# Micro edge finder



## Swede (Nov 20, 2011)

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.


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## maverick (Nov 20, 2011)

You've built a very nice and useful tool to be sure. You are correct regarding edge finders on CNC mills. I got quite proficient at relapping
 the faces, repairing the spring eyes and reassembling the pieces. Took awhile to get the hang of it.


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## /// (Nov 21, 2011)

This might sound stupid, but I always wondered how these things worked :
Just found this video(youtube.com/watch?v=f0od-cp_9dg)
Very cool.
I will have to make one myself, looks better than the cigarette paper method I've been using.
Thanks!


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## Swede (Nov 21, 2011)

If you want to make one, go for it, as it'd be a good project either for fun, or as a turning and boring exercise, but it's hard to argue with the low cost of the commercially-made product. If I could have purchased one with a 1/4" shank, I'd probably have done it, but they are unavailable AFAIK.

The regular edge finders for a mill are (for me at least) one of the most-used pieces of spindle tooling I own. Not only can they find an edge, they can be used to center a round solid or even a round bore with ease. A really handy tool to have and use. I think the extra $$ spent on a Starrett or similar is worth it, they seem better made, and the jumping action is more visible and positive.


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## mklotz (Nov 21, 2011)

Fisher Machine, near me, makes a 1/4" shank edge finder...

http://www.fishermachine.com/index.php?content=updatecart&id=31

I have one and it works very well. IMS, Fisher makes edge finders for B&S.


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## Swede (Nov 23, 2011)

mklotz  said:
			
		

> Fisher Machine, near me, makes a 1/4" shank edge finder...
> 
> http://www.fishermachine.com/index.php?content=updatecart&id=31
> 
> I have one and it works very well. IMS, Fisher makes edge finders for B&S.



Haha! Now I find out. Oh well. The problem is, I am tempted to buy one to see if it works better than my own... which it probably will!

Added: Well, I feel vindicated, a little. The Fisher EF looks good but they cheated and used a 3/8" body with a stub 1/4" shank. For $11.50, though, that's a good deal.


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