edge finder sensitivity

snipped-for-privacy@hotmail.com wrote:


No thats not so. Take a couple cases and see what I mean: If you happen to be at exactly 90 deg to the high/low axis than it will be exactly the same at both tests. If half way between the high/low and the zero/zero (say 45 deg) then the amount high on one side will be the same amound as the low on the other. So any case it will the mean of the two tests. ...lew...
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snipped-for-privacy@hotmail.com wrote:

Wolfgang:
    You wouldn't need to know, or be, on the maximum high point of any eccentricity to average out the runout in one axis. Let me try to explain it this way. Let's say the edge finder was bent toward the X+ side by +.001, so therefore the X- side would be bent away by -.001. Now when you touched the X+ side, (recorded your reading) then turned the edge finder 180 degrees and touched it again you'd have theoretically have a .002 difference. So half that difference would be roughly the center of the runout and spindle. Now the Y+ side of the edge finder could be +.005 and the Y- side could be -.005, BUT they don't necessarily influence the amount of runout in the X+ and X- sides.     Was that clear as mud, or did it help?
    One thing that "could" influence the measurement of runout would be the the angle of the stem. If the very tip was touched on one side, and the other side was touched further up the stem due to being bent over... then the true runout would be skewed. Is this type of situation the ball tip electric edge finders would nullify any "bent tip" inaccuracies.     
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On Sun, 17 Aug 2008 02:57:14 -0700, BottleBob

=========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.
I see several people have mentioned the Schmidt edge finders, https://www.hermannschmidt.com/productcart/pc/viewPrd.asp?idcategory=8&idproduct 8 anyone have comments on /experience with the ones from Flexbar? http://67.59.156.7/merchant2/merchant.mvc?Screen=PROD&Product_Code 509
Are these that much better than B&S or Starrett, or just more expensive?
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
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F. George McDuffee wrote:

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.

https://www.hermannschmidt.com/productcart/pc/viewPrd.asp?idcategory=8&idproduct 8
    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/product_id/16635?utm_medium=cpc&utm_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.
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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
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snipped-for-privacy@hotmail.com wrote:

Wolfgang:
    Is that really your name? It's pretty cool if it is. Anyway, we all make the occasional conceptual boo-boo, it's no biggie.

    Actually, I've got a magnetic "chair" and the "corner finder", but I seldom use them for the very reasons you mentioned above. Possible out of square issues.

    Correct, and that particular method was what I was referring to when I mentioned "direct indicating the edge". And of course a "tenth" indicator is sometimes used when the tolerance requires it.

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BottleBob wrote:

    I did a little comparison test at work today. The above process, outlined by Wolfgang, I'm labeling as "Direct Indicating of the Edge". Which I compared to a kick-out edge finder, and using a "Chair" tool.
http://tinyurl.com/6gm3dq
    I was edge finding the hardened & ground steel solid jaw on a Kurt vise. I indicated the vise jaw parallel to the machine's ways. Then I indicated it vertically to make sure it was square (the indicator needle did not move by going down in Z for the length of the stem (.0005 Indicator 1 1/2" dia. dial).
    First, I "direct indicated" the jaw with a Jo block as explained at the top of this post. It took 4 min. 50 seconds. A lot of that time was used to get the indicator precisely centered vertically AND moving the machine a "tenth" here and there to get the needle to be aligned to the zero within the limits of my vision. For the sake of this test I'm going to assume this process as the most accurate of the three, and will assume the location it displays as true zero within the tolerance range of the indicator and the process itself (indicator is 4 months old).
    Second, I used an edge finder with a .200 tip and .500 body. Moving over in .010" increments, then .001" increments, then .0001" increments until it "kicked out". This took 2 min. 38 sec. All these times include the housekeeping chores in the control (Fadal) for setting fixture offsets. The difference in the final zero position of the edge finder compared to the "direct indicated" zero position was .0004".
    Third, I used the "Magnetic Edge Finder" tool (upside down chair looking item), with the indicator reading zero. This took 2 min. 5 seconds. The difference between the "chair" zero and "direct indicating" zero was .0003". That could be due to any number of factors, but I would assume there may be a tolerance in the manufacturing of the "chair" device.
    This was not meant to be a definitive/exhaustive comparison of these processes, just a quickie test to see if there were any gross differences. The Z travel of the head could have off a slight amount, but I think that unlikely since the machine makes reasonably accurate close tolerance parts on a regular basis. All tool tapers (and spindle taper) were wiped clean before beginning.
    I've crossposted this to amc, since it's relevant in there as well.
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BottleBob wrote:

Bob, I wonder if the Herman Schmidt edge finder, with lapped surfaces, would be any better? I guess Haas has linear ways so sticktion would be minimal? I wonder when your moving in tenths on a boxway machine what the results would be?
Best, Steve
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Garlicdude wrote:

Steve:
    I suppose we'll have to await the results of Jon's test with one of the new Herman Schmidt edge finders they just got.

