Heated Bed

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Heated Bed

Postby rocketwiz » Mon Apr 01, 2013 1:22 am

As I've been taking my time with the build I've finally got to the commissioning stage, having recently got my new z-wobble pieces and qu-bd upgrades from Bart.

Turned on my heated bed successfully for the first time today. The bed's a Mk2a with a 6mm sheet of cork tile in between the bed and the carriage plate. It took about 20+ mins to heat up to 110 degrees (measured by the thermistor) but the ikea glass mirror on top took a lot longer to heat up (easily another 25 minutes).

Also despite the cork (ok it's not that thick) the carriage plate still gets hot, nearly 50 degrees. The drive belt is cool but I'm a bit concerned about the nylon bushes on the V wheels. Should I be worried?


EDIT:

Here's a thought - I'm thinking I could use a hot air gun to preheat the surface of the glass to 100degrees.
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Re: Heated Bed

Postby cvoinescu » Mon Apr 01, 2013 1:21 pm

rocketwiz wrote:Here's a thought - I'm thinking I could use a hot air gun to preheat the surface of the glass to 100degrees.

If it was borosilicate glass (aka pyrex), I would have said go ahead. With ordinary window or mirror glass, you'll probably crack it. In any case, be careful not to heat other parts of the machine or your desk while heating the glass. Hot air will spread all over, it won't heat just the glass. Wires and belts are particularly vulnerable, but it doesn't take much to destroy V-wheels either.

It's much easier (and safer) to cover the glass with an insulator until it reaches the temperature (another cork sheet, for instance).
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Re: Heated Bed

Postby brnrd » Mon Apr 01, 2013 2:53 pm

I've preheated window glass using a hot air gun before printing without any issues. Just be careful not to aim the nozzle too close to avoid hot spots.

Also, dead air a much better insulator than cork: http://www.engineeringtoolbox.com/therm ... d_429.html. It would be better to put dead space than a solid piece of cork under the PCB heat bed. I'm sure that the bed will heat up faster without that cork. Perhaps it would be best to cut holes in the cork spacer and just keep the border solid.
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Re: Heated Bed

Postby rocketwiz » Tue Apr 02, 2013 1:18 pm

I like the idea of covering the glass with some cork during the heat up process.

I've got a couple of mm air gap between the bed and cork tile. I also found that a layer of aluminium foil taped to the top of the tile helped. But the carriage plate still got up to about 45 deg - still fairly hot. As the nylon bushes on the wheels should be ok up to 100 deg or so and the delrin belt clamp even higher am I being unduly concerned?

It looks like I need to reduce heat radiating from the bottom of the bed. One possibility which I've just come across might be high temperature exhaust heat wrap (which come in 2 inch widths and only 2mm thick) which has a lower thermal conductivity than cork. I'm thinking of taping some to the bottom of the heated bed (I see the helios beds come with something similar) which should also help the bed to heat up more quickly. Just need to be a bit careful handling this (in particular cut ends) as these are fibreglass based.
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Re: Heated Bed

Postby REdington » Tue Apr 02, 2013 1:47 pm

I used McMaster Carr part #4057K8 on my 300 X 300.

On the 200 X 200, I used 4 layers of fiberglass mat taped with double sided fiberglass reinforced carpet tape. Then taped aluminum furnace tape over the glass mat. It takes about 7 or 8 minutes to heat up to 110 C with the MK 2 heatbed. I have the heatbed about 1/2 inch off the alum bed.

Rodney
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Re: Heated Bed

Postby vgordin » Tue Apr 02, 2013 3:51 pm

I mentioned this in a thread here a few days ago, but Ikea sells a 8.5x11 borderless picture frame. I use the glass for the bed and the backing for an insulator. They're called "Clip" and are 4 for a dollar.
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Re: Heated Bed

Postby rocketwiz » Wed Apr 03, 2013 3:30 am

How did the hardboard work for you?

I've got some exhaust wrap on order and will try that when it turns up in a day or 2. Another alternative may be aerogel based insulation like spaceloft which has an even lower thermal conductivity than air.
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Re: Heated Bed

Postby SystemsGuy » Wed Apr 03, 2013 2:10 pm

LOL - I'm using PyroGEL on the Ordbot, and have a 24x24 piece of AeroGel as well. Read the MDS before you use 'em, they generate some nasty dust.

FYI, you can hold the 10mm PyroGel in your hand and hit it with a torch and not feel a thing - amazing stuff. And yes, I know it's overkill.


rocketwiz wrote:How did the hardboard work for you?

I've got some exhaust wrap on order and will try that when it turns up in a day or 2. Another alternative may be aerogel based insulation like spaceloft which has an even lower thermal conductivity than air.
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Re: Heated Bed

Postby rocketwiz » Thu Apr 04, 2013 12:26 am

As luck would have it I spotted a source of spaceloft (actually spacetherm - same thing) after ordering exhaust wrap. It comes in 10mm thickness - just right to slide it straight under the bed without any need for mounting. I might get some for my next printer :D

LOL - pyrogel is WAY overkill! Spaceloft is rated to 200deg, which should be well within the limits of the bed.
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Re: Heated Bed

Postby bloomingtonmike » Thu Apr 04, 2013 12:43 pm

what gauge wire are you guys running to your bed from RAMPS?

I can get to 95 degrees using a helios bed with two pair of 18ga wires running from the RAMPS.

I am about to try a temp 14ga line from PS to bed through a relay with its coil switched off the ramps to see if I can get to 100+.
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