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Edge finder question.

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John TV

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#1
So just wondering about my technique of using a edge finder. I am new to the milling world and used an edge finder for the first time the other day. I have watched enough YouTube to see it often but it was not as "clear" to me where the edge was as it seemed watching other people. That said, my Rpn was quite slow,300 to 400 or so. Did not have the time to play with rpm speed. Does the edge finder work better with higher rpm? Other techniques you might suggest?


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SCLead

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#2
I typically run them at ~1,000rpm. I've run some a fair bit higher (accidentally...) without issue, but I've also seen them come apart if run too fast.

Some people like to "flick" the tip to throw it farther out of alignment before creeping up on an edge. I don't really think it's necessary, but up to individual preference. If it's visibly far out of alignment, you can watch it change as you close in on your edge, where if it's relatively well aligned (running concentric) to start, you might come in to your edge too fast and be surprised when it "breaks." Play with both and see what you prefer would be my advice.

Good lighting (as everything else in the shop) is pretty critical as well. I've run some machines where you really have to focus to see it jump over because of awkward lighting. If you've got a lamp on the machine, having it somewhat backlit seems to work well for me.
 

BaronJ

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#3
Hi John, Guys,

There are many ways to find the edge of ones workpiece. The old fag paper trick is one, small ball race on a mandrel is another, or you could used a rotating laser beam. This last one is actually very useful for finding the center of a hole or rod. I use mine on both the mill and the lathe.
Here are a couple of pictures of mine. Sorry I don't have pictures of my other ones.


01022015-001.jpg 01022015-003.jpg
 

kvt

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#4
BaronJ where did you get or do you have plans for the laser setup you show. For some reason I have a hard time with the edge finders, Light and not as good at seeing things at times may be to blame on my part. I have tried fast and slow, to fast and it did not like it.
 

BaronJ

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#5
Hi Ken, Guys,

The laser edge find that you see is my interpretation of one that I saw on the net a couple of years ago.
However if you want to build one it is very easy to make. A caveat first ! Find a suitable laser, not all lasers are suitable !
Let me explain, The first laser pointer that I tried didn't have a circular beam, the spot was actually a quite lobsided oval and produced a thick line.
Then I picked up this very cheap laser pointer in the local Aldi store.

30012015-005.jpg

As you can see I broke it in half. The top bit is a ball point pen and a pullout pointer. I didn't need that bit. The bit that is needed is in the bottom half. Batteries and all. The button is one of those press and hold to turn the laser on. Testing this one I found that it produced a sharp round spot, ideal for this application. At a distance of 6" to 8" inches I get a bright round spot about 1.5 mm in diameter.
In the first picture of the previous post you can just see the button peeping out the side.

Once you have a suitable laser all you have to do is decide on the angle that you need to get the spot in the right place on the table. If I remember correctly, I used about 15 degrees. Then you need a suitable piece of aluminum plate, about 60 mm square or so and thick enough to drill for a spindle. I used a length of 1/2" inch drill rod. Then using a protractor to set the angle, clamped it in the mill vise and drilled a second hole so the two met at the bottom. The second hole was drilled with the same size drill. It turned out that 1/2" was the right size for the laser body.

At this point I had a square piece of 20 mm thick aluminum plate with two holes though it intersecting at one end. At this point I heated the plate and pressed the spindle into the first drilled hole. Using this spindle as a reference, I milled the two sides at an angle to match the angle of the laser pen body. I machined the non hole side first, so all I had to do was rotate the work 180 degrees to do the other side and machine a slot down that edge to clear the switch button.

01022015-004.jpg 01022015-002.jpg

One of the things that I aimed for when I made this, was symmetry. Though at the speed that you spin it, which isn't very fast, there is no noticeable out of balance. You will also notice that the spindle has deformed the metal in the hole that the laser fits into. This happens to be lucky chance, because it prevents the laser from slipping right through the hole.

I hope that I have given you enough information to go ahead and build one for yourself. If you have any questions just shout out. Being new to this web site I'm not sure exactly how that works, particularly when the notification Email I get informs me that I will not receive any further mail about this thread unless I visit it again. To be honest I'm not exactly thrilled at that !
 

Ed ke6bnl

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#6
Hi Ken, Guys,

The laser edge find that you see is my interpretation of one that I saw on the net a couple of years ago.
However if you want to build one it is very easy to make. A caveat first ! Find a suitable laser, not all lasers are suitable !
Let me explain, The first laser pointer that I tried didn't have a circular beam, the spot was actually a quite lobsided oval and produced a thick line.
Then I picked up this very cheap laser pointer in the local Aldi store.

