I wanted an accurate tacho for my lathe and found an easy way to do.
Firstly I found a display unit that can be used as a counter or tacho by altering DIP switches.
Unfortunately the retail price is about £250 but I managed to win a bid for one on e-bay for under £30.
That was the cornerstone to the mod.
The unit runs on either 240v or 110v by a switch on the back.Also the unit has the ability to use a divisor or mutilplier for all sorts of applications.
All that is needed to input to the unit is either a magnetic switch. pulse, or proximity sensor.
The device I used was a proximity sensor that can be supplied either already wired or with a lead with plug assembly.
The sensors are about £30 but again I found one on e-bay for £12 and another £5 for the plug assy.
The photos in the photos section under Tacho show how i first drilled and tapped a 5mm hole in the angle part of the spindle pulley. I then screwed in a Cap screw and locknut making sure that it didn`t interfere with any moving parts.
The sensor is mounted on the headstock backplate with an angle alloy plate and the plate drilled and tapped 6mm. The sensor can be adjusted so that it is appx 4mm from the cap screw when positioned close to the proximity switch.
Three wires from the switch go to the appropriate connectors on the back of the display unit.
I you are careful with positioning the angle plate the 6mm hole can be drilled and tapped without removing any existing parts of the lathe.
To test operation select single count on the dip switch and slowly rotate the spindle by hand with the unit switched on and each time the cap screw passes the sensor the led indicater on both the sensor and the display will flash for each pass and will display one increment for each pass on the display.
Once you are happy this is working ok, set the dip switch to "auto-ranging" and to "tacho".
Now run the lathe and the revs of the spindle will be shown.
The unit is very versatile and has a number of setting for different applications.
I was lucky in that the parts cost me £40.
My suggestions would be to source the display firstly as this could be the most expensive part.
It was a very easy mod to install and I am well pleased.