Wednesday, September 28, 2011

Graphing temperature - Part II

Being able to easily graph temperature has allowed a quick evaluation of heating performance with different fan positions and air flow arrangments. The primary objective of the exercise was to find a good balance between active cooling (fan) and heating the 'heater-block' to a given target temperature.

The active cooling is necessary to prevent heat rising through the stainless steel tube to the cold-end. Since my design does not incorporate a thermal barrier material (e.g. PEEK) it is necessary to provide cooling, but too much cooling would prevent the heater-block from reaching 'target temperature', as I had experienced.

An excellent balance has now been achieved through the process of graphing the temperature curve, and tweaking my cooling set-up. Here is a graph of the key findings.

Observations: Heating with the fan 'off' resulted in a prompt climb to the target temperature, but the heat was quickly rising throughout the assembly and I had to shut it off. This hot-end arrangement could not function without active cooling.
With the fan 'on', but the air-flow not focused, the temperature in the heater-block rose more slowly and did not ever reach the target temperature (210Deg C). I attribute this to fan air also cooling the upper brass portion of the brass nozzle (see photo or previous blog posts).
The best result was achieved (middle graph line) when I positioned some 'teflon' sheet to direct the air toward the stainless down-tube and the attached heat-sink, and away from the brass upper portion of the nozzle. See photo below for visual illustration of the successful cooling arrangement.


Conclusions: 'Target temperature' can be achieved with a good balance of cooling and heating.
Careful directing of air flow is essential.
Stainless steel is an excellent alternative to PEEK as a hot-end support material because of it's relatively poor head conductivity and it's superior strength, but works best if cooling is assisted with some kind of heat-sink and active cooling (fan).

Additional note on the graphing process: An unexpected benefit of moving from FiveD Firmware to Marlin Firmware on the Gen6 board was the excellent temperature feedback. The readings were echoed to screen neatly and to two decimal places. Moving this data to Excel for graphing was a doddle! Simply 'select' copy/paste, then find/replace 'ok T:' with 'blank', and a new line of data can be added to the graph in seconds.

Pronterface showing Temperature readings illustrated above.

Thanks for viewing.
NumberSix

Monday, September 26, 2011

Graphing temperature - Pronterface manual 'hack'

I wondered if there was a better way to log the temperature change over time as the heater block warmed up. It's only something you'd do occasionally if you were assessing something in particular, so it's just a bit of fun, and may be of value to others. I had observed how Pronterface would read the temperature at regular intervals and echo the reading to screen, once the 'monitor printer' box is checked. If you leave it 'echo' as the heater block warms up it will log that entire process in the window.
Once a desired temperature is reached you can scroll back through that entire data stream selecting it as you go. Then copy/paste to Excel. You can clean it up quickly in Excel by adding Headers, Filter on Column A, only selecting rows beginning with "T". Copy/past those readings to a new Tab. The slightly unscientific bit is adding the time-line. My estimate is that there are 3seconds between the temperature readings, so with that info added to a second column I was able to graph my temperature graph (below).

Graph of Heater Block heating from room temperature to operating temperature, with cooling fan 'on' and 'off'
Other detail: Target temperature set to 210Deg C, 12v supply, aluminium heater block with 6ohm resistor, 100k thermistor, Gen6 electronics, 'teflon' lagging jacket!

Observations: Despite the heater block never reaching target temperature, I could see the PLA beginning to ooze from the nozzle as the temperature passed 170Deg C, and if I manually fed turned the cogs it would easily extrude plastic which from experience I could see was flowing well enough to start printing with.

If I allowed it to heat further I could hear the plastic beginning to crackle, so I cut off the heater. That's where you see the 'no fan' graph top out at about 190Deg C after about 3.5minutes.

All my printing in the previous post was done with a temperature reading levelling out at about 185Deg C, but never reaching the target temperature of 210Deg C (which I know is a bit high anyway).

