How to Grind taper tap into a plug/bottom tap

M

martik777

Active User
Registered
Joined
Apr 19, 2011
Messages
1,144
I need to thread closer to the bottom of a blind hole so I'm thinking I could simply grind down my spare 5/16 tap. Anything I should watch out for?
 
That would probably work. If your time is worth anything you would be better off buying a bottoming tap.
 
I have done this...they have been a bit hard to start, so I start with a taper tap first. After doing this for awhile, I agree with Illinoyance and bought tap sets with three taps of each size, bottoming, taper, and whatever the third is called.
 
I don't know what's tough about it. I have done this numerous times. Just take the tip off, grind until you have about 2 threads of the taper left. You are good to go.

Not sure why Illinoyance and wingrower think it's a losing prop. it takes a minute , literally .. What's time consuming about it.
 
"To do good is noble...to tell others how to do good is even nobler, and much less trouble" - Mark Twain.
 
A taper tap has between 5 and 7 partially formed threads, as opposed to 1 to 3 for a bottoming tap. You can cheat a little and grind the tip of a taper tap but you won't achieve the same result. You will have better chance with a plug tap which has 3-5 partially formed threads.

I have ground down taps to get closer to the bottom of a hole but usually stop at the point where the threads start cutting. I have cut a short chamfer on broken taps to finish a threaded hole after threading with a good tap. I grind the ends of a tap flat to the first full thread and grind relief as I would on an end mill. I drilled a 1/2" deep hole in aluminum and threaded with a 1/4-taper tap. A bolt would seat to a depth of .3". Switching to a bottoming tap, I could seat to just over .4". Then I used my modified tap and could seat to a full .5".

I have also ground a cutting edge and relief into a bolt to extend the thread to the bottom of a threaded hole but that was in plastic.
 
WobblyHand said:
I wouldn't want to do a lot of them, or really big ones, but, yeah, what @woodchucker said. Field expedient... Need a bottoming tap and don't have one, grind off the tip. Done.
Click to expand...
Yes, thank you.

Also great for recycling old taps. The first thing to go on a tap is the entry. So many times there's plenty of life left if you just make it a bottoming tap. You are only trying to get to the bottom of a hole. Most of the threads are formed already.
 
RJSakowski said:
A taper tap has between 5 and 7 partially formed threads, as opposed to 1 to 3 for a bottoming tap. You can cheat a little and grind the tip of a taper tap but you won't achieve the same result. You will have better chance with a plug tap which has 3-5 partially formed threads.

I have ground down taps to get closer to the bottom of a hole but usually stop at the point where the threads start cutting. I have cut a short chamfer on broken taps to finish a threaded hole after threading with a good tap. I grind the ends of a tap flat to the first full thread and grind relief as I would on an end mill. I drilled a 1/2" deep hole in aluminum and threaded with a 1/4-taper tap. A bolt would seat to a depth of .3". Switching to a bottoming tap, I could seat to just over .4". Then I used my modified tap and could seat to a full .5".

I have also ground a cutting edge and relief into a bolt to extend the thread to the bottom of a threaded hole but that was in plastic.
Click to expand...
I found just grinding the taper tap flat to the 1st good thread results in a hard to turn "bottom" tap. The relief grind makes it easier to turn
 
You must log in or register to reply here.
Back
Top