Hot End Fail

I’ve had a bit of a break from my RepRap project recently, mainly caused by my disappointment when my first hot end lasted all of about 1 hour continuous printing before failing. It looks like the force of the filament being pushed down into the barrel was sufficient to cause the threads to slip on the PTFE interface. Probably partly due to heat making the PTFE more compliant. It does look like some plastic has made its way into the thread, but I’m not definite that it’s not just remnants of the PTFE tape. I’ve ordered the new design hot end components so looking forward to assembling that.

Meanwhile I’ve made a couple of adjustments. I’ve moved the USB connection from the top board to the lower board next to the power connection, I’ve added a switch (salvaged from a broken kettle) to the 12V power, and also added an LED strip to the underside of the upper board which nicely lights up the build area. Although I am now starting to think that it would be better to have all the electronics encased in a project box and have the rest of the machine stand alone.

I’ve also been working on a side project; using my android phone as a remote control for my Samsung TV using an Arduino connected via Bluetooth. It worked a lot easier than I thought and showed me how simple (and cheap) it could be to add wireless capability to any Arduino project. Documentation is a little sparse at the moment but hoping to add more soon, but if you’re interested the info can be found here:


http://sites.google.com/site/jsrsprojects/androidir

Extruder Stepper Bypass using Pololu A4983

I have decided to bypass the onboard extruder stepper motor control to use a separate Pololu stepper driver to run the extruder stepper motor. The reason for this stems from the original RepRap which was designed to use a DC motor for the extruder and not a stepper motor, therefore used some electronic trickery to control the speed. Using some clever programming they hacked the driver to control stepper motors.

However this is now what is causing my stepper motor to emit that high pitched noise. It is possible to bypass the information sent from the motherboard to a separate stepper controller, and leave the extruder board to just control the hot end. This method is documented on the RepRap wiki and suggested in a couple of forum posts I have seen.

I have made a carrier for the Pololu board from strip board using Tony Buser’s layout as a guide (http://www.thingiverse.com/thing:3761). I ended up changing it a bit as I wanted screw terminals for the power and motor connection and not headers. As the screw terminal spacings are wider than the header’s I had to use more short jumpers to get everything wired correctly. I have tested it and it seems to work very well. It is now much quieter and the motor seem to run a bit cooler.

From Mendel

From Mendel

First Almost Print

Just thought I do an update on my initial testing of the machine. I was quite pleased that I have managed to get everything wired up correctly and the extruder heated up. I have spent a while trying to level the bed, a job that was more tricky than I imagined. I am not really happy with the way the bed bolts to the y axis plate. On the Prusa design there is a nut above and below the y plate, I find this a bit annoying when adjusting the bed level – I have to keep adjusting both nuts, I can’t see why there can’t be just one nut below the plate, I might test it out at some point.

At the moment I am using RepRap host but I have also been testing with ReplicatorG to see if that will work. I can connect with ReplicatorG fine using the “experimental” Mendel machine profile. The control panel jog’s the axis (although sometimes the distances seem a bit random and sometimes it moves 2 axes instead of just one). The control panel also controls the temperature of the hot end fine however it does not turn the extruder stepper. When I try and print an object with ReplicatorG it starts ok, but then extruder starts to cool down, it doesn’t seem to control the extruder temperature. Not sure how to access the temp settings, I assume it might be part of the Skeinforge profile, but not sure how to get to that at the moment.

With the RepRap host things are working pretty well. Below you can see my first attempt at printing the 40mm test cube object. As you can see I aborted the print part way through, the object is less of a 40mm cube and more of a 40mm filter. The extrusion seems to be patchy, and thin even when it is extruding. I think this could be caused by a couple of things. First my “hobbed” bolt on the Wade’s extruder could be not gripping in certain areas – or the springs set too loose. Second I might not have set the extrusion length correctly (the steps per mm value) so not enough filament is being supplied for the required extrusion. Third the temperature could be too low causing a blockage as filament is being melted. See the picture and video below and let me know if you think you know which of these it is. At least the x and y dimensions seem to be correct!

