First print!

First print...
The 'repstrap' prints... it actually prints! :) I know that's the whole purpose of the device I've been building, but it is still quite exciting and amazing when everything starts working in harmony and it actually comes to life in a productive way, for the first time!

After months of construction, assembly, alignment, calibration and testing, this past week saw my resprap pass a new milestone. I took a set of STL files (Greg Frost's adaptation of Wades Extruder) and turn them into a useful set of three dimensional objects, right in my own home! It may have gone unnoticed, but up until this point, the objects that these printers produce and the components that make them up, had been completely virtual to me, only existing in the photos and videos of the various RepRap related sites I visited. They're not exactly 'down the shops', or it's not like someone else in the neighbourhood has a 3D Printer spitting out interesting bits'n'bobs that I could get to see and touch.

 I've been working in wood and metal exclusively up to this point, and today everything changed! It was like taking delivery of a StarTrek Replicator! Just magic! :)

(Pict showing general overview of my bench as things came toghther in the last few days.)

I'm really just an enthusiastic follower of this concept, but hopeful that the observations I make and obstacles I overcome along the way, and document here may be of some benefit to other like-minded followers. The real credit and thanks goes out to those who have pioneered this concept over the past few years and kindly shared their work on the RepRap.org site and many associated blogs.

The last mile...
The biggest hurdle for me was getting a stable extruder working, and the current design is hanging in there. The next biggest challenge was the software. Things are not exactly at stage where one could expect to double-click some setup file, take all the defaults, and be up and running in 5min! Our expectations in relation to software have changed greatly, and you need to brace yourself when entering the software world that is used to enable these little devises. My chosen path, through much blog reading and good guidance of others, was Skeinforge for STL processing to gcode, and currently RepSnapper for sending the gcode to my Gen6 hardware, and controlling the temperature.

RichRap's blog has good practical tips on getting started with Skeinforge. Also, once you install the software click on the help button. There's a tone of good links from within the package. The number of settings within Skeinforge' is a bit daunting, but if you follow the links on it's Help page you will build a picture. e.g. Help will link you to it's main Wiki: http://fabmetheus.crsndoo.com/wiki/index.php/Skeinforge.  From there you can find a link to a "Configuring Skeinforge: basic terms" page, or even a list of Skeinforge settings. I found all of these links of some value, but my key point is that they are all anchored back to the help button within Skeinforge.


I'll conclude this post with some very amature video clips of my repstrap printing it's first real objects...

http://www.thingiverse.com/image:53945

and...

http://www.thingiverse.com/image:53942

Thanks for viewing!
No.6

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New build platform

I had reservations about the suitability of my original MDF (6mm) build platform and this past week proved it wasn't up to the job. With my latest extruder incarnation working consistently I was ready to start laying down some plastic, but no matter how much I fine tuned the level there was inevitably some part of the surface that was too high or too low. It proved too much of an obstacle so it had to go! I'm also dubious about the four-point spring loaded levelling approach that's in common use but reworking that is for another day.

I got lucky in my junk collection and dug out a 12mm thick rectangular piece of Perspex (acyclic). What ever it's previous use, it had four domed rubber feed, nicely positioned, one in each corner. They were threaded in place which made them potentially ideal should I need to level the new platform in any direction. I figured it had sufficient weight on it's own to not need much bolting down, so I came up with the following way of positioning it on the Y-buggy.

Above you see the 12mm thick Perspex and it's rubber feet. I've put blue-tape on the top surface.

To seat the new build platform on the Y-buggy I cut a "H" from some MDF and bolted it down (no adjustment). I drilled cone shaped holes using a large countersink bit, in each corner, in positions corresponding to the feet on the new Perspex platform. Then I simply sat the platform feet in to these recesses. It's own weight held it in place. See below photo of my new build platform in place!

Initial alignment testing, by moving the extruder to various locations, showed this new arrangement was much more satisfactory, even without any adjustment of the feet. I tweaked two of the feed a tiny bit and away I went. I laid down a test print with a raft and it took to the surface nice and evenly!

The added bonus is that the platform can be easily removed, and returned, if desired, without any apparent impact on it levelling.

