Hi, got a problem with my spindle drive speed. Bought myself one of those digital rev counter to check my spindle speed as it seems to slow down depending on the length of time I use the mill.

For example when I dial in M3 S1000 or use a pre-programmed set of codes when I first use the mill in the morning it gives me 1400 rpm, after 10mins of machining the machine settles at 1000rpm. After an hour of use the spindle speed settles at 800rpm although I'm still calling for 1000rpm. I'm using a Denford Triac bench top mill with a very old LYNX spindle drive board. It uses 4 wires from my BOB with a spindle drive card attached to it to send a voltage to control the spindle speed. I realise it must be the voltage the LYNX board is receiving but cant find any visual problems. I know a very small change in the voltage signal will effect the spindle speed so have shielded these 4 wires from external interference but still get differing speeds. Has anyone got any suggestions as to how to solve this problem apart from replacing my LYNX unit. Just to compound the problem this variation in spindle speed does not happen all the time but the more often than not.

Suppose the best way would be to monitor the voltage to see if it varies, if it does then its not the drive but more likely the controller, if it doesnt then it is the drive.
Another way would be to hook up a constant voltage supply such as a small dc output transformer and let it run and see if the speed changes.
Hood

Oh and if its a DC motor check the brushes as I would imagine worn brushes could also have similar symptoms.
Hood

Hi Hood OK will try tomorrow. Jim