Another thing is the extruder stepper is getting HOT (on a long print I think it could get damaged), I have tried trimming down the pot but to get the current up enough to turn the stepper. I have decided to use a Pololu for the extruder stepper in the hope that the stepper will run cooler (and quieter).

Settings:

Host: RepRap Host
Electronics: Techzone Gen 3
Temperature: 200°C
Material: Black PLA
Extrusion Steps/mm: 2.508

From Mendel

Start Up Procedure

I was having a little trouble when I hooked my extruder up. Although everything seemed to be wired correctly I found that I was getting a zero temperature reading. I checked the resistance across the thermister and it seemed to be right. Looking on the internet I found out the 0 reading is given when the extruder board is not connected. I recollected having this problem when I first tested the electronics, see post here, but couldn’t remember how I solved it. All I wrote was that it was something to do with the order I started everything up. A little searching on the internet and I found this post that was very helpful. Following the comments shown there I worked out a starting procedure that works every time.

Start with everything off and disconnected.

1. Start PC up wait for everything to boot up (or if it is already on, leave it on).

2. Power up 12V on Mendel (I really need to connect a switch up to make this easier).

3. Connect USB to Mendel (Could I connect a switch up for this as well, maybe on the +5V line?)

4. Press Reset on motherboard. Wait for motherboard to resume blink.

5. Start RepRap host, some errors are reported (0 temp measurement).

6. Close RepRap host.

7. Open RepRap host again, no errors reported this time, now everything works!

All electronics and hardware up and working. Success sounds like a high pitched whine (where did I put that Pololu board?!)

X Axis Belt Tension

I noticed I little lashing on my x-axis, it looked like it was being caused by the slack in the belt. The tension is set when first using the clamps, keeping the belt tight whilst tightening the clamps is a little fiddly. So I decided to try and improvise a tensioner. I looked around the house for torsion springs that might be suitable, I found a promising one in a cheap clamp (Tesco DIY little hand clamps). The un-tensioned legs of the spring were set to about 110° apart, and had long legs that I could bend around to hook onto the belt. The spring works really well in keeping tension in the belt, I might need to do some more reshaping or use tape to ensure that it stays in position in the long term. Here are some pics:

From Mendel

From Mendel

From Mendel

From Mendel

Wade’s Extruder Build

I have decided to abandon my previous Adrian’s extruder built from cast plastic parts, the oval gears were a nightmare to shape down to circles and the never seemed to mesh quite right. The printed plastic parts bought from nophead came with the parts for a Wade’s extruder (much better quality), so I thought I may as well build one.

For the Wade’s extruder build I needed to make a hobbed M8 bolt. Originally I was going to use the M3 tap set up I had seen before, but I came across this method that uses a Dremmel to cut slots in a threaded bolt to create spikes that will grip the filament. I thought this looked a little easier to do so I thought I would try this method first (plus less likely to break my one and only M3 tap). I found it really easy to cut the slots, though it did eat through a couple of cutting disks to do it. My cuts aren’t as tidy as the ones in the wiki but hopefully should do the job, I’ll let you know what the results are when I get my new stepper motor and I can test it out. I think it would have been better to have used masking tape so I could have marked evenly spaced cuts.

The Wade’s extruder build instructions recommend the use of springs to keep tension on the idler to help grip the filament. I’m not sure if there are some standard springs that will fit, or if people are making their own. I didn’t fancy much making the springs myself so I looked on ebay for something suitable. I found these springs that were cheap (25 for 99p), they measure 9mm in dia by 9mm long with a wire dia of 1mm. They fit fine around the M4 bolts and held in place by M5 large washers and M4 wing nuts. They seem to give plenty of force when tightened up, if one spring on each bolt is not sufficient I do have room to double up to increase the load. The M5 washers do clash a little but by rotating them I can get them to move past each other.

Getting the idler bearing on the short piece of M8 bar was not fun, if doing this yourself I recommend using a short bit of M8 threaded rod, the bearing will fit much easier.

See my previous post here on how I made the hot end.

Here are some pictures of the build.

From Mendel

From Mendel

From Mendel

Prusa Video

I've uploaded a video of my newly constructed Prusa to youtube. You should be able to see it below. I still have some calibration to do and finish off the Wade's extruder before I can start printing for real.

