Arcol blog Just another RepRap weblog

6Feb/10Off

Warming up!

First prototype of my heated bed.

Since my epic fail, I worked on my heated bed.
First I wanted to replicate prusajr version,
aka. a thicker plexi sheet is heated with nichrome wire. I saved some heated wire from a hairdryer:

The problem with this design, that the heating wire is really hard too place accurately on the sheet. So I bought a dremel cutting attachment 566, to cut path inside the plastic, so I could embed my wire into it:

I tried to cut routes in plastic, but even with a guide, it couldn't follow a straight line. At this point nophead published his version, with aluminium and Kapton tape. At that evening I ordered my Kapton tape, which arrived the next week:

I wanted to buy aluminium, but could not under 1000x2000mm for about 200+ EUR. So I decided for a prototype, I should use what I can find around the house. I have found scraps from an old electrical enclosure.
I wanted to use steel at that time, because of my magnet idea (securing the Kapton tape using magnets to the sheet).
I also got some 230/12V transformators from spot lamps:

(Sorry for the green-yellow colored cables, its a prototype, so I dared to use earth cable, only that I had around. They are not connected to real earth.)

I used 6 6.8Ohm 25W power resistors with three of the above transformators (I believe two is enough, see my plan for the next version of this heating bed below) connected in parallel. Also as nophead predicted the steel is pretty bed heat conductor, so at the edge I can touch the bed without burning my fingers. So the heat distribution is not uniform at all, there are 6 heat focuses on the table:

Surprisingly it does not affect the printing quality.

And also here comes an another example why it is extremely useful to have a rapid prototyping machine.
The sheet didnt have the original z limit switch attachement:

So I needed to design some temporary solution. First I fixed the z limit switch with a piece of copper wire and CD cover:

Maybe it is difficult to see, what Im talking about, here is an another view:

While it printed the raft I levelled the bed manually. And I printed my first try of the z limit switch (made in blender):

You can see, the raft was really bad quality. Here is an another picture while almost finished:

The finished limit switch holder is the post picture also:

The big hole was misaligned, so I fixed it with my power drill, and printed the second version of the limit switch. And also a series of refinement. Here is a picture of all prototypes:

Bugs: First prototype's hole was misaligned, so I needed a power drill. The second version had an oval hole, and also I made a little wall, so it does not turn around. The third version had a wall at the other edge of the table.
In all versions I always made some milimeters of placing the holes, the wall, so the final version (which is not pictured here), what is on the machine is a tight fit.

Im not totally satisfied with the z limit switch, and probably I will redesign it in openscad. It is much more suited for this kind of modelling.

It turned out, the steel sheet is not totally flat. It has an error of about 0.5-1mm at the middle.
So I designed a dremel holder in openscad, and let the machine fix
its table.

Stay tuned, the next episode will be more interesting!;-)

IMPORTANT! The next version of my heated bed will be made of aluminium and the kapton tape will be fixed to it using the magnet idea from nophead.

I intend to sell it, I can ship inside the EU. The bed will be a drop-in replacement for the bitsfrombytes' Rapman machine. I want to ship everything needed to get a heated bed up and running, thats include the power supply too.

If you are interested (no obligation!) drop me an email to preorder (at] arcol [dot) hu.
The price will be around 100EUR (+shipping) if there are more then 18 buyers, and 150 if less.

If you have any suggestion, comments, just write it here.

Comments (3) Trackbacks (1)
  1. Take a look at Stratasys FDM process.

  2. (”steal” vs “steel” ;) )

    Do you get issues with thermal expansion of the polyacrylic?

  3. > (”steal” vs “steel” ;) )
    corrected.

    > Do you get issues with thermal expansion of the polyacrylic?
    I didnt tried out heating the polyacrylic finally.

    But the current plexi sheet deformed a lot, so I assume it cant withstand the thermal stress. (I fixed with 12 additional screws. So it was flat enough finally).

    I do believe aluminium sheet is the way to go.