View attachment 273761

As you can see I broke it in half. The top bit is a ball point pen and a pullout pointer. I didn't need that bit. The bit that is needed is in the bottom half. Batteries and all. The button is one of those press and hold to turn the laser on. Testing this one I found that it produced a sharp round spot, ideal for this application. At a distance of 6" to 8" inches I get a bright round spot about 1.5 mm in diameter.
In the first picture of the previous post you can just see the button peeping out the side.

Once you have a suitable laser all you have to do is decide on the angle that you need to get the spot in the right place on the table. If I remember correctly, I used about 15 degrees. Then you need a suitable piece of aluminum plate, about 60 mm square or so and thick enough to drill for a spindle. I used a length of 1/2" inch drill rod. Then using a protractor to set the angle, clamped it in the mill vise and drilled a second hole so the two met at the bottom. The second hole was drilled with the same size drill. It turned out that 1/2" was the right size for the laser body.

At this point I had a square piece of 20 mm thick aluminum plate with two holes though it intersecting at one end. At this point I heated the plate and pressed the spindle into the first drilled hole. Using this spindle as a reference, I milled the two sides at an angle to match the angle of the laser pen body. I machined the non hole side first, so all I had to do was rotate the work 180 degrees to do the other side and machine a slot down that edge to clear the switch button.

View attachment 273762 View attachment 273763

One of the things that I aimed for when I made this, was symmetry. Though at the speed that you spin it, which isn't very fast, there is no noticeable out of balance. You will also notice that the spindle has deformed the metal in the hole that the laser fits into. This happens to be lucky chance, because it prevents the laser from slipping right through the hole.

I hope that I have given you enough information to go ahead and build one for yourself. If you have any questions just shout out. Being new to this web site I'm not sure exactly how that works, particularly when the notification Email I get informs me that I will not receive any further mail about this thread unless I visit it again. To be honest I'm not exactly thrilled at that !
I started collecting for this project but have yet to build it, I also picked up some little centrifugal switches so that it turns on when the spindle rotates. they are small capsules. Since starting this I picked up a center finder that has a 60x eyepiece that you look at the part through and it cost not much more than the batteries cast at the swapmeet.
great job on the project still want to make one, it is on the list.
 

BaronJ

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#7
Hi Ed, Guys,

Thanks for your post :) You just reminded me, :oops: I forgot to say that I use an elastic band to depress the switch
 

ChrisAttebery

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#8
I always use mine at 1500 rpm. If you go too slow it won't flick very sharply.
 

mikey

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#9
Starrett recommends 800-900 rpm for their edge finders. Seems to work fine for me.
 

BaronJ

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#10
Hi Guys,

I found another picture, it also corrects some dimensions that I recalled incorrectly and gives the date I made this.
I didn't realise that it was nearly four years ago.

Center_Finder.jpg
 

Bob Korves

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#11
Some standard friction type edge finders do not work as well as others. They need to be high quality, and they need to be taken care of, keep them clean and don't crash them. Buying a used one sometimes is asking for someone else's problem child. I have a 3/8" Starrett that I bought new and a 1/2" Micro Tools (USA) that I bought used. Both work well, and it is nice to be able to fit two collet sizes. I also have an import set of four edge finders that I bought new as a newbie. I have never even tried that set, though it is shiny and pretty and also has cone shaped tips (???) and also has both 3/8 and 1/2" shanks. I keep the mill between about 700-1000 rpm when using them, faster when using the .200" contact points. I try to not let the edge finder run on when kicked over, I think that might cause wear that may slowly ruin the snappy kick over.
 

RJSakowski

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#12
The 1/2" edge finder is my go-to tool for precisely locating and edge. One main reason is that the edge finder is independent of spindle runout; something that cannot be said of probes, including

A characteristic of the edge finder is that if you approach too fast, there are two things that can cause a false trip. The first is if the finder is wobbling, it can trip prematurely giving an undershot reading. Secondly, if moving too fast, you can overshoot the edge before it edge finder can trip.
I will approach an edge relatively rapidly to get a rough sense of where the edge is. I then back off and begin a slow approach.I have a DRO on the mill/drill and the CNC has the ability to jog in .0001" steps as well. I will approach the trip point at about .001"/sec. The final approach is done at about .0001"/sec. I repeat my process to verify that the trip point is consistent within .0001". To reset the edge finder, I back it off by about a thousandth and use the face of my fingernail to center the edge finder.

