# How to Grind taper tap into a plug/bottom tap



## martik777 (Feb 21, 2022)

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?


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## Illinoyance (Feb 21, 2022)

That would probably work.  If your time is worth anything you would be better off buying a bottoming tap.


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## Winegrower (Feb 21, 2022)

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.


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## woodchucker (Feb 21, 2022)

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.


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## Winegrower (Feb 21, 2022)

"To do good is noble...to tell others how to do good is even nobler, and much less trouble" - Mark Twain.


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## woodchucker (Feb 21, 2022)

Come on, really not hard.


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## WobblyHand (Feb 21, 2022)

woodchucker said:


> Come on, really not hard.
> View attachment 397508
> View attachment 397509


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.


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## RJSakowski (Feb 21, 2022)

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.


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## woodchucker (Feb 21, 2022)

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.


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.


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## martik777 (Feb 21, 2022)

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.


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


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## RJSakowski (Feb 21, 2022)

martik777 said:


> 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


I also grind a relief.  (middle of second paragraph in my previous post)


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## woodchucker (Feb 21, 2022)

Winegrower said:


> 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.


BTW, a bottoming tap is not meant to start a thread, it's only meant to get you to the bottom of a threaded hole.


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## benmychree (Feb 21, 2022)

Winegrower said:


> 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.


It is called a plug tap. I have a relief fixture for sharpening or modifying taps.


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## woodchucker (Feb 21, 2022)

benmychree said:


> It is called a plug tap. I have a relief fixture for sharpening or modifying taps.


care to share details?


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## benmychree (Feb 21, 2022)

The attachment is based on the main parts of the Weldon end mill sharpening attachment, with a spring loaded rocking quill that is rocked by a series of cams for different numbers of flutes and various rises for different sizes of taps, it is on a swivel base for different degrees of chamfer, and is hand cranked. The cams can be used for right or left hand taps by simply reversing them on the spindle.


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## woodchucker (Feb 21, 2022)

benmychree said:


> The attachment is based on the main parts of the Weldon end mill sharpening attachment, with a spring loaded rocking quill that is rocked by a series of cams for different numbers of flutes and various rises for different sizes of taps, it is on a swivel base for different degrees of chamfer, and is hand cranked. The cams can be used for right or left hand taps by simply reversing them on the spindle.


I guess I'm out.


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## Illinoyance (Feb 21, 2022)

I acquired a Polychoke tap sharpening jig.  I haven't tried it yet.


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## martik777 (Feb 22, 2022)

What is the purpose of that sharp point on the end of a die. It just reduces how far I can tap in a blind hole


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## woodchucker (Feb 22, 2022)

martik777 said:


> What is the purpose of that sharp point on the end of a die. It just reduces how far I can tap in a blind hole


A die doesn't have a point, A taper tap does.
The point is questionable except on really small dies, the purpose of the taper is to align , and start small cuts. Both taper, gun taps, and plug taps have a taper. It's just a difference in the amount of taper and the amount of threads that are useful.

I can't answer how far you can tap in a blind hole, it varies.  I would say you want to stop as soon as you feel the bottom if hand tapping, if power taping, you should know your depth and back out before it.  You don't want to break the tap. put a sharpie mark on the tap  marking the holes depth and a little less if power tapping. or set your quill stop.


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## martik777 (Feb 23, 2022)

woodchucker said:


> A die doesn't have a point, A taper tap does.
> The point is questionable except on really small dies, the purpose of the taper is to align , and start small cuts. Both taper, gun taps, and plug taps have a taper. It's just a difference in the amount of taper and the amount of threads that are useful.
> 
> I can't answer how far you can tap in a blind hole, it varies.  I would say you want to stop as soon as you feel the bottom if hand tapping, if power taping, you should know your depth and back out before it.  You don't want to break the tap. put a sharpie mark on the tap  marking the holes depth and a little less if power tapping. or set your quill stop.


I use a collet chuck in my tailstock to tap and when it slips I know it's gone as far as it will go.


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## martik777 (Feb 23, 2022)

RJSakowski said:


> I also grind a relief.  (middle of second paragraph in my previous post)


A relief on each flute? Can you describe or post a photo?


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## RJSakowski (Feb 23, 2022)

martik777 said:


> A relief on each flute? Can you describe or post a photo?


I first grind the end of the tap flat to the first full thread, then I grind the end of each flute to provide clearance. similar to what would be done on an end mill. It would be the 1st peripheral relief angle in the drawing below.



