Some video of current print speed

I printed this little toy catapult that appeared on Thingiverse recently http://www.thingiverse.com/thing:23051 . Can't say it chucks a penny very far, which is probably a good thing since it got taken to school by my son the following day! I'm sure the teacher just loved me for printing it! :-)

I shot a little bit of video of it printing. If I recall the settings correctly I'm running 40mm/sec on Perimeters and 60mm/sec on infill, first layer at 50% speed. I used the latest Slic3r to generate the gcode, and am running Marlin on my Gen6 hardware. Here's the video...

If you're not bored yet, here's some bonus material of the infill in action, and the last clip shows the last solid layers going in!

As always, comments and questions welcome.

Enjoy!

NumberSix

Simple control of heated bed...

Printing without a heated bed has it's limits. Larger objects begin to curl at the corners and lift off the bed. The plastic just doesn't sit well. I had reached the limits of what I could print without a heated bed so decided to build one. There are a few designs out there, just search under "heated bed" on the RepRap wiki. I chose an aluminium plate with heat resistors as a starting point. I had some scrap aluminium to hand.

The Gen6 electronics has no heated bed control, so I was faced with a challenge, like many other Gen6 owners. (Gen6 Delux board has been introduced in recent months which does have heated bed controls.)

I started with this popular hobby thermostat kit.(also visible here.) In it's standard operation it has a temperature range of 5DegC to 30DegC, and uses a 10k NCT thermistor, and you can manually vary the cut-in / cut-out temperature setting by adjusting the trim-pot. You can change the behaviour of this little thermostat by changing resistor values. They have printed tips directly on the board, e.g. Decrease R5 to increase Max temperature.

With limited electronics knowledge and help from my friend Google, I figured out that changing R5 from 120K to 33K would raise TMax well above the range I'd need for PLA (somewhere between 40 and 60 Deg C), and swapping the 10K R4 resistor for a 100K resistor would allow me to use a 100K Thermistor instead of the supplied 10K one (the 100K resistor (R4) is soldered to the back of the board so looks missing in the photo - don't ask! ) The hysteresis can be changed by changing R7.

From what I had read the little realy on the board wouldn't be up to switching the heated bed, so I salvaged a MOSFET from a scrapped UPS to act as the switch. I had read in Adrian's Prusa Notes how a MOSFET could be used to switch large DC loads that would be drawn by a heated bed. I also watched this mosfet tutorial on how they work and how to wire them up.

The mosfet has 3 pins, Gate, Drain and Source, seen above from left to right. The white wire supplies a voltage, managed by the thermostat, to the Gate pin of the mosfet. The mosfet then allows a more powerful current to flow through from the Drain pin to the Source pin switching on the heated bed. The mosfet can take a much greater load than relay contacts, which would burn out from the switching of a large current. Note: The mosfet will stay 'on' even without a voltage applied to the Gate pin unless there is a 'drain' resistor linking the Gain and the Source pins. This is typically a very high value resistor. My resistor is not visible in the photo but is soldered on the underside of the board.

The next thing I had to do was beef-up the power supply situation. I kept tripping out my salvaged power supplies, so I bought one of these 12v 20A supplies. It's the business! (pict below)

I bolted four heater resistors (2.2ohms) to some 3mm aluminium sheet, two pairs in parallel, then in series. That came to an over all resistance of 2.2ohms and with 12v gives 65Watts roughly. I figured that would do me as a starting point for use with PLA at least. Resistor layout shown below.
I used M3 countersink bolts, tapped the resistor holes and secured them down with some heat conductive paste ensuring good heat transfer to the aluminium sheet.

I thought I might be able to get things to heat faster if I put a higher voltage through the resistors... Above is what happened when I reached19v! There was a popping sound and a puff of smoke! Now I know what's inside these little resistors!

As part of the new heated bed I printed a thumb wheel to make the bed easy to level. I found that springs from some clothes pegs worked nicely on each levelling leg. The little thumb wheel hangs nicely over the edge and makes levelling very easy.

