Sunday, December 4, 2011

Idler broke... I broke it!

My 'Idler' broke! Well... I broke it! I applied too much pressure to it and 'snap' went the hinge. See photo:
In recent times the extruder was performing poorly. The flow was struggling and weak. The hobbed bold seemed to struggle to feed filament also. You could hear the filament chipping. It wasn't good. I couldn't figure what was going wrong, and was suspecting a jam somewhere towards the hot-end. The nozzle temperature was reaching it's, by now, usual 185Deg C, and I hadn't changed any settings in recent times, for a change! So, in a moment of frustration I over tightened the springs on the idler, and that broke the hinge.

It was one of the first parts I had ever printed, some months ago, and wasn't of great quality really looking at it now, but would have lasted quite well if I hadn't been so impatient with my troubleshooting. But with it now broken I was faced with a dilemma since I hadn't a spare one. How could I print a new one? But in addition, what was the problem with the extruder, as that would have to be solved before any more printing could resume.
Getting over the broked Idler was easy, if a little temporary. I glued the broken Idler back together and crossed my fingers it would hold until I got a new one printed. And, might aswell use a RepRapped clamp, something I had print earlier!

But what was wrong with the extruder? With a calmer troubleshooting approach now under way I soon diagnosed that the filament wouldn't feed by hand at all. I took the extruder apart, unscrewing the stainless tube from the brass one and removing the PTFE liner. There were no leaks evident, no blockages aparent. It was a puzzle. I reassembled the hotend and clamped it in a vice, plugged it in and brought it up to 185Deg. The filament would feed smoothly by hand as far as the start of the heater, but no further. With nothing visibly wrong I could only conclude things just weren't hot enough. I increased the temperature in steps of 5Deg C, and things began to flow again. When I reached 200Deg things began to flow smoothly again, with hand fed pressure. I took it to 210Deg and it began to blob and crackle (too hot).

In recent days the outside temperature in these parts have dropped to single digits (Centigrade) and frosty at night. The temperature of the garage, in which I keep the printer, had dropped considerably, and I it seems the very cold filament now takes a higher hot-end temperature to compensate. I've been using a blow heater to bring up the air temperature of the garage in the evenings, but obviously the temperature of the filament spools take longer to adjust. I'm going to run the printer hot-end at a target temperature of 200Deg C (PLA) for now and look long term at better heating for the garage!

So...I got it printing...with some bracing on the Idler.

...and soon had a new Idler printed, and another as a spare.

Here's the new one fitted. It's actually a mutch more snug fit, and giving more consistent filament flow. The old one was a bit loose at the hinge.

Finally, you may have noticed the addition of a little 'pull lever' to the top of the Idler. This was easily done in Sketchup, aided greatly by being able to qucikly clean-up imported STL files, using a Sketchup Plug-in called "Cleanup" (tt_cleanup.rb). Taking default settings you can clean up most any imported STL files in an instant. It removes any redundant lines from the model. See screen-shot below showing the imported Idler.stl before and after clean-up and modification. Credit to Greg for the original idler.stl file.


Ok... enought talk... back to printing! :)

Thanks for viewing!

Sunday, November 27, 2011

Look... no fender washers! (608 bearing Idler hub)

With feedback to my previous post suggesting stationary fender designs of any kind were really the wrong direction to be going to reduce belt friction, I "bit the bullet" this evening and went to work on proper hubs for my idler bearings! Here's one of my new idler hubs now fitted to my y-axis. You'll notice the absence of the large fender washers, and I'm glad to see the back of them! :)


I began by reviewing the existing designs such as this one: http://www.thingiverse.com/thing:503 and this one: http://www.thingiverse.com/thing:3970 and even printed some of them out, but didn't like them so I devised and sketched a split hub design, did some test prints to hone in the dimensions and then knocked out a set...


