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Old 08-04-2018, 12:18 PM
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Default EdgeFinder Question

When using an edgefinder, I understand that you get both pieces lined up and when the bottom piece kicks out it is lined up with the edge. That doesn't make sense. It seems to me that when both pieces are lined up it is at the edge, and when the bottom kicks out you just went past the edge.
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Old 08-04-2018, 01:03 PM
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Well I thought that when I started using one.

Then I realized I did not need to think so much.

When it kicks over it has removed the air and oil that may be in between the part and the finder.

Just a thought.

Scott


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Old 08-04-2018, 01:56 PM
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Quote:
Originally Posted by alchemist View Post
It seems to me that when both pieces are lined up it is at the edge, and when the bottom kicks out you just went past the edge.
Correct.
A good edge finder you went past by 0.001

Not all edge finders act the same. likely the difference is by brand (grind) best to get use to the one and stay with it..... that is once you find a good one.

Some take a lot to kick-out and maybe around .005 and some don't kick very well. other issue can be the collet/chuck... has too much run-out.

I like 3/8 shank single end more so than 1/2" finders.
had issues with double ended ones not ground to the same diameters so they don't hold well ... front part larger than the shank dia.
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Last edited by GWIZ; 08-04-2018 at 02:09 PM.
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Old 08-04-2018, 04:59 PM
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When you use an edge finder start with the movable tip offset by 1/16" or so. No need to try and line it up before you start--you'll get more consistent results starting with an offset. Spin it up to about 700-800 rpm and slowly move it against the edge you're locating. You can see the tip starting to centralize; as it gets really close make your final movements very gently and stop the instant the tip kicks out. I usually repeat the operation just to make sure my feel and eyesight were good but with a little practice you'll find that you only need one try. Unless you're doing some really precise stuff using one of the mechanical edge finders is plenty close enough.

I have found that running the edge finder fairly fast improves the action and therefore the accuracy. You want the tip to kick out with a visible jump. If you run too slow I find it tends to just kinda slide over with no really defined break point. I have found that the above mentioned 700-800 speed is pretty optimum but sometimes--if I want a bit more accuracy--I'll crank the speed up a bit. Just be aware that if you get much over 1000 rpm you run the risk of launching the tip across the shop. In fact the tip doesn't actually fly away but the centrifugal force is enough to fling it out and stretch the internal spring--at that point the edge finder is toast. I know this because I have a collection of edge finders with dangling tips. My most common mistake is to forget to turn the speed down from a higher speed that I was using--it's all over in a second.

Another trick I often use, especially if I already have an endmill or tool in the machine, is a piece of cigarette paper held between the workpiece and the tool. Hold the paper loosely between thumb and forefinger, slide it in between the rotating tool and workpiece and slowly move the cutter toward the work. Cigarette paper is so thin that when the paper is pulled from between your fingers the tool will be virtually touching the edge of the part you're working on. BE VERY CAREFUL WHEN DOING THIS! Hold the extreme end of the paper and only put enough of it between the tool and the workpiece to allow it to grab--this keeps your fingers away from the pinch point. I use an edgefinder as much as I can but using the cigarette paper can save a lot of time when you're already set up with a tool in the spindle and need to find another edge.

And one last thing. Whatever method you're using, after you have located an edge remember to move your tool or finder over half of its diameter so that the centreline of the spindle is lined up with the edge of the workpiece. I've ruined more than one part because I forgot to do this--when I drilled holes or machined features they were out of position by 1/2 the diameter of whatever edgefinder I was using...
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Old 08-04-2018, 06:44 PM
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If you want to get fancy, use a Renishaw probe. Just don't rapid in with one first thing in the morning before the coffee kicks in. My boy's pic of a $2,500 (or more) mistake ...

Fisher Machine makes nice edge finders in addition to a few other things like sine bars and pee dee wires. Old school, USA made. Very reasonable price. I bought an edge finder direct from them, and requested a catalog. I got the catalog with a hand-written note from the second generation company owner.
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Old 08-04-2018, 10:09 PM
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I tend to run edgefinders between 800 and 1000 rpm, and have used the same 3/8” Starrett one for 20 years.

Along with Keith’s use of paper, I’ve also used magic marker on the shank, and when it rubs off, you’re touching.


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Old 08-04-2018, 10:20 PM
Lew Hartswick Lew Hartswick is offline
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I've been using my Starrett 1/2" one (with the one end pointy which I've never used) for 20years at the 1100 RPM setting on the step pulley Bridgeports.
...lew...
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Old 08-05-2018, 05:49 AM
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I tend to use the paper trick also. Even had the other machinest tell me I should use the edge finder because it’s faster. Couldn’t understand his reasoning, because I was using the tool I wanted, and did not have to spend time switching out tools.
Most of the time I just rip off a piece of my note pad paper, which usually is about .003. After touching, I will move the table an extra .001 to .002 depending on how hard I touched the paper. This usually gets me close enough for my tolerances.

I do find I have to be careful with the one drill chuck on shops big mill. The chuck body has significant runout, probably at least .020. It burned me on a job last week trying to make two matching parts. My holes were about .050 off, and did not look as good as I would have liked, but boss said the Forrester guys would not even notice, they are so hard on their equipment. It’s on my list to figure out if there is something I can do to fix that chuck. It has a 1” shaft arbor that is mounted in a 1” mill holder for Cat 50 mill taper. I guess my initial thought is the arbor is slightly bent from being crashed.


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Old 08-05-2018, 10:48 AM
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"Cigarette paper is so thin that when the paper is pulled from between your fingers the tool will be virtually touching the edge of the part you're working on. BE VERY CAREFUL WHEN DOING THIS!" -- LKeithR

Full disclosure : My total machining experience consists of about 6 months running a Bridgeport mill when I was about 20, so, 44 something years ago.

I have run an edge finder, I don't recall ever busting one or forgetting to move half ball over for true edge.

I have never heard of using magic marker (awesome idea) or cig paper to find edge.

My question is, Keith,(or anyone) you really stressed the safety aspect, which I totally get (fingers into end mills,yummy).

Would it work if you didn't have to hold it? Say you wet it the tiniest amount on the corner of the paper.

Would the paper suck enough of the liuid (saliva?) away so the thickness of the water wouldn't be a factor?

And, would it even stick to the part?

I'm thinking that it would stick, and the extra thickness of the liquid would be negligible. I'm curious if my opinion on this is right or wrong.
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Old 08-05-2018, 10:59 AM
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Just use a piece of tape at one edge instead of your finger.

The marker works better on solid diameters, so something like a long dowel, drill blank, or whatever else of a known diameter. I have a couple 1/2” diameter pins I use, so touch, then move over 1/4” to be right on edge.


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