Prusa and Wade Firmware Changes for Gen 3

I’ve now got the three axes of my Prusa up and working with some temporary wiring, woo! Time for some calibration, now when I first set up my electronics I was doing it with a standard Sells Mendel in mind. To get the Prusa to work correctly I’ve got to make some changes to the configuration file of the firmware.

The first one is the z axis steps per mm, now I think that as the z axis is now directly driven rather than via a pulley and belt, this needs to be altered. The pitch of M8 rod is 1.25mm, so for every full turn of the stepper motor it should produce 1.25mm of travel. My steppers have a step angle of 1.8° (for a full step), now I think Gen 3 works in “half” steps, so for one full turn of the stepper I have (360/1.8)x2 = 400 half steps. Therefore the z-axis value should be 400/1.25 = 320 steps/mm.

The second one is the x and y axis, as I am using newer design pulleys (9 teeth rather than 10) I need to change the steps/mm. The belt pitch is 5mm, so 9x5 = 45 mm circumference. Therefore the steps/mm should be 400/45 = 8.889. (Interestingly the value given in the firmware is 8.9307 I wonder if it allows a little extra).

Thirdly is the extruder steps per mm. I am now going to be using a Wade’s extruder rather than Adrian’s. This has a gear ratio of 39/11 rather than Adrian’s which has a ratio of 59/11. I’ve had a go at calculating the steps/mm using the equation given on the wiki. For my set up, assuming a pinch wheel diameter of approx 5mm, nozzle of 0.5mm, and 3mm filament size, I make it: ((400x(39/11))/(pi x 5))x((0.5/3)² = 2.508 steps/mm.

Prusa progress

I have found the build much easier with nophead's proper printed parts. It only took me a couple of hours to get this far. I think I should have a carteasian bot up and running in the next week or two.

Switch to Prusa

I've decided to switch my build to a Prusa mendel after a long time getting frustrated drilling the cast parts. The cost of printed parts is now much less for a Prusa kit. Last week I purchased a printed set from nophead, can't be more pleased the quality is fantastic and the geometry is spot on. It has taken just a couple of hours to assemble most of the frame. Progressing well now, I'll upload some pictures soon.

Back, RDR, X-axis and Solidworks

In the past few months I have discovered that there are a few things that are very bad for progress on building a RepRap:

1. Moving house.

2. Changing Job.

3. Red Dead Redemption.

Having completed the above three I am now back building my reprap. I have almost finished the x-axis. See the below photo of my progress. Struggling to find time for the build at the moment so progress is likely to be slow for a while. Drilling and shaping the cast plastic bits is becoming quite annoying, wish I had held out and bought proper printed parts, never mind hind sight is 20:20!

From Mendel

I have also been practising using Solidworks at work, so what better to tune my skills than with the Mendel Solidworks files. See below for some videos I made using Solidworks. I have changed the model quite a bit, fixing a few errors and making the limits rights so you can only move the axes to the allowable positions. I will try and post my adjusted assembly files soon for those who are interested.

Sketch it Up

Just thought I would write a few words about using SketchUp for modelling with RepRap. I'm not sure if it's just me but very few people seem to be using SketchUp for doing their designs for the project. I really like Google's SketchUp and think it is fantastically easy to use. Capo's recent comment reminded me of the fantastic model he put together of Mendel and prompted me to have a play again myself. A quick look at Capo's blog and you can see how he has used SketchUp in a number of ways for both presenting idea's and for component design.

The below video shows Capo's model that I have coloured then animated.

Link to the SketchUp Mendel Model by Capo:
http://sketchup.google.com/3dwarehouse/details?mid=86dc5e3cc80958355ad914839c51e370

Link to Capo's Blog
http://capolight.wordpress.com/

Geared Extruder and X Carriage

I've done some more work on the extruder build. I had some problems getting the gears to mesh correctly, I found that the large gear seemed to be slightly ovalised which meant that as it turned the wheel would grind in some places and miss in others. I think I have solved this by filing down the teeth that were grinding using a triangular file (note the red marks I have put on so I know where to file) until eventually the gear wheel was circular. It's still not perfect but should be workable I think. I still need to glue the nozzle assembly in place.