Conclusions: I have a lot more to learn about the heating process, the feedback loop, and calibrating it.
I need to measure the temperatures accurately (borrow a digital thermometer) if I'm to understand better what's going on!
The fan could be having a cooling effect on the thermistor (they are both on the same site. I might move the fan and observe what happens, now that I have an easy way to graph the heating process.
I don't know how it is self-regulating to a nice temperature for printing, other than the fan is balancing the temperature nicely (seems unlikely).

Note: If I've got my estimate of the temperature reading interval wrong in Pronterface then my graphs are off (but not my much hopefully!). [Now don't anyone tell me there's a button in the program to graph all this already! :)  ]

Feel free to drop me an email or post comment if you have anything to share on control or calibrating this heating process.
Contactable on forums.reprap.org  Username "NumberSix"

Sunday, September 25, 2011

Extruder evolution - 1.75mm with stainless support

I've build a new extruder. I started with a 'pre-owned' 1.75mm brass nozzle I acquired from a fellow Irish Reprapper ( AMK ), following terminal failure of it's PTFE insulator.


My new extruder consists of  Greg's style cold-end, adding a raised tab to the idler block, similar to RichRap's mod here. That was my first exercise in modifying an existing design using Sketchup. It worked well.

I added an aluminium base plate to the cold-end to protect it, and to give me an anchor point for the stainless steel down-tube/support. I've been evolving the stainless steel down-tube for a while now and this variant consists of a 8mm (approx) rod, about 60mm long, threaded at both ends and drilled through with a 4mm hole, to take a PTFE sleeve of 4mm OD and 2mm ID. Note: I sunk a 4mm hole an additional 2mm into the brass nozzle to receive the sleeve beyond the joint of the stainless rod and brass. This is so the joints are not all aligned, reducing risk or leakage.

The aluminium plate is threaded and the stainless tube locked in position with a standard M8 nut on top. I had to file the edges off the nut to allow it to fit snugly in the hole at the base of the PLA cold-end. The 'standard' brass nozzle was threaded on to the stainless tube.

I re-employed an aluminium heater block, which I had cut and used previously in an earlier design (seen here ), but this time wrapped it in PTFE ('Teflon' oven tray protector). I cut the wrapper such that the brass nozzle would thread down through it, holding it neatly in place. I punched holes in it for the heater resistor and thermistor also. Neat holes were easily punched using a hobby leather punch. I'm hoping the little 'lagging jacket' will give better heat retention in the block and prevent undesirable radiating heat onto freshly printed surfaces below.

Photo shows 'teflon' jacket prior to fitting to heater block.

Here's a photo showing many of the hot-end components just prior to assembly. Not shown in photo but important to my construction is the PTFE sleeve (tube with 4mm OD, 2mm ID). I also encorporated a small heat-sink on above the nozzle, which is visible in other photos.


In this photo (above) you can see the small heat-sink which was drilled and threaded (M8) and fitted to above, but not in contact with, the brass nozzle. This is to rob heat from the stainless tube.


I learned a while back that it's important to support the wiring well. To do this I wrapped some heavy copper wire into a spiral and secured it with a bolt onto the aluminium plate (visible in photo above).

Here's a reverse angle shot of the entire extruder assembly. I'm still using my little salvaged stepper. It's smaller than a NEMA 17 to adapted a face plate. This stepper not as powerful as the NEMA 17 but seems to have no difficulty driving this extruder, especially with the advantage the gearing gives it. It's even easier for it to push the 1.75mm filament through. It is also lighter in weight.


Critical to this design is active cooling. I mounted a compact but powerful fan to the x-carriage and angled the bracket slightly so the air flow was hitting the heat-sink, stainless tube, and aluminium base plate, but avoiding the brass nozzle. In the photo above you can see the cooling fan, and the first item I printed on this new extruder, a 20mm single wall test piece.


I was printing with this new extruder within a few minutes of adjusting one of the delivered SFACT Profiles. I reduced the print speed, and turned Raft off. While I was doing that the heater block was warming up. I ran a few mm of filament through it in open air, then homed it and loaded the test object. I was very impressed with the quality from this .35mm nozzle. It will be excellent for detail work.

