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From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: While we're talking about edge finders... what about conical tips?
Date: Thu, 09 Sep 1999 02:41:03 GMT

These double ended devices ar called "Edge and Center Finders"

The cylinder is for edges, the point is for centers, center drilled holes,
center popped locations...but particularly for aligning very accurately with
scribed center lines.

You do this ONE LINE AT A TIME!!  Don't try to do both at once!

First center the point by pushing the edge of your rule against it while the
point is about 25 thou clear of the surface.  Yes, you can use your thumb
nail..but the first time it rides up over it will be the last time you pull that
fool stunt!!!

Back the point about 100 thou away from one line, bring it down to within a few
thou of the surface and align it as accurately as possible, with the other line
using a good glass and a light.

Now, set that axis at zero and BACK it away from the first line.  Set it to the
second line with glass and light and finally return your first axis to zero.
You are now on center.

The old timey toolmakers, (Including my good self,) used to get "on center"
within a thou, REGULARLY!!  Closer if the job demanded and using nothing but a
"Sticky Pin"

Believe it or not..I had never heard of or seen an "Edge and Centerfinder" until
I came to the USA in my mid thirties.  Nor had the venerable George H
Thomas..who independently "reinvented" it in his eighties!!

They were not in common use in the UK..perhaps now..but not 40 years ago when "I
were a lad"


BillDarby wrote:
> I've thought about how to use the "pointy end" a good deal and I believe that
> accurate readings may be taken in tight places with it ,,,,,,,,,so long as you
> remember that the edges being defined have to be at equal height and the pointy
> end must be set to the same height for comparative readings.
> For instance:
>           If you wanted to set up over the center of a slot about  .100" wide
> then you would first have to consider if the sides of the slot were (well
> defined) and of equal height.   Then so long as that condition was met then no
> error due to difference in height / ill defined edge, would be introduced.
> Then the pointy end could be brought into the slot and moved against successive
> sides noting the readings of each, while taking care to have the quill set to
> the same height for each reading.         It is realized that there is little
> likelihood of requiring any quill movement during such work in a single slot but
> the principle applies nun the less, and if, for instance, you were trying to
> locate the center of the space  between two slots then it would, undoubtedly be
> necessary to alter the quill height in order to move from taking the reading on
> the wall of the first  slot to taking the second reading on the wall of the
> second slot.      IE you'd have to move "up",   "over"  and "down" to get the
> two readings.
> Regards Bill Darby
> Brian wrote:
> > One question along similar lines: I've got a double ended edge finder with
> > one end a 0.2" cylinder that works great. Now how/why/when do I use end #2
> > which has a conical tip? Use of the cylinder is simplicity in use and
> > understanding but I can't see how you could get any accuracy with the cone.
> >
> > Brian

From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: Newly "discovered" devices
Date: Thu, 09 Sep 1999 12:16:32 GMT

John Stevenson wrote:

> There are always what can best be described as vacuums in all trades.
> I've been into machining all my life and I still come across setups that
> others do that are so obvious but I or people around me haven't heard
> about.

I came across one the other day:

Two years ago I had the good fortune to pick up almost the entire contents of an
old toolmaker's a Garage sale! for a "song"!!!

Among the many, top quality tools and bits and pieces was a little "square" of a
type I had never seen before. It has a makers name on it, "Moore Tools, Bpt
Conn"  I knew the name but I had NO idea what this particular little, precisely
made "gizmo" was used for.  Many is the time I picked it out of my tool box and
mulled it over..but for the life in me I couldn't fathom its purpose..perhaps
part of a special setting jig, was my best guess.

Let me describe it:   It is a tiny "angle plate"  1 1/2 long, x 7/8" high x 1
1/8" wide. Made of two precisely hardened and ground plates, joined with a step
joint and two 8-32 capscrews.  In the center of one side is a rectangular hole,
again, precisely ground formed by a slot in one plate and the steped edge of the
other plate.  One thing I failed to take significant note of...was that the
inside edge of the "angle plate" coincided EXACTLY with the center of this slot.

