Dial Test Indicator Flaw

Hi
I am doing a project using dial test indicator.
As seen in Image 1, I have clamped the part in such a position that it is 45 degrees to X & Y axis.
Now as shown in Image 2, I go 20 mm offset from the zero point (Zero Point is shown in blue color) & move in Y axis until reading is shown on dial.
On similar grounds, I go to 20 mm offset from zero point in opposite direction (see image 3 ) & move in Y axis until reading is shown.
The machine movement in Y axis from Zero Point should be same in both the conditions as mentioned above. But there is variation of 0.453 mm in both the positions (Refer Image 4).
In short, the dial test indicator needs feeds of different values to create the same reading on dial.
We have ensured that the dial clamped is perfectly parallel to Y axis, so there is no issue of contact Point Error.
I think this problem has never been noticed by anybody in history till date:mg:
How can this happen & what should be the error & how to compensate that error.??
It is definitely not a Co-Sine Error (Refer Image 5). It is clearly visible that the angle of lever arm is almost 90 degree to the part.
To know more, I had a broken Dial Test Indicator & then disassembled all the stuff to know actually how the dial mechanism works. ( Refer Image Internal Assembly )
As you can see In Image 6, how the mechanism works. It doesn’t seem to be a unbalanced dial. It is a simple mechanism & logically there should be no error.
Need help

2 attachments were pending as discussed in previous post.

So attaching the same.

Zirok

I don't have the time right now to sort out the issue, but a couple things come to mind to rule out:

1. Are you sure the angles of the piece being measured are precisely correct?
2. How are you measuring the machine movement? Is it accurate?
3. Is it .453 mm? 453 microns? How can you measure that with a test indicator?

1. Are you sure the angles of the piece being measured are precisely correct?
Its a Slip Gauge which is undoubtely a perfect square

2. How are you measuring the machine movement? Is it accurate?
Its a CNC Mill. So the accuracy cannot go beyond 25 micron at the most.

3. Is it .453 mm? 453 microns? How can you measure that with a test indicator?
I Zeroed Y axis on Machine screen when the dialed on the left hand side & then moved to right hand side & after dialing, saw the difference in Y axis on Machine Screen.

Thanks,
Zirok

That type of indicator is only accurate when the plane in which the needle swings is at 90 degrees to the measured surface instead of 45 degrees.

The measuring force, even though very small, will push the needle sideways (left and right) resulting in different readings.

You're asking the indicator to perform a measurement for which it was not designed.

Stijloor.

See, the part moves the needle to provoke readings. In short the part fights against the weight of the needle to move it.

So why not increase the weight on 1 side (where it is showing deviation) .

& in short balance the side thrust so as correct results are achieved.

Zirok said:

See, the part moves the needle to provoke readings. In short the part fights against the weight of the needle to move it.

So why not increase the weight on 1 side (where it is showing deviation) .

& in short balance the side thrust so as correct results are achieved.

Click to expand...

OK. Why do you want to do this? What is it you're trying to figure out?
The application is wrong, so why pursuing it?

Stijloor.

Ya, i know that i am driving crazy in wrong direction.


Just to give a chance...Who knows wonders