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Distributor's Link Magazine Spring 2021 / Vol 44 No 2


148 THE DISTRIBUTOR’S LINK LARRY BOROWSKI MEASUREMENT OF NON-STANDARD FASTENERS from page 112 Generally speaking, a Non-standard drive will require special measuring tools or gages, that are either designed by the engineer that developed the drive, or designed by an independent gage manufacturer based on the engineering print of the product. There is no simple measuring solution to accommodate all Non-Standard drive types, as they are specific to the design. This is why it is important to make sure that the screw print completely defines the profile, tolerance, and depth of the recess so that the gage designer can do his job effectively. Measurement of Non-Standard Threads Non-Standard or special threads can be easy or very difficult to measure, it just depends on the equipment you have, and the thread profile. Special threads can be in the standard 60º thread form with a non-standard pitch diameter, which are probably the easiest threads to measure. If variable thread gaging such as a tri-roll gage is available, these specials can be measured directly based only on the diameter and pitch of a standard thread form. Tri-roll gasges are comparative type measuring devices, so the comparison is the known value of a standard set plug to the unknown value of the special thread size. The other option is to have special GO and NOGO thread rings made, but they are specific to the particular non-standard thread being measured, and cannot be used in other applications. Other thread forms can include asymmetrical threads similar to a Buttress thread with a 45º and 7º thread angle, or some other combination of thread angles that are not equal. These types of threads can either be measured using specially made GO and NOGO thread ring gages, or a lower cost alternative would be to use the 3 wire method. The only problem with the 3 wire method is doing the math involved to calculate the pitch diameter. It can be a long complicated formula if software is not available to aid in the calculation. Some of these thread forms can be measured on a variable thread gage, but it is advisable to check with the manufacturer to see if the geometry is achievable on the rolls or segments. Optical comparators can also be used in conjunction with transparent overlays to measure some special thread forms. Other non-standard threads that can be found are modifications to standard fasteners in the threaded area. These can be in the form of channels, missing threads, combinations of more than one thread next to the other, flats, notches, deformation for a locking feature, etc. Typically, the pitch diameter of the thread can no longer be accurately measured after the original thread is altered. There is either something in the way, the modification did not leave enough material, or the thread is completely missing. Sometimes a variable type gage can be used because it can be positioned on the thread as to not interfere with the modification, but that is not always the case. CONTINUED ON PAGE 149

THE DISTRIBUTOR’S LINK 149 LARRY BOROWSKI MEASUREMENT OF NON-STANDARD FASTENERS from page 148 Conclusion Measuring non-standard Fasteners can be challenging, but if the time is taken to understand the requirements though industry standards or engineering drawings, and the correct equipment for the job is chosen , it can be rewarding. Make sure to fully understand the customer’s requirements when dealing with non-standard fasteners, because it may require special tooling or gaging that can easily be overlooked. A modified standard fastener cannot be expected to meet all the same dimensional requirements as the original fastener did, either because material is missing, or the modification has made it impossible to re-measure. If an existing fastener is modified, make sure to do a full inspection before the modification, because it may be impossible to do afterward. LARRY BOROWSKI | GREENSLADE & COMPANY INC


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