Drill size for thread forming taps11/30/2023 ![]() ![]() But that two per cent reduction in thread percentage will reduce torque on the cutting tool and increase tap tool life. The slightly larger drill diameter still provides a 73 per cent of thread value, which is more than acceptable. Tap life is greatly reduced in an effort to theoretically increase thread strength.Īs an example, a 7/16-14 UNC cut thread is usually denoted as a letter “U” 9.3 mm (0.3680 in.) diameter drill on most older tap drill charts that equates to a 75 per cent value for percentage of thread, but a 9.4 mm (0.3701 in.) drill might be a better choice. According to some, 100 per cent thread specification is only five per cent stronger than a 75 per cent thread specification, but requires three times the torque to produce. It is important to realize thread strength is not directly proportional to per cent of thread. By increasing the pre-drilled hole diameter, the machinist can increase the life of the tap by reducing the amount of force required to form the thread. Many tool manufacturers suggest using a percentage of thread values between 60 and 70 per cent for most pre-drilling applications. Making the correct tap drill size choice will affect the machining operation. High speed drills typically cut larger actual hole sizes than carbide drills. Many tap drill holes are now being created with high performance carbide drills and these carbide drills generate more accurate holes than high speed steel drills. Another reason why some tap drill charts are outdated is that most drills for producing tapped holes were high speed steel or cobalt when the charts were created. The percentage of thread values that older tap drill charts provide is higher than needed in most cases. To reduce the risk of thread failure, the design engineer was often cautious and specified high percentages of thread height in tapped holes. Not intentionally of course, it is just that most machinists are using outdated charts designed back in the 1950’s when high speed drills were the norm. One of the most common mistakes a machinist makes when tapping a hole is using the wrong size drill. Of course application is relivent.Are you really getting the best results from your taps? Avoid common mistakes. So I don't think that min specs are good enough for ID formed threads. 002 undersize and cut tapped - they wouldn't'a never failed IMO. They stripped out as the formed peaks rolled over and played dead. I have seen rolled threads fail that were on low limit or just outta spec. On ID threads - leaving a big valley in the middle does not IMO give as good'a threads. ![]() I know that formed threads are known to be stronger - but that premise is on OD threads that are ran to or very near 100% all the time. IMO this is NOT anywhere's near the same as a solid thread with cut threads. well - even if you doo have the minor in spec - a formed minor anywhere's close to min spec will have two very distinct peaks with quite a valley between. ![]() (You may have to think aboot the process for a while to understand that.)ī) As per the QC comment. Reason being that you are pushing up into such a small area now - and you are pushing up from an ever bigger area. As you get closer and closer to 100% threads - each. ![]() 003 is prolly true at one particular point of the size ratio - but that is always gunna be a moving target ratio. I want to challange some of Pros comments tho:Ī) The. I don't ream my holes - but I don't generally run 6-32 either. 001 counts for a lot more on a form tap that a cut tap. I say ream as drill/ream as Pro said - to hold size best on the small pitch sizes - but also to use a decimal reamer for the RIGHT size on a really small pitch as each. ![]()
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |