Edge finder accurracy

[Captain Jerry]

How accurate are these things supposed to be. I recently got one of the old standby units with one pointy end and one small cylindrical end, the kind that kicks offset when it contacts the edge. I had been using a piece of .25 drill rod and a piece of paper to find an edge but thought these would be better. To eliminate or at least reduce operator error, I usually touch of on the edge until I get three consistent values. I thought I was getting good results but I found out today that I was off.

I wanted to find the center of a 2" face to mark for the lathe center. I located one edge and zeroed the DRO (caliper) and the raised the quill and traversed to the opposite side, lowered the quill and approached the edge. The width is known to be .002"
under (1.998") and I was surprised to find see the edge finder kick out at 2.212". Subtracting .200" for the diameter of the contact cylinder leaves 2.012" or .014" off. Finding the center was OK. I just backed up until the DRO read 1.106". I zeroed at this point and confirmed the two edges at 1.106" and -1.106" OK, that's center but what about the dimension, can I trust the edge finder to do its job? I measured the contact cylinder to be .203" instead of .200" but that's not enough to account for the difference.

Should I expect more?

Jerry

 

[Lew Hartswick]

Bogs is right on. The finish on the mating surfaces of the "inexpensive" ones and the
possibility of too heavy a lub is the problem. My Starett is always within a thou
and if I take care better.
...lew...

 

[Captain Jerry]

Bogs

Thanks for the response. I never thought about oil. I'll give that a try tomorrow. I have been giving it some thought. The cheapy DRO (caliper) could be at fault as well. I'll have to work out a way to test/verify that as well.

Thanks,
Jerry

 

[Captain Jerry]

Lew and Bogs,

Does the tip diameter on your pricey Starrets measure as stated. I guess if I get the lube worked out, I guess I'll have to allow .1015" offset to center.

Jerry

 

[mklotz]

A three thou error in that dimension is insane. Granted, such an error is possible but I find it very unlikely. I would check the measurement again with a freshly calibrated, quality micrometer.

 

[don-tucker]

After reading this,I shall order a Starrett with a .200" probe tomorrow,if I can get Bogs's results i shall be more than happy.My elongated thread on the subject did not come to any conclusion.

Don

 

[Lew Hartswick]

As a matter of interest, I just today had a problem with the "click" type edgefinder
a student was getting ready to use on a project. I was helping him pick up all the
tooling for several operations on a mill. Finding the centre of a round bar and locating
along the rod, drilling and taping a 1/2 - 20 thread (to not go through) and counter
boring .187 deep. We have 3 of the same edgefinders in the drawer and I checked
the ease with which it would push off to the side. WOW it was really stiff. checked the
other two and about the same. (Wish I knew where they were bought) So I went and
got mine for him to use. I pointed out to the teacher the problem. Any way after
class I took all 3 and cleaned the interface between the shank and the moving part
and then proceeded to check all three against my Starrett on a mill with a DRO
against a tall parallel. The all kicked within .0002 BUT the school ones only moved
about half as far as mine did (maybe even less). Sometimes hard to see with the
poor lighting on some of the mills. The moving peice is black on the school ones
while the Starret is all shiny, really helps to see the movement.
...lew...

 

[Omnimill]

Hhm, any alternatives to using Clock Oil? What about Camellia oil - I've got a bottle of that somewhere.

http://www.raymears.com/Bushcraft_Product/624-Camellia-Oil/

Vic.

 

[Kmot]

I have an imported (to the USA) set of edge finders. They are supposedly the audible click type. I have never heard the click. I have a Sieg mini mill, and it is rather noisy. Are the audible click type edge finders supposed to be heard easily over the noise of the mill motor? ???

 

[GailInNM]

Vic,
I use 10 weight machine oil, also known as ISO32 or DTE24 hydraulic oil. It is non drying and seems to work well. I is my general purpose light duty lube oil that I also use on small engines.

Knot,
I can hear mine easily over the noise of my Bridgeport. You can visibly tell the audible style by the flat on the side of the round measuring tip.

Years ago I read an paper produced by Brown and Sharp or Starrett on the optimum RPM for accurate edge finding with this type of edge finder. It concluded that somewhere around 1000 rpm was best but that it was not very critical.

Gail in NM

 

[bearcar1]

How would Marvel Mystery Oil stack up in terms of lubricating such fine interfaces and tools in general?

BC1
Jim

 

[mklotz]

Starrett instrument oil...

http://www.use-enco.com/CGI/INSRIT?PMAKA=505-1335&PMPXNO=942312&PARTPG=INSRHI

It's dead cheap and is well suited for the job. Used judiciously, a single bottle will last for years.

 

[el gringo]

Any comments on BC1's question abt Marvel Mystery oil for light/instrument use?

raym

 

[Lakc]

I dont know if the peppermint oil in MMO would get sticky or not, but I assume any good automatic transmission fluid should work.

 

[Troutsqueezer]

I have an imported (to the USA) set of edge finders. They are supposedly the audible click type. I have never heard the click. I have a Sieg mini mill, and it is rather noisy. Are the audible click type edge finders supposed to be heard easily over the noise of the mill motor? ???

Sounds like you're due for the upgrade to belt drive. Are you still using the plastic geared setup? The mill quiets down considerably with the belt mod. Available at LMS around $129 or so.

I can hear mine click easily on my mini mill.

-Trout

 

[Ken I]

After reading this thread I thought I would give my edge finder a clean and a lube job.

Since the spindle is hollow I placed a few drops of ATF (automatic transmission fluid - my oil of choice when in doubt) inside - figured it would act like an auto lube-feeder.

The results were horrible - the damn thing no longer kicked over but simply wandered around slightly off centre and the further you went the more it happily ran off center without "kicking" over.

The transition was impossible to detect and results were simply all over the place.

So I cleaned it in thinners and ran it dry - results - spot on.

I guess the thing can be too well lubricated, I'm guessing it's one of those friction critical devices where too much (or worse gummy residue) or too little are going to be problematic.

What the .... we learn something every day.

Ken

 

[Drei]

Ermm, where do you put the lubrication on the edge tip between the work and the tip or between the shank and the tip which moves?

Drei

 

[Tin Falcon]

well I would thik just a little oil where the button moves sideways. keep the peice that touches your part dry that is where you want friction.
Tin

 

[ttrikalin]

also Bogs commented that 3 in 1 oil is not a good choice to lubricate this tool cause it leaves a bit of residue.

Someone (Marv?) suggested Starrett tool oil. Not too expensive, and if used only on such tools it'll outlast me.

take care,
tom

 

[Metal Butcher]

I tried to oil mine on several occasions using different types of oil mentioned by the previous posters. The result was a slowed reaction time. Rather than snapping over it would 'waddle' over and give inconsistent (not accurate) results. I took the edge finder and tilted over the working end, and then held it open with a wood tooth pick. I squirted in some lighter fluid to wash out 'most' of the oil. That solved the problem, and after wards my edge worked the way its supposed to. On the occasion that it starts to act up again, I shut down the mill and wipe the working surface of the edge finder and the work piece, with a small piece of paper towel moistened with lighter fluid. That instantly solves the problem, and I get back to the project at hand.

I suspect that a small amount of remaining internal oil 'creeps out' to cause the 'inaccurate waddle' behavior.

-MB