A simple door hook...

Quick post...
There are many hooks on Thinkiverse, but I noticed this Headphone Hook by Misguided had employed a curve on the hanging tab to add strength to what otherwise would be it's weakness, a 90 Deg bend with a flat tab. A few minutes in Sketchup enabled a modification of the design to produce a very useful door hook!

I narrowed the "U" so the door would close, even with the hook over the top (3mm gap). I also added two ridges to the "U" to grip the door and give the hook a snug fit. The printed item looks well and is very strong when printed in ABS plastic.

I've seen hooks on sale in the shops but they tend to be for narrower doors. I was able to print a hook that fitted our internal doors perfectly (45mm - 1 3/4"). I've placed a bunch of sizes in the Sketchup file and posted it to Thingiverse .

Enjoy!

Earbud holder with keyring tab...

The Earbud Holder from Thingiverse caught my attention recently. There was a comment asking if it could have a key chain loop added... it sure can! It's a matter of personal preference whether you print the version with or without the keyring tab, or take the design further. It's great how designs evolve.

 I fitted a small ring and short length of cord to the holder.

Notes:

I dropped the original Core .stl into Sketchup and drew on a tab with a hole in it, to which you could fit a keyring. I then took the evolving cover design from here: http://www.thingiverse.com/thing:38292 and put a notch in each cover so it would still close around the new keyring tab.

I then exported the new .stl files and ran them through Netfabb Cloud Service . It always does a good job of cleaning up the stl. They were now ready for printing... ABS, 50mm/sec, .4mm nozzle, .3mm width /.45mm height.

My first set of covers cracked as I tried to clip them on to the core. They broke along the print lines. On examination it was evident there was poor bonding between layers. I've been pushing the speed in recent times and at this point I expect the plastic just wasn't hot enough for the speed (230Deg C at 50mm/sec).

I increased the temperature to 245 Deg C. and reprinted just the two covers. Now, you know you should never change more than one parameter when troubleshooting, but I couldn't resist altering the layer height/width also, to increase the horizontal resolution and give a better fit between the parts. The covers were reprinted at .25mm height/.375mm width, 70mm/sec. 245 Dec C.

I've uploaded the modified design to Thingiverse: http://www.thingiverse.com/thing:39767

Enjoy!

NumberSix

A focus on ABS and a new printer hood (with video clips)

ABS is a tough, impact and temperature resistant plastic. It can be injection moulded and extruded. It has many common uses, from Lego to car bumpers. Being able to print in ABS is an important progression for me in terms of the robustness of the objects I might design, prototype and print.

My first ventures into printing with ABS did present some challenges. It's extrusion temperature, in the region of  240 Deg C, is a good deal higher than PLA (185 Deg C). The rising heat from the hot end to my PLA x-carriage was a first concern but the use of an un-ducted fan to cool the underside proved problematic. The freshly extruded ABS was very sensitive to the cooling airflow, causing poor adhesion of the first layer to the print bed. If' you've only printed in PLA you'll find PLA prints better with some cooling, preventing curling, but the first layer of ABS is far more sensitive and does not like stray cooling at all. Fitting a ducting to the fan (light green part visible in photo below) focuses the air flow across the J-head insulator, also keeping the underside of the x-carriage cool. I may eventually print an x-carriage in ABS for peace of mind.

The big addition to my set-up is the hood (see photo). It's a simple box construction made of 6mm MDF and light timber frame. The front has a clear acrylic panel. 

The purpose of the hood is to maintain a steady raised temperature around the printer. I found it levels out at around 28 Deg C at the moment. The printer is located in the garage with a frequently used large door, so heating the whole area isn't practical, and in the winter time the printer extruder and heated bed struggle to get to a working temperature without the hood. The addition of the hood has made a great difference to temperature management in our colder winter months (Ireland). With the hood externally vented it has also eliminated minor concerns about any fumes the ABS might give off if over heated, although I've had to control airflow through the vent to reduce air loss from hot-air convection through that pipe.

