Do you mean the minor diameter? Is this for a male thread, or a female one?
Check your Machinery's Handbook. 1.115[ ]inches is not a standard thread diameter, but the thread tables will show you the depths needed to calculate what you want.
This is a 1.115-32-2b non-standard thread. We (QC)do not have a thread gage for this and we are inspecting a 1st article from a new source of supply. We are checking this part against the mating part (which is known to be good)and it doesn't go. Using the formula;
1 / 32 = .031 x .75 = .023
1.115 - .023 = 1.092 ID
Actul ID is 1.083 so it does not seem to be a minor dia. problem if we got the formular right.
I cannot see your formula anywhere in my Machinery's Handbook. I did not search that carefully.
The minor diameter is not the only thing that might make a thread not mate. My understanding is that thread gauges test for pitch diameter.
Can you supply a known-good mating part to your fabricator?
External threads can be checked with an optical comparator, if you can find one. This allows you to check your part thoroughly, or to check your mating gauge thoroughly. You have not told us if your thread is male or female. A male thread can also be checked over pins.
Internal Thread Minor Diameter 1.081"/1.089"
Internal Thread Pitch Diameter 1.0947"/1.0996"
These are based on a 1-32UN 2B plus .115.
I would check your externally threaded shaft with measurement over wires/pins. I would also check your threaded shaft for thread form using an optical comparator. Make sure this is a 60 degree thread versus say a 55 degree Whitworth thread. Measure the pitch of the thread making sure it is .03125". I would be hesitant to say this thread is a 1.115-32UN thread until it is verified. I would also verify that this is a single start thread.
Oddball threads like this are usually there for a reason so I would expect the unexpected.
This assumes a saw tooth profile of the threads.
Peek to peek of H
where H = 0.5*3^(0.5)*p p= 1/32
Top is cut off at H/8
Depth is cut off at H/4
New max to min is 5H/8
threads are cut at 60 degrees
Pitch diameter is calculated from
Dp = 1.115-.649/25.4 (This equation is from ANSI B1 and is converted by the 25.4 from metric to inches.)
= 1.08945
And the minor diameter is (for external threads)
Dm = Dp - H/4 (instead of subtracting H/4 add 3H/8 for internal threads)
= Dp-0.5*3^(0.2)*p/4
= 1.08945-0.006766
= 1.08267 (which matches your measurements)
Also, you will need to look closely at the part to determine if there is a radius at the bottom of the threads. The above equations are for 60 degrees corners and some machinists will do a radius instead. Also from my experience the minor on custom female threads will not be to spec as they may used a standard drill to cut a non-standard hole.
As others noted, there are several things that might be out of tolerance with your internal thread, including pitch diameter, pitch diameter runout, accumulation of pitch-to-pitch spacing errors, etc. Class 2 fits are normally rather loose. If you are confident that the externally threaded part you are using to check the internal thread is accurate, then I would speculate that the problem is most likely the pitch diameter of the internal thread is out of tolerance.
Internal: 1.1150-32 UNS-2B
PD Max: 1.0997
PD Min: 1.0947
Maj Dia Max: N/A
Maj Dia Min: 1.1150
Min Dia Max: 1.089
Min Dia Min: 1.081
Root Rad Max: N/A
Root Rad Min: N/A
Thd Height (Ref.): 0.0169
Root Width: 0.0039
Thd Pitch: 0.0313
Wire Size: N/A
Max Wire Size: N/A
Min Wire Size: 0.00000
Helix: 0.00.00
Helix Comp: N/A
The stuff dentists use to take a mold of your teeth for crowns etc, can be used to take a mold of a portion of the thread on a female thread item and then inspected on shadowgraph or similar.
This is an ID thread. We have just used Flexbar casting compound and it looks like the corners are flat as Dougt alluded to. I just looked at it with a loop but will have to throw it up on the comparator to check the pitch
Thanks guys
