Sunday, June 04, 2006


Making the 0.5mm nozzle work

Prior to each test run I have to go through this ritual of finding out which connection is faulty due to intrusion by felines. After flattening the prongs on a few connectors to make them harder to pull out, I got the whole thing going again this morning, with a 3.5mm hole in the middle of the new PTFE block to cope with badly-mangled feedstock (the threaded extrusion mechanism was distorting it somewhat). Still, I've managed to lay down a closely-filled test article with the 0.5mm nozzle, using the aforementioned strengthened 16mm PTFE insulation block to hold the heater. This one is not going to pop out:

But a number of undesirable changes were needed to make this work. The extrusion speed had to be dropped to around 25% of maximum, with the stage speed needing to be dropped slightly as well (215 out of 255). Attempts to extrude at higher speeds resulted in the 3mm Polymorph/CAPA feedstock getting wrapped around the threaded rod in the Mk2 extruder as shown below. I have modified the design of the poly-holder to prevent this from happening, and Adrian is running one off on the Stratasys.

The extruder mechanism also becomes exceptionally sensitive to feedstock quality under high load. Motor speed becomes uneven at variations of 0.2mm (note the uneven edges of the hexagon above), and joins have to be perfect. I achieve good joins by forcing the melted ends of feedstock into opposite sides of a 3mm hole in a block of PTFE.

A better build of the extruder's threaded rod might help, as will a suggested future addition of a speed controller for the extruder. What would help is if someone could extrude some 3mm feedstock for us. Anyone got a spare plastic injection machine that'll do it ? :)

Simon has changed the code to allow different deposition speeds when depositing on an angle, and also to move down one layer before repositioning the head for the next layer. This should reduce some of the smearing. We also need to move the head to one side while re-heating the extruder, and to deposit a test line before each extrusion to ensure the nozzle is fully-charged.

Any leaks around the removable nozzle are soon exposed at these pressures. I have not yet needed to use PTFE tape to take up the slack, though a silicone 'O' ring or washer cut from tube might be useful. I might drop back to using a 0.8mm nozzle for the next round of tests. 'Course, I'll have to build one first...

Vik :v)

Hi Vic, very nice progress with the extrusion, moving further away from the "blobogon and squeer"you showed us a little while ago!

From what I can understand, making small dia nozzles (like 0.5 or even 0.3mm) is not an issue, just the preasure needed to extrude with them is causing difficulties?
This is real nitty gritty stuff! Great work Vik! :-D
***the stage speed needing to be dropped slightly as well (215 out of 255).***

what's that in mm/sec?
Idle observation. Still looks like you're extruding way too hot.
Making nozzles: I can make fine nozzles, but the pressure needed to make them feed so far is prohibitively high. This may improve with my manufacturing technique.

Speed in mm/sec: Dunno yet. Not timed it. But I will :) (I think Simon has even built this in to the driver).

I don't think I'm extruding too hot. The grey colouration is definitey due to bearing fragments. The dust is even deposited on the face of the PTFE.

Take a look at the 0.8mm extrusion which is done at the same temperature but with less force - and so fewer bearing fragments.

Vik :v)
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