Next post is on how well the printing has in the past week... It has gone well as hinted in the above photo! :)

Thanks for viewing!
No.6

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Extruder Hot-end v2

The previous extruder hot-end served me well as a 'proof of concept'. It showed that a stainless steel down tube, attached to a fan-cooled heatsink, could ensure the filament remained solid and ridged until it entered the hot-end melting chamber, and my single resistor hot-end had the heating capacity required to melt the PLA moving at a steady, if not slow, flow rate. It also allowed me to exercise my cold-end feed mechanism. It worked well initially in a clunky sort of way, but due to it's hand-built nature is soon suffered from repeated stalls. I put this down to the imprecise nature of my hand drilled holes in the SS tube and aluminium nozzle. I felt the introduction of an inner PTFE tube liner would help matters, so over the past few weeks I designed and build a new extruder. Here's some detail:

The stainless down tube is made from a stainless socket head bold. It's head was drilled and tapped with M8 thread, it's shaft drilled out with 6mm hole. The nozzle is an M8 threaded brass rod, tapered cone tip with .4mm hole. The nozzle is drilled out with a 3mm hole to within about 2mm from the tip. The back end of the nozzle has a cone lead-in to the 3mm hole, visible in the next picture.

(A big thanks goes out to a friend for drilling out these components.)

PTFE tube is from http://www.adtech.co.uk/TubeSize2.html   I put the PTFE in the freezer for 10min and tapered the tip with a pencil sharpener until it matched the cone in the back end of the brass nozzle. The heater block is aluminium and unchanged from the previous extruder. I like the heat conductivity capability of the aluminium so am sticking with it for now. Many other designs use brass heater blocks.

I assembled the unit by first threading the brass into the stainless steel tube. There's about 8mm of thread in the SS. The brass was wrapped with plumbers PTFE tape and tightened home into the SS tube. I filed two flats on the brass nozzle to get a good grip. It's a good hand-tight. I had to widen the hole in the heatsink and clamp block to 8mm to receive my new SS tube. I inserted the ss tube into the heatsink as far as it would go and tightened the clamping block up (clamp nuts visible in picture above).

The last assembly step was to thread the heater block onto the brass nozzle. I fitted a Teflon sheet between the heater block and the ss shaft to act as a heat shield. This is off-the-shelf baking tray protector (rated to 260deg C). It also provided a nice air duct for the little fan which I moved to the face of the heatsink, keeping the cold air away from the heater block. The fan is held on with a dab of hot-melt. In testing, the heatsink remained cold to touch at all times once the fan was running.

Detail note: Initial testing of this new design showed that some method was needed to ensure the PTFE tube was held firmly against the cone seat at the top of the brass nozzle. Initially the PTFE tube moved upwards within the SS tube and plastic leaked between the two, jamming the hot-end. I have addressed this issue by chilling the PTFE, inserting it and trimming it flush with the top of the SS tube, and then placing a small washer to cap the PTFE flush with the SS tube. The wooden block was then slid on over the SS tube to hold the washer firmly in place.

Here you see the wooden block that sits on top of the SS tube, (washer not in position). This wooden block pushes down of the washer that caps off the SS tube and is bolted in place with two bolts through the aluminium heatsink bulkhead.

I've had limited printing success with this new extruder, as you can see from the scrappy objects in the photo above. I do need to step back and get the extruder calibrated properly. On the other hand my x and y axes is square and general dimensional accuracy is good. The 40mm square is 40mm! I also need to learn a whole lot more about GCode. The above tests were printed by just downloading the STL files, converting to GCode in RepSnapper and hitting Print!

I'm reading a lot about people using Skeinforge instead of RepSnapper. Should I get into Skeinforge at this point? I don't know... opinions welcome.

Thanks for viewing!
No.6

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Extruder assembled... more testing!

I got the extruder fully assembled, attaching the hot-end to the cold and clamping it all to a static location. I then connected the extruder motor and hot-end to the Gen6 electronics and launched RepSnapper. I knew from hand feeding 3mm PLA filament through the hot-end that it would melt it fine, and from my temperature testing I now knew it could sustain temperatures on the hot-end and not get hot up along the feeder tube once the little 25mm fan was on. It was still interesting to see what might happen once I asked RepSnapper to "Run Extruder"! I made some little video-clips of the special occasion! :-)

This has been great progress. You will notice the extruding filament may seem a bit thick. I've a 1mm hole in the current nozzle, but now that I have it running in a very basic fashion, I'll swap it out for a .5mm nozzle and see how that goes. The extrusion tests in the video are with a RepSnapper manual "Run Extruder" settings of Speed=2000 and Length = 780. These are completely arbitrary units of measure I'm sure, as there are so many other factors at play here, i.e. gearing ratios, the nozzle hole diam. I'm going to have to do a bit more reading now that I have an extruder to test and calibrate! :-)

Thanks for viewing!

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New heater block... new tests!

I made a new heater block. During the previous experments I concluded that my heat block was probably too large and impacting on 'time to target temperature'. I cut the new heater block from some aluminium square bar, working to dimensions from a more established design, and  managed to successfully transplanted the thermistor and resistor from the old block.

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As others have pointed out, it's easily made, if you drill the holes in the block before cutting the final width, in this case 10mm wide.  You can see the newly cut block below beside my original first-go heater block. 