For my first run of the heated bed I placed a piece of glass from an old halogen-lamp, on the bed, covering it with kapton tape. It worked well as a test. It heated nicely. I measured the heat at various points around the top surface using a laser thermometer. I ran some test prints and observed how the PLA was sitting.

The tempered glass was undersized and quite heavy, so when I read how much success RichRap was having with cheap mirrored glass I got a €2 mirror, cut it to size, and clipped it on to the aluminium heated bed. It worked a treat! I'm only heating it to about 60DegC and so far it's surviving nicely. I'm only clipping it on in two places so it's not constrained or over stressed. Hasn't budged yet. I wanted something flat to test print on the mirror so I printed this box. It came out very well. Seen in pict above.

Here's the under side of a z-motor bracket I printed on the mirror heated bed. It's smooth, uniform and perfectly level. It stayed firmly attached throughout the print, and just clicked off once the bed cooled down.

Here's a view of the top-side of the same part.I'm very pleased with the finish. Tech note: 1.75mm PLA, .35mm nozzle, .25mm layer height, 20% fill, 40mm/sec perimeter, 60mm/sec in-fil, 80mm/sec travel.

Through trial and error I've established a position on the thermostat trim-pot that gives a good print bed temperature for printing PLA. I've market that position so I can easily return to it. The thermostat has a convenient red LED that clicks on/off as the bed temperature is reached, drops slightly, then is raised to it's target temperature again. I've found the current hysteresis pattern of the thermostat to be satisfactory but if I wanted it to respond more quickly to falling temperature I could simply swap out resistor R7 for a different value. 

Conclusions:

Low number of resistors gives uneven heat distribution and possible hot-spotting. This is only been observed by taking temperature reading from various points around the board after the heater has been on for a while. We'll see how things go as I try print larger objects or multiple objects.

The little thermostat controller board is a convenient semi-manual way to manage a heated print bed. A mosfet is a key component for switching larger DC loads.

The cheap mirror makes a good print surface for PLA. I might get a second one so I can remove one job and start a second.

Thanks for viewing. Comments and questions welcome. I'm also contactable on the RepRap forum under the username "NumberSix".

Y-carriage upgrade.

If you're like me, initially buying just the bare essentials and building practically everything else around it, you will at various stages along this road want to, if not need to, replace and improve many parts of you printer construction. So it was with my y-carriage, the old one pictured below.

I printed four lm8uu bearing holders (http://www.thingiverse.com/thing:10287). There are many to choose from. I chose these ones because they stand the carriage plate off the rods. That allows the printer platform to compress further onto it's springs, increasing tension and stability, but still overhang either end as it travels. 

The new y-carriage is made from some 3mm aluminium, cut to 230mm x 140mm aprox. Holes marked and drilled to bolt on the bearing holders. Picture also shows y-belt clamp and tensioner, which I transferred from the old carriage.

My older platform had only three bearings. The new one has four. My observation at this point is that while four bearings might seem to be better from a support and stability point of view, it brings alignment challenges you don't have with three. It proved tricky and time consuming to get them all aligned and the carriage moving smoothly before tightening down the bolts. I had to drill slightly oversized bolt holes in the plate to allow fine adjustment.

Conclusion: Moving to a metal base-plate for the y-carriage has increased rigidity and support for the print bed. With this factored in, I'm not sure there was any advantage in going to a four bearing carriage. I think a three bearing carriage is probably as good, is much easier to align, and saves on a bearing!

Double bearings for y-belt.

I've placed double bearings on either end of my y-axis for the belt to travel over. The belt settles in to it's own path. Various previous arrangements invariably led to some level of side-wall friction. Replacing bearing fenders with double bearings, has proven a cleaner solution. Thanks to MaxBot (MendelMax) for this suggestion in a comment a couple of posts back. I've noticed others adopting this solution. Keep it in mind if you are still at the construction stage.

I've been working away and have made a few more changes including fitting a heated print bed. This quick post is just an ice breaker, getting me back into posting. More to follow.
Thanks for viewing!

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!

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

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