I used the "Multiply" function in Skeinforge to print multiple matching pairs. Then added a dab of adhesive to the inside and clamped them up sandwiching the 608 bearing in the middle.



And here you go... a set of three idler bearings with hubs!

Backing out the threaded rods to remove the fender washers and fit the new hubs to the printer wasn't as big a job as I thought. My printer is screwed to a baseboard so nothing could move very far when I removed the threaded rods. Here's a view of the newly fitted bearing hub from a different angle. The small washers and nuts grip the center hub of the bearing, and the other rim and printed hub are free to rotate smoothly with the belt.
What has struck me is how quick and easy it has now become to devise and evolve a solution, with the combination of a simple drawing package (Sketchup) and the 3D printer at hand!

(I'll throw the Sketchup file for the hub design up on Thingiverse in a while. There are many hub solutions, even similar to this one I expect, out there, but no harm is sharing this one also.)

Regards,
NumberSix

Saturday, November 26, 2011

Belt fender and other ideas...

The traditional Mendel design has large stationary metal washers (fender washers) on either side of the 608 bearings keeping the drive belts on the bearings. The problem many people have experienced with this arrangement is the belt can rub and grip on the washer, causing resistance and leading to motor step skipping, that can ruin a print job.

Despite spending a lot of time aligning my pulleys with the belts on both the X and Y axes, ensuring my stepper power is set to an optimum level, and checking the carriages are running smoothly on their rods, I've still occasionally had the motors skip.

It's as much an experiment in 'design and print' as anything but I devised a clip-on T-bar that keeps the belt aligned on the pulley with minimum resistance. It can also be retro-fitted without removing the bearing.


Sketchup is proving an invaluable tool for a quick 'idea-sketch-print-modify-reprint' way of working. I went on to evolve the 'retro-fit' T-bar concept into the following design (below)... but it's heading back to the washer type solution which I'm trying to avoid. Ultimately, I may just have to strip out the bearings and fit proper rimmed sleeves to the bearings. But for now I'm happy to play with different ideas and possible solutions.

  
You can see the above design in use on my Y-axis, at the motor end of the printer (see photo below... excuse the working chaos!). Not sure it's any better that the washers, but again, it can be retro-fitted without removing the bearing, and it has less contact surface with the belt, and is a slipper material.


By the way... My acrylic sheet had lost it's grip. I couldn't get the first layer to take to it at all. I tried the blue tape but couldn't get plastic to stick to that if I paid it! (no heated bed yet). So I flipped my acrylic sheet (12mm plate - salvage) over and continued on the under-side. I print the first layer really close to the ground to force it onto the surface and it takes nicely. It does leave a lip around the base of the printed objects but that's not a problem for me at the moment.

I discovered later that a quick wipe of white spirit cleans the acrylic surface nicely and renews it's willingness to hold down the first layer. I still have issues though with larger objects which lift at the edges as the object cools. I do need to get a heated bed. I'm looking into the options.

In the interim, there was an idea on Thingiverse that adding 'mouse ears' to your design could help keep it stuck down to your print bed, if you didn't have a heated print bed. I had to try it out, and it seems to work. See the 'mouse ears' I added to the object in the photo below. That illustrates what I'm talking about.
The object is a replacement 'quick release tripod plate'. (It attaches to the base of you camera and attaches to your tripod... unless you loose it, and have to design and print another one! )
Here's the finished item... I'm delighted with the print quality and turn-around time on these one-off items!

The above exercise was a modified derivation of a plate componend of this item: http://www.thingiverse.com/thing:13184 I imported the plate.stl into Sketchup, increased the height so my longer blot would fit, and made it wider so it sat better into the receiver.

(Technical note: Nozzle .35mm, Layer Height (mm) .25, Extrusion Width (mm) .45, speed 40mm/sec, 20mm/sec on perimeter, Pronterface/SFACT.)
As always... questions and comments welcome, and happy printing!
NumberSix

Sunday, November 6, 2011

"We can rebuild..."

