Wednesday, May 12, 2010

 

A Heated Bed for Mendel

A little while ago, Nophead made a Dibond heated bed. Dibond is a sandwich of LDPE between two aluminium sheets, and is very flat.

I thought I'd have a go too. Instead of the TO220 resistors he used, I used nichrome wire taped down with Kapton on the back.



Then I insulated that with crack-filler foam, cut down to about 10mm thick with a bread knife.




It seems to work well. Here are the larger Mendel parts printed on it in PLA with it set to 50oC. Their bottoms are f. as pancakes.



I used a piece of ordinary aluminium sheet clipped on the top with bulldog clips to give me a removable tray with good thermal conductivity. That is what has the blue tape on here. The tray is flexible, but the Dibond holds it flat.

I thought it'd be clever to use the 5v supply out of my PC PSU, as that's not being used for anything else. But the current (16A) is a bit silly - connectors and so on get warmish. For the next one I'll run it at 12v and about 7A.

Dibond is rated up to 80oC, which means it's fine for PLA, but might not get hot enough for ABS.

I've integrated it into the host software, the G Codes, and the firmware and updated the copies in the repository. I have to go to Cardiff tomorrow to give a RepRap talk to the British Computer Society, but I hope to put all the details on the wiki over the weekend.

Labels: , ,


Comments:
one thing to keep in mind about the can foam or any type of foam like that. is that when it cools it can warp your bed, or anything you need to stay flat,

but a tip for it, give it a light spray of water, after you apply it, that will help it cure faster
 
Yes - In fact, I sprayed water on the board (pot-plant mister...) before the foam was applied to get it to stick well.

I don't think that distortion from the foam will be a problem. A 10mm layer is mechanically really quite weak, and not capable of applying any serious force.
 
i used to spray polyurethan foam insulation and putting it on a wet surface was the last thing you wanted to do. it is close product to can foam, but not the same. water would cause the foam i worked with to not stick at all to the surface, how has yours stuck.

one thing i would be warry about is the heat from the nichrome would start to melt the foam. the fumes are pretty bad for ya if it is burning.

but good work overall it dose look nice.
 
The can says to apply it to a damp surface if possible... I think water drives the polymerisation reaction (like cyanoacrylate).

At 55 C the foam seems quite happy. Again, the can says it's OK up to 70 C.
 
I am wondering if an extruder controller can be used to control the heated bed, and also an extruder. I believe A6 and A7 could be attached to a Thermistor, and PWM output A could be used to drive the bed. Maybe this is what you already did, I await the designs on the wiki.
 
Good idea for the crack foam. I seen some "heat resistant" foam that (the can states) can go up to 150C .. should be ideal for the bed. I'm using attm "raw wool" as insulator and for the first tests it works like a charm.
 
I use the extruder controller to control the bed temperature as Giles suggests - see the wiki page (http://reprap.org/wiki/Mendel_heated_bed) when I've done it for all details.

It makes more sense to control it with the motherboard, but there aren't the appropriate pins available on the Gen 3/Sanguino one. When we go to Arduino Mega based motherboards there will be no problem of course.
 
don't we have i2c bus on the sanguino? I just made super simple i2c slave controller for the heat bed, should be easily made for atmel type board also .. (could also lose the display and go with even smaller mcu, but I like display's :D )
 
Post a Comment

<< Home

This page is powered by Blogger. Isn't yours?

Subscribe to
Posts [Atom]