And so the puzzle remained until, surprise, surprise, in browsing through Ebay
(surprise, surprise) I came across this item:

Unfortunately the auction is ended now and the photo is gone from the archive.
But there, Large as life was my little "angle plate"..Only now it has a name and
a purpose!!

It is called an "Edge Locating Chair" and is used by popping it on the edge of
the work piece and indicating, first one side of the slot (using a finger type,
auto reversing TDI), bringing the dial reading to zero and noting the cross feed
dial reading.  The other side of the slot is then indicated, bringing the TDI
reading to the same point and again noting the cross feed dial reading.  Lastly
(and with due allowance and care in taking up backlash) the crossfeed dial is
brought to the midpoint which point the spindle centerline is
EXACTLY over the edge of the work piece!!

I haven't had chance to try this out in practice yet..but when I do I will
report on it's efficacy and accuracy..compared to other methods of edge

Live and learn!


From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: While we're talking about edge finders... what about conical tips?
Date: Thu, 09 Sep 1999 12:41:21 GMT

The "Kick out" feature on the double end type, lets you know precisely when the
point is centerd and running true.  This as you center it with a rule or against
an edge.  With a well made E&C it will center or kick out within a tenth or so.

Alignment with the scribed lines can then be done with the spindle stationary.
Which is not a bad Idea when getting up close with a magnifying glass!!


BillDarby wrote:

> What I find perplexing is that the center finders that I've seen all
> have the "kick out" feature.
> Now, if you use it , as Robert suggests, to optically get aligned on a
> scribe line then why bother incorporate the "kick out" design, as any
> old pin ground to a point would do that for you.  or;
> If you use it in round stock as John suggests, how is it done?  Do you,
> align it optically with the hole and adjust the X Y by trial and error
> until you can go down into and back out of the hole without "kick out"?
> If / when it kicks out, do you have some way of knowing which edge it
> kicked away from ?? or is it just sort of just best guess?
> I do not ask these questions to be in "any way" critical of anything
> that's been said.  I simply ask as an amateur machinist wishing to
> understand how to do things properly.
> Regards Bill Darby
> > Robert Bastow  wrote:
> >
> > >These double ended devices ar called "Edge and Center Finders"
> > >align it as accurately as possible, with the other line
> > >using a good glass and a light.
> > >
> >
> > John Stevenson wrote:
> > THey list that vee shaped centre finder that you put in a collet chuck
> > and lower onto the round stock in a miller or drill to find the
> > centre. So obvious but I hadn't seen one before nor had my apprentice
> > and he's 73.

From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: While we're talking about edge finders... what about conical tips?
Date: Thu, 09 Sep 1999 17:02:31 GMT

BillDarby wrote:

> Robert,,,, thank you for responding, but forgive me for being just plane
> thick, but I just don't get it.  Are you saying that the function of the
> center's "kick out" feature is to let you know that it's tip is running
> true?
> I can see how you could use it to optically align the point onto a
> scribe line, but then any pin ground to a fine point could do that.

That is true..but only provided that the point on the pin is ground "Dead on" in
the first place and that it is held "dead on" in the chuck or collet of the
machine it is used on.

Both are unlikely circumstances in the greater scheme of things and certainly
not guaranteeable.

The function of the kick out is to tell you when you reach concentric running of
the disc or the point..if the point is undamaged from its original grinding,
then it doesn't matter where, along the cone, you make contact..the result is
the same...the point will run true regardless of any eccentricity in the body or
the holding of the body.

