Minor updates to my printer (Mendel90 scratch build)

Quick post showing some minor printer updates I've made in recent times:

Moving to the newer Mendel90 x-ends, with their 4-screw bar clamps, has made a good difference to my printer. The older design, (second photo below) was unable to clamp the bar tightly enough and I was loosing belt tension over time. The clamp was also beginning to split along layer plane. The newer design doesn't have this issue as the layers are in compression because of the clamping direction.

Newer x-end installed above. Nophead relesed this design back in Oct 2013, and has been incorporating this design in the kits he sells since then, but if you have an older printer it's worth updating. Full detail on this and other design improvements he has made to the Mendel90 can be found here: 

This is the older x-end design, with it's weaker x-bar clamp arrangement.

I'm trying out an E3D V6 hotend at present, swapping it out for a J-Head which, by the way, I've never had an issue with. I just want try some printing in some materials that require higher extrusion temperatures, beyond that supported by the J-Head.

 To mount the E3D Hotend on Mendel90 without loosing any Z-heignt, I took inspiration from the hot-end clamping idea devised by Ralph Hilton which he shares here: http://www.thingiverse.com/thing:371252. I applied this hot-end clamping approach to Nophead's original extruder, importing the original STL into Sketchup and hacking away there until I got it as I wanted it. It's not pretty, but anyone is welcome to the Sketchup original if you think it's of use. (just give me a shout on the RepRap Forum under user name NumberSix).

Screenshot of extruder modified to clamp E3D V6 hotend in a way that does not result in loss of Z-height. The keen of eye may also observe I've moved the left extruder clamping hole. I want to be able to attach/detach the extruder to the x-carriage without having to remove the E3D fan assembly so have also made an x-carriage with an enlarged hole. See screenshot below.

X-carriage with wider opening to allow E3D hotend to be inserted/removed without taking it's cooling fan off, or detaching it from the extruder block. (one in picture not in my current colour, just test printing it)

One thing leads to another, and if you swap out the j-head (on a Mendel90) for an E3D hotend you'll soon realise the original work cooling fan doesn't fit over the larger heater block of the E3D. So that lead me to Daniel Bull's Fan Duct  which he drew in in Autodesk 123D Draw. A fine job he mad of it too, but it's distance below the x-carriage is set for the E3D fitted to an original (M90) extruder and in a much lower position.

The screenshot above shows my modified version of Daniel's fan duct. I've lowered the mounting points, and adjusted things to make room for the x-belt. It was a struggle but a good way to learn more about 123D Design. Daniel provides a great starting point in his shared fan duct. I added the little cross you'll see in the middle of the duct to help with bed adhesion on this narrow circle. The cross is cut away after printing.

That's it for now! Thanks for viewing.

Ivor.

Print quality issue [Resolved]

With a good number of hours under my belt, a print quality issue began to show up on the new printer. You can see it evident in the side walls of the battery holder pictured below.

A closer view (photo below) shows lots of gaps and a general poor finish.

I entertained a number of possible causes: Too much "retract" when executed, resulting in extrusion not resuming flow in time for printing. I even entertained ambient temperature changes being an unlikely but possible cause of the problem, as Winter was setting in, and considered increasing the hot-end temperature as one of the things to try. But before changing anything, I set another print under way, with a slow print speed (20mm/sec), and had a close look at the printing process in action. (I've made a cut-away fan-duct just for easy inspection, which I must post about.)

On observing the "gaping" happening a number of times during the test print, it was obvious that the large gear that drives the hobbed bolt was slowing down and sometimes stopping, when it should have been turning at a steady rate. Closer observation of the smaller gear revealed the issue. The extruder motor shaft was slipping within the small gear.

I knew from past experience that simply tightening the grub screw was most likely not going to be a long term solution, as had the grub screw been resting against the "flat" on the motor shaft then it wouldn't have slipped even when it had worked a little bit loose. The reversing action of the motor would have resulted in more of a clicking noise than full slippage.

On removing the small gear, it was now clear that the "flat" on the motor shaft was not long enough for the position of the grub-screw on the small gear. I should really have spotted that on first assembly. The grub screw needs to tighten down to a flat surface on a shaft to best secure it in place.

The above photo shows how the "flat" on the stepper motor shaft doesn't extend enough to align with the grub screw in the small gear.

The "flat" was easily extended using a flat needle file. The bearing of the stepper was protected from filings with some 'blue tack'. The shaft was gripped in a small vice. (See photo below.)

The new "flat" doesn't have to be perfect, just enough for the grub screw to seat against. (photo above)

The small gear was refitted, and the grub screw tightened down, ensuring it aligned with the newly filed "flat".

I then reprinted the battery holder and the difference in print quality was immediate (photo below). The plastic flow was consistent and the print finish excellent.

