Short version: How fast are you setting speed/acceleration on the c-beam with the 8mm leadscrew, particularly the 500mm or longer ones? Long version: I just put a 250mm across the top of a 500mm, and turned my lathe into CNC. Unplugged, turning the lead screws by hand there is no end-play and it is smooth. Powered it up with LinuxCNC , and if I set acceleration to any setting faster than "arthritic turtle" both axes sound terrible and on the 500mm length the 8mm lead screw starts whipping side-side. I couldn't even run it long enough to test the accuracy because it sounded like it wanted to explode. (These are the new 8mm lead screws that now come pre-shrunk to save us the unbearable agony of sanding down the ends.) I've got other machines that you could run in a library and nobody would complain, but they are using a belt/pulley system. How fast have you guys been able to push the c-beam/8mm setup?
My C-Beam Sphinx has 500mm c-beam axis running tr8x8 OB lead screws on both the y and x stages. I run at 2500mm/min ( 100ipm ) max speed and my acceleration is set to 100mm/sec. I do get the normal resonance sounds one would get with any extrusion based cnc. Otherwise It is running really smooth with no adverse affects or additional sounds. Over in this thread talks are beginning on ways to dampen or remove the sound resonance you get by filling void cavity's.
Thanks - I had already seen the thread on dampening, it seemed like overkill for my needs. I wasn't hitting anywhere near 2500/1oo yesterday so I spent the day stripping it down and reassembling one screw at a time. I also milled out a handfull of new aluminum hold-down brackets to lock the bottom c-beam more securely to the table. It's reassembled now and it looks like I can run it around 2000/100 before it complains - plenty fast enough for a small woodworking lathe and I can turn up the radio loud enough to drown out the remaining noise. (If you can't hear it, it doesn't exist.)
