Tunalover
Mechanical
- Mar 28, 2002
- 1,179
Folks-
ASME Y14.5M-1994 states that by default a positional tolerance of a threaded hole applies to the pitch diameter. We've been able to find a gage that will center itself in a 6-32 UNC-2B hole by contacting both the minor and major diameter (The Multi-Ball gage by TPC) but nothing smaller.
My company is in the optics business and the extent of optical alignment depends on positional tolerances; the tighter the positional tolerance of an optic mounting hole pattern the smaller the amount of alignment work required.
But how can we accurately inspect pitch diameter positional tolerances of internal threads smaller than 6-32? We use many 4-40 UNC-2B, 2-56 UNC-2B, 1-64 UNC-2B, 0-80 UNF-2B, 1.00 UNM, and even 0.50 UNM threaded holes for optic mounting hole patterns.
Currently our fabricators are using the minor diameter to find the thread position but every dimensional metrologist and D&T practitioner I've talked to advises AGAINST this practice.
Does anyone out there have experience and knowledge to share on this subject?
Tunalover
ASME Y14.5M-1994 states that by default a positional tolerance of a threaded hole applies to the pitch diameter. We've been able to find a gage that will center itself in a 6-32 UNC-2B hole by contacting both the minor and major diameter (The Multi-Ball gage by TPC) but nothing smaller.
My company is in the optics business and the extent of optical alignment depends on positional tolerances; the tighter the positional tolerance of an optic mounting hole pattern the smaller the amount of alignment work required.
But how can we accurately inspect pitch diameter positional tolerances of internal threads smaller than 6-32? We use many 4-40 UNC-2B, 2-56 UNC-2B, 1-64 UNC-2B, 0-80 UNF-2B, 1.00 UNM, and even 0.50 UNM threaded holes for optic mounting hole patterns.
Currently our fabricators are using the minor diameter to find the thread position but every dimensional metrologist and D&T practitioner I've talked to advises AGAINST this practice.
Does anyone out there have experience and knowledge to share on this subject?
Tunalover