What is also evident, with consistent print quality is that the z-movement on the Mendel 90 is so smooth. Each layer is laid down perfectly above the other on a vertical wall, such as that seen in photo below.

Technical Note: .2mm layer height, with a Width over Height Ratio of 1.8, sliced in Skeinforge. Print speed 50mm/Sec. Now to tidy up my rechargeable batteries!

Thanks for viewing.
NumberSix

Installing and PID tuning new J-Head Extruder

I recently received my new J-Head V Extruder Nozzle. Hotends.com are also now selling a 15mm long 30W cartridge, which fits the J-Head nicely. This is good since the fan ducting on the Mendel90 surrounds the heater block, and it wouldn't fit very well, if at all, with a larger heater cartridge. The 15mm cartridge is neater, and the currently popular 20mm 40W cartridges I've seen around. I also like that it draws slightly less power, at 30W, as I'm always concious of the risk of overheating connectors, wires or even some component a controller board.

The bits and pieces came well packaged. It included a heat resistor, but I plan to use the cartridge. It's good to have the heat resistor as a spare. It has a 100K thermistor, and since the last time I ordered, now includes suitably sized PTFE sleeves for insulating the thermistor and resistor wires. All the heater cartridges seem to sell with wires pre-crimped on and very well insulated, which is great.

The cartridge heater was a close fit to the hole in the J-Head brass heater block, and with one or two wraps of tinfoil it pushed snugly into place. (Cartridge wrapped in tinfoil and partially fitted, in photo above.)

I fitted the little PTFE sleeves to the thermistor, soldered some wires on and insulated the joints with heat-shrink. I inserted the thermistor into the hole in the heater-block, and surrounded it with some car exhaust putty. The wires from both the thermistor and heater cartridge where then zip-tied to the barrel (photo below.).

I thought about using car exhaust putty to secure the heater also, but the wiring is quite stiff, and it's a good fit to the block so it doesn't seem to be drifting. The one reservation I have about the cartridge arrangement is the bend in the wires. I was careful not to kink the very stiff wires, and hopefully they will be fine since they are secured well to the peek barrel. We'll see how it goes.

The J-Head Nozzle is secured to the extruder with three M3 bolts, M4 washers and M3 star washers to ensure nothing vibrates loose. This is Nophead's design, an excellent method of securing the nozzle. The M4 washers sit against the shoulder of the groove in the PEEK barrel and lock it firmly into the perfectly sized hole in the base of the extruder. It's not going anywhere!

I left the exhaust putty to dry for a few hours, connected the thermistor and heater into my connector board, plugged in my ribbon cable and gave the block a few hours at 100 Deg C to bed dry out the putty completely.

PID Tuning

A purchased printer kit, such as Nophead's Mendel90 will have pre-established PID values in the firmware, which will have been set for the characteristics of the extruder. The purchased M90 kit ships with a power resistor (at time of posting), but since I've chosen to try out a cartridge heater in the J-Head nozzle I've retuned the Marling firmware PID values using an auto-tuning feature. The auto-tuning is called on using an M303 Gcode command which is manually sent to the controller from the host software. If the command is executed on it's own it sets a target temperature of 150 Deg C, but to calibrate for different target temperatures the S parameter is added, e.g. M303 S230. You may want to obtain separate PID values for different target temperatures (different materials). 

Once the PID tuning has completed its process it will return a set of constants for you to note and enter.

The PID values can be later sent via a Start-Gcode, written to EPROM if supported, or hardcoded to the firmware. For hardcoding, the values are entered in the Configuration.h file, the firmware compiled and downloaded to the controller.

e.g.

// J-Head Mk V with cartridge heater. IOS 20131002

    #define  DEFAULT_Kp 27.95

    #define  DEFAULT_Ki 4.22  

    #define  DEFAULT_Kd 46.25

Repetier Host has a convenient temperature plotting capability which illustrates what's happening as the auto-tuning runs. You will see it tuning (pict below) to a target temperature of 220 Dec C, although I later repeated it to a target temperature of 230 for ABS, and at 185 for PLA, noting the value set for each.. The nozzle should be allowed to cool completely before repeating a calibration.

The graph shows the calibration process in action. The power is first applied fully, then as the target temperature is reached it is cut, then applied in cycles, reducing a little each time. The power is shown as % over time in Green, and Temperature plotted in Red. The concluding values and finishing message is also shown in the picture below.

After writing the new PID values to the firmware I set a target temperature and turned the heater on. The graph below nicely illustrates the rate of heating, climbing quickly on full power to well over 200, then PID Control cuts in within 10 Deg of the target, set in this firmware line "#define PID_FUNCTIONAL_RANGE 10",  and from there you see the temperature curve climbing again but quickly smoothing out to the target temperature. Also visible is how the power delivery settles to modulate at a much reduced level, maintaining the target temperature nicely (green graph below.). The red curve drops down when the heater is turned off.

