# centering indicators



## 777mechanic (Nov 9, 2014)

what is out there that will help me find the center of a hole if the part is moved and needs recentered . I've looked at co-axial indicators but some people hate them , so what else is out there that can help . my project was boring the center out of brake drums for a friend and had a heck of a time zeroing out x and y . pictures of the tool would be great and name brand thanks . also how would you open up or enlarge the hole from 3'' to 5.125 , myself i used a flycutter but would like to know how you'd do it.


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## Terrywerm (Nov 9, 2014)

If your mill has a DRO on it, you only need an edge finder and a calculator to find the center.


[video=youtube;G8qvRe_Y4tg]https://www.youtube.com/watch?v=G8qvRe_Y4tg[/video]



As for enlarging the center hole, a fly cutter can be used, but a boring head would probably be easier. The only problem is finding a boring head that large.  If you have a lathe large enough, you could cut the center out with the lathe very easily.


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## xalky (Nov 9, 2014)

I love my coaxial indicator. It saves so much time in finding the center, I don't know how I operated without one. I think the people that hate them have never really learned to use it and understand it. It's the simplest thing in the world once you know what you're looking at.

Marcel


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## darkzero (Nov 9, 2014)

I use a coax, a Noga mounted in the spindle, or a Noga mounted on the spindle using an Indicol clone. I had an original Indicol but didn't like it much, too wobbly & loose. It was the newer red blue models, maybe the older black ones were better or maybe it was just the one I had (it was brand new)?

FWIW my coax is a Blake USA & not an import, I have no complaints about it & like it a lot. I use mine without the restraining arm.


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## JimDawson (Nov 9, 2014)

I have had my Blake co-axial indicator for about 30 years and don't know what I would do without it, a very handy tool.  There are others that are a copy of the original Blake.  They would not work well for a very large hole, like a surface of a brake drum. (unless there are some attachments that I'm not aware of).  You can make a large hole center indicator out of some drill rod or also use the rods from a mag base indicator, you just need the offset to be able to reach the diameter you need with the indicator.  Basically, anything you insert into the spindle and attach the indicator to will work fine.

It really depends on what tooling you have.  In the case of a brake drum center hole, and given the large change in diameter, I might use a hole saw to rough in the new size then finish with a boring head.  You could also do it on a rotary table with an endmill.


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## darkzero (Nov 9, 2014)

terrywerm said:


> If your mill has a DRO on it, you only need an edge finder and a calculator to find the center.



I've done it that way too, although I do have a DRO it can be done without a DRO also. I use an electronic edge finder & it makes it easier on radii.

I don't favor this method cause the hole your indicating needs to be fairly precise. Sweeping the hole allows compensation of any irregularities.





terrywerm said:


> The only problem is finding a boring  head that large.



Don't necessarily need a large boring head. My Criterion & Yuasa boring heads allow you to mount a boring bar sideways to give you a wider diameter range. I'm not sure if other style boring heads have this feature but the Criterion clones all should. 

Bellow is showing a 2" boring head with my shortest boring bar which could easily cover a 6" through hole & probably bigger. A brake drum, maybe not unless you have room to clear the boring head used this way.


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## Terrywerm (Nov 9, 2014)

Ya, Will, I never gave a thought to putting the boring bar in that way. Don't know why, but it completely escaped me.


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## xalky (Nov 10, 2014)

terrywerm said:


> Ya, Will, I never gave a thought to putting the boring bar in that way. Don't know why, but it completely escaped me.


 THAT'S WHY THIS PLACE IS SO GREAT! We learn new ways to skin the cat every day.


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## 777mechanic (Nov 10, 2014)

thanks for all the comments and this gives me tons of ways to do this now .


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## Holescreek (Nov 10, 2014)

This is the gold standard indicator setup for edge finding, centering etc. I have left over from my jig grinding days. I've been using it daily for over 30 years now. I see that the adjustable arm technology has changed somewhat based on the photos above, the the concept hasn't.


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## Philco (Nov 10, 2014)

Holescreek said:


> This is the gold standard indicator setup for edge finding, centering etc. I have left over from my jig grinding days. I've been using it daily for over 30 years now. I see that the adjustable arm technology has changed somewhat based on the photos above, the the concept hasn't.



Holescreek, would you mind going into detail on how to use this method? Not everyone has a DRO, wiggler, or the electronic devices used for centering. Most everyone has a DTI. This would be a good teaching moment for some of us to learn.


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## Holescreek (Nov 10, 2014)

Philco said:


> Holescreek, would you mind going into detail on how to use this method? Not everyone has a DRO, wiggler, or the electronic devices used for centering. Most everyone has a DTI. This would be a good teaching moment for some of us to learn.



Can I do that inside someone else's thread?


I guess a mod could split it later.

Picking up an edge.
1) Get the ball of the indicator under the spindle centerline by moving the joints (mine are only tight enough to hold position after adjustment) and tilting the indicator side to side.
2) you know it's on center when the ball appears to stay in position wen you rotate the spindle by hand.
3) turn the spindle by hand so the indicator body is parallel to the edge you want to indicate.
4) adjust the hand wheels so the ball is centered over the edge by eye.
5) pull the indicator back a little bit and lower the Z axis so the ball can touch the edge.
6) without twisting or turning the indicator push it up to the edge so the ball makes contact and the indicator needle moves .01~".015" (my Interrapid has .06" travel)
7) rotate the spindle CW and CCW to find the high point on the edge and set the indicator dial to a reference number of your choosing. You may need to adjust the indicator swivel to the high point contact is made when the front of the ball touches instead of the side of the ball.
8) raise the spindle then rotate the spindle 180 degrees over top of the edge you just touched.
9) place a ground object (I use an old gauge block) against the edge  you're checking and bring the spindle down so the ball can make contact with the gauge block.
10) adjust your axis hand wheel based on the reading you get on the indicator dial wen the ball touches the block as you rotate it back and forth.
11) Continue alternating the two positions (0-180) until the reading on the indicator dial is exactly the same.

It's way harder to type instructions than to actually do it. If you see it done (might take a minute?) you just say wow!  You can also use a similar technique to measure radii and offset boring bars to an exact size. All you need to know is the distance from the known edge.

I do prefer to use an edge finder in conjunction with a DRO for most milling work but if I'm doing something important, or inspecting a part, the indicator is as close as I can get to a CMM in my home shop.

I found some old photos in my PB account that might help:


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