Removing taps from aluminum

[gr8life]

New to this board, first post. Just read the post about removing taps. I am building a small Ferris Wheel. The outside is a 12 sided polygon. Each piece has two 2-56 x 1/4 SHCS, a lot of drilling. When I made the posts to hold the seats I picked a # 49 bit out of my index by accident and did not realize what I had done until I completed the drilling operation. When I put the 2-56 tap in the hole I think I said holy smokes ( or perhaps something stronger). So being a bit lazy and not wanting to do the job over & not being able to increase the screw size I thought I would use some locktite to hold them in. When I tried the screw I found that it tapped the hole quite well. I tried the same method with some short #6 & #8 on scrap and they were ok. Don't think I would use this method as normal practice but like everyone else I hate breaking small taps. Hope this helps someone.

 

[jpowersny2]

If you decide to build a full-scale Farris wheel, I won't be buying tickets! ;D

 

[Davyboy]

Hello gr8life. My book from Morse Twist Drill & Machine Co. shows that #49 drill for 2-56 tap yields 50% thread. For aluminum the book recommends 70-75%. softer materials more %, and tuffer materials less %. At the bottom of the page it reads:

"Tap drill sizes shown are for holes as deep as the diameter of tap. A 53% thread will break the bolt, before it will strip-in most cases. For thin stock use 75 to 80% thread tap drill. For very thin stock use 100% thread tap drill."

Now the kicker:

"A 100% thread is only 5% stronger than a 75% thread, but it requires three times the power to tap."(emphasis is mine)

I sometimes use a slightly larger tap drill for ease and confidence when tapping. We're only building models, but if using live steam or compressed air, then ( as jpowersny2 says ) safety should be a concern...

Good topic, I would like to hear other opinions. Dave