Finally, for comparison purposes I generated the same graph on my older printer, with it's Gen6 Controller, J-Head IV Extruder and 5.6 ohm power resistor. See picture below.

There are a number of aspects to compare, the rate of temperature rise and time to reach target temperature, the draw on power, the quality of PID control. There are explanations for the difference in each comparision, but one major conclusion... my new set-up is significantly better in all respects and I look forward to printing with it!

As always, thanks for viewing!

NumberSix

Active cooling of J-Head insulator...

Construction of my self-build Mendel90 continues. Recently my new J-Head hot-end arrived, the final part of the jigsaw! Experience from my other printer has taught me that active cooling beneath the x-carriage has a number of positive benefits. Placement of a small fan that directs cooler air horizontally beneath the x-carriage causes a disruption to convected heat rising from the hot-end, preventing a temperature rise in the x-carriage that might cause deformation if overheated. It also cools the PEEK insulator on the J-Head which then maintains a short thermal transition zone, essential to prevent jamming. (There is a good illustration and explanation of thermal transition zone here on Nophead's blog.)

The current (at time of posting) Mendel90 x-carriage design didn't have a mounting point for such a fan. I had been designing a clip-on fan bracket when I saw Goopy's x-carriage modification to take a direct drive 1.75mm extruder, which included an under-carriage 40mm fan mount. Goopy's x-carriage wasn't suitable for me as he had also altered the carriage opening and extruder mounting-hole positions. So I imported the original x-carriage stl into Sketchup and modified it to meet my fan mounting needs. I also included M3 nut-traps into the design, which makes fitting the fan much easier, especially after the carriage is fitted to the printer. Goopy's lower shroud (half ducting) was of use as it directed the air flow above the stock cooling duct.

Illustrated above is the design change to the M90 x-carriage. 40mm fan mount. Design shared on Thingiverse.

Photo above/below shows first fit of 40mm fan and half-ducting.

Photo below shows new J-Head V in position. 

Below is a view from beneath the x-carriage, showing the new fan in position (right of pict) and the existing larger fan ducting for cooling the work. The half ducting on the new fan redirects air nicely up and over the larger ducting.

Finally below, a side view of the new fan mounted in position. It sits flush under the x-carriage resulting in no change in the length of the the carriage.

Controlling the fan:

The fan takes it's power via the ribbon cable to the x-carriage. The Mendel90 design has spare capacity on the 20 strands of ribbon cable that run to the x-carriage. I have the fan turning on/off automatically from the the Marlin firmware. A pin on the Azteeg X3 controller board becomes active when the temperature of the hot-end rises above 50deg C. This is all set is the ConfigurationAdv.h tab of Marlin (Section shown below.)

// Extruder cooling fans

// Configure fan pin outputs to automatically turn on/off when the associated

// extruder temperature is above/below EXTRUDER_AUTO_FAN_TEMPERATURE.

// Multiple extruders can be assigned to the same pin in which case 

// the fan will turn on when any selected extruder is above the threshold.

#define EXTRUDER_0_AUTO_FAN_PIN   5 //IOS 20130914 //-1

#define EXTRUDER_1_AUTO_FAN_PIN   -1

#define EXTRUDER_2_AUTO_FAN_PIN   -1

#define EXTRUDER_AUTO_FAN_TEMPERATURE 50

#define EXTRUDER_AUTO_FAN_SPEED   255  // == full speed 

The benefit of this is the fan operates automatically under firmware control, and I don't need to add any start/end g-code to drive it. It remains on after the job has finished, but automatically shuts off once the nozzle temperature has dropped below 50, or some other temperature specified in firmware section above.

Thanks for viewing!

Comments and questions welcome.

NumberSix

Extruder wiring connections (Mendel90)

I'm building a Mendel90... A dimension of the prescribed design utilises a ribbon cable to bring power to the hot-end, extruder motor and fan(s) and carries the hot-end thermistor reading back to the printers motherboard.

The Kit version of this printer, designed and sold by Chris (Nophead), has quite an involved connector assembly between the x-carriage and the ribbon cable that connects to it. In scratch building the Mendel90 I came at this connector fresh and have gone with my own take on it, though the essence of the design, a ribbon cable to the x-carriage, is maintained.

I've built a functioning prototype using various connectors from my junk box. I'm using the screw-down connector for heavier wired hot-end power, and simple push-on connectors for the motor and fan(s). The under side has a spaghetti of wires soldered to the various pins.

