How to get extrusions to stick well?

Sticky rafts? Or not sticky enough?

I'm having trouble getting the ends of my rafts to stick to the build area of my Reprap. I've had a couple successes by covering the build area with electrical tape, but even then I often have to push down the corners of the rafts just after they are extruded, as they have a tendency to curl up and away from the build area.

Any ideas on how to stick the raft down better? Once I get a decent raft, I seem to be able to build on it nicely, but sticking the raft is problematic. I've been extruding ABS at 8mm/s, slowed down to 4mm/s for the double thick first raft layer. 200 deg C seems too cold for the first layer, 215 works sometimes, haven't tried much at 230.

Wade

Check out nophead's blog - I'm not sure if he ever ID'd his mysterious base material, but at the very least his rafting/temperature build strategies are worth checking out. Also, IIRC Metalab is printing in ABS at 220 C, so that might work for you.

I think my base material is PVC plus a fibrous filler: [hydraraptor.blogspot.com]

Baring accidents it can be use over and over again: [hydraraptor.blogspot.com]
I have made all the parts for my Darwin without having to replace it.

A sheet of ABS should work if you get the temperature just right.

I think Adrian uses balsa wood and smears the first layer of the raft into it to get a mechanical bond.

---

[www.hydraraptor.blogspot.com]

I've been using a sheet of polymorph. When the build is done, I heat it up, peel it off and roll it out for the next build. I've been using a pasta roller to make the sheets.

I use MDF and put the print head so it rather smooshes the extrudate into the bed. Causes a good mechanical bond. Then they normal layer height step evens things out and I get a good build. Also, had to up the temp a bit too.

Demented

A thought just occurred to me. Craft stores have this stuff called "plastic canvas". It's usually used for yarn needlepoint. It's basically just a sheet of plastic grid. Probably PVC or nylon. Tends to come in letter-size (A4) sheets for about $0.50 per sheet. It usually comes in #7, #10 an #14 sizes (indicating number of holes per inch) so that would be 3.6mm, 2.5mm and 1.8mm pitch.

Any thoughts on how that might work as a raft?

If it's flexible you have the problem of how you hold it down. Normal glues don't work because the heat melts them unless the raft material is thick enough. Even the vinyl board I use, which is about 3mm thick, needs to be glued down with Evostick contact glue and held down round the edges with a metal strip. Otherwise when you make a large object like the x-motor-bracket it warps the bed material.

---

[www.hydraraptor.blogspot.com]

Quote

If it's flexible you have the problem of how you hold it down

If you had some rigid strips (presumably of plastic or wood) that were the width of the bed, you could lay them across the edges of your fabric raft, and clamp or screw the ends down at the very edge of the build area.

So long as neither the bed or the retaining strips were too flexible, it should clamp the fabric in place.

Yes but unless the fabric was perfectly inelastic the warping forces would lift it. They have mechanical advantage as a small lift near the middle only has to stretch the fabric a much smaller amount along its length. If you only hold the fabric at the edges you would have to tension it with an almost infinite force to prevent it lifting a significant faction of a millimeter.

---

[www.hydraraptor.blogspot.com]

Ahh. I hadn't thought of that one, clearly

... you can use doublesided duct-tape ...

Viktor

I stopped by the local craft store and picked up some #14 plastic canvas. Attached it to the bed with some double-sided tape. Never got as far as testing warping. The ABS doesn't stick to it.

After several tries, I've given up on the plastic canvas. If I lower the nozzle enough to make the extrusion stick, the plastic canvas melts.

Odd thing is that plain old Scotch double-sided tape by itself worked better than the plastic canvas. Not quite good enough to prevent warping, though.

I also picked up some 3mm balsa to see how that worked. I didn't have much time to play with it yesterday but it looks pretty good. I ran the first layer as close to the raft as I dared and that seemed to help bond it. The raft needs to be held down to the bed pretty tightly, though, as it's fairly flexible. Maybe a thicker piece would be better.

I've also tried printing on a raft of ShapeLock (polymorph). When heated, it sticks to the bed fairly well. Extruded ABS sticks to it but the heat softens the raft and allows the part to pull away as it warps.

And, just for fun, I tried double-sided duct tape by itself. It pretty much sticks to everything except ABS.