"We have the technology... we can rebuild..."
It's more like "spot the difference" really, but regular followers will observe that the transition from wood to plastic has commenced. I've replaced my wooden x-axis components with newly printed plastic (PLA) ones. As I've become more fussy about print quality I've realised a little looseness here and there, and tiny wobbles in the z-rods were showing up as patterns in my printing. I've printed quite a few components for a complete new RepRap at this stage, but with the accuracy of some components now being impacted I chose to do an interim rework of my repstrap.

It's got a new x-end idler. This one http://www.thingiverse.com/image:63587, but instead of fitting real LM8UU linear bearings, I've fitted these printable PLA substitutes http://www.thingiverse.com/thing:12238. We'll see how that experiment goes!
Now, just to mix it up a bit I've put the more traditional x-end motor bracket, http://www.thingiverse.com/image:63177, on the far end, but I've modified it slightly. I'm only using one nut on the z threaded rods. Can't see the point of the second nut and the spring between them. I know it's an anti-backlash design, but I've had only one nut in my wooden design and gravity looks after backlash in the vertical direction. I've no plans to print in zero gravity. :-) Also I couldn't bring myself to use that overhanging motor design, so my motor stays inboard for a more balanced look.

 Final update worth a mention has been my move to printed z-rod couplers, the symmetric ones... http://www.thingiverse.com/thing:11220. I had a steel rod coupler, seen here, but was so rigid it exaggerated imperfections in the threaded rod, resulting in motor and x-axis wobble. The new arrangement is much more forgiving and visibly smoother as the x-axis assembly moves up and down.

I've retained my wooden z-motor brackets and vertexes(?). They are solid and accurate.
The x-carriage and extruder is now fully RepRap, and as you can see from the part on the bed, I'm printing a spooler!

But a key part of improving print quality has been a fresh examination and fine tuning of basics like squareness, perpendicular z-rods, frame triangle distances all equal. I've screwed the unit to a base board to increase rigidity also. Finally, the introduction of better belt-tensioning technique such as found on Gregs x-carriage, and this little unit (http://www.thingiverse.com/thing:10274) have been invaluable in removing print quality issues due to backlash. The use of these fine tuners allows belt tension to be adjusted a little at a time without over tightening, that might strain something else out of alignment.

Here's a quick look at two test pieces fresh off the newly rebuild rig. I'm pleased with the current print quality.


Now to make it go faster! :-)

Happy printing!


Wednesday, November 2, 2011

More extruder improvements...

My extruder design has evolved some more... The last iteration (seen here ) worked quite well, but would succumb to jamming after a few hours of printing. After having to dismantle it once too often it was time to think things out a little further. Here's my latest construction, and some detail on the changes I've made.
Latest extruder iteration pictured above, printing a set of PLA bushings for a friend.

Pict (above) showing most of the components making up my latest hot-end construction.

I identified some issues with the previous design that were addressed in the new version. Here's some of the issues I encountered.

Heat migration upwards through through the stainless pipe was taking place over longer print runs, despite the cooling fan and small heat-sink. When I increased the cooling (larger fan, closer to heat-sink) the hot-end could not reach it's target target temperature.

The heating of the stainless tube and subsequently the PTFE liner and filament was leading to an expansion of the PTFE and softening of the filament, too far from the hot end. It would loose it's rigidity, expand, even buckle and eventually jam.

