Drill size for titanium (1-72 screws)

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warshard

Joined
Aug 23, 2006
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I am currently tapping holes for 1-72 screws in .050 titanium--have stepped up from a # 53 drill bit to a #51drill bit--what is the upper limit of drill size I can use and still sucessfully tap the 1-72 thread--
Regards to all--
 
I wouldn't go any bigger than a #51 myself. What kind of tap are you using? I like thread forming taps for titanium. They seem to work much better and they can get a higher percentage of thread engagement without breaking.
 
Thanks for your reply, Jason--I am not familiar with the term "thread forming tap" I am using a spiral tap--can you share with me the difference between the two--
Regards
 
A thread forming tap doesn't have cutting flutes. It looks like a screw. The threads have little lobes that push the material into the threads. So instead of cutting the threads it's basically forging them in. They are kind of expensive but they don't break nearly as often as cutting taps. Conventional taps don't have the right geometry for cutting Titanium. That's why we have to drill the hole oversize for tapping titanium and only get 50-60% thread engagement. You can buy cutting taps made for titanium but they cost just as much as a thread forming tap and still don't work as good.

Disadvantages of forming taps are that there just isn't as much leeway in what size hole you drill as there is in a cutting tap so you have to actually use the exact right size drill. They also need a different lubricant. I use motor oil. In larger sizes they take a lot more torque to turn.

http://image.thefabricator.com/a/articles/photos/1057/fig1.jpg Here is a picture of a thread forming tap alongside a cutting tap
 
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