    I've put a tenth indicator on the Fadals & Haas, and after any backlash is deal with, they both move a tenth at a time when you are moving in one direction in the mid range of my indicator. At the ends of the travel of the indicator there may be a cosign error due to stem angle.
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Ive got a starret and a herman. The herman definetely kicks over quicker. The starrett seems like it has to make its mind up before moving. I wouldn't want to edge find to a tenth, but the herman looks like it would hold it if the conditions were constant. But for some reason...I like the starret better. the herman is big and gay, and the starret feels like an edge finder? lol
One thing, if the starret doesnt get used for a year or 2 i have to "lap" it back and fourth a few times, after 10 years of no use, the herman still feels like i just bought it. SuweeeT!!!
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vinny wrote:

Vinny:
    Just speculating now, but both the slow reaction and the "stickiness" of the Starrett may be due to the congealing coolant. Since you said that's the edge finder you use more frequently. The Herman may move freely, and like new, since you don't use it.
    I'd be interested in the results of a comparison between "direct indicating" and Herman S. edge finding by you.
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BottleBob,
Great report on the comparison of 3 different ways of edge finding. I think this is the first time I have seen this done.
You also saved me some $$$ as I was going to buy the "chair" tool; now I think that the difference between the kick-off and chair tool accuracy is not sufficient to warrant the expenditure.
It's also nice to have my assumption confirmed on the .0005" accuracy of the kick-off tool, and that the point of accuracy IS the kick-off, not the observed concentricity prior to kick-off.
The ultimate test for accuracy of each method would be to locate the edge using each method, move over the work piece by say 1.0000" and drill, bore, ream a .5000" dia. hole. By measuring the remaining ligament between edge and hole the accuracy of each method would be established. Granted this is being anal about this process but I find it interesting.
As it is your tests prove the relative accuracies between processes and, assuming that the error in direct indicating is +/- .0001" based on your new indicator, you have given us valuable NUMERICAL evidence of each process' capability.
Thanks,
Wolfgang... Yes it is my real Christian name.
Gunner, what other middle names do you have, you said ONE of them was... :-)).
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Has anyone actually measured the 0.200 tip to see if maybe they make it a tenth or three undersize, so that the kick-off is the correct indicator, and not concentricity? Just curious. Oh, and thanks for the great report.
-- Regards, Carl Ijames carl dott ijames aat verizon dott net (remove nospm or make the obvious changes before replying)
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Carl Ijames wrote:

Carl:
    All the edge finders I've ever measured were the exact size (the .200 size ones WERE .2000, the .500 size ones WERE .5000).
    If you have to go .0004 FARTHER than half the tip diameter to have it "kick-out", then I think you'd want the tip diameter to be .0008 oversize for compensation purposes. If I've got it backwards, I'm sure someone will surely tell me. LOL
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BottleBob wrote:

Anyone needing precision in the context implied is obviously setting up somethng to be recut after having screwed the thing up, or at least after it's finished. When, Bob, was the last time you guys intentionally ordered stock ground to finish size for a job? I'll save you the trouble and tell you. Never.
Neither does any other sane person. Not for production on a short run basis and I'll be I could spend a month in Valencia and never see such a thing.
Intresting thread but when you get to process planning you'll be into something that's useful.
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John R. Carroll
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John R. Carroll wrote:

John:
    Not necessarily. A job with multiple operations will often have to located accurately off a previously machined surface or feature.

    You're right, not often. But I wouldn't say never.

    Come on over, I've been edge finding a part in different setups with multiple operations all week.

    Process planning? You mean planning the order of operations in your before you begin machining? Isn't that an integral part of the job description of being a CNC programmer, eh? LOL
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BottleBob wrote:

Planned in advance you might be able to use features as tooling holes. You know, where you drill, bore and ream a .2505 dowel pin hole where there is a 1/4-28 tapped hole. LOL

Ok, very infrequently.

I, yes me - moi, am taking a week off. I'm in San Diego with my mother. She's old and having a little trouble getting settled with health insurance and prescription drug coverage. GM is dumping their pensioners.
I decided that it was a better use of my time than telling Kris, our favorite welder, that he needs either a second debilitating sand buggy accident or another line of work. BTW, that's a lot calmer statement than I would have made Friday so I guess the time off was a good choice.
See me next week if you are around. We'll "edge find" our way around a couple plates of Vince's lasagna. Plus or minus a fork full.

Maybe, but what I meant was looking a job over and planning it so you didn't find yourself trying to figure out where the thing was as you went along with indicators or edge finders. That ought to come in concert with whoever quoted the work in the first place.
The real key to success in your environment is planning the last operation. That and the fixturing to make it happen accurately and repeatably.
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On Aug 20, 8:16 pm, "John R. Carroll"

BottleBob, my "BB" commentary was addressed to "Bipolar Bear" @ 12:59, NOT to you.
I had a look at your website and concluded that you do not require any opinion from me on how to do things accurately and precisely :-)).
Bipolar made some commentary on spindle squareness or such, and I thought it worthwhile to elaborate a little on other unmentioned requirements for accurate edge finding.
Wolfgang
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snipped-for-privacy@hotmail.com wrote:

Wolfgang:
    I'm sorry, everybody calls me BB so I never even considered that you might be referring to someone else. My bad.

    We're ALL constantly learning. When we stop, we're ready for that proverbial dirt nap.

    I believe I saw that. Something about a quill. My opinions/comments are usually from a CNC perspective. Although I was a manual machinist for many years prior to that. And still do some fixture & second op manual machining.
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On Aug 20, 8:16 pm, "John R. Carroll"

Jon A.:
Thanks for that precis on the MOORE tome. I must beg, borrow, buy? a copy. If anybody has a line on one, especially at reasonable price... Thanks, and please let me know.
Wolfgang
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