A quick tour of my 3DR as it prints a life-size model of a hand
Having the bearings in place allowed me to complete the build of the 3DR printer. Naturally, there were a few little problems to work out along the way (wrong size nuts for the idler bearings, USB cable plug interfering with one of the Hall effect end-stops, where to position the extruder, how to calibrate the end-stops to set the Z height to 0) but I guess that’s why we don’t buy ready-made printers from the shops. That and the cost, of course - state of the art delta printer for £300 anyone?
The first big problem I faced though was that only two of the motors were homing correctly. The third one would either grunt or fly wildly in the wrong direction. I had completed the build just in time for the 2013 TCT &Personalize Show at the NEC in Birmingham where I was hoping to meet Rich Horne for the first time, so I quickly shot a video of the strange movement on my phone hoping that someone would be able to tell me what was going on.
As well as meeting Rich at the show (and hear his presentation which was a real pleasure), I was also fortunate to be able to spend time with Jean-Marc from RepRapPro (who designed Huxley I used to print the 3DR parts) and my friend from the North-West of England, Chris (NopHead) the designer of the Mendel90. Rich wasn’t sure what was causing my motor problem so I showed the video to Chris who suggested that a faulty motor wire was the most likely explanation. Sure enough, when I got home I was able to use a resistance meter to find the culprit, a poorly soldered joint, and fix it easily.
I managed a couple of small test prints (gnomes scaled down to half normal size) which confirmed that all the parts were in working order, and then set about the process of fine tuning the printer.
I wasn’t completely happy with the nylon bearings. The fit was good but the movement wasn’t smooth enough, often snagging and stuttering as the arms moved up and down. So I swapped in the steel bearings expecting the noise level to increase dramatically, but actually it wasn’t too bad - and the movement was much smoother.
Then suddenly, the next morning, I only had two working motors again. Sending the home command worked on two of the towers, but the third arm made a small move away from the home position and stopped, instead of returning home. The problem seemed different but I checked the motor wires again (twice, just to be sure), swapped the motor plugs over and pondered for a bit. Finally, I twigged that it wasn’t a faulty motor this time, but a faulty end-stop sensor. Sure enough the signal wire had come loose from the connector, preventing the homing sequence from working correctly. Another simple fix and I was back in business.
The first set of nylon bearings were a bit tight on the rods and wouldn’t slide smoothly. I tried drilling them through with a 6 mm drill but then they wobbled on the rods. I decided to have another go after redesigning the parts myself in Blender.
I made three test bearings each with the central hole 2%, 4% and 6% larger, respectively. Can you tell which is which?
It is important to remember to use a craft knife to trim the bottom 0.5 mm off each bearing because the bottom layer spreads out more and makes the hole smaller here. Trying each of these out led me to conclude that a 5% enlargement of the hole would be the perfect size.
I reprinted six nylon bearings in the new size, trimmed the bases off and fitted them to the machine. They seem to move nice and smoothly and should last a long time.Of course, the very next day the packet arrived from China with the steel bearings inside. I’ll keep them in reserve - RichRap says the nylon ones should be quieter.
I got fed up waiting for the steel linear bearings to arrive from China, so I used the Mendel90 to print some bearings in Taulmann 618 Nylon. Should be strong and quite smooth. I found the bearings here http://www.thingiverse.com/thing:24990
1. Upside down view - top and base joined by rods and aluminium extrusions
2. I cut the motor plugs off to the feed the wires down the tubes then soldered them back on and covered with heat shrink tubing
3. Sanguinololu electronics and Hall effect end-stops fitted to the underside of the top plate
4. Nozzle carriage with three pairs of arms connected to universal joints; these have to be carefully adjusted to the same length and then superglued in place
5. Wooden blocks set up as a jig to make the six arms for the nozzle carriage
6. Close-up of the universal joint ring sitting in the slot in the jig
7. Completed extruder with Arcol Hyena hobbed bolt
8. Spectra filament wound onto one of the three spools and fitted to the drive motor
Huxley 3D printer still hard at work printing parts for the new RichRap 3DR printer. It’s really beginning to take shape now.
All of the large frame parts are printed; starting on the extruder mechanism next (that’s a herringbone gear being printed by the Huxley).
