Heated bed mounting question

Hello, I am designing my own 3d printer and I ordered most of the electronics so I can take measurements of actual size. The heat bed is a lot more flexible than I expected(I got the PCB MK2a I believe). I had origionally planned on mounting it just with screws on the four corners and putting a layer of kapton tape on it for a printing surface. After reading some more on the wiki, I have found that this is far from the best way to do things.

The bed is slightly warped already just from the shipping, any suggestions on how to get it flat again?
How would you suggest I mount it?

Things I've thaought of:
Between 2 panes of glass(holes would have to be drilled in four corners I think for mounting. surface mount components would get in the way.)
Metal "X" platform of some sort maybe with some sort of insulater on it(would screw on in four corners and hopefully support the bed well enough that it doesn't warp.)

If you mount the PCB with the solid face up, when it heats it should bow upwards. Just use bulldog clips to secure a piece of glass on top (sized so it doesn't hit the screws and components, i.e. shorter slightly on one side), and when it heats up the bowing should press the PCB against the glass. That is how I mount the PCB heated bed anyways. You shouldn't need to sandwich the PCB or use any sort of bracing.

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Could I attach the glass with kapton instead of clips? If I used clips would I need kapton, or could I print straight onto the heated glass? If I remember correctly kapton is expensice and it would be nice if I could avoid it. Would a piece of plexiglass work in place of glass? I don't know that I will have glass redily available.

The reason most use glass, is that glass is very flat and it stays pretty flat during use as well.
If you print PLA you should be able to print directly on the glass when it is warmed up.
If you print ABS you need to put kapton tape on top of the glass for the ABS to stick. If you search this site you will also find that some are using other means of getting the ABS to stick. Instead of kapton tape some use ABS dissolved in azetone which is then painted as a thin layer onto the glass, forming a thin coating of ABS film on top of the glass.
Glass is a very cheap and effective way of getting a flat bed.
You can also use an aluminium plate on top of the heated board instead of the glass but it may not stay as flat as glass does.
Make sure it does not short any contacts on your pcb
You still need the capton tape for ABS and I think you need blue tape if you use the aluminium plate and PLA.
This is all info from this site, I have only used ABS myself and use glass and kapton tape.
Glass is normally available from any framing place. I use 3mm thick glass. 2mm is probably ok as well.
Using clips to mount the glass makes it easy to remove, and you can have several ready to go onto you bed for rapid printing/change.
As mentioned by NewPerfection above, I also mount my pcb with the solid side up (tracks on the underside). It will then become pretty straight/flat when heated up.
I have also put some kapton tape underneath the pcb near the adges and on the lip of the clip that touches the pcb on the underside. This to prevent or at least make it more difficult to scratch the pcb when removing and applying the clips.

EDIT: I use 4 2mm screws and nuts in each corner with a spring on each to mount the actual pcb with. The springs are from 4 pens (that no longer works that well )

All the best
Jan

Edited 1 time(s). Last edit at 09/13/2012 03:50AM by IceMan.

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fwiw, the guys who got me into this use regular single strength window glass (3/32" in the US, don't know/care what the metric crowd uses but would assume a similar thickness converted) .

Any hardware store that sells glass has that, and most "normal" hardware stores (prolly not home depot types, though I don't know as I don't use them for glass) can cut it to size and will for no extra charge. a ~200x200mm square of glass is probably one of the least inexpensive pieces of this build. (excluding individual screws), and it would pay you in the long run to purchase a couple of them so you have a backup pane.

I am designing a colapsable printer. The bed will be stored in a verticle position. I want to be able to print with ABS, so I will probably just tape the glass to my bed. Kapton isn't electrically conductive is it?

No, Kapton tape is not electrically conductive. Taping sounds like it could work quite quite well if done properly.

The biggest problem I see with taping it on is that at the moment the bed is warped. If I taped glass on it then the bed would flatten out when heated. I think this would make the tape loose.

xiando Wrote:
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> Any hardware store that sells glass has that, and
> most "normal" hardware stores (prolly not home
> depot types, though I don't know as I don't use
> them for glass) can cut it to size and will for
> no extra charge.

I get my glass from Lowe's, about $2.50 per piece, cut to size.

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If taped around the entire periphery I'm not sure the warp would remain. Mine has a slight twist in it, (warp is on an axis roughly corner to corner) and if I were to tape it to a piece of single strength glass I'm pretty sure that warp would disappear. The main thing I'd worry about or will if I use that technique, is the sharp edges of the glass plate when stored and/or moved while in a vertical position, where the weight of the glass is resting on a single edge. speaking from practical experience, (I've replaced nearly every window on my home, including the "old fashioned" storms, and built many as well, glass edges are sharp and only a slight movement can cause a great deal of cutting pressure.

Just flatten the MK board onto the glass plate during the taping. The FR-4 bends relatively easily. ***Unless it has significant warp of more than a few mm, in which case I'd contact the seller and ask for (and if necc, demand) a new board.

I would not use glass with sharp edges. A dremel with a sanding or grinding bit should bevel them easily enough.

yup. I agree. just sayin....never quite know what to expect from folks anymore and feel a certain responsibility to play safety cop

I think you'll be fine as long as you press the MK down gently until you have good contact and tape enough of the edges. I'd be inclined to tape the whole periphery, although it might be overkill.