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Check your center finders for accuracy!!!

Tags: center finder run out

January 29, 2012
1:30 AM

ironring1

Vancouver, BC

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I dropped one of my center finders and dinged its point a teeny bit, so I put it into a 3/8" collet on my mill and was planning on spinning it at ~1500rpm and restoring its point with 400 grit sandpaper. However, when I began to spin it, I realized that it's entire cone was off center somewhat, I guess what you would call run-out, but in the finder's tip instead of in a spindle. Well, it was a fair amount, perhaps 15 thou! At any rate, I wrapped some 220 grit on a popsicle stick and spun up my mill to 1500 and I brought the whole darn thing back into alignment. Then I polished it with 600 grit.

At any rate, these are the 3/8" diameter center/edge finders that Grizzly sells in a set. The edge finders all are good, but I advise all of you to check your center finders if you have them for run out, especially since it is so easy to fix.

-Chris

January 29, 2012
1:54 PM

Jerry

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I'm a little confused by the problem, do you have a pic of the type of centre finder you use?

January 29, 2012
4:13 PM

kwoodhands

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January 1, 2012

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ironring1 said:

I dropped one of my center finders and dinged its point a teeny bit, so I put it into a 3/8" collet on my mill and was planning on spinning it at ~1500rpm and restoring its point with 400 grit sandpaper. However, when I began to spin it, I realized that it's entire cone was off center somewhat, I guess what you would call run-out, but in the finder's tip instead of in a spindle. Well, it was a fair amount, perhaps 15 thou! At any rate, I wrapped some 220 grit on a popsicle stick and spun up my mill to 1500 and I brought the whole darn thing back into alignment. Then I polished it with 600 grit.

At any rate, these are the 3/8" diameter center/edge finders that Grizzly sells in a set. The edge finders all are good, but I advise all of you to check your center finders if you have them for run out, especially since it is so easy to fix.

Chris,I have the same center finder as you and also the other type that changes shafts from a point to two different

size edge finders.Both of these wobble types are less accurate than a ground point in the chuck or taper holder.

I took a 3/8" shaft broken endmill and ground it to a long tapered point.I did this by hand by chucking the endmill in an electric drill and grinding on a bench grinder.The long taper makes it easier to see the point.I simply eye the layout with the point over it. Magnifying shield helps here.

I rarely center punch as I found more accuracy in a sharp layout.

I do occasionally use the edge finder on either of the sets i bought.

mike

January 29, 2012
5:14 PM

ironring1

Vancouver, BC

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This is the kind of center finder that I mean:

The problem with mine was that the axis of the cone ground onto the end was not concentric with the axis of the body of the center finder. That lack of concentricity introduces a systematic error into the measurements, but it will vary randomly depending the orientation of the center finder in the collet/chuck. At any rate, since the free end of the center finder has a section of ground cylinder at it's base, I was able to put it in a 3/8" collet right up to the base of the conical end. This held the two pieces in alignment while I applied some aluminum oxide sand paper wrapped around a piece of bar stock to the cone. After a few minutes of this at 1500rpm, the eccentricity disappeared, making the tool accurate again.

January 30, 2012
9:24 AM

Jerry

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Right, clear now thanks. I've never seen a cone like point on a centre finder before, only long needle types. With the needle type, as is the dab of modelling clay and a pin, the needle is centred itself before being used to align something. The idea of this is simply that you can not trust tooling being in the centre of rotation, so this negates the mentioned randomness of that by aligning the needle to the right place each time it's mounted.

It may be that this is also the intention with your cone finder, the cone itself, not the OD, is what should be aligned each time, which I why I struggle a little with it being a cone, as needles are far easier to true up by simply touching them under way, immeasurably small forces to do that.

This is one of those annoying tools that seems to arrive with no instructions assuming the person that bought it knows exactly what to do with it! I had a costly Eclipse 'wobbler' set for years which contained parts I never understood Confused .

January 30, 2012
10:49 AM

ironring1

Vancouver, BC

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The advantage of the cone-style center finders is that you can use them to center the machine over already drilled holes (albeit those smaller than the diameter of the cone's base). You use it by pecking with the quill while the machine is NOT powered, and feeling with your fingers for alignment of the movable tip with the center finder's body. You don't true it up like a wobbler.

-Chris

January 31, 2012
1:17 AM

Tyler

Seattle, WA

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The problem with mine was that the axis of the cone ground onto the end was not concentric with the axis of the body of the center finder.

Wow, really? I'll have to check mine. I have the same style as yours that I got from Grizzly … or was it Enco …? Anyway, thanks for the heads up!

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February 1, 2012
11:11 AM

ironring1

Vancouver, BC

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Yeah, although to correct one thing that I said, it's not that the axis of the cone was not concentric with the axis of the center finder's body (since it makes no sense to talk about concentric axes…). What I should have said was, the conical tip of the center finder and the body of the center finder were not concentric (or coaxial). I think that everybody got my meaning, but I just wanted to be clear ;)

-Chris