Reprap Build: Phase 1
By alecjw on Tuesday 18 September 2012, 23:55 - Permalink
Ohai, first post and all that. Whatever.
I've been looking into building a reprap lately, mostly just because it would be awesum to have one on my desk, but also because there have been plenty of situations when i've thought, "I wish i had a reprap right now..." I decided on the Prusa mendel iteration 1, because i was told that there are a few problems to be ironed out with iteration 2.
The printed parts were loaned to me by Glen Searle, who runs a 3d printing business. I would tell you to check out his website but it seems to be down at the moment. How do you loan parts though? Surely i need to build them into my own printer? Well the answer is I build mine, print out a new set of parts and give them back to him. I also bought an extruder hot end off him for £50 - he threw in some threaded rod too. (edit: Glen has asked me to add that the non-sky-blue parts were printed while we sat there eating pizza. And good pizza it was too.)
I've also ordered a couple of other non-printed parts: I got some stepper motors and linear bearings from aliexpress (essentially like ebay but cheaper and more chinese) and I'm basically going to get the rest of the mechanical parts from screwfix/ebay. I'll post links for my complete bill of materials when I'm done, but for now I don't want to be making recommendations before I'm sure I haven't been ripped off myself.
Today I was at the hackspace working on the heatbed for my reprap. I have a load of 160x100mm photo etch PCBs, so i figured I could do something with that - cut them down to squares and tesselate four together to make my 200x200mm heater bed. I'm not yet sure how i'll fix them together but we'll cross that bridge when we get there... Anyway, I decided on a zig-zag patten of parallel tracks, 2mm apart and d wide. I did some calculations to find d based on the fact that a typical heater bed resistance is 2 ohms (so I aimed for 0.5 ohm per board) and the copper will be 35 microns thick. As you can see from my calculations below, I ended up with a track width of 2.28mm. If enough people hassle me for it, I might write a script to automatically do these calculations and spit out an SVG file. Although this time round I was lazy and made the design in libreoffice. PDF is here.
First impressions were these seemed to have been a success. I measured the resistance of one with a multimeter and it came out as 0.5 ohms. I then hooked them up to a few linear power supplies and found that they didnt actually get that hot: with 9 amps flowing through them, they were still less than 100 degrees. At 7 amps, they seemed to be about an ohm each. Not to worry though, nothing which can't be solved by MOAR VOLTZ: I'll just wire them up differently: either 12V straight across one or 20v in series parallel. That's all for now, I'll document all further progress here. But first I'll leave you with a picture of my test setup: for those times when two linear PSUs stacked on top of each other just don't cut it...