DIY Custom nichrome wire heated bed

[michaellatif]

Here is my design (basic and common to others) for a custom nichrome wire heated bed for the H-1.
Most of the parts are available through a few sources and at your LHS.

Required parts to build heated bed:

1. Nichrome wire x1 (sold per 5 foot section - ultimachine.com for $3.50 USD)
2. 6"x6"x1/8" aluminium plate x1 (McMaster-Carr part number 88685K1 for $5.68 USD)
3. 18"x6"x1/32 aluminium plate x1 (LHS - Home Depot ~$7.00 USD)
4. 12"x6"x1/8" birch plywood (Found at your LHS or Michaels/Jo-Ann's/Art shops ~$4.00 USD)
5. 6"x6"x1/8" heat-resistant borosilicate glass (McMaster-Carr part number 8476K161 for $13.58 USD)
6. Copper wire (~24awg solid core is recommended)
7. Thermistor - pick your favorite
8. Kapton tape (several sizes will help with assembly - E-Bay)
9. flat head phillips screws, lock-nuts and washers, M3 Size, 30mm Length x4 (any size will do, this is what I had on hand. Note the lock-nuts are important, they make keeping the bed together and leveling it easier)

I am putting together instructions on how to assemble the heated bed and will post later this weekend.
Also, I will add instructions on how to mount the heated bed to the H-1

Heated bed specifications:

• Surface area: 6"x6"
• Resistance of attached nichrome wire: ~3.0 Ohms
• Voltage bed is run at: 12 Volts
• Current consumed: ~3.8 Amps
• Max bed temperature: 247F (non-insulated)
• Time it took to heat to 200F: 11 minutes

Assembly of HPB:

• Cut the 1/32" aluminum sheet into three equal 6x6 inch squares OR just cut off a 6x6 inch section for this purpose
• Cut the 1/8" birch plywood sheet into 6x6 inch sections
• Cut the nichrome wire into three 14-15" sections
• Bend nichrome wire into U shape, leave one leg about .25-.5" longer then the other - the size of the bottom of the U is approximately 1.5"
• Start by taping the middle of the three nichrome wires using kapton tape
  Note: I built my HPB so that the three wires run in parallel giving me a resistance of approx 3Ohms (each 12" section is about 8Ohms) running at 12V/3.5Amps - You can decide to run them in series if you want, but in parallel, the HPB heats up faster.
• Continue by taping the remaining two nichrome wires - Its important to leave the tips of the wires exposed for attaching the copper wire!
• Expose ~1/2-3/4" of an inch of the nichrome wire - this is difficult because the coating is adhered well - be careful because the wire can be damaged! Repeat for each end
  Note: I did this by using an exacto knife run along the wire - with my thumb pinching the oppisite side. This technicque works well but if you are not careful you could cut yourself!
• Now attach the copper wire to three of the six nichrome wire leads
  Note: I use wire wrapping technique for this, in the past I have use brass crimps
• Use kapton tape to cover the copper wire
• Use a DMM to test resistance, you should read ~3 Ohms - if you read higher, check your DMM, sometimes the DMM leads add 2-3Ohms.
• Repeat for second copper wire (remaining 3 nichrome wire leads)
• Now tape your thermistor to the center of the HPB and feed the leads out along the copper wire
  Note: At this point I taped ALL of the sheet with kapton tape, this is optional, but assures me that everything is insulated well
• Make a cut out/recess for your thermistor and leads in your 1/8" birch plywood (see picture for details)
  Note: This is necessary only if your thermistor/leads protrude too far as mine did
• Place second aluminum sheet on top of birch plywood and build plate
• Drill four holes in the corners of the bed, mine are 3/4" in from the edges
  Note: I used binder clips to help hold everything together while I drilled the holes
• Use bolts and lock-nuts to hold the sandwich of aluminum/birch/thinner aluminum together

At this point I tested the HPB, seems to work well, equal heating and can handle high temps without issue.

Next will be mounting and leveling (to be continued).

Below are more pictures of the heated bed assembled and being tested.

[michaellatif]

It took about 11 minutes to heat to 200F. I left the heated bed on and it continued to climb, got up to about 247F and struggled to go beyond that. When I attach the bed to the H-1, I will have insulation below the bed that will help retain heat and drive that temp higher!