I didn't want to have to go down the road of a more powerful heater, so I chose to address it from a different angle. I made some basic changes...
a) I narrowed the neck of the stainless tube just above where it meets the brass. This reduced the cross-sectional-area of the tube, reducing the heat bridge, and made a most amazing difference reducing the heat migration rate considerably. This was evident by a faster time to target temperature, due to less heat loss, and the cooling fan was now able to keep-up with cooling the stainless tube, while the heater block easily maintained targer temperature.

b) I cut off some of the upper portion of the brass nozzle, reducing contact area with the stainless steel.

c) I threaded the ss tube fully, drilled and tapped an aluminium block, and fitted some salvaged heat-sinks to the block. This is a bit over-kill in terms of extracting heat from the ss tube, but it does work well, and takes just a little air flow from the fan to keep everything cool.

d) A final problem I experienced, worth mentioning, was the PTFE liner tube moving within the stainless tube. If the PTFE moved away from where it met the brass, the soft PLA would enter that gap, and would eventually cause a jam. My observations are that PTFE expands and contracts significantly with changes of temperature, and this expansion and shrinkage, especially with the length of PTFE I'm using, is problematic. (I can see myself moving towards a fully stainless solution soon - no PTFE liner).

With the PTFE expanding due to heat migration upwards, I also found it pushed out of the top of the ss tube, so I devised a better way of capping the tube, to hold the PFTE in the tube. this is the purpose of the domed cap-nut you see in the photo above, and also below from a different angle.


Here's another photo of the domed nut which caps the ss tube, holding the PTFE liner in place.



I drilled a 2mm hole in the top of the domed nut. Also visible here is the much reduced and newly shaped aluminium plate, which is shaped to slot into my new x-carriage (I'm now using a "Gregs LM8UU X Carriage" ). The domed nut slots nicely into my extruder cold-end which is a "Gregs hinged accessible extruder". I printed that also, so it's been an amazing process printing enhancements! It just gets better and better! :-)



With the extruder fitted and working nicely, I then went on to print a better fan ducting, that would attach nicely to the x-carriage. Rich obliged by sharing his design... Here's my printed version.


That's it for now. Happy printing!

Monday, October 31, 2011

Gen6 Electronics cover...

Recently, there was a neat cover for the Gen6 electronics posted to Thingiverse: http://www.thingiverse.com/thing:12302

It was just what I needed. Up until now my electronics sat to the front of the printer, and quite exposed, as you can see here in an older post. I also wanted to fit a different sized fan than the 40mm one in the original cover design, so I drew-up my own fan holder in Sketchup and printed that off also. It's great having a 3D printer! :)

Here are the components that make up the box. It has a nice base plate with clips securing the lid.


 The cover was a neat fit and all the holes were well positioned to receive the many cables. The ducting spreads the airflow across the heat-sinks below.


I drew the new fan ducting in Sketchup...



Moving the electronics from the front of the printer to the side has given greater access and visibility to the print platform and extruder. I'm very happy with the new location of the electronics and of course the cover.

Happy printing!



Sunday, October 16, 2011

Fridge door shelf repair... Putting the 3D printer to a practical use!

The 'drop-in' shelf in our fridge door broke again this weekend. The original design had weak tabs that hook the shelf on to the door. I repaired these tabs before with epoxy resin but it failed again at the weekend.

It was an excellent opportunity and exercise to apply all the design and printing skills I'd been building up over the past while. I started by taking some measurements from the broken shelf bracket and the tab on the door that held the shelf in place, and then came up with a better stronger bracket which I drew out in Sketchup.

I was able to incorporate the little notches that hold the shelf in place, and even allow for a taper in the door receiver slots. A quick one-layer print was done so I could offer the piece up and fine-tune it's size, then I made a mirror copy and exported .stl files for the left and right hand pieces. The original light plastic bracket had broken off on both sides of the shelf.


test print of new bracket. Excuse the colour! I've no white plastic!


There's the new bracket attached to the fridge shelf. you can see what remains of the original skinny piece that broke away, and the epoxy from previous repair attempts.

I considered a number of ways to attach the new bracket but settled on three small pop-rivets.

(Above) Here's the new bracket which drops into a slot in the door panel.


(Above) Here you can see the pop rivets which secure the new bracket. Final shot below is of the new improved fridge shelf!
A practical application for the 3D printer!

Happy printing!
NumberSix

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"