The double ended type, with the spring loaded caps are, if made properly, VERY
sensitive and VERY old Starrett will indicate edge or center
position within less than a tenth either way.  I certainly don't need to take a
"mean of multiple readings"

> As for using it against any edge, I do not see how it could be accurate
> unless you were getting the mean of multiple readings under given
> conditions.  Beyond that, I do not see how getting the point to kick out
> against a single edge would be of any value because in order to get it
> to kick out you have to have the edge touch the side of the point and if
> you touch the side of the point then you are not touching the tip of the
> point and if your not touching the tip of the point then you are not on
> center

  Yes you are..see my above remarks!  I think you are confusing the function of
the EDGE finder with that of the CENTER finder.  All my remarks have been with
regard to the latter.  The objective is not to find the edge of the work by
bringing the pointy end up against it..If that were the case your above comment
would be perfectly true.  With a CENTER finder, Th. objective is to bring that
to a true running touching it with or against an edge..ANY
edge..even a thumb nail if you must!!   The true running point is then used to
line up with layout EYE!!

> kind of a circular argument and to compound matters I doubt that a tip
> can be brought out to a perfect point.

Of course it can..the very act of grinding it cannot produce anything but a
perfect point..down to the point ?? of molecular level..then you are on your

My Starrett is twenty years plus "young", examine it with a glass and it is
still sharp and concentric..perhaps because it has never been abused!

> Would very much like to know what you mean by " Closer if the job
> demanded and using nothing but a"Sticky Pin" "

A "sticky pin" is just that!  A pin or a needle stuck in a glob of wax, putty,
chewing gum..whatever, and stuck in turn on the end of the cutter.  Trued up
while running..yes we used our thumb nails..but that didn't hurt like a regular
center finder does, when it runs amuck over your nail bed!!  For real "picky
jobs" we would use a gramophone needle..I still have a tin of them in my tool
box..That would be trued up with a feeler blade with the pin point only a few
thous from the surface.  Holes could be drilled and layout lines..that
would be within a few tenths of dead position.

For really REALLY picky stuff.we went to either toolmakers buttons or to a jig
borer with optical centering and dead length scales.

Hope this helps.


> Thanks in advance Robert.
> Regards Bill Darby

From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: While we're talking about edge finders... what about conical tips?
Date: Thu, 09 Sep 1999 17:49:30 GMT

Here we go again....8^) wrote:

> wrote:

> > The "Kick out" feature on the double end type, lets you know precisely
> > when the point is centerd and running true.
> I'm still missing something here.

I think so

> We're talking about the center finders with conical tips, right?


> If one jams the cone into a hole that one wishes to indicate to,
> and uses a fingernail to see when it is on center (not under power)
> then that is practically useless it is so inaccurate.

The human fingertip can detect discrepancies (steps) between two surfaces of the
order of a couple of tenths of a thou!!

> If one runs it under power, and gets it to kick out on the
> inner edge of the hole, one has no idea of what distance the
> spindle axis is from the hole edge, by virtue of the cone shape.
> The same can be said for going to an edge with the cone end.

Absolutely NOT the way to use it and, not what I said.

> And if one centers the cone under power, and aligns it 'by eye'
> with a scribed line or a center punch mark, then things are still
> pretty sloppy.

Not true!!! With good light and magnification, the human eye can line up two
"fiducial" reference points or lines within a few millionths of an inch.

> I have to weigh in on the side of the folks who do not have
> a really good understanding of exactly what those cone-shaped
> center finders are for.

I'm not sure what you mean by the above statement..Are you saying that because
you don't understand it then it must be no good?

As I said in my previous response to Bill..the objective of the cone shaped
center finder is to have an accurate point that can be set VERY accurately, to
run TRULY CONCENTRIC and to be able to do that quickly and reliably.

Using it then, to align to a given Center Point depends on how accurate you want
the alignment.

First let's dispense with the center pop.  In the first has no reason
or right to be there!!  Best just leave the lines as can do a far
better job of alignment.  You would in any case align to the lines
individually..remote fro the actual intersection..just as I outlined in my
earlier submission.

Aligning to a center drilled hole.  Can be done, by eye with the spindle
running.  No question here of running the point into one side or the
are right..that doesn't work.  What you do is carefully lower the true running
point into the hole WITHOUT making contact, and gradually adjusting X and Y as
the annular space gets smaller...probably only good for a thou or two

But then the idea is to move the centered point up and down in the center follows, by definition if you like, that if it contacts one side before
the will "Break" (or at least make a visible attempt to break)..thus
indicating that it is not yet on  true center.