 I had a situation where I was making 10-32 threaded ports which had to hydraulically seal with fittings which had a full thread, hence the necessity to thread to the bottom of the hole


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## woodchucker (Feb 23, 2022)

RJSakowski said:


> I first grind the end of the tap flat to the first full thread, then I grind the end of each flute to provide clearance. similar to what would be done on an end mill. It would be the 1st peripheral relief angle in the drawing below.
> View attachment 397716
> 
> 
> I had a situation where I was making 10-32 threaded ports which had to hydraulically seal with fittings which had a full thread, hence the necessity to thread to the bottom of the hole


So, I have never done this when creating  a bottoming tap from another tap.  Wouldn't the relief already be in the existing tap already???
I am only looking to cut the bottom of the hole, and I have not had a problem with my ground taps. I learned this from a machinist who gave me his box of tools. He had done this to many taps. I have continued to do the same.


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## RJSakowski (Feb 23, 2022)

woodchucker said:


> So, I have never done this when creating  a bottoming tap from another tap.  Wouldn't the relief already be in the existing tap already???
> I am only looking to cut the bottom of the hole, and I have not had a problem with my ground taps. I learned this from a machinist who gave me his box of tools. He had done this to many taps. I have continued to do the same.


Grinding the initial flat will remove any relief from the tooth.  Maybe not necessary if grinding with a precision setup but I just grind by hand so there is a distinct possibility that one of the flutes has negative relief.The secondary grinding ensures that it again has relief.


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## woodchucker (Feb 23, 2022)

RJSakowski said:


> Grinding the initial flat will remove any relief from the tooth.  Maybe not necessary if grinding with a precision setup but I just grind by hand so there is a distinct possibility that one of the flutes has negative relief.The secondary grinding ensures that it again has relief.


well, again, I have been using my hand ground just pull the point off and remove leaving as many threads, and they have been working fine. Maybe not perfect, in a machinists eye, but they are doing what I need, which is to put threads to the bottom of the hole.

I wonder how much different having the relief vs not would show up in the thread. Maybe it's time to do a test and cut one open for each.


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## RJSakowski (Feb 23, 2022)

woodchucker said:


> well, again, I have been using my hand ground just pull the point off and remove leaving as many threads, and they have been working fine. Maybe not perfect, in a machinists eye, but they are doing what I need, which is to put threads to the bottom of the hole.
> 
> I wonder how much different having the relief vs not would show up in the thread. Maybe it's time to do a test and cut one open for each.


I have just ground the point off as well which will generate some extra depth.  That still leaves unfinished threads though.  In the case I quoted above, I need to have a plastic fitting positively seat on the bottom of the hole which necessitated a fully cut thread close to the very bottom.  There was a thin gasket so probably one thread away from the bottom.  Ideally, these would have been done with a thread mill but I didn't have that capability at the time.

But the bottom line is do whatever meets your needs.  In most cases, I try to design with additional drilled depth to accommodate the intended fastener.  Sometimes though, material thickness imposes constraints,


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## woodchucker (Feb 23, 2022)

I hate to beat a dead horse, but I usually do. I just pulled out a bunch of taps that I have ground. I also have a couple of sets of taper, plug, bottom taps.  I thought I would show you... they looked better on my camera, I may need to re-take them again. but since I wanted to get these out...
and I am upstairs now... I'll post them, and repost again if I don't like them.

These 2 are the same tap, an old GTD, I ground it the other day for my 10-24 on my quill stop.
Just a plain flat grind. Notice that the tap has relief all the way through the tap. It's not really apparent from the side, but it is from the top.



These are Vermont taps wood bottom box (OLD) they are *ground *taps. Notice no apparent back relief.
I'll post an end view later of the bottoming tap..
in order bottoming, plug, taper.



2 Flute, notice the back relief in the tap itself. Plain flat grind on the tip.

So Why do I need to grind a back relief???? It appears that the taps already have them built in. At least the quality ones.


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## sdelivery (Feb 23, 2022)

Yes. Watch for color change. LOL
Back handedly I am trying to say KEEP IT COOL do not generate to much heat and stick it in cold water.
Cool along the way


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## woodchucker (Feb 23, 2022)

Here's that Vermont Tap on end.  (Commercial Ground Hand Taps)  No 3105 GH3  9/16-12 just for info.
This is the bottoming tap.
The relief appears to be all through.


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