My previous hot-end had the feeder pipe and nozzle threads of equal length, but given the aluminium is much more heat-conductive I thought I'd make the nozzle thread longer, presenting more heat to the melting chamber area. The new nozzle was simply cut, threaded and drilled from some 6mm aluminium rod, keeping the materials the same. There was no question of using one piece of SS straight through. The stainless steel feeder tube was by choice because of it's lower heat conductivity (see here for comparative conductivities), a key part of this design experiment. But anyway, there was no way I would have been able to drill a small hole in the top given the challenge I had drilling a 3.5mm hole in it. Slow drill speed and lots of pressure with a good feed rate was the trick to drilling stainless steel.

I had wrapped the resistor in tinfoil and bedded the thermistor in some PTFE tape so they were easily recovered from the old heater block. I was interested to see how it survived it's regular toasting. Here it is...just after removal.

I refitted them to the new heater block, secured them with some high-temperature silicone, then mounted the assembled heater block back on the aluminium heat-sink ready for some heat testing!

The keen observers may notice I've removed some fins from the heat-sink. I figured it was way too efficient so we'll see how it works now! I also want a short feeder distance, with a quick transition from cool to hot.

The tests: I connected the hot-end back up to the Gen6 board, and plugged in my laptop, launching RepSnapper. I did two basic tests, manually logging the temperature every 10sec as the new rig was set the task of heating to a target temperature of 200Deg C, i) without the little cooling fan on the heat-sink, and ii) with the fan on. The fan was a 25mm/1" 12v fan. Here are the results...

Observations:

The new heater block is a complete success, in terms of reducing heating times, exceeding 150Deg C in under 2min, whereas the old block took more than 5min to reach the same temperature!

The temperature rose more quickly in the 'fan off' test, and stabilised more closely to the target temperature, maintaining about a 3deg higher stable temperature than the 'fan on' test.

The 'fan on' test took about 2min longer to reach it's max stable temperature.

The target temperature in both tests was never reached in the 'actual' temperature display in RepSnapper. The heater-on green light would flicker from time to time as it approached the target temp (200DegC).

Observations surrounding heat transfer to the aluminium vained heat-sink... 

In the 'fan off' test the heat sink warmed up after a few minutes, and eventually reached a temperature at which it was uncomfortable to touch (that's as scientific as I can measure it at the moment! :-) ).

In the 'fan on' test the heat sink remained cool for a good while and eventually reached a touch warm temperature.

Conclusions:

A combination of reduced heater block size and reduced heat-loss through the feeder tube, by using a less conductive material (stainless steel) has brought the 'heat to target temperature' time in to an user acceptable range. (heater block and nozzle are still aluminium.)

The use of a cooling fan on the heat-sink is essential to maintain a cool filament feeder tube (in this design). Remember, a cool feeder tube stops the filament softening and potentially swelling and jamming in the feeder tube, and in extreme cases of upward heat creep, deforming under the pressure of the idle bearing against the feeder spindle. Cold rigid filament gives a good piston effect on the molten plastic in the melt zone and gives good retraction when reversing.

The use of a cooing fan on the heat-sink from the time you turn on the heater is counter productive, and simply reduces the 'time to target temperature' unnecessarly. A better design would be some kind of simple temperature feedback loop from the heat-sink to the cooling fan, turning it on only as the temperature in the heat-sink began to rise. My setup right now is either 'fan on' when heater on, or fan not on at all.

Final conclusion for today is that the stainless steel feeder tube on it's own offers a very rigid and stable method of supporting the heater block and extruder nozzle, no other supports or supporting materials required. While I haven't conducted full extruder/printing tests, initial impressions of the rigidity of this structure are very positive.

Here's another photo from the rear of the heat-sink where you can observe how the stainless feeder tube is clamped in place and passes through the heat-sink vanes.

Thanks for viewing!

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Extruder heater with stainless steel tube...

I wanted to quickly test Nophead's comment in the previous post, that a stainless steel feeder tube to the heater might result in less heat conductivity away from the heater block, allowing the block to more easily reach a desired target temperature. This, as he suggests might be more successful due to stainless steel being a poorer conductor of heat than aluminium.

To test I took a 6mm stainless 'bolt'. It's actually another leftover element of the salvaged bearings from an old set of Rollerblades. I cut one end off and threaded it (M6 die), removed the aluminium tube and fitted the stainless one.

I then inserted the new tube into the heatsink passing through three vanes, giving sufficient contact for this test. I switched on the heater and observed what happened.

Without the fan running this was the result, with a target temperature of 200Deg C set in RepSnapper.

The heatsink was touch warm, but not hot which was an amazing difference in comparison to when the aluminium tube was used. With the aluminium tube you wouldn't keep your finger on the heatsink if the fan wasn't running. With the stainless tube and the fan running on the heatsink the max temperature I recorded was 178Deg C (readings from RepSnapper).

