Cookbook Threads

[[Me...]]

I noticed the cookbook uses the term "Circle path with pitch" when giving instructions for the strategy of measuring threads.

Does that just mean Helix path?

[[Te...]]

Yes

[[Br...]]

Yes, so when you set the "Grade/Slope", it's the distance from thread to thread. For example, if you have an M3x0.5 thread, you would put 0.5mm into that field. With Standard threads you have to do a little math. If we have a 1/4-20 thread, the "20" represents threads per inch. Simply divide 1/20 and to find a Grade/slope of 0.05".

[[Me...]]

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Thanks Brett,

I'm extremely familiar with the grade/slope method and do it quite often, I was just wondering what Zeiss meant exactly in the cookbook about "Circle path with pitch" because that is not an option in the strategy window. They should've used Helix path instead because it may confuse beginners.

[[Ch...]]

For everyone who measures on threads, what are you thoughts on helical scans with and without self-centering.

Is it work the extra time it takes to measure?

Remember, no one on here needs an explanation on what self centering on threads is or how everything is situationally dependent. Just trying to pick everyone's brain here.

[[Me...]]

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I've found that following the cookbook is exceptional, unless you have a .002 (in) True Position or less.

Someone either on here or through a 3rd party inspection lab gave me this:

Threaded_Holes_metrology_conf_2011.pdf

[[Cl...]]

If you need hole position and don't have flex plugs, just create 6, or 8 linear scans
(cyl form lines) up the sides of the ID.This method has worked very well for me in the past.

[[Br...]]

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On smaller threads with the XXT I've had a hard time getting the self centering thing to work. It gets hung up real easy. Maybe I'm doing something wrong. IDK. Ideally, It best represents a position tolerance since you're actually getting into the pitch, but probably 99.9% of the time, the pitch is so concentric to the Minor diameter that it wont make a difference. So to answer your question, In my experience, no. It's not worth the extra time. The helical scan works great as long as they cut the correct threads, in which case, you're going to fail it for the threads anyway. I find it to give me more repeatable data than the linear scans everyone likes as well . also i don't like the flex plugs because you're essentially measuring a projected location and they are really inefficient to use in a production atmosphere.

[[Me...]]

[[Je...]]

I use an RDS XXT head and find self centering to be finicky at best. Very unreliable. According to Zeiss you aren't even supposed to be able to do it.

I use linear scans starting at the bottom of the thread and scan out towards surface at a rate of .1-.2" per second (.0002-.0004" point spacing). Scanning outward allows me to use a smaller styli as the shank follows minor diameter and prevents excessive bouncing by styli impacting threads. Evaluate feature as a maximum inscribed cylinder and constrain the vector direction. This gives an accurate location and allows the report of minor diameter. It correlates with a sprung true pos locator and helical scans within .0003-.0005" consistently in my studies. As diameters increase, line scans increase. My personal formula is scans = 4 + diameter of hole in inches (ie; 3 inch ID gets 7 lines).