How to vary the speed

Since I am going to use this flex shaft grinder for something it was not intended to do, namely be the spindle for a CNC Milling Machine at this great site Lumenlab (http://www.lumenlab.com/forums/index.php?showtopic=25411), I would like the ability to vary the speed of the tool to suit different situations . Different materials different cutting tools, etc. The unit is supplied with a foot control for varying the speed, but I don't want to be strapped to that thing for the duration of some machine operation which could take hours, overnite, ??

So I decided to take apart the controler. This is what I found

I unscrewed the four philips head screws shown in the photo and took out the little plunger unit




This is a variable resistor activated by the foot pedal top which I removed. The resistance varies from 0 to over 2MOhm (the limit of my meter). There is quite a taper to the resistance meaning at one end of the plunger travel there is very little change and at the other it is quite dramatic. However when depressed by the foot pedal or even by hand it is possible to control the speed quite well. I think that there is a way to depress the plunger with a cam arangement so that the speed can be set at some value. This probably won't hold as the tool is working, but could be useful.





I bent a little bracket to hold the variable resistor behind .





I then used this tool which General Tool calls a "Multi Use Rule & Gauge". I love that name. I actually like the tool too. I just don't find that much use for it in daily life.





Cute, isn't it? Anyway I scratched a prelimenary drawing of the cam and tried to imagine it working.




I could have used Sketchup or another drawing program, but I like to use a pencil sometimes. I think I made the radius a little large. I will cut it in half maybe then cut it out of hardboard to control the speed. I bent an "L" bracket to hold the variable resistor on the backside of the post above the working surface where I could reach it.

Maybe I'll get the hardboard cut out tomorrow.