The Go and No Go Thread ring gage is the simplest and most economical method of inspecting external screw threads.
Thread ring gages are very easy to use.
The user must first select the correct size thread gage for the corresponding externally threaded product.
Thread ring gage sizes should be clearly labeled on the face of the gage. Green sealing wax is used to seal the adjustment screws for the go member and red wax for the no go member
The user of the thread ring gages should ensure that the correct major diameter, TPI/pitch, Class of fit, and pitch diameters are clearly specified.
It is important to confirm that pitch diameters on the gages match the part specification.
In certain cases the gages may be marked with a P/P or B/P to indicate preplate or before plate sizes.
A part gaged prior to plating will have special pitch diameters. The thread ring gages selected should be engineered and made correctly to the preplate or before plate pitch diameters.
An “S” after the Unified designation indicates that the thread size is special. A “J” in the Unified designation means that the external thread being inspected has a modified root radius.
The user should also confirm that the gages conform to the proper national or international standard.
In the USA adjustable style thread ring gages are supplied as the standard. In other countries the solid style thread ring gage is considered. The advantages and disadvantages of both is explained in our technical section at threadcheck.com
Finally the inspector should confirm the gages are calibrated. It is always advisable to recheck the thread ring gages with a matching setplug gage prior to use regardless of the calibration sticker’s current status.
Many companies arbitrarily select annual frequencies of calibration rather than basing calibration frequency on usage. This can be dangerous as thread ring gauges can be worn out of tolerance or accidentally dropped and knocked out of size.
The best thread gaging practice utilizes several sets of thread ring gages. One or two gages can be used for in process inspection while another gage can be used for final inspection and a master thread ring gage retained for dispute in the event that gages fail to correlate on acceptance or rejection. Its ideal if all the gages can be set to the same setplug.
A clean thread prior to gaging will provide the inspector with more sensitivity of thread fit. Thread ring gages should be cleaned with solvent or air and then frequently recoated with a rust preventative/gage preservative. In clean room environments Isopropyl alcohol may be substituted to help reduce friction on the gages. Ring gages should be turned onto the parts with care. They should never be hand spun onto the part.
Thread ring gauges should be protected in plastic cases or coated in wax when not in use to prevent nicks to the threads. All gauging whenever possible should be done over an inspection table in the event that the gage is accidentally dropped. If a gage is dropped it should be immediately re-inspected with a setplug gage.
The go thread ring gage should engage the external threaded part with very little force used. The engagement should be smooth. There is no specification regarding torque or pounds of pressure for using thread gages. Common sense should be applied based on factors of thread size, pitch, and application. If the gage starts to bind, the inspector should stop before damaging the part or the gage. The part may be oversized or tapered. Other possibilities include lead error or a damaged thread. With fine threads the inspector should be careful to not cross thread the parts.
It is important to use the no go gage as it checks pitch diameter exclusively. It is unaffected by other conditions in the screw thread as it is intentionally truncated on the crests and with greater clearance applied on the roots of the thread. The no go thread ring should not enter the part more than 3 turns although in practice it is advisable to limit the amount of turns to 1 ½ - 2 turns max. The user just simply counts turns.
The end user should review the applicable thread specification in detail as there are variations to the above practice. /no-go-gaging-per-ansi-asme-b1.2-1983-an-american-national-standard/technicalinfo/.
9 авг 2017