I'm tempted to take the various failed ABS prints and melt them down into rafts.

I have not tried balsa with ABS yet but it works well with PLA and PCL. To get it stiff enough I glued two sheets of 2mm balsa together with the grains running at right angles. I.e. home made plywood!

---

[www.hydraraptor.blogspot.com]

Good idea. It did seem to warp on the grain.

nophead Wrote:
-------------------------------------------------------
> I have not tried balsa with ABS yet but it works
> well with PLA and PCL. To get it stiff enough I
> glued two sheets of 2mm balsa together with the
> grains running at right angles. I.e. home made
> plywood!

Tried actual plywood?

No, not as porous and thermally insulating, but might work.

---

[www.hydraraptor.blogspot.com]

Has anyone tried using a heated raft? Something like a ceramic heating element or a peltier coffee cup warmer mounted on the bed with, say, some sort of unglazed ceramic tile on top?

I tried cork last night. Found some A4 size sheets at the local craft store. Less than 1mm thick and about $1 per sheet. I attached some to a board and tried it out. ABS extrusion sticks very well. The main problem is that it's pretty much single-use. You can't remove the print without destroying the cork.

I managed to print on a CD last night with ABS. It gives a great surface finish, but it's difficult to keep the CD flat. Small working area too.

I'm trying to remember if anyone has tried using CAPA as a raft?

Presumably you could heat some up and then roll it out to an even thickness on a suitable underlay. Apply hot water to unstick, or whatever. CAPA sticks to all sorts of things quite readily, and would play nicely with a heat-to-detach peltier in the build bed. Reusable to boot.

I've got vague niggling memories of something like this being mentioned before, and more suspicions that it might come apart in odd ways if really hot plastic was extruded on top of it...

I tried that with Shapelock. The main problem with it is that the melting temperature is too low. The heat from the extrusion melts the raft enough that the build can pull away and warp.

Ahh, I assumed as much. Good to know, anyway.

Sounds like thermally not conductive plus either a affinity to the plastic used or a good porous surface is the key.

I have mentioned it before but how about a melting sugar (185c melting point) onto a flat surface, cooling it, and using it as an extrusion base?

I believe nophead is extruding abs above 200c for at least starting layers. If the sugar melted and then resolidified around and to the extruded plastic it could provide a sufficiently strong base to resist warping. It would be destructive to the sugar base to remove the object but sugar is cheap and relatively easily dissolved in hot water. A sugar extruder could also be used down the line to generate a raft.

Potential Problems:
If the temperature of the extruded plastic is too high it could just burn the sugar base.
Could be too brittle to resist warping forces. Thicker layers or perhaps a composite mixture of sugar and ... fiberglass?.. could make a strong enough base.

One thing I'd like to try is melting down failed prints and rolling them out into rafts. Maybe texture them to make separation easier.

PS all of the information people are gathering on printing temperatures adhesion, layers, and base materials would be great to have in the wiki. Standing on the shoulders of giants, learning from our mistakes, and all that.

Has anyone thought of using PVOH/PVA as the raft material? It was the most promising support material (AFAIK). I think the biggest worry was that it wouldn't dry fast enough during building, but I don't think this would be as much of a concern when making the raft (which is before building). I don't recall whether anyone reported any success in adhering it to our plastics (or adhering our plastics to it), but it would probably work.

So, paste down the PVOH raft (using the paste/support extruder), letting it set (or forcing it to, perhaps with a fan or a heater or something) for a certain amount of time (ranging from the full set time to no time at all), and then building the object on top of it (in such a way that the plastic sticks to the PVOH but not the build platform, and the PVOH sticks to both the plastic and the platform). Then, after building the entire object, remove the build platform and wash it with warm/hot water (this, uh, might not work so well with PCL...), which should dissolve the PVOH and release the build object from the build platform.

I must admit, though, I don't understand the chemistry of the PVA/PVOH, so I'm a bit limited by this. [Edit: removed some silly thoughts.]

Edited 1 time(s). Last edit at 09/10/2008 07:07PM by Joshua Merchant.

How about glass?

I have an old flatbed scanner with an nice flat glass plate in (& a stepper motor + slidey bits).

Tried glass, not sticky at all with ABS. Yeah, this needs to be on the Wiki.