As many know, I've been working on my CNC bench mill that has a small and very fast spindle. The largest tooling it can accept is 1/4" or 6.35mm, and I have been missing the use of my edge finders, the smallest of which is 3/8" shanked. I decided to make my own.
They seem simple, but I found it took a bit of fiddling and redesign to make one that works like its bigger brothers. The first step is the tip. I made mine 0.200", although in theory it makes little difference so long as you know the diameter. But 0.200" allows me to jog the table exactly 0.100" to center, and this is a one button operation with my mill.
The material is A-2 tool steel. O-1 would be fine, as would just about any other steel.
The tip was parted, then drilled and tapped 2-56 for a fastener that attaches to an internal spring.
The parts layout. The spring connects the tip to a top cap, and when it is all assembled, the spring provides tension to the tip. The tip to body interface must be accurate and lapped. I did this a bit crudely by simply using 2000 silicon carbide paper, oil, and a surface plate.
It took a few tries to determine the correct amount of spring tension, but in the end, I had an edge finder that worked well. The hole in the bottom of the shank portion was drilled 0.135" or so. Too small, and the "jump" action is hard to see. Too large, and the tip section loses accuracy and stability. The interior of the shank was bored to 0.210" or so to provide room for the spring, which must have space to shift laterally. The boring goes to within 0.032" of the bottom.
The reason I went to this trouble is because this sort of edge finder allows one to overtravel without damage, and this is helpful with CNC, where overtravel with anything fixed can cause damage or stress.
They seem simple, but I found it took a bit of fiddling and redesign to make one that works like its bigger brothers. The first step is the tip. I made mine 0.200", although in theory it makes little difference so long as you know the diameter. But 0.200" allows me to jog the table exactly 0.100" to center, and this is a one button operation with my mill.
The material is A-2 tool steel. O-1 would be fine, as would just about any other steel.
The tip was parted, then drilled and tapped 2-56 for a fastener that attaches to an internal spring.
The parts layout. The spring connects the tip to a top cap, and when it is all assembled, the spring provides tension to the tip. The tip to body interface must be accurate and lapped. I did this a bit crudely by simply using 2000 silicon carbide paper, oil, and a surface plate.
It took a few tries to determine the correct amount of spring tension, but in the end, I had an edge finder that worked well. The hole in the bottom of the shank portion was drilled 0.135" or so. Too small, and the "jump" action is hard to see. Too large, and the tip section loses accuracy and stability. The interior of the shank was bored to 0.210" or so to provide room for the spring, which must have space to shift laterally. The boring goes to within 0.032" of the bottom.
The reason I went to this trouble is because this sort of edge finder allows one to overtravel without damage, and this is helpful with CNC, where overtravel with anything fixed can cause damage or stress.
