HELIX PATH

[[Cl...]]

I curious what the general opinion is about using helix paths in cylinders?
I have a customer program that uses this strategy for several cylinders.

[[Mi...]]

I will use the helix path if the is any form tolerance (cylindricity etc.) just for full coverage of the feature. If I don't have a proper stylus to do it then circles with line paths along the axis

[[Cl...]]

What about as a Datum?

[[Mi...]]

Yes even if the feature is used as a datum, with the appropriate Evaluation. Although there may be some additional arguments because it shows any form issues that may be going on over the length of the part and not just where the circles are located

[[Ri...]]

Helix paths are fast and can be slightly more imprecise then lines on a cylinder. Full disclosure, that opinion is based only on a couple days study on a limited number of sizes, materials, and surface finishes. Testing on your parts and finishes would be the best course. What are the constraints here? Is run time the issue or precision? What are the manufacturing methods? Jig bore or stamping or regular machining practices? One of the big problems with measuring cylinders is the short, large diameter cylinder. Is that an issue here?

[[Cl...]]

Thanks Richard. I went through their program and found
datum features using helix strategies. I replaced the helix
path with circle paths, and improved the position results
by 2x. I rarely use this strategy, so I was curious what the
difference would be if I made the change?

[[Ri...]]

In my 27 years experience with CMM's part programming, both in UMESS and Calypso, two circle paths will get the job done. That's for generous tolerances and solid, repeatable manufacturing methods. For close tolerance bores or for bores made from less dependable methods, I liked a combination of circle and line paths.

[[Aa...]]

If you're evaluating the cylinder using a tangential evaluation technique, I would strongly advise against using only a few helical paths. The position/orientation results can be unstable.

[[Da...]]

I check cylinders all day, every day. I never use helix. The most stable way to check cylinders for our parts is to use several circles the recall feature points into a cylinder only for Cylindricity. This way we have roundness of individual circles available for analysis if needed. Viewing the circles individually make it easy to spot contamination. Honing can produce a perfectly round hole that is bent like a banana.

Can you extract circles from a helical scan? can you analyse roundness? I build features that answer question that I know will arise from a not so good part. Saves lots of time in the end. Just my 2 cents.

[[Ca...]]

I only use helix scans for threads. For holes, I use circle scans for size, and recall lines through circles for location. Some of our customers have requested these methods.

[[He...]]

I have found it will give very repeatable results, but not accurate results for true positioning.

[[Cl...]]

Yes, that's what I'm seeing too. thanks to everyone for the input.