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glasswalker

Heated Bed Ideas & Questions

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So I'm thinking up ways to put a heated bed on the Ultimaker...

I have a bed using power resistors and an aluminum block as a bed for my RepRap. Was thinking about something similar. Problem is the Power Resistors are huge and hang under the board (like 1.5cm) and the Ultimaker bed is very close to the wood plate, not leaving much clearance in there.

So then I thought, I could use a cartridge heater (similar to the heater in the extruder) clamped between 2 pieces of aluminum with half-circle channels milled into it to clamp and provide nice thermal interface to the cartridge heater. This would fit better (And I could use a couple if need be) but the aluminum bottom plate would be likely in direct (or near direct) contact with the plywood plate. What kind of temperatures would be "safe" with the wood that close?

Any other thoughts/suggestions?

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Have a look at my solution

http://www.thingiverse.com/thing:17747

Uses a Mk2 heatbed reprap

As much as I love Arduino etc, it's probably easier to use a commercial PiD controller, especially since you can get kits (PiD, TC and RRS) for $40 on ebay (see https://groups.google.com/d/msg/ultimaker/mDmrWB8ZJd0/ZzAySaBbn9gJ) ... I am waiting for my PiD to arrive and then will get cracking making a heated bed.

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Has anybody tried using TEC/peltier elements for this yet? a peltier element can cool or heat, but with a horrible efficiency.

Proposed setup:

-------------thin glass top---------------------

==========Alu top====================

[peltier] [peltier] [peltier]

==========Alu bottom=================

When you heat up the top, the bottom plate will cool down. When your print is done, you reverse the current trough the peltiers and the top cools down quickly. Hopefully that does not break the glass, but will allow your print to pop off effortlessly.

You do need a full H-bridge to drive it, so either use an extra pin on the arduino, or drive it with an extra pin in tri-state configuration.

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Hello

I use peltier elements for some other applications.

It is important to know a couple of things about Peltier elements:

A single module will produce a temperature difference between its 2 sides that is limited (usually around 65°C). This implies that the temperature of the bed at room temp will be limited. The workaround is to stack several layers of elements...

this temperature difference limit also implies that you can't just add 2 aluminium plates on each sides of the elements.

The top plate will heat and the bottom plate will get colder. If you don't "actively remove the cold" from the bottom plate (eg: by warming it with ambiant air), the heating process will stall very quickly.

Another thing is that Peltier elements lifetime is dramatically shortened when driven with PWM. The elements junctions trend to break when subjected to pulses...

Then either you should keep the modules always at a constant full power voltage (which makes accurate temperature control complicated) or drive them with a stable variable linear power supply.

Gael

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For my bed I ended up at the local metal supply store found here for the USA.

http://www.metalsupermarkets.com/

 

I had them cut me a 240mm (9.44in) by 240mm (9.44in) by .5 in piece of M6 Aluminum Plate.

strait out of the shop it has a tolerance of .005" This is pretty good. And MUCH ! more square then the ultimaker plastic bed.

I clamped the ultimaker plastic bed to the aluminum block and drills the holes where appropriate. 1/8in drill bit.

Installation: I removed the springs and used the longest screws from the kit

From BELOW the bed going up I screwed in these screws. So all my bed leveling adjustments are done from the bottom of the bed

Once the screws were all the way screwed in from the bottom. I used the lock nuts left over from kits. I screwed them about 1/4 in on each screw

I rested the aluminum bed on the protruding screws.

The aluminum block is not attached to the screws, the weight of the bed rests on the nuts.

 

Advantage. You can easily get to all the screw for adjustments, with out the hot end getting in the way.

I feel I get a more accurate bed height with out using the springs.

Its close to perfectly square. I was tempted to bring it to my local machine shop and have them mill it down to .01mm tolerance, but I haven't had platform leveling issues yet with this setup.

Heating the bed is even and easy with aluminum.

Still using blue tape, waiting for the kapton tape in the mail.

BEWARED: You don't get that 1/4in flex if you run your extruder head into the bed. The only flex is from the Arms from that support the bed.

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