![]() ![]() Plug taps have little or no lead-in and are used primarily for tapping blind holes. Both spiral and plug-type cutting taps were used, in addition to a thread-forming tap. We precision bored 5/8-in.-18 UNF tap holes into the ID of the tube stock to create 1.75-in.-long specimens. The basic material properties were 91-ksi yield strength, 99.7-ksi tensile strength, and 27% elongation before break. ![]() AK steels have finer grains and see less work hardening during plastic deformation. The “AK” stands for “aluminum killed,” meaning aluminum helped remove oxygen that causes bubbling in the molten steel while ingots formed. The tubes were ASTM A513/SAE 1026AK steel - mild plain carbon steel with 0.26% carbon and a maximum of 1% manganese. We fabricated specimens from tube stock with 1-in. To test this theory, we bored and tapped holes in tube stock, varying thread-forming techniques and diameters, then tested them. This includes light alloys and steels with tensile strengths up to 174 ksi and hardnesses below 35 to 40 on the Rockwell C scale. The prevailing wisdom says formed threads are the way to go for strength if the material is soft enough for cold forming. in diameter may be more susceptible to incorrect dimensions because they are fabricated by boring or turning, not with standardized drill bits. The process is generally taken for granted since drill and tap geometries are standardized and repeatable. Whether threads are cut or formed, fabricating them takes two steps: drilling or boring a tap hole and cutting or forming the threads. But internal threads are a different story, especially when internal-thread material is weaker than the bulk material or thread dimensions are incorrect. In fact, the first three threads have been shown to take up 81% of the axial force. It’s well known that the external threads of properly fabricated bolts are stronger than the bolt itself. ![]() Recent tests show there are some nuances to the strength of internal threads. Once the hole diameter and thread type are set, there’s little need to consider the strip-out strength of the internal threads, right? Wrong. Specifying internal screw threads isn’t the most thrilling task for engineers. ![]() Simulia, University of Tulsa, “The nuts and bolts of specifying fastener torque,” Machine Design, July 9, 1998, /MDFastenerTorque Incompletely formed threads in oversized tap holes can appear good to go/no-go gauges.Cut threads are much more tolerant of oversized holes than cold-formed threads.Cold-formed threads are no stronger than cut threads when holes are correctly sized.Tapping difficult jobs needs to be planned with the proper taps, cutting compound and correct speeds. We very rarely broke a tap and discarded old taps. When I ran my own business I spent from £10 - £100 for specialist taps on each job and always came out a winner by using a tapping head. Ask your tap manufacturer for the correct speeds and cutting compound for the material you are working on. If you have volume work to do then source a tap with clearances and back rake for the material you are using.ħ. If the material is similar to nylon it will bind if the workpiece heats up, use plenty of coolant and tap by hand or tapping head.Ħ. Unless you are an absolute expert use a tapping head with a set clutch for tapping, if you are an expert then use the CNCĥ. Arrange with your customer the maximum core diameter, you should be able to remove 25% above the minimum core diameter to ease tapping operationsĤ. In the UK a grade of tap know as 1066 was the best tap for difficult materials, it was a specially coated tapģ. Find a supplier who can supply you specially made taps for all application don't just but from standard suppliers, go out of your way to find a dealer who has a direct contact with a manufacturer.Ģ. There are a number of considerations when tapping depending on the amount of work you have to do.ġ. I am in the Uk and always used the best taps available and discarded old taps, old taps can cost you a fortune when/if breaking on an expensive workpiece. depending on how many holes you have to tap you should source the right tap for the material. I've never used this material, it seems like a plastic. ![]()
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