Friday, October 17, 2008
The complete screw holder is straight off the board without any trimming, the thin section is more a test to see if the text could be improved.
Material: PCL, 210DegC, 7.5mm/s, 27.5mm/s fast move.
Extrusion rate 9mm/s using 0.5 nozzle
Dimensional accuracy of the part varies from zero to +0.3mm
My material has now run out so printing has stopped for a while, hence the recent blogging.
By the way, many thanks for posting all your work on this and Hydraptor I have used it as a reference from day one, reading it reassured me that we could get some nice parts off the machine.
Can I ask what control you are putting on your Darwin machine, are you running the Ethernet solution?
Forrest - not first try, just the best so far....
Thanks for your intro into Reprap politics, I dont want to go there!
Thanks for your intro into Reprap politics, I dont want to go there!"
Best is just to do what you want to do and ignore dogma in all its forms. Sounds like you are headed in some really interesting directions. :-)
I haven't done PCL recently, but when I did my thermistor was mounted on the nozzle, so running with a fan was no problem. I was extruding at 120C-150C. IIRC Ian's extruder design has it in the fire clay with the heater. I think that may be why people are having problems.
I will probably use a Coldfire with on board Ethernet PHY for my next controller as I have one lying around. I can develop and debug with Codewarrior but release with gcc, so it might be acceptable.
A quick Google tells me gcc can do PIC32, so you might be able to do the same. I.e. develop with MPLAB but release source code that builds with gcc.
I have posted some pictures of Reprapped text for comparison. About the same I think.
I think it needs a 0.3mm nozzle to do it justice.
I am running one of Ian's extruder's and it is fitted with the thermistor in the fire clay just above the tip. For calibration I had a 3mm K-Type thermocouple down through the heater with its tip resting on the back of the nozzle. Temps measured this way were about 10Deg lower than at the site of the thermistor. I remapped the thermistor to the thermocouple. Not the most accurate method but readings should be in the right ball park. I will confess that I have not done any measurements at the tip with the extruder working, having said that, I would be amazed if the true readings were down as low as your settings, maybe the truth lies somewhere in between. I rechecked my notes on the items pictured on the blog, the complete screw holder was done at 205DegC and the test at 210DegC to see if it made any difference. The results are far from conclusive but I think the hotter one has the edge on detail. I will complete these tests as soon as I get resupplied with plastic and let you know. I will also see if I can recheck calibration when running to make sure we are comparing correct temps.
Regarding the compiler, I had also seen some reference to GCC even on the Microchip web site, I think that C32 compiler was developed in GCC. I must have a look to see how compatible they actually are.
Thanks for posting the pictures, I think you still have the edge on detail, I have yet to try other plastics on my machine, I thought I would stick with one type for now and try to get some experience under my belt before I move on.
I think that now a few people are starting to print, is it worth trying to put up a Gallery of printed parts? Maybe split into material type each with brief setup notes. It would be a valuable resource to gauge progress as individuals tune their machines and also to catalogue development of the machine.
PCL melts at 60C and is quite fluid at 120C, much less viscous than HDPE at 240C, so I would be really surprised if you could not extrude it at 120C, which is why I suspect your readings.
There is a gallery of things I have made here.
Thanks for the comments, the heater and thermistor assembly on my machine has given problems with heat loss and lack of power. The current heater has a thick layer of fire cement over the core, the element is wound onto this, the thermistor is positioned just on top of the heater with what I suspect is a very thin layer of cement. I did not assemble the heater so can not be sure. The more I think about it the less confidence I have in the readings I am getting.
I will try and track down some JB Weld and do a new extrusion head with the thermistor on the nozzle to see if I can reproduce your results.
Sounds like the next experiment is shaping up!
I did a quick test last night to get an external reading on the tip. Temps without the fan running were 13DegC Lower than at the thermistor. Conduction down through the K-Type probe must have been significant during calibration. With the fan running it would be much worse.
The Aluminum nozzle has a very sharp reduction in section approaching the tip, the internal drill dia coming very close to the external taper. This will give a high resistance to heat flow or in dynamic terms, the temperature gradient will be considerable from the barrel measurement to the conditions at the tip. This is what I was getting at with my initial comments about the dome nut being relatively good having much more cross section to efficiently flow heat to the tip.
Opening the debate up a little, I am not convinced the use of an extended tip of any kind is a step forward. I have seen mentioned use of Pentel pencil for the nozzle, if anyone does go down this route I bet they finish up cutting off most if not all the extended tip, also I think the CSA is small in terms of heat flow. I think it was one of your designs that is the best “off the shelf” version I have seen ie using a dome nut with a very small nipple machined at the point of extrusion. For a more academic approach, I am sure if we put it out there, one of our fellow Rappers could work up the Thermodynamics to give us the optimum profile of the tip.
Links to this post: