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Diameter Measurement - PGI Novus Alignments and Methods

Let's have a look now at alignments and methods of measurement of diameter.

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Cresting and tips offset (in x and y)

For example, on this ring gauge here to make sure that we measure right at the crest here and that when we measure in the reverse bias mode that we also are on the crest and in this case, in this diagram we’re fine. We've measured exactly on the crest the smaller the ring gauge the more critical it is to measure on the crest are the smaller the part I should say not just for engages.

.Cresting and tips offset

In this case we've deliberately shown an error in the y direction. This is in the y direction so we're looking into the travis unit and we've deliberately shown an error here in the y direction and this is the tip offset in y and if we measure correctly at the base here if we crest and find this point and then we measure at the top just by moving straight to the top..

We will be some way out from the from the crest and that of course, will cause a diameter measurement error. So, we're dealing here with tip offset and we’ve just looked at tip offset in the y direction. There is also a tip offset in the x direction, but we'll come to that a little bit later.

So how do we solve this problem of the tip offset there are two approaches.

One is to after we've crested at the bottom here when we move to the top, we can of course crest again but that could take some time now the PGI Novus gets around that because we know through the calibration routines the tip offset in the y direction and so what the system does is: it won't move the it won't press again, but it will actually just move directly it will move this stage this y movement stage directly to the crest position because it knows the tip offset between the top and the bottom tip and the advantage of that is it can save a lot of time.

Gauge Alignment:

Here's something else that's very important and the PGI Novus again has built-in software to detect this error and also to allow the system to be set up very precisely and this is the movement. This is looking right into the gauge. Here this is a ball that we're measuring for example or it could be a cylinder but it's a ball in this case and we're looking into the gauge.

Guage alignment

So, there's the start lower stylus tip. There's the upper stylus tip and you can see that the whole gauge is tilted slightly anti-clockwise counter clockwise and clearly what that will do is that it won’t describe the right path on the part on the right-hand side, we've resolved this by aligning the gauge using the special calibration routine and now we're certain that we're measuring right over the crest and all the way correctly around this.

This ball and that really is critical and again the smaller the part we're measuring for measuring the more critical that is and that will seriously affect the reliability and the accuracy of diameter measurements.

Diameter Measurement Methods - PGI Novus:

So, let's look again at diameter measurement on the PGI Novus.

We're going to look at two different methods the first is what we call engage range measurement and the second is using a column move.

So, what's the difference between these two?

Let’s look first of all at diameter measurement with a column moves and what we've done here is on this large bearing we've measured near the center of the gauge range we’ve taken a balanced trace at the bottom here and the gauge range the gauge is in its near zero position.

Diameter Measurement Column Move

We've now moved up and what we've done is moved the gauge into reverse bias mode. So, we're dealing with this tip here and then we move into contact with the bearing again and again, we're near the center of the gauge range but notice that the column has moved on the right here through some considerable distance on this large bearing.

We can also do diameter measurement in the gauge range and in this case, we're measuring internally and we can we've taking a side view we've got a cut looking internally at what we're measuring and it's a cut part and we’re measuring the first diameter, the second diameter and the third diameter. We then without moving the column move the gauge into reverse bias mode to measure the three diameters again.

Guage Range Measurement

 In both cases whether we're measuring large bearings or small bearings the PGI Novus will give us excellent results accurate results for diameter measurement one of the things that's necessary when we're using the column moves that we saw in the previous example is that the quality and alignments of all of the axes are very precise and that the material and stability of that column is very critical if we're going to claim to be measuring diameter accurately.


Angle Measurement:

We can also measure angles as well using the column move in the same way and in this case, we've measured this injector needle and we've measured a balanced trace about zero and we've measured over onto the cone itself.

Angle Measurement

We’re now measuring the same thing underneath and again; we've moved the column in each case and the typical results here we might see for cone measurement often injector cones will have several different diameters and you several different angles on them and you can see these here along with the surface finish example on the right is actually measuring a spherical bearing where we've taken two traces and again, we’ve been able to look at the diameter between them.

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