This is the Salton Hotray H4 food warmer. I'm thinking it could provide an excellent heated bed for PLA as it easily reaches 100° C it's approximately 2 foot long by 1 foot wide, and I'm thinking if I can get another one, then I could have a bed approximately 2 foot square.
The element quickly rises in temperature to 100° C, significantly the "hot spot" is approximately 20° C hotter than the rest of the device.
The Salton Hotray has a very short mains lead. I had a spare two metre lead with a kettle end, but it wouldn't fit because if you look at the white end shown in the picture it has a semi circular cut out which corresponds to a semi circular pin in the socket on the tray. I suspect this non standard kettle lead is just a proprietary device to sell more mains leads.
However it did occur to me that the Salton Hotray may not have standard wiring, hence the inability to use a normal kettle cable. Would be worth bearing this in mind and examining the wiring before adapting it to use a standard kettle lead.
In the following six pictures although it looks like I've got the Hotray upside down, it's actually the infrared temperature sensing metre that's upside down, I have turned the pictures upside down so that you can read the display easily.
I think using this hotray as a bed for printing on offers several advantages. It has its own power supply so it will not tax the Power Supply of the RepRap, in fact using this bed as a stand-alone separate module simplifies the arrangement somewhat.
The main issue will be to ensure that the bed reaches the correct temperature so I'm thinking of adding some sort of digital thermometer to keep an eye on the it. The other issue is the "Power Supply" in that with the bed reciprocating then there is a risk of chaffing the mains power lead, not a good idea!
A quick and simple solution would be something like A Caterpillar track arrangement to support the lead making sure that the lead does not happen to bend around in a tight radius.
The other option would be to come up with some sort of sliding connection with Electric Motor brushes arranged to slide back and forth on a rail of some sort, however I think this would be a little on the elaborate side, and difficult to make electrically safe.
Ian said: Surely speed of printing will be limited because of the weight of it? That's a good point. I'm wondering about using two or more stepper motors in use, like used on the "Z" axis.