 Two longer bolts replace the motor bolts, allowing the connector block to be mounted on to the back of the stepper motor. A piece of plastic is placed between the board and motor for extra insulation on my prototype.

You can mix and match connectors to your own preference. The screw-down ones are definitely a good idea for power to the heavier duty wiring on the hot-end, and multiple strands of the ribbon cable are needed to carry power to it. The push-on connectors are fine for fans. The 16 pin ribbon connector might do with some kind of retaining clip to prevent it working loose when printing. We'll see how it goes!

I don't have access to PCB etching or any way of producing a more professional PCB connector block, so this is probably as far as I'll take this idea. I'm happy to share it so others might evolve it if they wish.

There's lots more to blog about with the Mendel90 build. This is just to get things moving again!

Thanks for viewing!

NumberSix

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!



Extruder 'hot-end'...

I've been trying to come up with an extruder 'hot-end' design that doesn't use the expensive PEEK material that is in common use in other designs. My initial thoughts have been to use a salvaged heat-sink, clamping the feed shaft from the hot-end heater, and using a small fan to cool the heat-sink. My experiments over the last few evenings have caused me to question this approach, based on challenges I've encountered during my tests. I think I'll outline my tests in a subsequent post, but for now here are some photos and a general description of my initial hot-end design and construction.

The heatsink and aluminium blocks are all salvaged from some scrap electronics boards. I drilled a 6mm hole to receive an 6mm aluminium feeder tube. It's an 'off the shelf' piece of 6mm tube with a approx 3.5mm hole. (The thermister is not fitted in the photo above.)

I filed the top 12mm of the tube flat on three sides, and cut a square slot to match in what I'll call my clamping block. This aluminium block (salvaged heatsink block) had two convenient slots in it's sides through which I fed two small bolts in order to clamp it to the vaned heat-sink. Here's another view (below) of this assembly in which you can see one of the bolts that clamps the solid block to the vaned heatsink.

My heater is a resistor from Mendel-parts, and a matching thermistor. I secured the resister with high-temp silicone, and wrapped the thermistor in a square of plumbers PTFE tape before inserting into a 1.5mm hole, 4mm deep, a tip I gleened from Adrian's approach documented here.

Here you can see where the thermistor is secured into the block. I added some high-temp glue (used to attach glass rope to stove doors. I had a little left over from another job!). I added some glue to the resistor also. I should use that Kapton tape, but I don't have any at the moment. I think I'll have to order some other bits and pieces soon... building a new wish-list!

The nozzle is a brass cap-nut with a .4mm hole drilled in it. It took some searching but I got some .4mm drills locally (Joe McKennas, Limerick) along with a 'pin vice' from Maplin, also local. There are many great suggestions on the net on how to drill a very small hole, but you know wht worked for me? I put the cap-nut in the vice, dinged and center hole with a sharp nail, then drilled the .4mm hole by spinng the pin vice by hand while applying pressure on the bit. Brass is relatively soft and the tiny drill bit just worked right through it. ( I did try my first .4mm drill in a power drill, catching the pin vice in the power drill chuck, but the tiny bit just snapped like twig - just as well I bought a few.) You should be able to see the tiny hole in one of the photos above. Here I'm using the drill to clear the hole during first extrusion attempt.

That's if for this post. I'll do a little bit on how I got on with wiring and powering it up and some heating experiments, in the next post.

Thanks for viewing!

Extruder "cold-end"...

Here are some photos of my Extruder 'cold-end'. The motor wasn't yet secured in this shot but is now bolted to the base.

The cogs are salvaged from an old photocopier. I realise the smaller cog has typically less teeth in other designs but we'll see how this one goes! The stepper motor is from an old 5.25" floppy drive!

The bearing recesses were achieved by clamping the two 15mm blocks together and drilling a hole 22mm diameter with a flat wood bit to a dept equal to the bearing width, so the bearing would recess until flush with the edge. These recesses hold the bearing snugly in either side of the block.

Here you can see the bearing mounting block for the filament drive shaft, and it's partner, the idle pressure bearing (smaller bearing pinned into the second block.)

This photos shows the nobbed center of the shaft. I nobbed it using an M3 tap following the Wade Extruder instructions. I've used 6mm steel shaft. I cut it to the desired length and threaded both ends and am using M6 nylock nuts on either end. The skateboard bearings came with sleeves which reduce the bearing centers to 6mm, normally an 8mm hole. I'm pinning the large cog wheel with a small bolt through a hole drilled through the shaft.

Here's a photo of my extruder filament drive mechanism components.Everything has been done with minimal power tools, a variety of drill bit sizes, some files, tap and die set, saws and a bench vice. I have some photos of the 'hot-end' which I'll post next.

Thanks for viewing. Comments and questions welcome.