Forestgnome
Stainless
- Joined
- Aug 2, 2008
- Location
- Californeeeah
Wondering what your experience is. Do spring loaded edge finders work on inside/outside curves, or is there error beyond what you'd get on a flat surface?
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Edge finder on curved surfaces?
- Thread starter Forestgnome
- Start date
- Replies 26
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hitandmiss
Titanium
- Joined
- Jul 31, 2010
- Location
- Rochester, NY USA
For round surfaces, I have had good results finding the center of a hole or hub.
The rougher the surface, or out of round objects, the larger the error.
Bill
The rougher the surface, or out of round objects, the larger the error.
Bill
tay2daizzo8
Hot Rolled
- Joined
- Nov 8, 2013
- Location
- north of Bean town
I have seen a guy use an edge finder on a .780 dia trying to find center...He was close...not....unless you are centerline of the part(in which case you wouldnt need to edge find cuz your already there) your error beyond that would grow depending on the dia of the part you are trying to locate...much easier to use an indicator
hitandmiss
Titanium
- Joined
- Jul 31, 2010
- Location
- Rochester, NY USA
I guess I didn't know I wasn't supposed to use the edge finder to find the center of round work.
My method is:
1. Find a point near the centerline of one axis, X for this example.
The operative word here is near, within .1" on 3/4" stock is close enough.
2. Touch off Y and zero both axis of the DRO.
3. Move only Y to the other side of the part and touch off, the other axis must still be 0.
4. Calculate the mid point of the measurement and position Y to that value and zero the Y axis.
5. Repeat steps 2-4 for the other axis.
If you aren't sure if you are there, touch off the 4 hits from center, are you close enough?
Most of the time I am within a couple of thou, and the time to do this is much less than setting up an indicator.
Many of the newer "machinists" really don't know how to make good use of the spring loaded edge finders or "wigglers". Many that I show this method, and the proper use of the tool, stare in amazement at how easy it is.
Bill
My method is:
1. Find a point near the centerline of one axis, X for this example.
The operative word here is near, within .1" on 3/4" stock is close enough.
2. Touch off Y and zero both axis of the DRO.
3. Move only Y to the other side of the part and touch off, the other axis must still be 0.
4. Calculate the mid point of the measurement and position Y to that value and zero the Y axis.
5. Repeat steps 2-4 for the other axis.
If you aren't sure if you are there, touch off the 4 hits from center, are you close enough?
Most of the time I am within a couple of thou, and the time to do this is much less than setting up an indicator.
Many of the newer "machinists" really don't know how to make good use of the spring loaded edge finders or "wigglers". Many that I show this method, and the proper use of the tool, stare in amazement at how easy it is.
Bill
tay2daizzo8
Hot Rolled
- Joined
- Nov 8, 2013
- Location
- north of Bean town
Most of the time a couple tho is out of tolerance for precision work...Newer machinists probably just know that an indicator in a drill chuck is just as fast as an edgefinder...and more accurate...there is no replacement for seting up your part with the best method possible...How much time do you save when you relize your "a couple tho off" and you have scrapped a part and now have to adjust and run another(possible scrap) part? If you take the extra 30 seconds you can indicate to .0001 and have location dead nuts...what you said i can really only see working in wide open tolerance +\- 1/32...anything else your just wasting time
tay2daizzo8
Hot Rolled
- Joined
- Nov 8, 2013
- Location
- north of Bean town
No problem...next time just use your edgefinder..im sure its more accurite than a drill chuck...or just keep an indicator in a collet. Thanks for taking what i said the complete wrong direction. The discussion is about edgefinding a round part...not how accurate your drill chuck is...maybe you should invest in a new drill chuck or an extra collet holder....either way edge finding a round part will only get you dead on accurate by shear luck. dont half ass something just to turn around and use the indicator anyway.
Bobw
Diamond
- Joined
- Feb 8, 2005
- Location
- Hatch, NM Chile capital of the WORLD
Like he said, some people just simply don't know how to use an edge finder... I've used his method a number of times, always within a thou or 2...
I find the hardest part of dialing in something with an indicator is getting close to center, so I'll do the edgefinder deal and then pop the indicator
in to dial it in... If it needs to be that close.
Fadal's have a built in little utility... Use an edgefinder to get the center point of any 3 point arc... If I'm using tenth pulses, within a thou,
one thou pulses, within .002... MAYBE .003 If I'm being sloppy...
So YES edgefinders work just fine on curved surfaces. Though you do need to realize that the edge finder radius is TANGENT to the surface/curve, not
necessarily in a straight X or Y line.
tay2daizzo8
Hot Rolled
- Joined
- Nov 8, 2013
- Location
- north of Bean town
just wondering in what situation is it faster to
1 eyeball centerline of one axis,
2 touch each side with the EF,
3 do some math,
4 move to centerline of first axis
5 touch EF off one side of other axis
6 move to center
7 indicate the part anyway cuz your feature is not in the correct location.
