Post By SND
I just purchased an edge finder having always found centre of a shaft by touching the shaft with the end mill and then moving it the required distance to the middle. For some reason I cannot get the whole thing to run perfectly, the end with the 60o runs true and the top but not the middle bit. I am wondering if my jacobs chuck is running slightly out or am I missing something else? Any help is appreciated.
Put your edge finder in a collet just like you would a mill. As far as you jacobs chuck it maybe spinning out, put an indicator on it and check it.
It's my experience that Jacobs chucks run at best a few thou run out and can get much worse. I think a collet would work better. Do you mill with a Jacobs also? While sweeping an indicator mounted in a JC works because the error is "baked in" so to speak, a EF needs concentricity to work properly. An end mill holder would also work.
Thankfully the edge finder's body doesn't need to run exactly true(though it is reassuring when it does). The wiggly bit will find the center of the spindle.
Now someone's gonna say that's wrong. and I'm gonna say edge find the hard jaw on the vise and zero the DRO, then put a .010" shim on one side of the edge finder so it wobbles all over the place, and notice it finds the same zero.
I didn't quite believe it at first either.
Oh and if its that bad, get a new drill chuck. Assuming its not just a POS edge finder cause I've seen a few really bad ones.
I want to try one of those $50 Herman Schmidt edge finders.
I bet they kick with repeatability.
Oh yes, edge finder in a chuck with runout is ok.
For deep edges I use a 3/8" steel rod.
Put a little ink marker on the lower half where you are going to touch off on the part.
Chuck up the rod, and it will wobble a bit (a good thing).
Move the table until the rod begins to scrape the ink away, and
stop moving then the ink rubs a line off all around the rod.
Then do the math and move over.
Thanks guys, the reason I used a Jacobs chuck is that the edge finder has a smaller shank than any of my collets but I could always make a sleeve for a collet size I have and shrink it on. I'll try that.
I like having a couple of edge finders, one with a 3/8" shank and one with a 1/2" shank so I can use the same collet as my most often used end mills but if I'm doing drilling work, I use the drill chuck for sure. It's also good to have an edge finder with a 1/2" tip for finding the sides of large cylinders. A 3/8" can't get tangent to those. I recommend the Fisher Machine "Big Jump" edge finders. They work really well.
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X2 to what Gordon Long says. I'm a fan of the Fisher Machine "Big Jump" edge finders also, haven't used my old Starretts after getting a set of the Fisher ones. The manufacturer is PM member. The recommendation to have multiple edge finders on hand for different tasks is excellent as well.
This goes against everything i know about my edgefinder.....i will try this in the morning!
Originally Posted by SND
what I do is, I test the runout of my drill chuck first (ie .002") then add that to my edgefinder dia, ie: .002 runout + .200" edgefinder divide by 2 = .101" thats what i move over by and zero.
I can't add much to the edgefinder thread, but WRT the chuck, you might replace with a Jacobs Super chuck, my 3/8" (11N ?) runs nearly as true as my Albrecht 1/2". If th OP's got a Super, he just may need to pop off the shank, then clean things up and refit.
I tested the "edge finder off center" some years ago and went all the way to .032 shim under one jaw. The only thing I noticed was that the edge finder got slower to kick out the further off center it got. While it was a lot harder to read it still seemed to pick up the edge. (This was using one of the Schmidt edge finders. The Fisher "Big Jump" I bought recently would respond in a similar manner.)
Originally Posted by vettepicking
Whenever I work off centers I pick up one side of the workpiece, zero the DRO, pick up opposite side, divide total move by 2 and move to that number (i.e.- to center), then re-zero. Or I just swing it with a spindle-mounted dial indicator to find C/L.
The DRO's 1/2 function is very useful.
One thing I did before on a sloppy mill and that I still do to this day out of habit is that if I'll be drilling I edge find with the quill loose, and if I'll be milling I edge find with the quill locked. Though on any decent machine it doesn't make much difference.
I use the drill chuck to hold my EF if I am going to be drilling with the chuck.For milling I chose to use the collet,not that I have had issues with using a chuck but that I like finding the edge of a part that I am going to mill with the knee/spindle as close to the same position with the EF that the mill is going to be operating from.When you use a chuck or even a collet extended farther down than were you will be milling if there is any error in how square your spindle is to the table it will show up by being off center because when you retract every thing up to milling postion because the spindle is at a slight angle to the table you lose center.
One of our big knee mills has a LOT of wear in the knee causing the table to sag in Y,you never EVER edge find then move more than an inch or so up with the knee after finding ZERO and expect it to be on center.
Speaking of Fisher "Big Jump," mine doesn't. Jump big, that is. The regular Fisher 3/8" I have is much snappier. I tried oiling, which made no difference. Any ideas?
Fisher Machine also makes some very nice sine bars. I have their 5" model. I bought mine from Brown & Sharpe but it is really Fisher Machine that makes them for B & S.
The Hermann-Schmidt edge finders are no longer for sale from H-S, last I looked.
IIRC, I did a test a couple of years ago on H-S, Starrett and FM edge finders and published a summary here on PM and they were all within +/- 0.0002" IF used carefully. As I ran the tests the results got better for each type. Because of this I concluded that practicing with an edge finder improves the accuracy in the finding of edges. Startling, I know!
Yes, practicing does help. And in the course of trying to squeeze as much accuracy as I could out of my edge finders I found that it was useful, after the finder had jumped, to back off the leadscrew ever so slightly as I put the slightest pressure on the finder end and see where it would just slide back. Doing so I could find a spot where it would just barely not jump and yet was not quite settled as it would have been with no pressure on the edge. This is the most sensitive method in my hands for me to find an edge repeatably and accurately. FWIW only.
Originally Posted by David Utidjian
David, I remember your testing back then. That came against a background of some people saying you could only get a thou sensitivity out of an EF. But, as you say, that depends on how careful you are. It is possible to do much better than that.