Here are some a last few additional general photos from this evening.


Printing an earphone holder from thingiverse.


At this stage I haden't even secured the extruder properly to the x-carriage as the little spring clamps testify, but it didn't budge and the print quality was excellent!

Happy printing!
No.6

Wednesday, September 7, 2011

"Can you hear me now?"

A little printing fun this evening...They call it a Phonecone:  http://www.thingiverse.com/thing:6348
I also like the bigger version they call a Meg-i-phone! http://www.thingiverse.com/thing:6957

I wonder what people would say if I produced it for a conference call in work? :)

On a technical note...
The extruder is working well now. I'm printing at 20mm/sec without difficulty (PLA, .5mm nozzle, 200Deg C). It's not exactly light-speed but things are improving constantly. The PLA bushings on the rebuilt x-carriage (see previous post) can run dry and stick a little on the rods so I've taken to applying a little PTFE spray to all rails with a q-tip. I also apply some to the edge of the x and y belts where they rub on the fender washers. That stops them binding.

I'm currently printing on to 12mm perspex. PLA takes nicely to it but I will need a heated bed (not perspex) for printing larger pieces. I abandoned the blue tape. It was a constant lottery as to whether the first layer would stick. The surface of the perspex won't hack it long term though. It scratches easily. I can see now why people use pyrex glass and other heatable surfaces with kaypton tape.

Finally... despite my best efforts I occasionally crash the nozzle into the print bed. (must secure the z-opto stop a little better) I don't have springs on my print bet so instead I've devised a sort of shock-absorber for the extruder. I've fitted a spring to a long M3 bolt that holds the front end of the extruder to the x-carriage. See photo... The clamp rises up if the nozzle hits the print platform.

Thanks for viewing!
NumberSix

Sunday, September 4, 2011

Improving my extruder...

I build my first extruder using an old stepper motor (old 5.25" floppy drive), and some salvaged printer cogs. It 'worked' but proved to be a bit weak, struggling a little if I tried to increase print speed. The under-powered stepper and poor cog ratios lead to stepper skipping. You'll see it here in an early photo. The good thing was it worked well enough to print new cogs, which you can see in the second photo...
Old exturder. I've replaced the cogs but retained the motor. The motor is compact if a little 'vintage'! :)

New extruder cogs (from Gregs extruder http://www.thingiverse.com/thing:6713 ).
What else have I changed?
Cut a new MDF x-carriage which receives the extruder easily, allowing removal for maintenance or swap-out.
I printed PLA bushings before I dismantled the old extruder, and bolted those to the new x-carriage. I chose these ones (http://www.thingiverse.com/thing:8282) with the bolt holes. I wanted to compare the PLA bushings to the steel bushings I had been using.
I rotated the extruder through 90 degrees, to give a narrower width and hence greater x-travel.
I cut a new hobbed bolt, this one an M8. The old one was in a 6mm bar. This fits the new large cog nicely and grips the filament a lot better.
I built new belt clamps and a fan mounting bracket. Some photos  below...
Rear view. The belt travels through the bridge in the clamps and under the motor.
Side view.

Front view.

Side view, showing cooling fan and it's new mounting bracket. (other experimental small fans since removed).
It's all still a bit 'rough and ready' but it works, and works better than the previous version of my extruder.

So.. why didn't I just print a new x-carriage while I had the original extruder working? Well, my design has the x-rods at 60mm between centers instead of the usual 50mm so I would have had to modify a drawing, and I'm just not up-to-speed on that end of things yet. If I were to change my x-rods to 50mm I'd need to print new x-mounts, z-motor-mounts... and so on, and with my printer so slow it would have been Christmas before it would finish!

It's  chichen 'n' egg as to what I do first or next to improve the speed and accuracy of my printer. Once I get it printing consistently at a moderate speed then I can get it to print a whole new printer rather than swapping out any more parts on itself!

Oh... finally for now, to make life easier the one accessory I really needed was a spooler, so I knocked one together from some scrap wood and a pair of 608 bearings. Works a treat!


Thanks for viewing!
NumberSix