However..there is another way!!

With the spindle stationary, drop the point right into the hole and adjust x and
y until you can neither see, nor feel, a "step" in the alignment of point and
body....this you can do with surprising accuracy!

Or you can use a micrometer to measure the diameter of the centerfinder at the
junction point.  If the CF is a dead .5000" diameter and your mic says
.5010" are half a thou off center..though you would be able to see and
feel that gross error withou needing a mic...!  Repeat at x and y locations,
adjusting as required.

One caveat..these last two methods DO depend on the body being held with
reasonable accuracy in the spindle.  Otherwise one would need to rotate the
spindle through the four points of the compass to be sure of getting an accurate

>  I prefer the wiggler type, anyway as
> they seem to be more versatile.

Yes they are more versatile...but GENERALLY less sensitive/accurate. I use
both..depending upon circumstances.


> Jim

From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: While we're talking about edge finders... what about conical tips?
Date: Sun, 12 Sep 1999 15:35:55 GMT

Well put!

Many time, in writing to this NG I am somewhat controversial, over- emphatic.
yeh, verily, even arrogant!

This is mainly for the benefit of the newbie..I have trained many Apprentices in
my time and the gol den rule is "First get their Attention"

Oft times this takes a two by four!!

Many time I make a deliberately Emphatic statement..I know it has achieved its
purpose-to make people THINK- when I get a host of replies pointing out the
obscure circumstances under which my statement would not hold water.

My whole philosophy..Like to teach the principle behind the skill
and enforce its practice.  Once that is achieved, the practitioner has some
basis on which to make objective decisions about when to bend the rules.  They
don't need my help anymore, to do that.


mikoberg wrote:

> In article <>, wrote:
> ----snip---
> > If you do it that way, then 5 thou accuracy would be a happy
> > wonder Grandpa used to bob him!!  ;^)
> >
> > Do it the way I described and a few tenths accuracy is obtainable.
> >
> > teenut
>    Ahh... Most time the bobs were well earned. I was just trying to desribe
> a short-cut when great acuracy was _not_ needed. Many times you need to
> line the center of the mill to a scribed line and thousanths are not needed
> by a job. Thats what I meant by the difference in accuracy of the object
> couldnt be told by grandpa, the final outcome would be within tolerances
> needed. He was just a perfectionist espesially when it came to leaning
> something. After you knew the skill well then you could bend or break the
> rules. The bob on the head remark was to show it was a non prefered but
> quick once you got the height trick down. The rest of the post was manly
> for the many lurker and newer users who don't have the advantage of a
> granfather to bob 'em once in a while.
>   Mike -well boped- Oberg

From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: Pointed Edge Finder
Date: Thu, 21 Oct 1999 18:23:17 GMT

A lot of valid points Tony so I'll try to answer them as I come to them..And
thanks for taking the time to read through Deja stuff as we can now start off on
the same page.

Tony Jeffree wrote:

> On Thu, 21 Oct 1999 13:48:08 GMT, Robert Bastow <>
> wrote:
> >Yes!
> >
> >Go read the Deja was all covered then!

Ouch!   Bit snippy wasn't I..Sorry Tony!

> >teenut

> I couldn't disagree with you on the principle.  The point (pardon the
> pun...) of my post was to question how accurately it is possible to
> get the point centered  over scribed lines using visual sighting
> methods.  A tenth of a thou? a thou? ten thou?

Half a thou  is fairly easy with a bit of care...Closer than that not a deal
more difficult..using a glass and the right techniques.

Scribing fine lines using a height gage, Jo blocks and a surface plate..and
subsequently "reading them back" or setting up to them (with the aid of a 10X
loupe,) to a repeatable accuracy of less that half a thou total spread, should
be..Certainly used to expected skill of any "toolmaker"  Professional or
self-respecting "amateur"


Yes, but how much closer would depend on luck and a following wind as well as a
pretty skilled operator.

