Friday, 30 July 2010

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.

Friday, 23 July 2010

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.

Thursday, 22 July 2010

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.

Thursday, 15 July 2010

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.

Tuesday, 13 July 2010

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.

Monday, 5 July 2010

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.

Thursday, 1 July 2010

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?