Measuring 10" Diam. Buttress Thread - Mil Specs

[QC Dude]

Hello all,

Anyone know a quick and accurate way to measure a a 10.375-8N BUTT-3 THD per MIL-S-7742. Print states: “Inspection of threads shall be by gaging method ‘A’ of MIL-S-8879 or MIL-S-7742, as applicable.” The minor diameter has a modification. I'll try to attach print.

I’ve read that spec and found “Methods A, B, and C have been eliminated.”, with no other methods mentioned other than a reference to FED-STD-H28/20. I then read the Federal Standard and it refers to "Gaging Systems 21, 22, 23". ...seems a bit vague to me.



SYSTEM 21 System 21 provides for interchangeable assembly with respect to functional size only. Functional size must be measured at the maximum material limit within the length of standard gaging elements. The characteristic known as NO GO functional diameter must also be verified. This can be accomplished by using fixed limit gaging or variable gaging with functional elements.

SYSTEM 21A (FOR METRIC THREADS IN ACCORDANCE WITH ANSI B1.18M) System 21A provides for interchangeable assembly with functional size verified at the maximum material limit using standard length gaging elements. This can be accomplished using fixed limit gaging or variable gaging with functional elements. System 21A also states that the minimum material limit (minimum pitch diameter) must be verified by inspecting two thread flank locations over the length of the thread. This can be accomplished by using variable gaging or thread roll snap gages with pitch diameter elements.

SYSTEM 22 System 22 provides for the interchangeable assembly with functional size verified at the maximum material limit using standard length gaging elements. This can be accomplished using fixed limit gaging or variable gaging with functional diameter elements. System 22 also states that the minimum material limit (minimum pitch diameter) must be verified over the full length of the thread. This can be accomplished using variable gaging with pitch diameter elements.

SYSTEM 23 System 23 provides for interchangeable assembly with functional size verified at the maximum material limit using standard length gaging elements and minimum material limit (minimum pitch diameter) must be verified over the full length of the thread. The gaging requirements for SYSTEM 22 would also apply here but in SYSTEM 23 other thread characteristics such as lead, flank angles, taper and roundness must have to be independently verified. Only thread characteristics, which are specified, will have to be inspected for SYSTEM 23 compliance.

**We don't have mechanical gages appropriate for the size. Should we use wires? Please advise.

Thank you!!

-Rich

 

[Gordon B. Clarke]

Rich, if you have access to CAD then I think the easiest, and cheapest, method would be to draw the thread up and find which diameter of wire you have or can easily get that protrudes above the thread OD and touches as close as possible to the pitch diameter. It's then easy to find the max min diameter over the 3 wires using CAD.

It looks like the PD tolerance is 0.0072" which should allow you to use a caliper for measurement if you don't have a micrometer that size.

The texts shown are to me more intimidating than helpful but if you stay away from the max min limits of the PD tolerance I don't see any problem.

Gordon

 

[QC Dude]

Thanks Gordon!

I asked our gaging supplier about this and he just offered to sell me a piece of equipment...which wouldn't have been able to accommodate this large thread anyhow. Damn salespeople.

Much appreciated.

 

[stiles]

That's an ID thread right? How can you use wires? When I cut a 1 tpi buttress thread I measure the minor diameter with an ID Mic. When I thread that bore I use a knife edge dial depth indicator to figure the major diameter.

Once the thread is cut your going to have to figure out a different way to measure the minor ID.

 

[Red James]

Your 'standard' states you may measure your thread by any 'acceptable method'. Sounds like a go - no go gage to me. Just document the measurement of the gages and you are good to go (pun sort of intended).

 

[Gordon B. Clarke]

That's an ID thread right? How can you use wires? When I cut a 1 tpi buttress thread I measure the minor diameter with an ID Mic. When I thread that bore I use a knife edge dial depth indicator to figure the major diameter.

Once the thread is cut your going to have to figure out a different way to measure the minor ID.

Certainly looks as if you are right and it is an internal thread

Instead of "wires" then 3 suitable steel balls with 2 of them placed on the bottom of the thread and the 3rd attached to the top (grease, glue?)

Making (and certainly buying) go no-go gauges in that diameter would be costly.

{spam deleted - TRL}

 

[stiles]

3 ball measurement. That sounds more painful than watching a 5 year old caught in a Chinese finger trap.

I remember how we measured the 4 tpi ACME thread PD. We had a gagemaker internal functional PD gage

 

[MH1]

You could cut a male plug and measure it over wires (or cut 2 a high and a low) then use that to check the internal thread. and as stated document what its (their) dimensions are and how you used it. (and probably stamp those dimensions on the plugs and hang on to em for at least a little while).

 

[Gordon B. Clarke]

3 ball measurement. That sounds more painful than watching a 5 year old caught in a Chinese finger trap.

I remember how we measured the 4 tpi ACME thread PD. We had a gagemaker internal functional PD gage

You'd be right if it was many items or a regular production. If the OP was making just one item then buying a Gagemaker product would be what I'd describe as "overkill". Care to tell others what they cost (and especially up in 10" diameter) and shock the hell outa them?

BTW thread ring gauges are calibrated using ball probes.