On Aug 17, 4:55 pm, BottleBob wrote:
F. George McDuffee wrote:
On Sun, 17 Aug 2008 02:57:14 -0700, BottleBob
wrote:
If the electric edge finder is spinning, AND if it runs out a little,
it will probably light up when the high point contacts a conducting
surface. But you really won't know if that high point is .0001",
.001", or even .010" off center. That's why I would contact your part
with the edge finder stopped (then zero out your axis), back off your
part, turn the edge finder 180 degrees and contact your part again to
see if there is a difference in the two positions of the edge finder.
Half that distance difference should be your off-center runout
==========
Good observations, but as an old German tool maker told me years
ago, after I took a drawing to him with 4 place decimals for some
hole locations, if you can't measure it, it doesn't matter.

Unka George:

It might pay to indicate your electric edge finder from time to time,
and tap it to get it centered if it runs out an appreciable amount.
As far as the needed accuracy for your job, that depends on the job.
Some can be scaled, some can be within a few thou, and some need to be
within .0005. In the latter case I wouldn't count on the accuracy of
electric edge finders, I'd either use a regular edge finder or
indicator sweep your part and move over half the distance of your part.

I see several people have mentioned the Schmidt edge finders,
https://www.hermannschmidt.com/produ...sp?idcategory=....
anyone have comments on /experience with the ones from Flexbar?
http://67.59.156.7/merchant2/merchan...uct_Code=18509

Are these that much better than B&S or Starrett, or just more
expensive?

I never felt the need to buy an edge finder more expensive than a good
Starrett or B&S. So with the knowledge of me having no direct
experience with Herman Schmidt or Flexbar edge finders... my OPINION
would be that your money would be better spent in another area. IF you
need better accuracy than a good Starrett edge finder can achieve
(around ±.0005) then you need to consider using an indicator to find
the edge of your part, either by "sweeping", direct indicating the
edge, or using a "chair".

http://www.wttool.com/product-exec/p..._medium=cpc&ut....

In using those you have to make sure the wall you're edge finding is
perpendicular to your table or you might get an angular error.

--
BottleBobhttp://home.earthlink.net/~bottlbob


Bottlebob:

Excuse the 'senior moment' on my part regarding the 90 degree babble.
You are of course correct.

As to geometric accuracy of the various features: Anyone who reads
this ought to understand that attention to spindle squareness to the
table, straight tool, work ref. surface finish and squareness is
mandatory for accurate results. The latter is particularly important
when using the 'chair gauge' you referenced. No sense in measuring
the surface finish of a plowed field in micro-inches:-)).

Jig borer operator in my training grounds used a gauge block held to
the side of the work. First they swept the work edge and then the
gauge block surface with the indicator. When the indicator needle
stopped moving the spindle centre line was dead-nuts over the
reference edge, say within .0001 or so. The beauty of this method is
that no tooling errors are introduced into the process. Theoretically
it may be used to achieve any accuracy required.

Wolfgang