Emco Unimat 3 low and high speed pulley set

thingiverse

The EMCO Unimat 3 lathe is a great machine for all its attachments, but it lacks a crucial feature: a back gear or slow speed pulley bracket like the earlier Unimat SL. This pulley set solves that problem with ease and gives you more headstock pulleys than the original for lower speed and higher torque. The larger pulleys provide higher speeds at the expense of torque, while the smaller ones give you faster toolbit spinning but also risk losing control of your workpiece. To avoid accidents, always wear protective gear when using these pulleys. I designed this pulley set because I needed a replacement for my own U3 lathe that came with a damaged pulley. After printing and testing them, I realized they are quick to install by simply unscrewing the original black pulley and screwing on the required size. The photos show how the M14-threaded 125% larger radius pulley (purple) is used with a carbide insert to easily machine large pieces of hard steel pipe. The idler pulley gives the lowest stepdown speed available, while the standard BS336 O-ring belt stretches over the larger pulley very tightly. For smaller toolbits such as tiny mills or dental burrs, using faster speeds can be beneficial. The smaller pulley sizes are at 50%, 75% and 67% radius of the original black pulley, and they use a small belt (BS331 O-ring). Another photo shows an M14-threaded 67%-radius red pulley being used with a small slitting saw to cut a piece of rectangular aluminium section. Also shown is the M12-threaded 67%-radius sized pulley on the milling column with a small grinding wheel cutting scalloped indents in a rotary craft cutter blade. SAFETY NOTES 1) With large headstock pulleys, the belt guard won't close, so keep your fingers clear. 2) When using smaller-than-original pulleys, be mindful that toolbits or chucked jobs spin faster than usual. Thus things like tightening tommy bars will fly out of the chuck with more force. Be careful and always wear eye protection. Note that for the smaller pulleys, I printed them in bright colors (red and orange) to remind me of the faster spindle speeds, while large pulleys are other colors. PRINTING NOTES Firstly, print the two test bosses before starting with the pulleys so you know the thread prints okay. There's an M14 boss for the headstock and an M12 boss for the milling column. When fitting the pulleys for the first time, make sure to thread them on squarely and evenly right up to the shaft flange. Grip the pulley with a piece of cloth and be careful not to cross-thread. I also fitted them immediately off the printer while they were still warm. Print the pulleys with the smaller rim upwards. I used PLA with 25% infill, no raft, and touching buildplate support. For larger radius pulleys like 150% or 175%, you'll need a different belt size like BS340 O-ring. The script uses the excellent OpenSCAD threads module by Dan Kirshner. Just put the library in C:\Program Files\OpenSCAD\libraries\Thingiverse and it should work fine. NEW ADDITION - Unimat 3 pulley with Unimat SL thread pattern adapter ======================================================== I was asked if the pulley could accommodate Unimat SL thread patterns, so I modified the script to produce pulleys with a 16.9mm dia lip and series of mounting holes. You'll find both STLs in the Files section, along with some pictures above. If someone can print either of those and let me know if they allow Unimat SL thread patterns on the Unimat 3, I'd be grateful. Thanks.