probe length

[[Ün...]]

Hello,

I have the Contura XXT TL3, I have a new part 285 mm long. (Outer diameter 91 mm, inner diameter 85 mm) I need to take measurements at a depth of about 162 mm in the inner diameter.

I know that a maximum length of 150 mm probe is connected to the device.
Do you mind if I connect about 165mm long probe for this measurement? Has anyone tried measuring this way before?

Maybe I can try with a star probe, keeping the probe length at 150 mm, but will it cause problems for the head to go into the part?

[[To...]]

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I believe the 150 max length is keep the stated accuracy of the machine/sensor. Honestly, if I were doing it, I would go ahead and qualify the stylus and verify the qualification against a known artifact.

An alternative would be to stay at the 150 max length and rotate the B by 10° to 15° and measure smaller segments around the diameters and re-call the points into 1 main feature. A0 B15, A45 B15, A90 B15, etc.

[[R...]]

Disk Button

2.jpg

[[Je...]]

150mm is the parameter for advised maximum length. The sensor will accept a longer stylus but you may have issues qualifying if the stylus is too heavy at the stylus tip. Qualifying with the sensor parallel to the granite is when the stylus weight will have its greatest effect on the sensor qualifying.

As Tom stated, you can set your rotation angles at + or - 15° so as to avoid sensor contact with your bore. Probe your geometry in 4 ~100 degree sections and recall all 4 individual sections into 1 feature for reporting use. This allows you to both use a shorter stylus configuration and also (depending on bore size) allow you to send the entire sensor into the bore of the part, effectively giving you another 100mm of stylus length.

Also, disc probes are definitely a no-no in this situation. XXT does not support disc probes of any configuration and at that length there is no method or trick that would result in any reliable accuracy to use a disc on the XXT sensor.

If you see an issue where you are constantly having a problem with stylus length being too short and have a large machine measuring envelope, have you looked into an XXT TL4 sensor? It has a optimal stylus length of 75-100mm longer than the TL3. There are trade-offs but many are unaware of the option of a different XXT sensor on some machines.

[[Je...]]

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.
Ünal,

I always noticed error on XXT probes when I used lengths of approximately 100m or greater. In the below image, a cylindrical square appeared to show taper that did not truly exist.

In the following post, Richard does an excellent job of explaining how the XXT acts like a fulcrum. See attached document for further explanation.

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viewtopic.php?p=44281&hilit=fulcrum#p44281

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[[Ow...]]

Maybe needless to say but, speed and probe force when scanning play a big role in accuracy/repeatability when using longer probes.
Probably nine times out of ten, it's almost always slower and lower than what the default settings suggest by form/size/location selections and sometimes slower than what the cookbook recommends.

[[Je...]]

If you are continuously attempting to use styli that are 75mm in length or longer then a possibility is to look into a TL4 sensor rather than a TL3.

The TL4 has a very similar measuring range of the TL2 but the CAA mode available as the TL3 does. There are pros and cons to the TL4 vs the TL3 also but if you are always looking to use longer styli and are unable, it could be an option.

In all comparisons of TL1/TL2/TL3/TL4 I know of, the TL4 is paired with the TL2 in terms of measurement range, force and weight limitations.

[[Da...]]

Since the probe you used to check the square did not change length as you used it, the taper is not because of a change in pressure from top to bottom, but more likely the probe shanked as it got lower on the square.

[[To...]]

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I agree there would be no change in pressure from top to bottom, but wouldn't the ID get smaller if you were shanking out?

[[Da...]]

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I thought it was an OD

[[Da...]]

I really don't think a 165 mm probe will cause much of a problem. Make sure it's lightweight. Use the robust setting, qualify and it should work fine. if you want you can double check by inspecting the upper diameter with a shorter probe then check the same diameter with the longer probe and compare results. If the probe is a straight down probe, it will be fine.

[[Je...]]

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I would agree there. That would be the first ID cylinder square I've ever seen.

And if the stylus tip diameter is too small then it will most assuredly shank at the top when measuring at max "depth". Most stylii designed for the XXT are not intended to be used over 150mm in length. As a result, the tip:shank ratio does not facilitate the steeper angle that it takes to apply the same probing pressure needed during qualification at such a length. FYI, the sweet spot for a TL3 is 50-70mm from the sensor. 0-65mm radially from centerline

[[To...]]

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Though the original poster's application was an ID, I missed seeing the "cylinder square" description. I would agree, as well. 🫣

According to the .0001" scale on the screen capture, it doesn't appear to be a very big part.