Accommodate Threading for Anodizing... how?

[glencandle]

I have been told that anodizing adds an extra layer of dimension to a part.  I will be anodizing two parts that will need to be threaded together. 

The thread size I'm using is 7/8-9... how would I modify the threads to accommodate the anodizing?  Would a looser Class 1 designation do the trick or is there more that needs to be done?  

[seth.madore]

Type 2 Hard Anodize or just regular anodize? Regular will build up .0002-.0005" per surface, so typically, you are going to need to run your thread/ring gages really loose, but not have the "NO/GO" start. Best practice is to obtain "pre-plate" thread gages, but those can be somewhat pricey. If you do a Google search, there are calculators for determining the thread specs. Is this being machined in a lathe or mill?

[glencandle]

Thanks Seth, I appreciate the response.  Re: lathe/mill, I honestly don't know, I'm going to send the solid to Xometry for the prototyping.  Would it make a big difference?

When you say run the gages really loose are you talking about the threading class?  I was thinking I would go with Class 1 to accommodate for the extra material added in the anodizing.  Is this kind of along your thought process?

[seth.madore · Accepted solution]

From a manufacturing perspective, defining class of thread isn't sufficent enough to guarantee proper fit after anodize. Why? For a tapped hole, the "NO-GO" size for 1B and 2B AND 3B are all the same size. The only thing that changes is the "GO" portion of the gage. It's entirely possible that your parts will be machined to that class, but still end up not fitting. 

Now, there's some protection that you can give yourself, as the designer. Define a Class 2B/2A fit, but ON THE PRINT, clearly indicate that "all dimensions apply after anodize thickness of .xxxx" amount". Consult your local coating shop to determine what their standard buildup is, as they all seem to have different ideas of what's "typical".

Now, if the folks on the end of Xometry are worth their salt, they're going to run the threads so the plug "NO/GO" barely starts, or perhaps starts with 1-2 turns (but no more than that). The OD thread is a LOT easier to figure out, since you can use a "3-wire" method of inspection, and no Ring Gage is needed.

[glencandle]

Wow, thanks man, this is hugely helpful!  Appreciate you taking the time to help a stranger out 😉

[glencandle]

The parts I'm threading together are aesthetic, not critical to the functionality of the assembly.  In other words, I don't mind if the threads are loose, I just want to make sure they fit at all.  That being said... would a Class 1B/1A fit be more of a guarantee in this sense?

[seth.madore]

Possibly, but not 100% guarantee. If they are using a plug gage for the 1B, they could conceivably get it to "just go" and then on the 1A side, it could also measure up towards the high side (over wires). After coat, there "could" be a chance that they just don't fit. You're going to need to do some digging and find out what the specs NEED to be before plating, and convey that info on the print.

[glencandle]

Copy, makes perfect sense. Thanks again!

[glencandle]

Copy, makes perfect sense. Thanks again!

[seth.madore]

Alternatively, you "could" just state: "Run threads loose", but your mileage may vary 😉