Sunday, April 22, 2007


What to do next

Just figured out that the polymer pump contains about 24-25 cubic centimeters of polymer and that it's going to take about 9 hours to print it. Keep in mind that I'm running this thing about as slow as I can while I learn how to run it. It's going to be going a lot faster as I get more confident with what I'm doing.

Right now a single axis speed is running 1.7 mm/sec and I'm using single axis prints so that I don't have to upgrade the control software to regulate polymer flow rates. Using diagonal infills will crank that speed up to 2.36 mm/sec. Shifting from 3/8-24 to the much more common 3/8-16 threaded rod will kick that speed up to 3.5 mm/sec.

Shifting over to 14:1 gear ratio hack GM2's, something that I don't intend to do with this model of Tommelise will push that speed up to 8.38 mm/sec. The Mk 1 AEM, as it stands, can pump polymer at an upper rate of about 12-14 mm/sec, so there's not a lot of redesign needed there.

So, for Tommelise 1.0 running at 3.5 mm/sec I can get a production rate of about 6.3 cubic centimeters/hour. Tommelise 2.0, should be able to achieve 15 cubic centimeters/hour.

One big thing I want to try in Tommelise 2.0 is to see if I can spin the thrust collar nut with a gearmotor rather than spinning the whole threaded rod. That should give the system a lot better response to changes in speed and direction and should save beaucoup current. It will also let me dispense with the flanged bearings which cost about $3.80/unit and make up over $20 of Tommelise's parts cost, which is just ridiculous.

Coming back from pie in the sky by and by, the new bushing in the Mk 1 AEM extruder seems to be working fine. I had to get used to the extruder putting out a lot more polymer for a particular setting than it was during the past week because the polymer pump is working a lot more efficiently than it was

I've discovered that I have three distinct vertical sections in the polymer pump instead of two. Again, that's no big deal. I've got the first two working with infill and I should have the third layer, for which I already have the perimeter working with an infill in the morning.

I've apparently got the drift problem sorted out. I ran several layers of the first two vertical sections of the polymer pump and that's looking good.

Now to look at problems I'm having and deciding which ones I should work on next.

First, I need for the control panel to pull the extruder head away from the print when it's finished printing.

Second, I need for the extruder head to lift a few millimeters when it finishes one line segment before proceeding to the next one, proceed there and then set back down to extrude. This should be fairly easy.

Third, I need to see if I can get away without pausing when I get to the end of a line of extrusion. This is a firmware issue. I think that I will try this first in the morning.

Fourth, I've noticed that features in a print job that consist of a bunch of short extrusion lines tend to melt down when they're printed simply because the hot extruder head perforce stays over the same area much longer than would otherwise be the case. I need to see if I can confect an algorithm which will pull the extruder head away for a particular length of time so that.

Fifth, I need to figure out a way to interrupt a print job, recover the absolute coordinates where it was interrupted and then save back the remaining print instructions so that the job can be completed at a later date. That would allow me to shut down the printer at night and start it again the next morning. I'm presuming that it's going to be some time before I'm comfortable leaving Tommelise to its own devices unattended for long periods of time.

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