On an edge finder there are two ends. The end you use to find the edge is pretty straight forward, but the pointy end is supposed to be for finding the center of holes, but for the life of me I cant seem to figure out how this is supposed to work.
Does any one here know?
Clamp it in the chuck and run the point down into the hole, lightly. I think you're supposed to mike across the sliding joint and adjust until it reads whatever the shank diameter is, but I just slide my fingernail over the step and move the table until I can't feel it on any side.
Once you've located the edges you can put the pointed end down to confirm that your 0,0 position really is the corner of the work, you didn't locate on a chip.
A burr or countersink can easily throw off the center finder. I just had to adjust some holes positions by 0.015" because the burr on a hole apparently shifted the countersink and I misplaced the vise stop on the next setup.
Jim Wilkins
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I was hoping somebody would give a better answer than mine. Seems you're not getting an answer.
I've not seen anybody else do this, so there may be a better way. On a very small hole, the pointed end will tell you which side you hit first as you lower the quill. Make an adjustment and try again. When you're all the way down, you're right over the center of the hole.
Karl
I use the finger nail method. Tapped holes are going to be a problem though.
Turning a tight pin to stick in tapped hole and indicating that might be more accurate. Usually when you are tring to pick up such a hole, there is something broken in it though :(
Wes
ore accurate.
en in it though
Usually when I've had to measure a tapped hole pattern it was to drill a mounting plate to match. I just put setscrews or Phillips heads in and visually pick up the center, or for better accuracy chuck a matching screw in a collet and turn a point or center hole on it. Two little flats ground on the sides make it removeable with tweezers.
When I asked the machine shop to measure one particularly critical pattern they used a height gage to measure snug-fitting pin gages in the holes, but I still had to open up the resulting mounting holes a little to make the screws fit. I think the tap may have raised an uneven burr on the ID of the threads.
If I really really had to be accurate I'd single-point a thread that fits snugly and make my own center plug. A small 5C-mount chuck works well for a part that has to be removed to check the fit.
Jim Wilkins
The point of an ordinary scriber fitted in the chuck can be used to locate an edge, a scribed line or a centre punch dot. It's pretty rough and ready because the point can be a bit c*ck eyed and not accurately represent the true spindle axis.
The pointy bit of the edge finder set is intended to do the same job but eliminate the spindle axis error.
Set the pointer end roughly on axis and close to a flat surface. Run at any convenient low speed and with a finger resting on the surface SLOWLY edge the point in until the point reaches dead centre and no longer rotates around a small circle. The point is now dead on the axis of the spindle.
It's pretty easy to learn to do this and it only takes seconds. It's then a versatile location finder.
This is the way it is supposed to work but the downside is that it means removing the cutter and replacing it with the edge finder. A more convenient kludge is the "sticky pin" system.
In ancient UK terminology a gramophone needle is stuck to the end of the already installed cutter with a lump of Plasticene. The point of the needle is then centred by finger pressure. It needs a little more skill to do this because, until you're used to it, both ends of the needle may initially be way off centre. However it's a skill well worth aquiring as it's very much quicker than messing about changing between cutter and edge finder.
Not sure about the North American equivalant. Gramophone needles are pretty rare now but the cut off end of a thick sewing needle does the same job.
Plasticene is a propriety brand of modelling clay which happens to have sufficient "stickyness" without being "rubbery". This zero "rubbery" is vital as the point mustn't spring back once it's centred.
Jim
Adjust the X and Y axis so that the pointed end of the center/edge finder is approximately in the center of the hole somewhat below the surface. With the spindle running slowly, move the X axis until you see the kick. Note the reading on the dial. Now move the X axis slowly in the opposite direction until you see the kick. Note the dial reading. Subtract the smaller reading from the larger. Now move the X axis toward the center of the hole for half of the calculated distance. The center finder is now exactly at the center of the hole's X axis. Repeat for the Y axis and you have found the exact center.
Adjust the X and Y axis so that the pointed end of the center/edge finder is approximately in the center of the hole somewhat below the surface. With the spindle running slowly, move the X axis until you see the kick. Note the reading on the dial. Now move the X axis slowly in the opposite direction until you see the kick. Note the dial reading. Subtract the smaller reading from the larger. Now move the X axis toward the center of the hole for half of the calculated distance. The center finder is now exactly at the center of the hole's X axis. Repeat for the Y axis and you have found the exact center.
Sounds good except for the backlash. I suppose if you had a DRO this would work just fine.
long travel dial indicator and magnetic base?
That may be more accurate if you have a well-lapped center finder but the cheaper ones aren't repeatable to any better than I can feel with a fingernail. I can barely make an old Starret repeat to 0.001" on a surface-ground 1-2-3 block.
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