Next item to get right for ABS is the heated print bed. PLA is happy with a heated bed in the region of 60 Deg C temperature, and with some PVA coating on the glass bed it will stick well. ABS is a different story. Experimenting by many has resulted with varying guidelines on what temperature is best for the heated bed under an ABS printed part. People seem to have had good success with temperatures ranging from 80 Deg C to 120 Deg C or even higher. This higher heated bed temperature for ABS is required for good initial adhesion and preventing warping as the object grows, but you should reduce the bed temperature after the first layer to prevent wall shrinkage at the base of printed parts. The use of PET tape or ABS juice (ABS/acetone solution) is also found to help adhesion. Some people just ensure the glass is cleaned thoroughly and get very good adhesion straight to glass.

The quickest and easiest way to give a guided tour of my current printer set-up is to post a short video. In it you will see the first layer of the Santa Sleigh being printed. It's being printed with 3mm ABS filament, with a .5mm nozzle at an initial temperature of 240 Deg C, bed temperature of  115 Deg C (approx). First layer is printed slowly but it picks up to about 50mm/s later.

As I move the camera around you will see the host software I'm currently using "Repetier-Host", my wall mounted spools, and the printer electronics, which are now moved outside the box (they need a cover!). Finally, for the keen eye, you will see some timber cross-bracing across the rear threaded rods of the printer. This has enhanced the stability of the unit immensely. My z-rods hang freely from the motors unconstrained. I only use a single trapped z-nut on these rods in each x-end, and no backlash springs.

This video clip shows the Santa Sleigh being printed a few layers in (.3mm height/.45width, 25% fill). I've a temporary temperature probe under the heated bed which shows a reading of about 117 Deg C. I expect the surface temperature of the printer bed is a good 15/20 Deg C less. My bed temperature is controlled via a simple circuit (see here). The temperature is set with a variable pot dial. I've various marks on the dial for PLA, ABS first layer and ABS. It's all a bit experimental, but works.

This short video shows the printing of the Sleigh, utilising a time-lapse shot every 20 sec, and a look around the finished item at the end. The printer bed is 200mm x 200mm so you can judge the size of the printed object from that.

Finally for now, here's a clip of the Reindeer being printed. All eight in one go, along with the support struts.

Concluding notes:

• Printing with ABS has greater temperature management challenges, for both the hot-end and printer bed.
• The single biggest tip I can give is to reduce the printer bed temperature immediately after printing the first layer of any ABS job. This will prevent shrinkage or distortion of the lower 5mm of the object, a phenomena dubbed 'elephant feet' on the forum, because of the inward deformation of the work around the base. I estimate a reduction in bed temperature of about 20 Deg C is not unreasonable, but I would recommend you experiment to find settings that work best for your own set-up.
• I've not found ABS parts to be as dimensionally accurate as the same parts printed in PLA. I believe this phenomenon is down to ABS shrinkage. You may want to allow for this in design.
• The finished ABS product has a smoother feel and any blips or minor stringing is much more easily removed than equivalent imperfections in PLA.
• While the print resolution is the same, ABS seems to look a lot smoother.

If you have any questions or comments regarding the set-up or operation of my printer feel free to post a comment of contact me via the RepRap forum (http://forums.reprap.org).

Thanks for viewing!

NumberSix.

Christmas printing fun...

Thingiverse Santa Sleigh driven by the Snowman! Some red acrylic paint easily added a touch of colour to the white ABS plastic.

A variety of other Thingiverse Christmas ornaments!

The Angel was creating by tracing some internet clip-art in Sketchup, extruding the shape a few mm and cutting slots so the two halves slide together. It's a simple construction but looks well.

Merry Christmas and a Happy New Year to all!

Printing a clock...

I've always had an interest in clocks. They can be hypnotic and fascinating, masterpieces of mechanical engineering, and things of beauty. But could a clock be printed on a home 3d printer? Would it work? I was delighted to see a clock published to Thingiverse (The Makerbot clock) but was disappointed to learn that the hardware kit was no longer available. That didn't deter me.

The finished item is a simple and pleasing open style, weight driven, wall clock with a 9" face and 3ft pendulum.

It was a printing challenge and will test the accuracy of any printer. For the most part the gears came out cleanly and meshed well with each other when the clock was mocked-up. Some test assembly and hand turning highlighted a few sticky points. They where easily sorted with a needle file. I printed using my .5mm nozzle but in hindsight a .35mm nozzle would have resulted is better meshing gears and post print tuning/filing.

