Bed material

From RepRap
Revision as of 15:03, 9 November 2011 by Pawl (talk | contribs) (Experiments with ABS on various bed materials)
Jump to: navigation, search

The bed material needs to satisfy two somewhat contradictory goals:

  • The bed material must stick to the plastic coming out of the extruder. Otherwise the partially-printed part will slide around, then the next layer of the part won't be aligned, and you'll have a big mess.
  • The bed material must not stick very strongly to the plastic coming out of the extruder. Otherwise you'll create perfectly-printed parts that are impossible to remove from the bed without damaging one or the other or both.

Some bed materials work better than others.

PLA and ABS are the most popular plastics for RepRaps to extrude; ABS seems much pickier than PLA about the surfaces it works on.

Experiments with ABS on various bed materials

ABS does not seem to stick to the MDF bed at all.

  • Electrical tape - sticks, but not well enough to stop warping.
  • Glass - doesn't stick at all.
  • CD-Roms - sticks well, gives a nice surface finish, but tends to warp. Build area is obviously very limited (and circular!).
  • Acrylic Sheet - works! ABS sticks to it quite nicely; I had some warping, but I only used 1.5 mm thick Acrylite FF P99 Acrylic Sheet from Cyro Industries. I've got some thicker stuff to test again as soon as I get my extruder running without the flexible drive.
  • 1/4 inch Acrylic Sheet - works very well. Strong enough to resist warping. Rafts need to be somewhat weaker than the part, otherwise removing the part is very difficult.

Wade 2008.10.01

  • Conductive foam (the kind that you use to ship IC chips I have found works very well and you can reuse it as long as your first layer is not deeply embedded.

Bruce W 2008.10.07

For HDPE, a good bed is a 'plastic' kitchen chopping board (probably itself made of HDPE). A raft, such as that produced by the skeinforge software, sticks to the bed, provides a base for the product and enables the product to be removed without damage to the bed.

Jon Wise 2008.11.14

  • Blue (Painter's) Tape

A surprisingly awesome surface. Not enough to stop warping, but relatively cheap and very durable. Some brands even work on a heated bed, so long as you do not attempt to peel them off above room temp (don't try, it's icky).

"Blue painters tape works fine for me with my heated bed at ~70c. As mentioned, it's very important to wait for the parts to cool though, or else the tape will tear when parts are removed. I miss the flat/smooth surface on the bottom of my prints though." -Pawl

  • Kapton Tape

Another good surface, especially when used with a heated bed. Not so great on the pocketbook, but with proper handling a good investment.

Experiments with HDPE on various bed materials

HydraRaptor has done a bunch of experiments with extruding HDPE onto a bunch of different materials -- pictures at "Sticking point"[1].

Of those bed materials tested on this (unheated bed) HDPE extruder, HydraRaptor points out two materials that work well:

  • common foamcore (aka "paper-faced foam board") seemed to work the best.
  • thin sheet of HDPE cut from a milk bottle: it welds to the extruded HDPE, so you would have to put on a new sheet for every bed of parts you make, but (after trimming) it becomes a smooth strong base for the parts.

Other researchers find that, even though the outer paper looks fine after the finished plastic part is peeled off, the interior polystyrene foam starts to melt -- is this going to cause problems for the next part printed on that foamcore bed?

Many people think that the molten plastic "sticks" better to relatively rough surfaces, so the fact that it sticks to the glossy surface of the foamcore is a bit surprising.

One theory that seems to explain his results:

  • When the molten plastic hits a cold bed with high heat capacity or high thermal conductivity, it cools down too fast -- the first tiny point to touch the bed solidifies a (relatively) huge radius of molten plastic around and above it, so relatively few points of molten plastic ever touches the bed, so it doesn't stick and the ends curl up.
  • When the molten plastic hits a cold bed with low heat capacity and low thermal conductivity, it cools down slower -- little or none of the plastic around the point of contact immediately hardens, so as the extruder pushes that plastic down, large areas of molten plastic make good contact with the bed, and it sticks.

And so (at least if you are using an unheated print bed) you want some highly insulating material with low heat capacity as the bulk material of your print bed. The heat capacity and thermal conductivity of the working surface is irrelevant if that surface is thin enough. More important characteristics of the working surface of a reusable bed is that it has a higher melting temperature -- so the bed doesn't melt and permanently bond to the plastic part -- and is relatively hard and smooth -- so pieces of that surface don't leave a residue embedded in the bottom surface of the plastic part.

Further reading

  • Heated Bed mentions some materials used for heated beds, but focuses on things beneath the surface -- the heater, the insulation, and the control electronics.
  • Frame material
  • materials discusses all materials we've used so far in building RepRaps and RepStraps.
  • category:Hot End is another place to discuss materials that won't melt when touching molten plastic.
  • Mendel heated bed seems to recommend using a glass bed.
  • One researcher[2] tried a bed made of a ceramic tile. With the bare tile, PLA did not stick; but PLA seems to work well with tile covered in blue tape.