I have also starting working on the x-axis. Beginning with the x-carriage. Nothing too difficult here except the captive nuts. A few of the nut locations had to be drilled to the correct shape to hold the nut, I did this using my dremmel clone with a small drill bit and file attachments, time consuming but works in the end. It is also important to remember which holes have to be drilled at an angle.

Adrian's Geared Extruder Build Part 1

The RP parts I have are for Adrian's geared extruder see the wiki here. For this you need some pats not listed on the original BOM list. There are a couple of different screws you need, nothing hard to find on ebay. Main parts you need are a short piece of M4 threaded rod. An M4 "Insert" - this is a splined piece used to grip the plastic filament. An M4 wing nut, and 3 bearings. The splined piece I got from ebay here is a bit different to the one shown in the wiki but serves the same purpose. It doesn't have a grub screw but it is internally threaded so should stay in place with bolts either side of it. It was listed as "Ripmax DYCO M4 x 0.7mm Coupling Insert" looks like it is used in the clutch mechanisms of model cars, trains etc.
After a bit of drilling and shaping the parts seem to fit together ok.

Belt Splitting

First thing I thought I would try out of my plastic parts was the belt splitting jig. I managed to drill the holes ok. The slot was a little trickier, I used my dremmel clone to do this. A tip I have found for drilling the holes in the plastic if you are concerned about it "biting" into the plastic and cracking it is to run the drill in reverse and it tends not to grab at the plastic, but takes longer to drill the hole. Below you can see the finished jig. It worked perfectly and I now have the belts split successfully.

Plastic RP Parts Here!

I now have my plastic parts. I finally went for a set of the cast or moulded parts being sold by fotonlabs on ebay for about £150. I decided it was worth the saving and do the drilling myself (I hope). The seller warned me that they had some breakages reported from the postage, and that they would replace any parts that were broken. They were right, a few parts did arrive broken, but they have been very good and are sending replacements out straight away. The plastic is quite brittle, and the seller has told me they are changing the plastic mix to be more flexible. I have had a go at drilling a few parts, and the seem to drill pretty well but I think as the plastic is quite brittle I will have to take care and not rush it.

I will be moving to a new house and job in a month, this might get in the way of making quick progress but I should still find an hour or two here and there.

Hot End Test

I decided to have a go at extruding some plastic through the hot end to make sure the temperature I was reading was correct. I used the ramp button to slowly get the hot end up to temperature. Everything went well, at about 160 to 170°C I could start to smell the PLA melting, smelled a bit like burnt sugar. Once it got up to 190°C I had a go at pushing the plastic through, it took some force, but it definitely worked, I can see why people are having problems with the brass nozzles coming out. Everything seems to work so far, woo! Check out the screenshot and video below.

Hot End Build

I've done some work building the hot end so i thought I would share. I don't have a lathe so I didn't fancy trying to drill out the brass nozzle myself so i bought one of the pre-made nozzles and barriers sold by reifsnyderb on ebay. I have used bare nichrome wire rather than insulated as I it was much more readily available. I have used 32 SWG nichrome bought off ebay. My thermistor is of the 100k variety and was bought from Watterott.

I measured and cut an approx 6 ohm length of the nichrome. The way i went about wrapping the nichrome onto the nozzle was to wrap the wire in the valleys of thread, then I "unscrewed" the nozzle which left me with a nice uniform spring of nichrome. I could then wrap a layer of Kapton or (Koptan - as mine is) tape around the brass to insulate it from the nichrome. I reapplied the spring of nichrome and taped it down with more Kapton. I wound a second spring of nichrome back up the nozzle over the first layer - this was a bit more rough than the first but I took care that there were no contact points between the nichrome coils. This was then sealed with yet another layer of Kapton.

The thermistor was applied with the leads well separated and the glass bead as close to the nozzle tip as I could manage. I am now a little concerned that the nichrome heating element is quite close to the thermistor as I have read that this can damage it, but I don't get that if it's rated for over 300°C how it can be. However I have a couple of spare thermistors in case I have made a mistake. The thermistor was secured in place by more Kapton.