The range of parts can be seen in the above photo. If you study the MakerBot assembly instructions you can get an idea of the hardware required, but I had to deviate from the original bill of materials in a number of items. I could only source the tubes that drive the hands in metric dimensions so I had to alter the hole sizes in some of the printed parts to match my brass tubes. I sourced the little bearings on ebay. They were inexpensive and came in a packet of 10. The pendulum shaft and second-hand shaft are welding rods. The weights are filled with 2 Cent coins (Euro). The original design suggested a 1 Cent US coin. They are the same size.

To give added strength and enable wall-mounting I cut a circular backing board from some 15mm chipboard, and mounted the clock base plate to that. I used longer bolts than specified and allowed them to travel right into the backing board for extra rigidity in the assembly. The upper frames were quite light and didn't hold the gears quite as well as I would have liked.

Modifying the mechanism
When I first started the clock it was running too fast. The published escapement wheel has 15 teeth. That results is the second hand advancing by two second increments for each pendulum swing. But combined with a 1 meter pendulum, the second hand completes a full revolution in only 30 seconds. That said, I expect this clock was only ever published as a printing show piece and for it to tick/tock away in any fashion could be considered a success!

On examination of the SketchUp file included in the Thingiverse publication I found an alternative escapement wheel which had 30 teeth, allowing a more refined movement of the second hand. The escapement paddles also need adjustment to fit this wheel. (For anyone that really want's to get into the detail I found a good publication on excapement mechanics here: www.abbeyclock.com/EscMechanics.pdf )
That article is a bit over involved for this purpose but does show you how to draw paddles that are a good fit for the escapement wheel.

I exported my newly shaped paddles to .stl, then printed and fitted the two new parts.

The finished clock
The clock is probably as good as I'm going to get it now, for a home printed plastic clock it's pretty amazing! It will only run for a few hours on a single wind so don't expect it to replace your kitchen clock any time soon. I've provided a little video clip below so you can see and hear it in action!

Thanks for viewing!
NumberSix

Bridging gaps (video clip included)...

Once your machine is printing well there are always new challenges to be overcome! I was printing some Mendel90 parts this past week and found some of the parts needed bridging, e.g. the bar clamps:  http://www.thingiverse.com/image:110664 , not to mention the x-motor-bracket:  http://www.thingiverse.com/image:110722

There are many bridging calibration test pieces out there and I was inspired by the thingiverse hollow cube and quickly drew up my own 30mm cube in Sketchup and printed it as my calibration piece. It makes a nice 'give-away' printed object!

Technical note: I printed it at .3mm height, .45mm width, slow speed. I'm currently using Slic3r 0.9.1 from within Repetier-Host (v0.70b). I'm happier specifying both height and width in Slic3r at the moment for what it's worth, following Nopheads guideline 1.5 ratio (.3mm *1.5 = .45mm).

The bridging works best for me when I set a Bridge Flow Ratio of .9 (in Slic3r... Print Settings... Advanced). That supplies less plastic than would normally be laid down for the given distance, therefore stretching the plastic across the gap. As the plastic cools it also tightens up, pulling straight. This can be helped by a fan blowing cold air at this point of the print.

I'm using 3mm PLA with a .5mm nozzle, printing at 185C (195C first layer). The only cooling going on is any air drifting to the work from the x-carriage mounted fan that cools the hot-end insulator (peek part of the j-head).

I captured the bridging moment on video for people to see bridging in action! Also visible in the opening minute is my new y-carriage, PCB heated bed and the ribbon cable connected beneath it, for power and thermistor. I thought that might be of general interest also.

Thanks for viewing!

Heated bed with three point leveling...

This recent collection of improvements to my printer stemmed from a desire to try some ABS printing, which I haven't actually got to yet. Again a case of one thing leading to another... It needs a higher heated bed temperature (110deg C I believe), and my resistor heated-bed just couldn't achieve those temperatures.

