I was taught a new way to use an edgefinder today. What are your thoughts?

[BaronJ]

Hi Guys,

Whilst I don't disagree with the comments made, RJ is the only one to mention

The edge finder contact surface and the surface of the edge being found should be clean and smooth.

Which in my opinion is one cause of the largest errors.

 

[BaronJ]

Never having used an edge finder and doubting if I will ever be able to afford a mill unfortunately I never the less found this a very interesting discussion.
Thanks to all concerned.
(no knowledge is wasted)

They are also useful for finding the centers of pop marks and drill holes with a drill press.
They are also easy to make !

 

[higgite]

Very interesting but can you verify which result was closed to the true edge? .008 is probably unacceptable to most of us.

Robert

If you’re asking which method came closest to finding the true edge, I’m not sure how I could verify that with the resources that I have available. But, the Fisher showed only .0006” difference in the 2 methods, which is well within my capability and need for precision. I’m sticking with the conventional method until someone convinces me differently.

If you’re asking which edge finder of my 2 edge finders was closest to finding the true edge, I’m giving the benefit of the doubt to the Starrett over the generic no-name, but again, I have no way to verify that.

I agree that .008" is unacceptable, even for government work.

Tom

 

[Dabbler]

-- So, in summary, the edge needs to be straight (or why find it?), clean, free of any residual oil or anything else bigger than .0002.
-- It seems the most common and agreed method is finding it, and then checking it at least once more.


For those with or without a DRO, here's a way to check your Edge finder and your technique (and maybe your DRO setup in the bargain).

Required: Yes - you will need a mill - an edge finder, a trusted micrometer, and a 1-2-3 block,or a gauge block or another item that has parallel surfaces.

Step 1: Find the edge on both surfaces, using your lead screw or DRO to make a measurement between them (just like you are using the edge finder to find the centre of the work)

Step 2: then measure the work piece, using your micrometer. Your measurements should agree.

I seem to recall in my high school, we did something like this on an unknown block as a test of our technique (45+ years ago!)...
In the above discussions, there is some variance in findings - this is self-proving, and will tell you if the inaccuracies are in the finder or the guy using it

 

[RJSakowski]

After Tom's post about the different results between edgefinders, I tried some of mine. I found that the Phase II set gave a much smaller jump but that they settled in a "centered" position on backing out about .0014" vs. the .006" for my old Enco. I suspect that the greater settling distance for returning to a centered position was due to the lighter spring tension in the Enco edgefinder. It is about 1 lb. vs. 2 lbs. for the Phase II edgefinders.

All the edgefinders that I tried found the true edge to .0001 or less, measuring a 1-2-3 block verified my micrometer measurement against the DRO reading. The DRO scales were recently calibrated against an offset verified by micrometer.

 

[RJSakowski]

-- So, in summary, the edge needs to be straight (or why find it?), clean, free of any residual oil or anything else bigger than .0002.
-- It seems the most common and agreed method is finding it, and then checking it at least once more.


For those with or without a DRO, here's a way to check your Edge finder and your technique (and maybe your DRO setup in the bargain).

Required: Yes - you will need a mill - an edge finder, a trusted micrometer, and a 1-2-3 block,or a gauge block or another item that has parallel surfaces.

Step 1: Find the edge on both surfaces, using your lead screw or DRO to make a measurement between them (just like you are using the edge finder to find the centre of the work)

Step 2: then measure the work piece, using your micrometer. Your measurements should agree.

I seem to recall in my high school, we did something like this on an unknown block as a test of our technique (45+ years ago!)...
In the above discussions, there is some variance in findings - this is self-proving, and will tell you if the inaccuracies are in the finder or the guy using it

If using the lead screw, you do have to take backlash into account.

I didn't use the Tormach for my experiment because the DRO on the Tormach uses stepper steps from a known position to determine position so it is actually referencing stepper motor rotation. As such, backlash does enter in and must be accounted for.

On the other hand, a DRO reading position on a linear scale actually records position. There is a potential for backlash in the pickup but it is usually quite low by comparison.

It can be measured as well using a .0001"/div. test indicator. Mount the indicator in the spindle or to the head and approach a fixed object on the table. Stop when the indicator is zeroed and zero the DRO. Back away away and the test indicator should track the DRO. If it lags behind the amount of lag is the backlash in the DRO.

 

[Silverbullet]

How about the old way of a slip of paper between a cutter and the piece . We were taught many ways to get to the edge. Mic the paper hold between cutter and part can be running or not or both ways till you get use to it. I used to turn spindle with a wrench and advance table till cutter drags on paper . May not be the super sensitive way but always works . Says a voice from the past.

 

[MrWhoopee]

How about the old way of a slip of paper between a cutter and the piece . We were taught many ways to get to the edge. Mic the paper hold between cutter and part can be running or not or both ways till you get use to it. I used to turn spindle with a wrench and advance table till cutter drags on paper . May not be the super sensitive way but always works . Says a voice from the past.

I, too, was taught this method. Just used it recently.