Fowler edge finder

Tinkertoy1941 said:
From where I was instructed by and old Journeyman machinist the youtube video above leaves a whole lot to be desired.
View attachment 308081
In my experience of running Jig Bores, Jig Grinders and CNC machines the chair pictured above is the most accurate and most efficient way to pick up the edge of any part. It is also the most economical for if you are really $$ wise you can make your own!
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I would love to know how this even works! I can't wrap my head around it, can you send some light?
 
GunsOfNavarone said:
I would love to know how this even works! I can't wrap my head around it, can you send some light?
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Tinkertoy1941 might have a better explanation than I do, but it seems that the "chair" is precision ground such that the lower edge is precisely midway between the two walls of the fork on top. If you were to hold this firmly against the part (or use the magnets), and then sweep a tenths indicator inside the fork, you should be able to dial in the machine where the high reading on each wall of the fork is even.

When this is true, you would know your spindle centerline is exactly midway between to two walls of the fork, which also means it is directly above the edge of the part (within the resolution of your indicator).
 
Tinkertoy1941 said:
The rotating edge finders with an experienced Journeyman machinist can guarantee an accuracy of plus/minus of .0015 and that is not close enough for gage work. .....
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Are these people mistaken about the accuracy of their rotating edge finders or am I missing something?


Fowler 3/8, 1/2 Inch Shank Diameter, 0.0002 Inch Accuracy, Edge Finder Set
Specs
Type Edge Finder Set
Head Contact Type Cylindrical
Head Diameter (Decimal Inch) 0.2000; 0.5000
Shank Diameter (Inch) 3/8; 1/2
Accuracy (Decimal Inch) 0.0002
Number of Pieces 4
Includes (4) Attachments; Plastic Sleeve

Tom
 
I'm pretty sure that is the diametrical accuracy of the tool. That is quite different from the accuracy of when it "breaks" on an edge. The exact accuracy and repeatability of this action is far from perfect. It will also vary depending on the cleanliness and age of the tool.
 
I have made a few of the electronic type. I show them in my videos. The one you show broken down if you remove the resistor then you should be able to use a 3v watch battery. I couldn't make about the color bands on the resistor but I'm betting its around a 7.5ohm. I also made an electronit height setter to set tools at exactly 1.00 I have drawings if anyone is interested. The edgfinder I know I have drawings for it also just not sure were I put them.
 
Tinkertoy1941 said:
From where I was instructed by and old Journeyman machinist the youtube video above leaves a whole lot to be desired.
View attachment 308081
In my experience of running Jig Bores, Jig Grinders and CNC machines the chair pictured above is the most accurate and most efficient way to pick up the edge of any part. It is also the most economical for if you are really $$ wise you can make your own!
Click to expand...


I have one of these also to get a dead on position you can do the same with little block and sweep the face of the block and the edge of the piece you want to find the edge of.
 
When you use a magnetic CHAIR as shown in the picture1576786221465.pngwith a tenth indicator the reference edge will be within .0001 TIR when inspected with a CMM "Coordinate Measuring Machine".
Sweeping the inside of the chair eliminates mistakes, such as spindle not concentric, drill chuck with run out and many other thing that could possibly go wrong!
Did anyone forget to subtract one half of the contact diameter before setting edge Zero!!
 
I know we're a bit off now, good stuff don't change, but I did reorder the same unit, no way the second will be half missing. It's like the R8-er32 chuck I purchased. The first was rubbish, the second works fine. Quality control doesn't exist in China.
 
Any edge finder was a no-no on any of our jig bores or jig grinders . You used a .00005 reading indicator only and you were taught this as an apprentice .
 
mmcmdl said:
Any edge finder was a no-no on any of our jig bores or jig grinders . You used a .00005 reading indicator only and you were taught this as an apprentice .
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I can’t argue with that. Thankfully I’m not working with tolerances that’s small that I have to worry about that but I would like to learn the “most accurate “ way of doing it. I’m already painfully slow, I’m hoping to do setup quickly so I’m going with electronic but would like to get manual edge finder working.
 
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