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External threadmill question


So not a Guru
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I have to cut a 9/16-18 UNJ external thread on a part. I always end up having to repeatedly add comp & rerun external threads (and sometimes internal too), because the geometry I use is inaccurate.

Does anyone have a good resource for what diameters to use as geometry for external (and internal, if they differ from the nominal thread size)?

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Yes you are okay with your method remember in 2020 you could modify the diameter if it was a different size that you were having to drive the toolpath from.

Sorry OT. 👮‍♂️

Remember and UNJ OD tool is different than a UNJ ID tool. The OD tool can be used for the ID, but the tool that can be used an ID will not cut a correct UNJ OD thread. The UNJ OD thread must have the radius on the threads. Most ID tools don't have the correct crest diameter on them and people normally make the ID oversize to make it within spec. SCT and others make the correct OD UNJ threadmill.

End OT. 👮‍♂️

 

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34 minutes ago, So not a Guru said:

Yes, we have the correct tool with the correct root radii. And I know it works to use geometry to drive the tool. But what I am hoping to find is a resource that can tell me what my diameter should be for external threads

Haven't cut threads for a while, bit when I did, I usually jist checked the handbook.

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1 hour ago, So not a Guru said:

Yes, we have the correct tool with the correct root radii. And I know it works to use geometry to drive the tool. But what I am hoping to find is a resource that can tell me what my diameter should be for external threads

Diameter never changes for the OD even on a UNJ. 9/16 = .5625 for what you program in Mastercam. What changes is the effective PD and where you need either a Thread Mic or a GO NO-GO set of threaded ring gauges to ensure it is correct. PD on a Class 3A is .523-.5264 and what is really what you are shooting for on the thread. I have never seen a Class 2 UNJ thread called out that I can remember they are always Class 3. Make sure you have the correct anvils on your thread mic for a UNJ seen some bad measurements because of the point anvils being used and parts scrapped over it. Gauges are the best and help ensure you are hitting the correct size.

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5 minutes ago, crazy^millman said:

Diameter never changes for the OD even on a UNJ. 9/16 = .5625 for what you program in Mastercam. What changes is the effective PD and where you need either a Thread Mic or a GO NO-GO set of threaded ring gauges to ensure it is correct. PD on a Class 3A is .523-.5264 and what is really what you are shooting for on the thread. I have never seen a Class 2 UNJ thread called out that I can remember they are always Class 3. Make sure you have the correct anvils on your thread mic for a UNJ seen some bad measurements because of the point anvils being used and parts scrapped over it. Gauges are the best and help ensure you are hitting the correct size.

Yes, but if his toolpath is built from Mastercam geometry, then it's an engineering problem, not really something on the machine,

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We will often buy the ring gages, but for one or two parts, like this job, we will just 3-wire it. I don't have a problem ensuring the finished thread is correct.

My problem is this: My Machinery's Handbook 26th edition does not have any data on UNJ threads (that I have found).

It gives data for external UNR threads.

For a 9/16-18 UNR thread the minor diameter max is listed as 0.4950"

From my past experience using this data to create my geometry for UNJ external threads, I will have to run the tool with no comp, then add some comp, rerun, then add some more comp, rerun, then add some more comp etc etc. Ending up sometimes with as much as 0.006" or more of comp.

Maybe this is simply how it has to be done, but I think the 0.4950" may be the wrong data to use for these UNJ threads.

 

 

My question was if anyone knows of a data source for the UNJ external threadform minor diameter.

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15 minutes ago, crazy^millman said:

You cannot do that. That needs to be removed that is a violation of SAE protocols. That is a purchased specification.

I did not get this from the site you linked.

I downloaded it directly from the web after doing a Google search for the thread data.

From page 1 of the document:

SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely
voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.”

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6 minutes ago, So not a Guru said:

I did not get this from the site you linked.

I downloaded it directly from the web after doing a Google search for the thread data.

From page 1 of the document:

SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely
voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.”

Okay just being safe.

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