I had a couple of goes at crimping the leads using different methods without much success, I think I really should have done this before applying to the nozzle. So my final solution was just to do the old split and twist the wires together, then added a bit additional security with heat shrink. This seems to hold the wires fairly securely.

I re-tested the resistance to make sure it was still approx 6 ohms across the nichrome.

I unscrewed the nozzle from the PTFE thermal barrier and applied PTFE tape to the thread on the brass nozzle, and screwed the nozzle back in.

I used a bit more Kapton tape to hold the wires in place and some more over the nozzle to provide some extra insulation.

TechZone Extruder Controller Testing

I have spent some time time trying to get the extruder board up and running. I hit a few snags along the way, and thought I would document them in case it helps anyone else.

Firstly is uploading the firmware, as with the motherboard you can use jumpers if you are unsure of your 10 pin cable, just make sure you get them correctly aligned, they are the opposite way round to the mother board so you have to put the extruder board on its back if you want to do it this way. First problem I had was getting the arduino software to correctly upload the firmware I was starting to think there might be a problem with the board. After a bit of looking on the Internet I saw many comments about pressing the reset button just before upload, I tried this and after a few attempts it worked! I was amazed. What I had to do was hold the reset button down, click upload, wait for the text to appear then let go of the reset.

The next was the wiring, i was baffled at first by how to set it up, there wasn't many clear instructions, but I did stumble upon the "official" guide which is hard to find (here is the link). On this site it shows a picture of how it is wired up. I copied the wiring and got some action when I tried starting the RepRap software, except to start with I was getting zero readings on the temp. It took a few attempts to get everything working, I'm not sure what I changed but it seemed like the boards needed to be started in the correct order, and having good solid wiring certainly helps, I've started using some premade jumper cables rather than the IDC connectors.

The extruder stepper now steps when i click extrude, and the thermistor is reporting the correct temperature. The only annoying problem is that the stepper makes a high pitch whine whenever it is not stepping, I tried trimming the pot down and it didn't help, just stopped the stepper from turning. I tried switching to the software PWM set current bypassing the pot but it didn't help either. I've been tracking the temperature and the stepper isn't getting hot so I'm not worried, but the noise is annoying. See below for a video of the setup printing the minimug.

Mendel's Vitamins

I have been buying alot of hardware recently and think I now have most of the vitamins for the RepRap Mendel. I still have not got the RP parts under the hope that the cost of printed parts would drop when more people started getting printers up and running. Anyway I thought I would make a list of the suppliers I have used in case they are of any help to people building in the UK.

Belts -> RS
Nut's, Bolts, Washers -> a mixture of ebay and screwfix
Thermistor -> Watterott Electronic
Nozzle and thermal barrier -> ebay (reifsnyderb)
Thick sheet (MDF) -> B&Q
Electronics -> ebay (TechZone Electronics)
PLA plastic filament -> Watterott Electronic
Threaded Stud -> screwfix
Bar -> ebay (binkysadler)

The last thing to buy are the plastic RP parts. What a headache looks like there are 3 options, buy a laser-cut version for (approx £150 + tax + delivery) but I am put off this option as there modifications to the design and different hardware requirements.
2nd option is recently there has been quite a few moulded plastic parts being sold by a guy in Ireland he is offering free delivery and as it is EU so there should be no customs tax. He has so far sold 2 grades A and B, the big downside is that the holes require drilling, this would be a real pain but for the cost saving it might be worth it. The sets are going for about £80 for B grade and £150 for A grade.
3rd option is fully printed parts. This would be my preferred option if it weren't for the cost. There seem to be very few people printing parts. One main contributor is the RepRap-god amongst us Nophead, who seems to be single handedly supporting the RepRap cause. Another is Adrian Bowyer himself, but despite promises of random buy-it-nows of £40 only one has been sold at this price, and not that many many sets have been up for auction. Because of this low supply and high demand these sets are reaching premium prices, there is a quite a range from about £200 to £450!

Any offers of printed parts I will pay £150?