I'm a fan of the three bearing y-carriage. I converted my y-carriage to a three bearing rig a while back (here), but the print bed (upper plate) was still leveled by adjusting four spring loaded screws. When Tony at Think3DPrint3D did a version of the PCB heatedbed that had a support hole in the middle of one edge (see here) I just had to try out an arrangement that had three bearings and only three levelling screws for the print bed.

A heated bed with only three support points would need a support plate that was as large as the bed, but a lot of that support plate would be redundant. I felt it was also best if these three support points were positioned over the bearings for maximum support. The resulting layout eliminates the smaller lower plate in typical Mendel y-carriage designs, but does mean that the y-rods need to be raised to the upper position as the printbed overshoots either end to achieve a full 200mm print area in a Y direction.

This is the new Y-carriage I built:

The carriage is made from 3mm composite sheet material, commonly known as DiBond. It's a plastic sandwich between two light sheets of aluminium. It's very strong and very light. I happened to find some in a black finish. This plate acts as both the mounting board for the bearings and the support board for the heated bed. This simplifies the construction and overall weight of the y-carriage. I used bearing mounts that have been joined by a simple triangle to position them (http://www.thingiverse.com/thing:19771). There's a huge variety of y-carriage bearing holders on thingiverse, some have integrated belt clamps, some without. I just transferred my existing belt clamp and tensioner, and my opto-endstop flag.

The composite sheet material was marked out and cut with a jigsaw, using a fine toothed blade. All the holes were carefully marked and drilled. The three holes to support the heated bed were taped to take M3 bolts, to allow a Nophead style mounting and adjusting method which he talks about here. I also adopted the insulation and cabling method he describes and utilises on his Mendel90 printer. 

Wiring the heated bed: 

The version MK2a (note the 'a') of the PCB Heatedbed has larger soldering tabs as well as the middle hole. Given I wanted to position the middle hole over the single bearing it meant my ribbon cable needed to take a 90Deg turn to position the loop it in the direction of bed movement. The photo above also shows how I soldered on the ribbon cable and attached the thermistor. The exposed contacts were covered with some tape to prevent shorting on the foil insulation which will sit beneath.

I cut a piece of corrugated cardboard and glued on some kitched foil to make an insulator for under the heatedbed.

The foil faced cardboard sits between the carriage and the PCB heatedbed. To secure the ribbon cable I cut a piece pvc tube to protect the ribbon cable from the edges when I used a small buldog clip to clamp it in place. See photo below.

(note the adjustment screw above was not what I settled on.)

The adjustment screws were made up as follows. I took a long M3 spacer nut, thread-locked a headless screw into one end, and cut a screw to fit the other end. (I use a small disc in a Dremel to cut bolts/screws to length.)

I wanted 'soft' washers to pad the lock-screw. The corner of the PCB is quite delicate and I suspect easily broken. To make some PTFE washers, I pushed some PTFE tube through a hole in scrap piece of wood, and used a sharp chisel to cut as many washers as I needed.

Below is a photo of the adjuster screw/nut  It works by loosening the top lock-screw, then turning the long nut to raise or lower the board, then tightening the lock-screw when done.

Here's the newly assembled y-carriage and PCB Heated bed. I cut a piece of picture frame glass to size for initial trials with PLA. I may have to get something better for ABS. There's a bit more work to do before I start into ABS. I want to build a hood and extractor next.

Conclusions:

The bed levelling process is so much easier with only three height adjusters. Start on the right, level front and back, then move to the left centre screw and adjust it until until the bed is levelled in a left/right direction. I level off the print-head tip, and perform the exercise with motors off moving x and y carriages by hand.

Raising the y-smooth rods to their top position only results is a small loss in z-height because the new layout has one less support plate. The original smaller board/plate that held the bearings is no longer required.

The use of Triffid_hunter's bar clamps allowed the rods to sit on the threaded rod, giving a print bed that was almost level before any adjustment. The amount of final adjustment needed with this construction is extremely little.

The whole assembly is much lighter than my previous one. The loss of one board and the introduction of the composite sheet material has contributed to this. The net benefit of a lighter y-carriage assembly is greater print speeds with less strain on the motors or less risk of skipping due to inertia.

That's all for now. Thanks for viewing!

NumberSix