I still think throwing an indicator in the spindle
1 eyeballing center
2 adjust one axis to 0
3 bring other axis to 0
now your exactly over center of your part...not within a couple...
1 eyeball centerline of one axis,
2 touch each side with the EF,
3 do some math,
4 move to centerline of first axis
5 touch EF off one side of other axis
6 move to center
7 indicate the part anyway cuz your feature is not in the correct location.
I still think throwing an indicator in the spindle
1 eyeballing center
2 adjust one axis to 0
3 bring other axis to 0
now your exactly over center of your part...not within a couple...
lowCountryCamo
Stainless
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- Jan 1, 2012
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- Savannah, Georgia, USA
Lately I have just been using a non rotating dowel pin in a collet and a .005 feeler. That seems to repeat better for me.
Forestgnome
Stainless
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- Aug 2, 2008
- Location
- Californeeeah
I should clarify. Imagine a rectangular box where one wall is curved. You need to find the edge of the inside of the curved wall. You're already on the center of the arc. The arc has radius of 1". How do you do it? In the case of finding the center of a hole absolute accuracy isn't critical. You can find the center as long as the error is consistent.
I don't know about you, but I can't get close with every edge finder. I've got one that I've learned I can rely on, maybe know the peculiarities of, and I stick to using that one.
And yeah, I rarely pull out the indicator first, I usually use an edge finder to get close.
I guess to each his own.
tay2daizzo8
Hot Rolled
- Joined
- Nov 8, 2013
- Location
- north of Bean town
Yup theres more than one way to skin a cat, some methods are just less messy
tay2daizzo8
Hot Rolled
- Joined
- Nov 8, 2013
- Location
- north of Bean town
in this case if you are already on centerline one way then yes u can touch the inside radius and then move to center...WAY different than finding the center of a complete circle when you have no absolute starting point.
But in the case of finding center of a hole, accuracy is critical if your customer want your feature(bolt circle etc) concentric or even just in the right place...
Do you work in a shop where accuracy is not critical???
round these parts when you make something that goes in the air you damn well better be accurate
HuFlungDung
Diamond
- Joined
- Jan 19, 2005
- Location
- Canada
I don't think the edge finder is very good at picking up inside of the curve. You might detect a jump point, but where is it exactly when it jumps?
When the edge finder is used on a straight edge, then the tip will climb along the straight edge but you've still got the location of that edge, assuming it is set up properly and parallel to a machine axis.
But depending where you have the finder positioned on the inside of a curve (one side of the longest axis or the other) the tip may have the tendency to begin to climb up the curve and deflection will be premature. Or on the other side of the longest axis, it will delay slightly because it climbs into clear space, and wants to restore to center of the diameter of the tip.
I mostly agree with the person above who uses the method of touching off each side of the quadrant lines and halving. There might still be a tiny systematic error because the direction the tip jumps is dependent on the direction of rotation of the spindle. Theoretically, maybe a guy should reverse the spindle when edge finding on opposite ends of the same chord. That way, the tip is jumping into clear space (or not, but both the same) when it makes contact.
I do tend to prefer a dial indicator if the part datum is critical.
I think there are some things to consider, but to my way of thinking, the edge finder will do a decent job of responding to the curved wall contact, assuming that the curved profile lies in the XY plane. Obviously, if there is curve in the Z axis, that's a different ballgame.
I suspect that on a concave surface, you would see a greater displacement of the edge finder than on a flat surface, assuming the same contact envelope depth. Conversely, on a convex surface, the edge finder would take slightly more engagement to displace equally. Then, the size of the radius will have a scaling effect on that basic difference. I would guess that this overall difference in effect is still within a fairly small range, a thou or so.
Forestgnome
Stainless
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- Aug 2, 2008
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- Californeeeah
What I'm saying is that if your edge finder is consistently off by .005", you'll still hit the center of a hole with much better accuracy than .005". It's like bisecting a line with a compass. The compass isn't set for half the line length, it just has to stay at the same setting for each mark.
tay2daizzo8
Hot Rolled
- Joined
- Nov 8, 2013
- Location
- north of Bean town
thats not exactly what you posted..but YES if your EF is .005 off and u account for .005 then you should be good...on a square surface...you still have all the caveats listed above when trying to find center ACCURATELY
quadzilla87
Aluminum
- Joined
- Aug 22, 2015
On small diameters an indicator is probably more accurate.
But what if you have a larger bore, say 12" or more, is the deflection of an indicator holder going to be an issue? Where as an edge finder is more supported and closer to the spindle. With either method I think it's more important to have the head trammed in than what method you prefer.
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But what if you have a larger bore, say 12" or more, is the deflection of an indicator holder going to be an issue? Where as an edge finder is more supported and closer to the spindle. With either method I think it's more important to have the head trammed in than what method you prefer.
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