Print top and bottom plates on Prusa

I am assembling my Prusa and wondering what is best to do with the print plates. I'm going to be using a heat bed and sheet of glass on top of that. So do I need the top thick sheet plate or just use the heat bed? Whats best to make it out of? I have 3mm ally plate, 5mm ply wood or 12mm MDF handy. I can go get a sheet of plastic to use if that would be better..?

Cheers,
Phiz

If you will be using a heat bed, then you will want something other than plastic. I don't care for MDF at all, so aluminum might work best for you.
Mine has steel from an old metal cutting bandsaw. It was the upright table for freehand cutting. It just happened to be the correct size.
Also it might be a good idea to insulate between the circuit board and the base ou choose.
This will also help keep the temps more stable.

Thank you for the reply.
Do I need a top and bottom plate as well as the head bed? Or can the heat bed be the top plate?

You will want to attach something rigid on there to attach the heated circuit board to. The circuit board isn't designed to be mounted to the bottom plate. No matching holes. Remember that heat changes the rigidity of lots of materials. There are plenty of pictures around. Build it similar to the instructions. Just save yourself the headache and forego any plastic as a bed support on a heated system. It isn't even good for a non heated bed. Printing itself will warp the plastic.

I use a 1/8" thick tempered hardboard from homedepot for my single build plate on the Prusa 2 with a Mk1 PCB heat bed attached with 4 M3 screws with 2 nuts and 1 or 2 washers as spacers and then a glass plate clamped on top of the PCB. It's been working really well and it's very light and cheap. You can see it in thingiverse.

So you did away with the base plate altogether? How is bed leveling handled? Or is it not an issue?
Thanks.

Actually, Prusa did away with the base plate in Prusa iteration 2. You can easily do this on the older Prusa design. Note that the smooth rod mounts over instead of under the front and rear threaded rods. In this design, there are no springs on the bed. The bed should come out very close to level if you jig the frame correctly. I think since I used cheap hardboard, which are not perfectly flat, I had to add another M3 washer (total of 2) in the rear to level the bed. To allow for give in case the nozzle crashes, the x carriage is either pushed down with a light spring or it just relies on gravity.

Ahh. Okay. Thanks for the info. Most of the prints I do are long rather than tall. Height hasn't yet been an issue, but length has.

I think the bed is still in the same location with this configuration. The only difference is that you save one part: the bottom build plate.

Look at my bed in the pictures here: [www.thingiverse.com]
That is in a prusa 1 configuration (rods below the bars) with a single aluminium plate as the bed.
I have wooden thermal insulators between the bearing holders and the bed.
I built 15 machines like this and only a couple of them needed levelling in the Y direction which was achieved by putting a paper shim between the wooden block and the bed.
Levelling across the X axis is achieved by differentially turning the Z rods.

Good stuff there.
Now I have thought about a stove eye being used myself, but what is that other item? Is it a clothes iron?
Other ready made heat sources I have considered is an old crock pot, hot plate, coffee maker etc. What would be super nice would be the small flat glass stove eyes, but I imagine the later would get costly to buy new.

Finally got the correct SSR to use with the Mendel heated circuit board though and that works great now. It now stays within 1 degree C of the set temp.

Here's how I set up my heated bed, I tried to create clear documentation:
Reprap Blog

Greg,

Wow, that's some heater element! You could fry some bacon and eggs, then start printing. Do you run the heated bed on AC or DC (AC is very dangerous)? How much power does it consume?

I like your designs on Thinviverse, and love your extruder.

Take Care.

I once built a DIY EMC test chamber that doubled as an environmental test chamber for designing and testing light fitting. The room was constructed out of galvanised steel but, because I wanted to mount the light fittings that I was going to be testing without screwing them into the steel, I lined the walls with three quarter inch MDF. It all went ok up until the point where I had to go into the room when it was at 55 degrees C to adjust a fitting. I knew it was going to be hot in there so I held my breath before going in. The adjustment took longer than I though so I was forced to exhale and take a new breath in the room. The fumes did something very wears to my lung and it was a lot of effort to breath out gain.

So, learn from someone who was stupid enough and lucky enough to learn from a big mistake: -

Never heat MDF, especially in confined spaces. I'd go further and say that you should always think twice before using any processed wood product for DIY projects. The fibres are known to cause serious lung conditions and fungicides are frequently used in the manufacturing process.

Leeway Wrote:
-------------------------------------------------------
> If you will be using a heat bed, then you will
> want something other than plastic. I don't care
> for MDF at all, so aluminum might work best for
> you.
> Mine has steel from an old metal cutting bandsaw.
> It was the upright table for freehand cutting. It
> just happened to be the correct size.
> Also it might be a good idea to insulate between
> the circuit board and the base ou choose.
> This will also help keep the temps more stable.

Ha, I just read this while waiting for my experimental chamber heater to heat up a machine in an MDF box.

---

[www.hydraraptor.blogspot.com]

brnrd Wrote:
-------------------------------------------------------
> Note that the smooth rod
> mounts over instead of under the front and rear
> threaded rods.

Why is that? I would assume there is some reason, since keeping the bars below would increase the amount of Z axis movement allowable.

EDIT: Nevermind, I started playing with it and realize that the Y axis becomes restricted 'cause of the size of the large print plate

Edited 1 time(s). Last edit at 05/26/2012 07:33PM by pwn4.