Note: I don't have any special temperature reading equipment. All the readings were taken from RepSnapper and are for relative comparison rather than specific calibrated temperature feedback purposes.

Conclusion: This was a satisfactory outcome, indicating the potential of a stainless shaft to be more effective as a structural connector between a cold-end mounted heatsink and the heater block (hot-end).

Deduction: This approach to extruder design would eliminate the need for more complex supporting side rods or PEEK T-bars. I will still entertain the idea of a PTFE liner inside the stainless tube.

Observing that some PLA that was on the nozzle had melted completely suggests to me that actual temperature on or near the nozzle may have been much hotter than my by now loosely constructed resister/thermistor arrangement was telling RepSnapper!

Photo showing melted PLA on the nozzle, after RepSnapper showed a reading of 190Deg C, an uncalibrated reading.

Thanks for viewing!

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Extruder / heater testing...the less scientific way!

Over the past few evenings I've been 'playing with' my newly assembled extruder. I've read many other blogs and studied the RepRap.org wiki, searching for extruder related posts, but there's been no substitute for trying things out myself! I suppose I could have bought more of the components and availed of the collective knowledge gathered by many, and probably been printing away by now, but for me it's also somewhat about the journey!

So... I got my heater/thermistor and stepper motor connected up, after this little interlude, and mounted the assembled unit on a bracket, not on my repstrap, and started testing. I even wired up my little fan. I started up RepSnapper and 'commanded' the heater to commence heating, 40, 50, 60... 80... 100Deg C, on it went. I got brave and punched in 180Deg C, but coax it as I might it would not heat above 140Deg C! What was wrong?

The heatsink is just too efficient it seems, and even with the fan switched off the maximum temperature I could achieve was 180Deg C. I'm sure some experts out there could have seen this coming, and probably also what happened next. Still itching to see what would happen I fed some filament into it (3mm PLA). Not satisfied with hand turning the wheel I kicked the stepper into action and in went the PLA, into the heater. I got a tiny purge of plastic from my newly drilled .4mm hole before the whole thing just stopped feeding. Reversing was also futile. There it stopped to await it's first autopsy! :-)

Reading back through some of the extruder related articles made a lot more sense now. A short as possible transition zone from hot to cool is good. See the guru Nophead's writings on the extruder subject here, and the benefit of a PTFE lining reducing upward heat migration, and smoothing the path downwards, is also manditory you'd feel if you study Adrian Bowyer's most excellent Universal Mini Extruder design. But flying in the face of the need for any PEEK or PTFE, and the long journey from feeder to heater, is the UP! Extruder design, with simple metal pipe linking 'hot-end' to 'cold-end', and not a special plastic in sight.

So where was I going wrong? Examination of the jamed extruder revealed that the idler bearing that applies pressure on the filament so it's gripped by the nobbed feeder spindle, had completely squashed the filament. See photo below.

In switching off the fan to allow the temperature to rise in the heater, the temperature also rose in the unlined feeder tube, causing the PLA filament to soften and be deformed by the idle bearing lateral pressure. The raised temperature in the feeder tube also cause the PLA to deform, expand and jam.

To remove the jammed PLA i had to heat the dismantled assembly slightly with a hot-air gun and the plastic bits pulled right out.

Determined to continue testing the hot-end I next separated it from the heatsink completely, insulated the shaft in with some glass rope and held it in a small vice. (see photo). There was no difficulty in reaching temperatures a high as 220Dec C in this situation. (12v supply to 6ohm resistor in the heater block).

While I'm not sure of the accuracy of current temperature feedback to RepSnapper I can expect it's a pretty good guideline indicator of temperature. Here's what the RepSnapper temperature control/feedback fields look like. You can also see the manual extruder speed/feed control buttons just below the temperature section. There is a 'heater on' green light also on the Gen6 board which is very handy.

And... by manually feeding some PLA I got a nice free flowing extrusion. (see photo below). It took only minimul pressure to feed the filament. The extrusion did curl as it emerged and I did have to pull it straight just to prevent it sticking to the nozzle, but over all a satisfactory result!

Conclusions:

My heatsink is too large for heat output capability of the resistor/voltage.

I either need a more powerful heater, like the UP! has... 24v 80W heat probe, or I need a better thermal barrier between the hot and cold ends of the extruder. That's back to PEEK/PTFE type design.

Some positive points... the extruder stepper, which I salvaged off and old 5.25" floppy drive, the old photocopier cog wheels, the nobbed drive shaft and the idler pressure bearing all worked very well as a feed mechanism!

Thanks for viewing... comments and questions welcome!

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