Measuring threads

[[Da...]]

Hello
I did the Basic Calypso and did not go into detail how to measure a threaded element.
I would like your help with how to measure a M8 x 1 mm thread.
I did as follows:
1 ° I made a circle element by activating through the Macro circle with 4 points, activating the thread and placing the pitch of the thread
2 ° In strategies, I set up the propeller mode with the speed and pitch of the thread.
correct ?????

[[Kl...]]

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Hey

two conditions
1st - which probe head is mounted on CMM
active one, like VAST, VAST XT, or VAST XTR
with this head ist possible to make self-centering probings
passive one, like VAST XXT
no self-centering is possible.
2nd - How accurate must it be
For a simple thread hole you can take the solution decribes (biggest stylus diameter) and take the Points an outer or inner
shape.
Sometimes the flank points (double contact by self-centering) are the refererence In that case you have to activate the
self-center mode inside the strategie.

Klaus-Dieter

[[Da...]]

Hello
I use a Duramax with VAST XXT TL3.
I need to measure a symmetry 0.10 mm
I used a 2mm tip to measure an M8 x 1mm.
When you activate circle macro, does it look for the V of the thread or not?
Thanks

[[De...]]

A circle macro is going to try to measure a circle.

A circle is by definition only in one plane, the V of the thread follows a helix and is a three dimensional feature.

So no, I do not believe that a circle macro will self center into the thread as it is made for measuring a circle in that is a planar feature.

If you want it to measure a helix you would need to make it a cylinder with a helical path.

That said, if you know the process and the minor diameter and the thread are cut at the same time, then you can likely define the feature as a cylinder and measure 4 or 8 lines on the minor diameter that run parallel to the axis of your thread.

These lines will pick up the high points of the thread as well as falling into the valleys on the thread, by using LSQ to evaluate them you will get a pretty good result for the location of the thread. For something that is 0.1 mm it is likely good enough so long as you know the process will locate the thread and the minor in the same machining operation.

If you absolutely have to measure the thread itself then you either need thread plugs or will need to write something that will in fact measure a helical on a cylinder - keep in mind though that even following the helical of the thread you need to make sure your not just hitting on the tips or you would still just be measuring the minor diameter.

[[Da...]]

Yes they are done at the same time, I did not imagine what it would be like to do with lines.
I'll try to do something here.
Thanks

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[[Ow...]]

It's been put on here a few times but, I'll attached for your convenience.
Nice write up on the best ways to measure them.

Threaded_Holes_metrology conf 2011.pdf

[[Ro...]]

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I've seen these on this forum before, is there somewhere we can browse through them all?

[[Br...]]

Dailton,

I have a lot of time on my hands due to unplanned downtime... Oddly enough, I was putting together a teaching aid about using helical scans on a M8 x 1.25 thread. I'm still tinkering with it and it has some rough edges. Maybe it will be of some use to you. See the attached pdf.

Kind Regards,
Brad Foster

FGMT - 002 - Tapped Holes TP - using Helical Scans.pdf

[[Ch...]]

I like the idea of using two helix spaced out like that. I typically would use one helix with atleast 5 revs.

One thing is that I would highly recommend using the self center method. It really cleans it up.

[[Cl...]]

Maybe someone covered this already. I didn't read all the responses. I've had a lot of success using linear scans inside a cylinder feature. Depending on the size of the hole, I use anywhere from 6 - 8 equally spaced scans. The gives pretty good results for true position, depending on the tolerance.

[[Ri...]]

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If you are doing this, I would suggest to heavily increase your point density, change your Outlier to 1/3, with 3 repetitions. This will allow you to be able to use LSQ, and only pickup the minor diameter.

[[Cl...]]

I do all that, based on (I believe) a post from (you) last year maybe?

[[Do...]]

#

[[Ke...]]

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We have had 2 opposing views on how to do this where I am at. As a beginner I am trying to soak as much info up, so I am interested to see what you have to say about this. My apologies if anything is conveyed poorly, you're dealing with amateur hour over here. One of the methods is as you describe with line scans parallel to the axis of the threads.

The other method is as follows ... "2 circle paths of single points on a cylinder offset from each other by x"
x=(1 / y) / 2
y=threads per inch

Example; so with a 8-32 thread, it would be 2 circle paths offset from each other by 0.015625.
0.015625 = (1 / 32) / 2

[[De...]]

Perhaps I misunderstand, but two circle paths offset from each other still will only touch the actual minor diameter in a couple of spots and the 'valley' of the thread in a couple of spots.

The inherent issue with measuring threads is to measure either the thread itself or measure the minor diameter but to not get mixed results of the two. I do not understand how the method you describe would collect results that accurately reflected the location of the thread.

The method of using a self centering helix that is described in the document that was posted is meant to measure the thread itself. The method I described using lines gives up on checking the thread itself and instead measures the minor diameter of the threads.

When I use the method I described using lines I make sure use at least 4 lines with at least 350 points per line (usually more) to allow filtering, then I run 3 iterations of outlier removal and use LSQ which gives an average of the points from measuring the peaks and valleys over the length of the thread.

In most cases, we control our processes by finishing the minor diameter and threadmilling in the same operation so this works well for us.