Runout of a cylinder/circle to a threaded cylinder

[[Li...]]

We make pumps for airplanes and there are many ports with threaded cylinders. Prints always ask for runout from another inline cylinder back to the threaded portion of the port. "See attached". I am having difficulty getting these runouts in spec. When it comes to the threaded cylinder of the port scanning the threads seems to be throwing the runout off. I've tried two scan paths of the threaded cylinder. Four/five line scans of the threaded cylinder and just a circle somewhere in the thd cylinder. To the print it is the pitch diameter that it wants to know for runout, but can't really get to it. So I just do the minor diameter. I always adjust evaluations/filters to see what or how it changes my results. I use either a 3mm ball or 5mm ball. I am going to try this ceramic half sphere I have to see what that give me.

What would you guys try that maybe I'm not thinking of?

How to measure runout.xlsx

[[Me...]]

Is using an threaded insert an option for you? If its accessible and wont get in the way, that may be your best option.

[[Ch...]]

I use self center helical scan on threads. Or I would recommend the flex type plugs.

Threaded_Holes_metrology_conf_2011.pdf

[[Mi...]]

yeah, I would self center the helical scan so it follows the threads better.

[[Ma...]]

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Is this possible inside a threaded hole?

[[Ch...]]

Right here.

[[Ma...]]

What kind of stylus arrangement allows self-centering with helix scan in a threaded hole without shanking on the minor diameter?

[[Mi...]]

you just can't use too small a tip. If I'm checking a 6-32sti I might use a 2mm tip, a 4-40sti would be a 1.5mm.

[[Ma...]]

So, the self-centering is not contacting the flanks of the thread, but at the intersections of the minor diameter and the flanks of the thread?

[[Mi...]]

see the picture above on the right that Chad posted? The probe drags up until it finds that valley and then sticks to it. You need to use a large enough tip to not shank out while still being able to fit. Oh, and before you ask, no that picture isn't to scale 😃

[[Ma...]]

I was thinking of self-centering on the thread flanks alone. I do this fairly often to approximate the pitch cylinder of the thread but it is only possible on external or larger internal threads and requires a rotary table.

[[Me...]]

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Have you tried this method with taking single points instead of scanning? I would be interested in trying it with single points because we have a lot of Thread True Positions that are not tight toleranced...

[[Ch...]]

Shawn,
I doubt this would work without scanning. You really need to flood it with points and then aggressively filter.


Mark,

This would be similar to self centering on a gear. I'm first to admit that it's unlikely that the probe is landing on the flanks of the internal thread. Most likely, when measuring on internal threads, we are just reporting the position of the minor diameter. Although this isn't ideal, if you can prove that the position of the minor diameter is statistically equivalent to the actual position of the thread flanks, then you have a good measurement strategy that fits the needs of the business and conforms to ASME 89.7.

[[Li...]]

I must not be doing something correctly. It is not travelling up the cylinder along the threads.

[[Li...]]

It is staying at one depth and scanning .

[[Ke...]]

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Just wondering how small of an internal thread you have measured. I have a rotary table that I check internal splines/threads with, but not sure how small is the smallest feasible.

[[Ch...]]