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...&idproduct=148
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...m_source=froog
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.
--
BottleBob
http://home.earthlink.net/~bottlbob