> If the answer is a small number of thou or worse, then you are not
> losing terribly much by using a solid pointed piece directly in a
> collet or chuck.

Real BAAAAD assumption..!!

"Accuracy is the result of methodical attention to extreme detail"   teenut's

At every stage, in almost every machining operation, errors tend to
multiply in fact.  If we get sloppy about the "tenths" at the front end then
there is no way to expect to hold tolerances larger by an order of magnitude

>Particularly if your next action is to cut metal
> using that collet or chuck, as the resultant cutting will itself be
> made inaccurate to the extent of the runout.

Fortunately the runout is negated if we introduce a boring operation.

I think we should bear in mind, that "wigglers" and "centerfinders" etc date
back to before DRO's and indeed to before the common availability of traceable
length standards...Johannsen Blocks and the like.

It was a vital part of a Toolmaker's skill to be able to produce and reproduce
extreme accuracy with simple bench methods.

Indeed, until quite recently, our international standards of length relied on
someone reading fine scribed lines on a bar, with a microscope!

Not many of us need or want that order of accuracy in our home shops.  But from
time to time some do..and it is comforting to know how to go about achieving it
should the need ever arise.


From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: Pointed Edge Finder
Date: Fri, 22 Oct 1999 19:59:25 GMT

> >Hmm.  Just how wide is a narrow scribed line?
> >
> >So a steel block is scribed with a sharp, new scalpel - with a
> >very light line.  And then plopped under the microscope and the
> >width measured with the stage translator.
> >
> >The answer is about 0.1 mm.  Which translates into about 4 mills.

Pretty heavy handed scribing if it is .004" wide (I take it that is what you
mean by that quaint phrase "4 mils" a "Mil" is an angular measurement  ;^)

> >Caveats:  That particular stage has a vernier that only resolves
> >to about .1 mm - so the answer could be 50% either way.  2, or 6
> >thousanths.

Kinda bringing a (Blunt) knife to a gun fight aren't we?

Rule # 1 of metrology..don't try to make an accurate measurement with a
measuring device that is less than an order of magnitude more accurate and
sensitive than the object being measured!

> >I am sorry to give such an imprecise answer but hope
> >to find a better setup for this today.  I honestly am curious.

Not made a few broad and inaccurate statements and now you are
scratching around for justification.

> >Now what I cannot find is one of those pointy edge finders.  We
> >all use the cylindrical ones - but I bet a coke that the radius
> >on the tip of the cone is about 5 thou right there.

For all I know the one you use serves as a centerpunch too.

Loose your coke..if we are talking about mine though....I use a honed needle on
a bit of chewing gum and a  10X loupe....I will guarantee it is a LOT sharper
than .005" radius

With a honed point on a scriber you can HEAR it click into a scribed line. With
a line the width of yours you would be able to feel the slop!  I have and still
can, set a pair of needlepoint dividers and step around a scribed circle, 33
divisions and come up with a CUMULATIVE ERROR less than the .004" you claim is
some limit of human capability!

Instead of theorising about what no person can do..just because you can't
envisage needing, wanting or ever being able to do yourself, why don't you get a
hold of a good book on the subject.

Get hold of a copy of "Accurate Tool Work" by Goodrich and Stanley. Published
early in the century, before Dial Indicators and Gauge blocks or even
micrometers were commonplace.  Learn how, with simple devices, ingenuitiy and
extreme attention to detail, those early toolmakers laid out and made the jigs
and tools for the Waltham Watch company.

Read it and weep!  Lindsay's publish a reprint so it is relatively easy to get a
hold of.

> >Yes, the human eye is probably one of the most remarkable sensing
> >devices around.  Dynamic range that's about 8 orders of magnitude,
> >sensitive to individual photons when dark-adapted.  Self-healing
> >and autofocussing.
> >
> >But if the things you are lining up to are wider than the resolution
> >you claim, then that's a pretty big challenge, even for a human eye.