When I have found my edge, I will zero the DRO, lift my edge finder to clear, move towards the the edge by 1/2 the diameter of the edge finder, and reset my zero. For finding the center of a feature, I find one edge and zero the DRO then move to the opposite edge , using care not to change the rpm or z axis and find that edge. My DRO's both have the ability to divide by two, which wi;ll place the zero point at the trrue center of the feature. This works for rectangular features and for circular features, both inside and outside.

For circular features I try to hit close to the center for the other axis and when finding the second edge, I make sure that I am at the same position on the second axis. Once the center is found for the first axis, I move on to the second axis and repeat. Usually, this is sufficient but if my estimate of the other axis zero was off, I will find the first axis zero again. Usually, there is no correction.

The same process can be done without a DRO. Just advance the dial by .001" and see if the edge finder trips. If not, repeat the process. With practice, you will be able to find an edge to better than .001" in a matter of seconds. This process accounts for any backlash, placing the zero point halfway between. Depending on the operation and the amount of backlash in the machine, you would want to correct for backlash by moving to your desired point and an additional amount equal to half the backlash.
 

RJSakowski

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#13
On addition to using an edge finder, I have a laser circle generator. To make it more versatile, I have mounted it in my boring head so that I can easily adjust the size of the circle. The circle generator is detailed here: https://www.hobby-machinist.com/thr...in-your-shop-today.14637/page-363#post-553286 in post 10,872.

I also have a digital microscope with about 300X magnification which allows me to find a feature to within +/-.0001", thanks to some software written by Jim Dawson.
 

kvt

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#14
Thanks for the info, Now to start collecting for one. And relook and try my edge finder also.
 

RJSakowski

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#15
Regarding a laser edge finder, all the laser pointers s that I have seen have a focusing lens. The pointers are factory focused for a parallel beam. Unscrewing the lens slightly would bring the focal point closer which does two things for you. First, it shortens the working distance and secondly, it produces a smaller dot with the shorter distance.
 

BaronJ

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#16
Hi RJ, Guys,

Unfortunately the pen/laser pointer that I used doesn't have that facility ! But I agree that it would be very useful in getting the smallest possible dot size.

I've since purchased several laser pointers including one that had interchangeable lens, non have any focusing ability. Most had rectangular or oval spots. Not really suitable. I did experiment with pin hole adapters, little tubes with various size pin holes in the end, which actually worked, but as the pin hole gets smaller the brightness drops dramatically. On the basis that increasing the laser power to compensate was not wise, I gave up trying to reduce spot size. I value my eyesight too much to take that risk.
 

kvt

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#17
If not mistaken on the pointers they have to use something that causes the true beam to be broken up some. That in turn causes the beam to spread more and not be as solid. Even on higher power things like I use for fibers, the beam is spread/distorted before it enters the fiber thus making a distorted/less solid dot. It will shine through a 2KM long fiber but will not make a nice dot on metal at 3 inches. Even still you have to be careful of reflected laser as it can almost be the same as getting it shined in your eye. But if your surface finish is like most of mine it takes a lot to reflect anything.
 

BaronJ

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#18
Hi Ken,

Yes the risk of eye damage particularly from reflections gets worse as the laser power goes up. I've seen the damage that can be done by laser diodes salvaged from blue ray drives.

This afternoon I took a couple of pictures of my other edge and center finders. So whilst I am here I've attached them.

10-08-2018-001.JPG
Sorry for the poor focus. The one on the right is a 12 mm diameter ball race, pushed on the end of a bit of 6 mm drill rod. The red is just a marker so that you can see when it touches. The one in the middle is my version of the Starret edge finder. It is made from 1/2 " silver steel rod 55 mm overall length with a 4 mm probe 15 mm long. It works very well, the small diameter probe allowing me to get into holes.

10-08-2018-002.JPG
This one is again a home brew center finder intended for use on bars and rods up to about 70 mm. The pin in the middle is a hardened center punch. Again made from 6 mm drill rod as are the pins pressed into the piece of 20 mm X 6 mm X 100 mm bar.
 

John TV

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#19
Thank you all for your input.

I love the the things you learn about different techniques and methods. Think I need to practice a bit more and keep saving those pennies for tooling. And by pennies I mean dollars and by dollars I mean....

John V. Minnesota


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