Minimum Effective Thread Depth

[[Ke...]]

Does anyone have any fun ideas on how to inspect the minimum effective thread depth, on a 18mm internal thread...using the CMM without sectioning the part?

[[DW...]]

Maybe using the appropriate pitch 18mm bolt and some math?

[[Ke...]]

The required inspection method that I have been given is "CMM"; not "Pass/Fail" or "Visual"... I figured I would do my due dliligence, before I tell them to count threads.

[[Ma...]]

Grind the head off of a screw and measure it's length, screw it in the hole as far as it will go, probe a point on the end of the make-shift gage. Use formula to create a point at the proper depth to represent the deep end of the gage. There, you can say you measured it on the CMM. 

 

[[Ke...]]

I think people are confused about the meaning of Effective Thread Depth... it isn't a simple "how deep is the thread gage or bolt able to be inserted"; it is "Is there actual threads at a certain depth". There needs to be a minimum number or length of threads so that there is proper thread engagement to ensure that there is sufficient thread engagement, so that the threads do not strip out during assembly or during active use after assembly... I'm sure noone wants their steering wheel coming off while they are driving down the road, because "the gage went in far enough", but there are missing threads.🤣😆🤪😝... and yes, these emoji are terrible. lol.

[[Ri...]]

Use a mold, inspect on a comparator.

To find the effective thread length, you have to find the first full thread start depth and the last full thread start depth.

A thread can typically have up to 2 or 3 imperfect threads at the entry of an ID or OD. (It's basically a rule of thumb and widely accepted).

See Incomplete thread per ASME B1.7-2006.

Please sign in to view this quote.