Measuring location of screw locking Helicoil

[[Gr...]]

Any thought on the best way to measure screw locking Helicoils? I typically use cylinder form lines on threaded holes but this type of Helicoil has protrusions on the ID of the thread which will most likely give me incorrect location numbers. These are 6-32 and .25" deep. Any thoughts would be appreciated.

[[Cl...]]

You probably though of this, but; If those "protrusions" are equally spaced, could you orient the lines to avoid them?

Sometimes a second set of eyes sees something different. 😃

[[Gr...]]

Hi Clarke. Yes I thought about it until I realized that the coils never sit in the same place twice. I have 8 holes per part. PS always appreciate your input.

[[Jo...]]

I know it's not ideal, but short of using thread plugs, how about a self center point with an probe that is slightly larger than minor diameter?

[[Ri...]]

You wont get similar results compared to initial inspection (No helicoils).
You will be lucky to get good results attempting to measure within a helicoil (locking or not).

Helicoils, locking or not, do not seat exactly within the thread flanks as they do when an actual bolt/screw or truepos is applied, this is normal. The tool to install helicoils is not an exact fit thread tool, they allow for removal of the tool as to not damage the helicoil, thus the flank engagement is not 100%.

I've tested this in the past on a ten count hole patterns without helicoils installed, helicoils installed, helicoils installed using gage pin inserted into the location, locking helicoils installed.
Only the "without helicoils" presented accurate results.
The other three methods failed 8 out ten locations and 8 out of 10 attempts (Patterns).
The only thread insert tested that still revealed nearly the same results as the actual tapped hole were Keenserts.

[[Mi...]]

I have several jobs that require me to check parts before hardware and after. All the Helicoils are locking. I use a helical scan, 2 revolutions. I usually don't have an issue but the diameters are always off (I use minor diameters as per NASMS33537) and I explain to my customers that they will be off no matter what because they are asking me to verify parts with locking helicoils in place. This in turn effects positional tolerances and if they want me to check hardware then they will just have to live with that fact. I usually don't push back at them too hard because the one time I did they then wanted reports from before hardware AND after which sucked because I then had to explain why there were differences. So, they usually don't want that now because it's just more paperwork for them... so we tend to agree there could be issues checking hardware.