UN thread checking
UN thread checking
(OP)
I am thinking about having out machinist make a 1 1/4-8 class 1A and 1B thread... I would have to order custom go, no go gages though... I am trying to figure out if these gages are really necessary to check threads... they are much easier, but can you do the same thing with a micrometer and pitch micrometer? Thanks





RE: UN thread checking
RE: UN thread checking
Software For Metalworking
http://closetolerancesoftware.com
RE: UN thread checking
You can also find literature on the subject from technology books in machining courses from a trade school. Other sources would be with online websites.
Typically I use the micrometer to size the nominal diameter of the thread and use the pitch gauge to obtain either the TPI for imperial or modulus for metric. You can then begin the analysis by consulting standard geometry for threading sizes. I would use the three wire measure to confirm the pitch diameter thus positively identifying the thread.
In the case of a bastard thread, you can interpolate between a set of known threads of the same TPI (imperial) or modulus (metric). I prefer the old fashion hand computation, there are several decent thread calculators out on the market. I use one that I custom made several decades ago, so I have the confidence with the numbers it kicks out. In general this is the better method, but you can look at the Thread Standards for UN Threads in the ASME Catalog. This gives you the exact equations for computations to the various threads, you can then program those into your preferred platform.
Good luck with it.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: UN thread checking
RE: UN thread checking
Software For Metalworking
http://closetolerancesoftware.com
RE: UN thread checking
Unless you have some very tight cost constraints, a proper set of master GO/NO-GO thread gages is a very worthwhile expenditure. The full set would probably cost you about $2000.
These master thread gages are especially valuable if each of the mating threaded parts are being made by different manufacturers. The master gages can be used by both manufacturers and will ensure compatibility and proper fit.
Having master gages is also important if replacement parts will ever be required in the future. Making replacement parts to the master gages will ensure compatibility with mating parts in service.
While it's not a consideration for most people, I personally love the look of a precision ground, polished, and oiled set of thread or spline GO/NO-GO gages in a hardwood storage box. It just projects the classic old-world image of precision and craftsmanship.
And finally, checking screw thread and spline fits using a GO/NO-GO gage is much faster and reliable than using gage pins/balls and micrometers. So don't be cheap!
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