Quote Originally Posted by Pat Barry View Post
The reason I was asking the questions was to get at the root cause of the problem. Having actually designed and worked with various motor speed controls I thought it would be wise to understand your circumstances better. Not having that, however, I will say that the type of speed control on a router like the one you used is an open loop design. It simply reduces the input voltage supplied to the motor by limiting the peak voltage and / or duration of each of tje 60 Hz voltage cycles. It has no way to monitor the actual speed or do anything to 'control' it. I suspect, in your situation, the rotational speed of the lathe, coupled with the speed of the router itself caused the router to be overcome by the lathe rotational speed. There is no way the router could do anything but "go along for the ride". Effectively the router couldn't keep up and because of the grinding frictional load on the grinding wheel, the wheel ultimately broke. The noise you heard was the wheel fracturing and disintegrating. Again, this wasn't a failure of the router speed control but simply overload due to the conditions that were set up. Maybe this worked for you previously and you were lucky, maybe this time the wheel was degraded enough from previous uses to fail, maybe the load was greater this time, maybe there wad a metal fragment that got into the motor speed adjuster, etc. Who knows.

Sorry for your injury. Thanks for your initial posting. We can all learn the need for more personal protection when using machines.
Hi Pat, I understood from his description that he was not grinding with it when it happened so the wheel wasn't in contact with the piece in the lathe. Also, even if the lathe and router were rotating in complimentary directions , the lathe was probably much slower.