Lots of bits and pieces on order waiting to be delivered. Total costs so far (including delivery and import costs):
- Plastic filament £40
- Aluminium channel £34.06
- Metal rods £15.50
- Nuts and bolts £7.63
- Skate bearings £3.80
- Linear bearings £4.69
- Motors £54.80
- Hall effect end-stops £28
- Hobbed bolt £11
- Spectra line £6.95
- Carbon fibre push-rods £6.09
- Universal joints £10.45
- Mini bearings £5.11
- Pneumatic fittings £3.00
- PTFE tubing £5.25
- More nuts and bolts £5.31
- J-Head MkV nozzle £27.75
Total cost to date £269.39
My Next 3D Printer will be a RichRap 3DR - I’ve started!
My love of printing with PLA has been rekindled thanks to some quality filament from Faberdashery and the discovery of diluted PVA on glass as the best surface ever to print on (see previous post for details).
For some time, I have been wanting to print a copy of Faraday 3 by Donald Osselaer. It’s a great puzzle that needed some great colours to do it justice. The Galaxy Blue and Bling Bling Gold printed perfectly first time at 185°C, but when I started printing the third set of pieces in Raspberry Spark, the problems started.
After only about 12 layers, the nozzle jammed and the filament stripped in the extruder. “Oh, bother!”, I thought. The reason I had bought myself some top quality filament was that I had been having exactly these problems with my translucent blue and copper brown PLA, so frequently that I had virtually given up using PLA at all.
The greatest difficulty, when this sort of thing happens, is knowing whether the problem lies with the extruder or the hot end. Is the nozzle jamming because the temperature is wrong, which then causes the filament to strip in the extruder? Or, is the idler tension wrong in the extruder leading the filament to strip first? There’s no easy test, as far as I know, to distinguish between these two so I cleaned out the hobbed bolt and began the trial and error process of tracking down the cause of these repeated failures.
For my second attempt, (5th photo, second set from left) I pushed the nozzle temperature up to 190°C and the print got a little bit further before failing again.
For the third attempt, I tried tightening the idler bolts, causing the hobbed bolt to bite a little deeper into the filament. This time there was a significant improvement but the print still failed just over half way through.
For the fourth and final attempt, I took the nozzle temperature up to 210°C and tightened the idler bolts another turn. This time the prints completed successfully.
- Some filaments need a higher temperature to print successfully than others.
- Idler tension can be the cause of print failure. Setting it correctly is still a bit of a dark art.
- The hobbed bolt must be clean and must bite into the filament but the idler should not leave a flat mark or squash the filament at all. The right pressure depends on the hardness of the plastic.
- Persevere with small changes and you will succeed in the end.
It’s been an awfully long time since I updated this blog - not for lack of interest; just lack of time.
I have made a number of significant changes to the Mendel90 and the way I use it since I last wrote. I’ll try and list some of them here for completeness of this record.
- Replacement power supply - the old one died
- New all metal hotend from E3D-online - the old one clogged
- New GT2 belts and pulleys for the X and Y axes - finer resolution means smoother movement
- Mirror tiles from Ikea for printing on - prints were sticking more firmly to the old glass bed and eventually it cracked
- Experimenting with some different materials including Laywoo-D3 (a wood-based plastic) and Taulman Nylon 615 (very strong and flexible)
The last major change happened a week ago after I read this post on the Google forums about how to print this MAKE torture test. I had tried 4 or 5 times to print this difficult object and had always failed before.
One contributor (thanks, Kamil) suggested using PVA glue diluted with water (1 part glue:10 parts water) spread onto warm glass as the best printing surface for PLA plastic. I had heard about this before but had never bothered to try it for myself. I was getting increasingly fed up with my attempts to print PLA as it often came unstuck from the Kapton tape or blue painters tape that I used before. Squeaky clean glass is also supposed to be good but for very small areas, like the end of the arch in the Torture Test, the bond was not strong enough to keep the part in place until the end of the print.
I watched the recommended video by Ohmeye and then had a go myself. Absolutely brilliant results ever since! PLA sticks perfectly to the PVA glue. At 55 degrees C the bond holds strongly throughout the most difficult prints. Afterwards, leaving a few drops of water applied to the edge of the print for a short while releases the glue leaving a perfectly flat bottom. I’m a total convert.
This beautiful curved model by virtox had proved extremely tricky to print for various reasons. My best attempt had been in black ABS and although the print completed successfully (unlike several earlier attempts) it cracked in several places whilst it was still printing. This, more than any other, was the model that prompted me to build a heated chamber for the Mendel90.
Here is the print, lying on its side, showing the cracks that appeared as the plastic cooled and shrank causing delamination.
This copy was printed in natural ABS inside the heated chamber at 35 C and, as you can see in the picture, the surface is smooth and blemish free.
And here are the two prints side by side.