How to Grind taper tap into a plug/bottom tap

[martik777]

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?

 

[RJSakowski]

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

 

[woodchucker]

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.

 

[RJSakowski]

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.

 

[woodchucker]

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.

 

[RJSakowski]

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,

 

[woodchucker]

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.

 

[sdelivery]

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

 

[woodchucker]

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.