I have a small mill. I do not have a DRO, nor how they work really. I cannot figure out why edge finders are used. The ones that run out and then center themselves. Can someone explain why they are used? Whenever a video says you've indicated your x or y axis I don't understand how this helps you. Total noobie. Thanks!
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Edge Finder
- Thread starter uchytil
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Even without a DRO, an edge finder is helpful. Without a DRO, you tend to need to do your measurements with the hand-dials (and correct for backlash of course!), but the theory of an edgefinder is the same. The purpose of the edge finder is to 'find' the edge of a part.
Consider you have a part, a block 2x2x2. The drawings say to drill a hole 0.250 inches from the top and the right. There are a few ways to do that.
First, is to try to measure off the machine, then try to pick up that point. This is going to be off in the realm of +/-10 thou, so perhaps good enough, perhaps not.
A second way to do that is to do the measurement on the mill! First, you edge find the 'right' side. Now you know that the 'spindle' is .100 (given a .200 round edge-finder, you actually find yourself a certain distance off the side!) to the 'right' of the rightmost edge of the part. Now you can use your hand dials to advance another .350 (.100 + .250), so now you know your spindle is in the correct place as far as the x axis goes. You can repeat that off the 'top' of the block and do the same thing! Now you should be accurate to within a few thou!
This isn't limited to just holes, it is any sort of feature on a part! If you're particularly good with handwheel backlash (or have a DRO!) you can even use edge-finding both the left-and-right sides to find the 'middle' of a block, which is often quite useful as well.
Consider you have a part, a block 2x2x2. The drawings say to drill a hole 0.250 inches from the top and the right. There are a few ways to do that.
First, is to try to measure off the machine, then try to pick up that point. This is going to be off in the realm of +/-10 thou, so perhaps good enough, perhaps not.
A second way to do that is to do the measurement on the mill! First, you edge find the 'right' side. Now you know that the 'spindle' is .100 (given a .200 round edge-finder, you actually find yourself a certain distance off the side!) to the 'right' of the rightmost edge of the part. Now you can use your hand dials to advance another .350 (.100 + .250), so now you know your spindle is in the correct place as far as the x axis goes. You can repeat that off the 'top' of the block and do the same thing! Now you should be accurate to within a few thou!
This isn't limited to just holes, it is any sort of feature on a part! If you're particularly good with handwheel backlash (or have a DRO!) you can even use edge-finding both the left-and-right sides to find the 'middle' of a block, which is often quite useful as well.
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There are other types also, such as the combination type that has a .100" disc on the end of a small diameter shank that is held in a friction ball chuck, also usually with a .200" ball end and a pointed scribe like for picking up center punch marks and another attachment for mounting test indicators. Another combination type has two opposite ends, one pointed for punch marks, the other end is usually .200" diameter or .500" diameter. The best for punch marks is the Blake CoAx indicator.
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Asuming you have no experience with machine tools:
Without a Digital Read Out, you have no idea where your tool (center of the spindle) is in relation to the work you are doing.
You put the edge finder in your chuck, (or indeed somehow in your spindle so it's in the middle).
Approach the work (block of steel in your vice, or whatever) with the spinning edge finder. Touching the .200 diameter to the surface of the side of the block, turn the handle slowly so that at some point the edge finder skates off to one side. At this exact moment, the center of the spindle is .100 from the edge of the work. At this point you stop the spindle and take the edge finder out. In theory, turning the appropriate handle one hundred graduations will put the center of the spindle exactly above the edge of the work. Having done this, loosen the dial and turn it so that zero is opposite the registry mark on the machine. Tighten the dial. Clamp the table. Now, if you want ot make a hole 1/2 inch frm the edge, you turn the handle/dial 500 graduations and the center of the spindle will be 1/2" from the edge. You can now make a hole 1/2 inch exactly from the edge of the work.
Sorry if I misunderstood your experience, but sometimes we have to assume you have no experience.
This is helping me to understand better. I'm sure I have a ways to go. Maybe I'll get a dro someday but for now I'll have to rely on the hand wheels, and backlash. My experience is I was a shipboard engineer (boilers/diesels/hydraulics/etc.) for 32 years. Now I have time to get into the precision stuff but have to learn it somehow.
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I use an edge finder similar to the ones below almost exclusively for finding edges or centers of my part.s. I do so because, with care you can locate an edge to within +/- .0001" and because the edge finder locates and edge relative of the spindle axis, regardless of any runout you may have. I use the 1/2" diameter one most as it seems to be more sensitive.
Used properly, you approach the edge slowly and as you do you will see any wobble in the tip reduced until it is spinning true to the spindle. As you move a bit further, the tip will jump to the side. This is the point of first contact with the edge. If you note your position on the dial or the DRO, you can lift the edge finder and continue moving 1/2 the diameter of the tip and your spindle will be exactly over the edge of the work.
If you are working from the dials, you will need to know what your backlash is to determine what the dial reading will be if moving in the opposite direction (away from the edge). Backlash can be determined by locating the opposite edges of a block or hole of known size. The difference between the measured and actual size will be the backlash. Keep in mind that backlash can vary with position, especially on a worn machine.
A DRO simplifies the process since backlash isn't of concern. The position is determined by the DRO reading. Even on a worn machine, it is possible to determine position to better than a thousandth.
Used properly, you approach the edge slowly and as you do you will see any wobble in the tip reduced until it is spinning true to the spindle. As you move a bit further, the tip will jump to the side. This is the point of first contact with the edge. If you note your position on the dial or the DRO, you can lift the edge finder and continue moving 1/2 the diameter of the tip and your spindle will be exactly over the edge of the work.
If you are working from the dials, you will need to know what your backlash is to determine what the dial reading will be if moving in the opposite direction (away from the edge). Backlash can be determined by locating the opposite edges of a block or hole of known size. The difference between the measured and actual size will be the backlash. Keep in mind that backlash can vary with position, especially on a worn machine.
A DRO simplifies the process since backlash isn't of concern. The position is determined by the DRO reading. Even on a worn machine, it is possible to determine position to better than a thousandth.
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- Mar 26, 2018
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Also, they sell electronic versions of edgefinders that make life a little easier. The light up when you touch the part and you don't need to run the spindle. Only good for metal conductive workpieces.
www.shars.com
3/4" Shank Electronic Edge Finder
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I was told many years ago that one could grind a small flat on the edge finder and it would make it more sensitive, this I did to one of mine; personally I think if one moves the edge finder until it skates off, it has gone too far, I usually hold a strong light behind it and move until light does not show through the interface; perhaps some of you the audience that has a DRO could try it both ways and report back. I had one mill in my shop that I sold with DRO, but it went with the shop.
If you do not rotate the spindle, non concentricity of the tool holding device could cause errors.Also, they sell electronic versions of edgefinders that make life a little easier. The light up when you touch the part and you don't need to run the spindle. Only good for metal conductive workpieces.
3/4" Shank Electronic Edge Finder
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For sure. I find the edge finder comes quite true from the factory. With a decent collet, you can achieve <0.0005" accuracy. Not a bad place to start.
Once I need better than 0.001", I'm usually using a more accurate technique with an indicator.