Checking (Calibrating) Truncated Thread Set Plugs

[Russ]

Does anyone have information on checking Master Truncated Thread Set Plugs? Does anyone attempt this in their own lab or do you all send these outside for checking? Just trying to get a concensus on how other manufacturers handle this calibration. What standards should I be looking at for in-house calibration?
Any help on this is most appreciated

[Hershal]

I recommend sending them out to an accredited lab for calibration.....

If you cal them in house you will likely need a super micrometer, trained personnel, an environment of 68 F +/- (not more than) 2 F, do your uncertainty calculations.....

Easier and cheaper to send them out, but make sure you have the lab give you the specific uncertainties for each item.

Hope this helps.

[TIMMYS - 2010]

This is an interesting subject. Basically Hershal's answer is sufficient. However, I would like to shed some light on this subject.

Last Summer I hosted an In-House seminar on Thread Gaging. The speaker was Mr. Stanley Johnson, President of Johnson Thread-View Systems.

The subject of Adjustable Thread Ring gages was discussed by Mr. Johnson. In fact, it was Mr. Johnson's Grandfather that invented the AGD Adjustable Thread Ring. The interesting fact about this is that this type of gage was never intended to be adjusted in the field. If you check this type of gage with a Setting Plug gage and it is too loose or tight, then you need to send it back to the manufacturer for adjustment and lapping. When you change the setting on the Thread Ring you will cause a "lobing" of the thread diameter.

I have been checking Thread Ring gages for over 25 years and this was a huge piece of news to me. There are many other thread gage "myths" that Mr. Johnson revealed and explained in his seminar. It was well worth the time.

Just thought I'd share that info.

Regards,
TIMMYS

[Tool_Inspector]

In Reply to Parent Post by Hershal

If you cal them in house you will likely need a super micrometer, trained personnel, an environment of 68 F +/- (not more than) 2 F, do your uncertainty calculations.....

Dont forget your calibrated 3 wire set corresponding with whatever pitch/tpi your threaded master is!
Working in metrology lab at (insert major brand name here) spark plug manufacturer i have first hand experience (SAE spark plug thread sizes anyway, mostly 14mm/go rings for max spark plug [.5159] and min engine head [.5192]) with truncated masters and adjustable ring gages. I calibrate masters yearly and we verify our ring gages weekly so the masters are used about 5x a week and it takes years for a treaded master to fall out of our tolerance (-.0003").
Adding to TIMMYS warning about RTG "lobing", I was advised of this also throughout my training and through attending the same lecture although at a different time and place. When I came forth and mentioned I'd adjusted them before and never had those problems it was explained that since we use a tight tolerance with the master this effect would be negligible.

[Wayne]

In Reply to Parent Post by Hershal

I recommend sending them out to an accredited lab for calibration.... Easier and cheaper to send them out,...

I agree with Hershal, unless you have a very complete in-house laboratory. Remember that these are in fact the masters for your ring gages.

That said, if the product manufactured in your facility is not safety critical, I see no reason that it can not be accomplished within your facility. The work of calibrating set plugs is little more than that of calibrating your working plugs.

It requires:
- 3-wire measurements of the pitch diameter done at front, middle and back with the ultimate goal of the same size in all three places.
- Major diameter measurements of the full form major diameter. This is critical surface for determining the wear on the ring gage and is the first place you may see wear on your set plug gage.
- Truncated major diameter is not a wear surface and should not change from its original manufactured position. The specified tolerance on this feature is large by gage standards but could be larger without affecting the function of the setting plug. You (and some gage makers) don't really care if it is in tolerance or not as long as it is a little larger than the pitch diameter and much smaller than the full form major diameter.

NOTE: Tolerances on setting plugs can be X or W. Basically W is half of X. When W is specified, usually only the pitch diameter is held to W. X-tolerance is the same tolerance used on working plugs. As a manufacturing plant I suggest that you work to X. If you were a commercial calibration laboratory there could be an argument made for using W, but it is still unnecessary in the grand scope of things.

I hope this has been helpful.

[Charles Wathen]

We do these in our lab using a Pratt & Whitney with a laser encoder, plus the wires and jo blocks. We use an Excel spreadsheet that I created which has a table of the specifications of our setting standards. I set it up this way so a beginning tech or intermediate tech can follow our internal written procedure and simply press keys to send the measurement to Excel using the old Hyper Terminal program from Win98. Works quite well, and there is no calculations for the tech to perform. It's done by Excel by displaying a pass or fail on the printed sheet.

[TImGraves]

So, is there any place that lists the tolerances for the ODs of the truncated ends?

[Wayne]

In Reply to Parent Post by TImGraves

So, is there any place that lists the tolerances for the ODs of the truncated ends?

I do not know of an unofficial chart of this data. The official place to find the information is the published standard. I know not if you are dealing with UN-series, M-series, or some other thread type. The parameters may be different for each type.

Truncated set plug gages are specific to USA standards:
For the UN-series the data will be located in ANSI/ASME B1.2
For M-series the data will be located in ANSI/ASME B1.16
If it another style of thread the standard will be different.

Thread Gage Design software is also available which will give you all the required parameters needed to measure/calibrate most thread gages. This is a very valuable tool for any calibration laboratory that measures thread gages. The one I use is ThreadTech. Available on the web is a free 30-day trial offer. If you find that you do not like ThreadTech, I can suggest others.

I hope that you find this information helpful.