Well I got the 3D printing bug! several months ago I decided I'd build a 3D printer. I would have got the MendelMax, but the kits were back ordered and they had stopped taking orders. Plus I wanted one NOW. So I got the basic mechanics of a CNC/3D printer from http://www.zentoolworks.com And added a hotend, extruder and electronics to make it into a 3D printer. I did actually use it as a milling machine a few times before that, and I milled several PCBs. As a Milling machine for wood and PCBs it is pretty good. As a 3D printer it prints reliably and nicely, but it is so SLOOOOOW, best speed is 25mm/sec. Picture here https://plus.google.com/photos/101797329177621784159/albums/5815274370084201361

What I didn't realize is that this new hobby is all consuming (actually becomes an obsession), and you never build just one 3D printer. So now I am on a quest to build a bigger and better printer. I loved the Delta printer/Rostock concept, but I also prefer lead screws to belts. So my initial idea was to build a Rostock-like bot, using linear actuators driven by 1/2" 5 start lead screws. But at 1" per rev the maximum speed for this using Nema17 (which run at max of 10revs/sec) is 254mm/sec, OK that is 10x faster than I currently have, but is also the top theoretical speed. Torque issues will decrease that I am sure. I wanted faster! at least 500mm/sec, even though you can't actually print at that speed, I am told, due to limitations of extrusion speed of the current hotends and extruders.

So started my quest to test linear actuator speeds. First up I got 1000mm of Makerslide with all the associated H/W of carriage plate, vwheels and bearings. Then I attached a Nema17 to one end and an idler to the other. using the current love of the delta bot community Spectra fishing line for the drive mechanism, I did get 450mm/sec without stepper stalls. See  video http://flic.kr/p/dvXMA5.

I am not convinced that fishing line is a good drive mechanism, although it was relatively easy and very cheap to setup. The capstan spools the line on and off very nicely so long as it is aligned just right, and the tension is just so. However my print head is going to be very heavy as I intend to put a full extruder on it and not use the bowden cable method of filament feeder, so a beefier drive mechanism is required, much like a small CNC would use. Lead screws would be great but too slow. Roller chain is used in many CNC machines, and I have some # 25 chain I ordered from McMaster, with a 10 tooth sprocket. This has virtually zero backlash (according to the internet), and will run at the same speeds as the spectra line drive as it has a similar mm/rotation. I have to figure out how to attach and arrange the various sprockets and drives, as there are several ways to do that with roller chain.My next post should include the results of that test.
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