Why?  Could you not line up two one inch wide blocks closer than 1"?

Do you never set the fiduciary line on your lathe feed thimble closer than half
the width of the line?


From: Robert Bastow <>
Newsgroups: rec.crafts.metalworking
Subject: Re: Pointed Edge Finder
Date: Sat, 23 Oct 1999 04:23:37 GMT

Norman Yarvin wrote:

> What I'd be curious to hear from Teenut is how the scribing is done
> accurately.  Ok, you scribe against a precision block, but what sort of
> scriber to use?  I suppose it has to be very sharp indeed, almost a
> perfect cone of small angle, since any significant radius on the tip will
> mean that the line ends up some distance from the gauge block.

My "Best" scriber is culled from a set of drawing ebony handle
intended to take a double nib pen, but fitted instead with the needle holder
from the dividers.  My "Best" dividers came from the same source.

The needle points are about .040" diameter, taper finely and are sharpened for
critical jobs on a hard arkansas stone (the translucent type) which has a narrow
vee groove in it ..originally for fly fishing hooks.  I use a loupe to check
progress and it is not difficult to get a point down to an almost "molecular"
level of sharpness.

Obviously at this level of "accuracy seeking"  layouts are not done with a quick
swipe down the side of a square or alongside a ruler mark..or even on marking

The surface to be marked must be capable of accepting the line..400 grit finish
is minimum if you expect to ever find it again!!

I mark on bare steel, or darken the surface with gun blue..Blue or red "ink" is
useless at this level.  I also have an old copper sulphate chrystal in my
toolbox..spit on the surface and rub with the stone and it leaves a molecular
thickness of copper "Wash" on the steel.

The most accurate you suggest..are done with gauge blocks.  Even so,
care must be taken not to tilt the point into the small radius on the edge of
the block.  I have an agate straight edge...3" long that is straight well within
"blue light" (Split waveband) levels, and this has a true square edge to it.  It
is the "Final Arbiter" along with a 5" "optical flat"

Less "Picky" know, the rough stuff to plus or minus a thou or so!!
:^)...Are done on a laboratory grade granite "Flat" with a vernier height
gauge.  Not a digital or dial one..but a REAL "verinear" that has provision for
accurate calibration and equally accurate setting with a Loupe.  The scriber on
this is a narrow wedge shaped carbide blade, diamond honed to a knife edge.  A
couple of scars on my hands and arms attest to the "molecular level" of THAT
scriber too!!

Setting dividers for accurate layout...Scribe two parallel lines on a plate by
methods described above and, with a strong glass, set the points to those

In the case of the 33 divisions I mentioned earlier (For a division plate)  I
scribed the circle on the lathe using Hoke Blocks and a 1/10000" dial indicator
to set the radius.  A dead sharp, narrow vee tool to cut the circle etc.

The chordal length for 33 divisions on that diameter was calculated
trigonometrically, two lines scribed and the dividers set to  the require

Once round to check revealed no more than four or five thou CUMULATIVE error.
Once round to scribe lightly. Once round the opposite direction to cross scribe
and SPLIT the error and the slave plate was mounted on the dividing head in
place of the regular division plate.

I used a needle point and a glass, in place of the regular plunger and generated
my real division plate from it.  Considering that what error I had in the slave
was thus divided by a factor of 40 I would say that my division plate is "close
enough" even by "teenut" standards.

Now, does anyone else want to bet a coke??

Thanks Norman



From: Robert Bastow <"teenut"@>
Newsgroups: rec.crafts.metalworking
Subject: Re: Miniature edge-finder?
Date: Wed, 05 Jan 2000 23:07:11 GMT

The advantage of cigarette (Or, in England, Izal Toilet "Tissue"????) is that it
will stick to the oil on the work piece.  Edge finding can then be done in
safety..using the CUTTER.  That way, regardless of any runout or size variation
of the know exactly where its outer edge will cut to.

