heated bed backing

If you have a heated bed, what, if anything are you using underneath it? I'm about to swap my old PCB one, which has warped a bit, for a new aluminium one, so thought I'd put a heat shield behind it to help it warm up. My PCB one won't go over about 90 degrees, takes an age to get that warm, and loses its warmth faster than I don't know what.

I'm thinking a sheet of cardboard would be sufficient? Under operational load it's nowhere near a fire risk, but I guess it could be if there's a problem... Possibly a square of fire blanket? I do have a spare one of those.

I think the best would be ceramic fabric cloth. It can be purchased in different thicknesses, can handle high heat, is one of the better insulators and is not very expensive. I looks almost like it's made of fluffy cotton.

The only problem is you probably have to buy it by the roll. I needed a 4" square piece for a project and I had to buy a 24" x 4' roll. (like $30). Oh, and you can cut it with scissors.

I would use something like Pipe insulation tape it's cheap and easy to apply and it's not fiberglass, ichy ichy fiberglass.. I see some people are using Energancy Blankets as insulation that would be another cheap way to go.

Thanks Mike

Edited 1 time(s). Last edit at 09/14/2014 08:47PM by Miertam.

I bought a roll of cork, used to make cork pin board's. Comes in differnt thickness and fairly cheep. Can be found at most hardware or craft store's.
I cut it to size. then used high temp gasket sealer, used on auto parts, to glue it on the bottom of the heatbed.

cork is good. comes as squares in the form of floor tiles

How about a piece of good old wool blanket? Has an ignition point of 560deg C, easy to get hold of and a proven thermal insulator.
Just a thought.

Excellent suggestions, I hadn't thought of Mylar blankets, although apparently it melts at 254c. I do have a couple in the car though. Ceramic fabric sounds perfect, although I can't find it on Amazon, so might need to extend my search a bit. The pipe insulation tape says in the description not to use on heat wires. Not sure what that means in the context of pipe insulation, but sounds iffy.
Cork sounds nice. Easy to cut and shape and fairly rigid. Apparently it doesn't support its own ignition and just chars slowly, so I think I'm going with that.
The blanket idea sounds nice, but bizarrely we don't have any. How odd is that?? We've got everything but

Use silicone!
I use a silicone hot pad (something you place a hot pot on to protect table)
Go to a kitchen gadget store and get a 8"x8" one for a couple of bucks.

Make your own with a tube of RTV spread out on a piece of wax paper.

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cozmicray
Use silicone!
I use a silicone hot pad (something you place a hot pot on to protect table)
Go to a kitchen gadget store and get a 8"x8" one for a couple of bucks.

Make your own with a tube of RTV spread out on a piece of wax paper.

Ha, If the cork doesn't work, I'm getting gasket RTV and doing the wax paper thing

Cork is very easy to work with, Cork is also Very Cheap, So cheap you would think it grows on trees.
you can see the thermal conductivity of Materials here, [www.engineeringtoolbox.com]

You can see Cork comes in pretty low conductivity (cork board is 0.043, while Aluminium is 205 (at 25c) coper is rated at 400)

and any insulation material wants to be around 0.035 - 0.16, so for your price cork is probably easiest to source

I have a roll of Cork on order, should be with me today, so fingers crossed. I've bookmarked the toolbox, that's a top notch resource From the list, if cork doesn't work I might try using "Beef (Lean)"

Robert uses a rescue blanket. This silvery foil to protect against the cold: [www.reprap.org] He sent me such a bed and it works very well.

---

Generation 7 Electronics	Teacup Firmware	RepRap DIY

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Traumflug
Robert uses a rescue blanket. This silvery foil to protect against the cold: [www.reprap.org] He sent me such a bed and it works very well.

I read through that whole process on the train home today and it looks entirely doable but I have to admit I find it slightly scary. The rapid heat up times appeal though, so I might try to build one as a prototype and see if I can run it without burning the house down.

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UkIan

Quote
Traumflug
Robert uses a rescue blanket. This silvery foil to protect against the cold: [www.reprap.org] He sent me such a bed and it works very well.

I read through that whole process on the train home today and it looks entirely doable but I have to admit I find it slightly scary. The rapid heat up times appeal though, so I might try to build one as a prototype and see if I can run it without burning the house down.

I'm going to give this a go, and have a couple of questions.

1)
First, the heating wire: He's using 24swg copper for the heating and 17(?)swg for the connection to power? 17 doesn't exist, I'm using an online calculator to convert what he's written to what I buy.

2)
I looked at Nichrome, but it has a resistivity of 100 ohm per meter and he is using 6 meters of wire in his design. Copper is 1.8 ohm per meter, so I'd have to use 50 times less or make it 50 times thinner. Is there a benefit of either (or more sensibly a combination of the two)?

3)
I assume the wire he is using is that stuff that looks like it's been laquered with Kapton. Is there a name for this? I've not done well googling it.
EDIT1: Hazzaah! Is this right?

4)
I've got a roll of 20cm wide Kapton, I assume this is a good option for insulating the aluminium from the wire and wire from itself AND sticking everything together?

From there I think I'll be fine

Edited 2 time(s). Last edit at 09/22/2014 03:19PM by UkIan.