Sunday, July 02, 2006


Fan-boys and hairspray

I've hooked up a 6 inch 12V cooling fan over the workpiece, manually operated for the moment. Cools everything down in about 15 seconds - including the extruder, causing many reheat pauses and making deposition proceed at a glacial rate. I tried giving it 8 seconds of cooling, but that's not good enough. The objects come out all distorted still. It has to be cooled solid. Looks like some ducting is needed to avoid cooling the extruder too much, and maybe a smaller fan would be better.

In an attempt to make things stick to the glass substrate, I sprayed the glass with a thin layer of "extra firm" hairspray purchased specially for the occasion. To the touch, it feels much less slippery. In operation, the plastic deposits fine onto it.

The problem comes with the new cooling. This causes the plastic to shrink slightly, and I suspect that this is causing the break in adhesion on any relatively rigid surface be it glass or hairspray lacquer.

Too little adhesion, and things curl up. Too much adhesion and you'll never get the blooming thing of. So, I have obtained a range of different sandpapers, and over the coming week (once I've fiddled with the fan and ducting a bit) will attempt a series of cooled depositions on the various grits.

Vik :v)

Have you tried polystyrene foam as a substrate yet?
Vik, (finally noticed I was spelling your name wrong, duh!) Been puzzling over your cooling problems.

Originally I had been thinking of a hose about 4 cm in diameter clipped to the side of the extruder and blowing air onto the work area. That might prevent the extruder itself from being cooled, but I don't know if your system could handle the extra load/mass of a hose. I guess it could be very light and flexible, like off of a vacuum cleaner, and it could dangle from above.

A simple supply of air for such a hose (if a common axial fan doesn't cut it) might be a cheap 12v car vacuum, the portable lighter socket type, used in push mode.

Now reading your update, and the extruder cooling issue, I'm wondering if a simple air deflector installed around the extruder nozzle might do the trick. A little piece of aluminium cut out from a soda can wrapped around it with enough air gap to prevent overheating?

BTW, could extrusion be done on a patch of double sided sticky tape? Sticks to many plastics, yet easy to slice off through the foam layer.
Why not lay down a layer of soluble support material, and build on that? Might help the adhesion, and is easily removed...
Haven't tried polystyrene yet. Dunno how readily the first layer will cool down on that.

I'll be installing cardboard deflectors initially, and see how we go.

I'd like to lay down soluble support material, but I'm not actually capable of extruding it yet. But if it's rigid, I doubt it'll help.

Vik :v)
Vik - how about a water spray? I'm thinking of one of those misters that are used for houseplants. Or methylated spirits (slight fire risk...) - that would evaporate and dry quicker.
Hmmm... a water spray might be the easiest to impliment. A quick visit to a greenhouse irrigation supplier should get you the microsprayer, tubing and solenoid valves for a few bucks.
I'd really like to avoid making everything soggy if I can. All sorts of waterproofing and wife calming issues involved, though I already have a range of aeroponics equipment to hand...

Ducted air blasts and sandpaper. Concentrate, Vik.

Vik :v)

Vik :v)
I've used hot glue guns on polystrene foam, if the gun is too hot, the foam bubbles up under the hot glue!

I have a another gun with two settings, the low one avoids this problem, so it might work for CAPA. If I try to glue two blocks together, encapsulating the hot glue, it takes quite a while to cool and solidify. But, a blob of glue exposed to the air seems to cool at a pace comparable to a blob on light weight wood.

This leads me to another suggestion, why not extrude onto a block of softwood? You can get a peach fuzz effect (think velcro) on softwood like pine easily if it is roughed up a bit with sandpaper. Blobs of hot glue stick to wood, but you can peel them off with your fingers. I've notice a thin layer of wood fibre stuck to the underside. Hardwoods don't show this effect.
I'll get a nice, flat bit of wood from somewhere. All the stuff nearby is somewhat rough or has leaves growing out of it.

I Just stuck some 240 grit onto a glass plate, so I'll be recalibrating and giving that a whirl soon.

Vik :v)
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