cost 3x more. ( 4,5Euro). Metal oxide resistors tend to lower its resistance (-40%) after first heating and after 6-9months copmpletely broke (in paralel wiring all resistors broke at the same time...). And i have found chaeper thermal expoxy glue (10euro for 5g) sold by computer stores called "ARCTIC ALUMINA AATA-5G ceramic Thermal Epoxy".
Main part are made from 3mm Aluminium profile (3x30mm). Any Al profile with 3 and higher width can be used. Even 16mm diameter rod (if u realy like milling). 4mm would be better for increased rigidity. U will need to cut, mill and drill 36pieces plus small simple tablet for termistor. Its good to join 2 corresponding pieces together before drilling central hole.
2-3W Resistors usually have 4,2mm diameter. For better contact use aluminium foil wrapped around the resistor. 10mm wide and 100mm long piece should be enough. Thermistor in separate tablet should be wrapped with small piece of kapton tape.
250x250x3mm Al sheet was used. For conventional mendel u will need to cut it to 210x210x3mm. Draw careffuly position of 8 holes for PTFE isolation blocks. Use punch for center of holes and countersink it to right depth. Bolts should be just unter surface of table. Holes should be countersunk from concave side of AL sheet.
Heating elements are bonded to the aluminum plate by epoxy adhesive with high thermal conductivity. It cost 20-30 Euro for 2-3 Al tables, but i think its worth of its price.
There are resistors with integrated ceramic housing. Maybe it can be glued directly, but remember very different thermal expansion value of ceramic and aluminium...
Thermistor is glued to AL table with small, 3mm thick, AL block 10*10mm, wrapped with kapton tape. U just need to make small 1mm groove in it.
As u can see in photos, im using my own energy chains design for wirings to Al table (and x axis). They are working perfectly and i plan to publish this design independently.
Another models and drawings
File:Ptfe dily 01.pdf Machined parts of ZemcikO Al table.
File:Al dily 02.pdf Machined parts of ZemcikO Al table.
File:Reprap sinuhed heated AL bed v2.zip Step format of zemciko AL heated bed, complete assembly..
File:Topna telesa na desce stolu.pdf Position of heat elements on zemciko Al heat bed. 250mm version.
3D model and photo of working AL table
Heated table works reliably for the second month. With an additional 21V power source is not a problem to reach 150°C in minutes. Using 12V PC supply is much slower (up to 1/2 hour), but it still works.
FE Analysys done in ansys.
- The tests clearly showed a better distribution of heat throu the heated table.
Heated Al bed works perfectly. i can see nice upgrade from pcb prusa MK1 table, next step is heated chamber.... If u have any qurstions or ideas, contact me at [email protected] .