More often than not, that is more important, than the actual placing of the
spindle centerline exactly over the "edge" of the workpiece

Approach the bit of paper steadily, when it disappears you are .XXXX from the
edge.  Proceed accordingly.

While edge and center finders are a wonderful idea..I, and generations of Brit
Tradesmen managed perfectly well without them.  Toilet paper or a "Sticky pin"
were more than adequate.


"Marvin W. Klotz" wrote:

> On Thu, 6 Jan 2000 14:54:27 -0500, "kenneth knaell" <> wrote:
> >I keep two Philips Audio Cassets (cassetts,casetts,  ?) in the vicinity.
> >One of them has tape that is 0.0006 and the other is 0.0003 thick.  Maybe
> >something a little stiffer would be easier to position sometimes though.
> >ken knaell
> >
> I inherited something from a WWII era machinist.  Couldn't decide what
> it was used for for a long time.
> It's a decoratively turned rod (apprentice project?) about 8" long with
> each end slit, cross-drilled and tapped to form a pinch clamp with a
> capacity of maybe 0.050".
> While struggling to hold a feeler while edge finding with a dowel, it
> suddenly occurred to me that this device was meant to hold short lengths
> of feeler stock with one's hand conveniently removed from the working
> area.
> I mounted pieces of 5 and 10 thou shim stock in it and now it sits
> permanently on the mill.  Beyond edge finding, it's useful for setting
> the business end of a fly cutter or shell mill a known height above a
> surface.
> I still don't know if that was its intended use but it is now.  Too bad
> these old-timers didn't document these neat devices they made to make
> life easier.
> Later I made something similar to hold pieces of a broken 6" scale for
> making measurements in areas inaccessible with a standard scale.
> Thought I was sooo clever until I discovered the same device for sale in
> the Starrett catalogue.
> Marv
> Email:

Newsgroups: rec.crafts.metalworking
From: (Russ Kepler)
Subject: Re: What's the right RPM to run edgefinders at?
Date: Sat, 26 Feb 2000 15:24:54 GMT

In article <>,
Brian Lawson <> wrote:
>On Sat, 26 Feb 2000 04:18:31 GMT, (Russ Kepler)
>>Dave Baker <> wrote:
>>>I'd be surprised if something wobbling about at high speed is any better.
>>Actually, it is.  I once put a gage block on the mill and indicated
>>it across the width.  Came out to .0002" off, which could have been
>>DRO error, sine error, or edge indicator error (pilot error?  I
>>hardly think so...).  Surprised me.
>I don't follow what you mean Russ.  Could you explain a bit more

DRO error: a DRO has error in calibration, temperature (relative to
what it's mounted on) etc.  Lots of minor error sources here, even
sine error (explained below).

Sine error: if you measure 2 surfaces that are parallel without
travelling perpendicular to the surfaces you'll get sine error.  In
the case of a DRO the scale may not travel square to the readhead and
give some small errors.

With "edge indicator error" I was referring to the possibility that
the nose of the indicator might not be exactly .200 in diameter or
could have some other imperfection that would cause a small error.

Anyway, since errors tend to be additive I was somewhat surprised to
have it come out close to the gage block width.

One thing: I've found that the movement of the indicator is a lot
more easily read if you run the spindle about 1600 rpm (this with my
Starretts with .200" noses, I think the .500 nose ones can go
slower).  For someone new I also have to point out that the indicator
nose moves perpendicular to the table travel direction, so looking
down the axis that you're moving is the best way to detect indicator
movement (and don't forget to deburr the edge, else you're finding
the edge of the burr).

Anymore when I'm looking for the center of a round or hold I simply
touch off the sides and take the midpoints on the DRO.  The
combination of the edge indicator and no-slack DRO readings allow me
to find the center in a minute to a precision I seldom need.

I'll be out of town for the next 3 weeks, minimum, so any replies
with questions will likely expire from my newsfeed.  If you have
additional questions send 'em to the email address in the header.

Russ Kepler                                    

                      Please Don't Feed the Engineers

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