# Buttoning Vs Plug tap



## Prinsen (Feb 1, 2020)

Hi all,

Recently, I've wanted to invest in some better taps and with that of course comes the first triple start. 

I want to get an M13x0.8 as I'll probably use that size most. Now turner's workshop offers a bottoming tap and Beaufort ink offers a plug tap as a set, with a separate bottoming tap as well 

I usually use both of these, as the bottoming gives you the best result of course, is this necessary though? I have a holder for in my lathe so I can definitely keep it centre. Would only having a bottoming tap be bad and would you recommend getting just the set from turner's workshop, or the plug set from Beaufort and that bottoming later. 

Thanks in advance,

Teun


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## monophoto (Feb 1, 2020)

The basic idea is that tapering the end the tap makes it easier to start the tap into the hole - the  initial thread are more shallow, and therefore easier to cut, and the taper centers the tap in the hole.  But as the tap proceeds into the hole and the full diameter of the tap can clean out those initial shallow threads.  

So taps are generally available in three degrees of taper - 'bottoming' taps have only one or 1.5 threads that are less than the full diameter, 'plug' taps have 3-6 , and 'taper' taps have the longest taper angle with even more reduced diameter threads.

When tapping a 'blind hole' (one that does not extend all the way through the workpiece) with a tap having significant taper means that the threads deepest into the hole will be less than full diameter, and that can cause the male portion of the piece to bind in the threads.   In that case, following up the initial threading with a tap with less taper can clean up the threads at the bottom of the hole.

On the other hand, if you have a hole that goes all the way through the workpiece, you can run the tap all the way through, and either a plug or taper tap is sufficient.  The same is true if you can drill and tap the hole deep enough that having shallow threads at the bottom of the hole doesn't matter. 

So the perfect situation is to have both a plug (or taper) tap and a bottoming tap, but depending on the application, you may be able to get by with only a plug (or taper)  tap.  But I don't see any reason to have both a plug and a taper tap.


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## More4dan (Feb 1, 2020)

The bottoming tap can come in handy if you plan to thread transparent material for your cap and body and want to limit the depth of the threaded part that shows. The bottoming tap will give you a full thread to end of the threads. If threading non transparent material or if longer threads are okay, just use a plug and thread deeper. I like the fact that the threads tighten up a bit near closing from using a plug tap. Keeps the cap from coming loose. 

Danny 


Sent from my iPhone using Penturners.org mobile app


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## Prinsen (Feb 1, 2020)

monophoto said:


> The basic idea is that tapering the end the tap makes it easier to start the tap into the hole - the  initial thread are more shallow, and therefore easier to cut, and the taper centers the tap in the hole.  But as the tap proceeds into the hole and the full diameter of the tap can clean out those initial shallow threads.
> 
> So taps are generally available in three degrees of taper - 'bottoming' taps have only one or 1.5 threads that are less than the full diameter, 'plug' taps have 3-6 , and 'taper' taps have the longest taper angle with even more reduced diameter threads.
> 
> ...



Thank you for the very extensive explanation! Most of it is according to how I've understood and used my taps. 

If I then understand correctly, just a bottoming tap is a no go. So it's better to get a plug tap now and a bottoming if I need it in let's say transparent material.


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## magpens (Feb 1, 2020)

You can get by with just a bottoming tap, but it is a bit risky.

Risky from 2 points of view: first, you can cause the material to crack by forcing the bottom tap into it too aggressively; second, at the start of tapping there is a risk of thread misalignment. . You seem confident that you can avoid the second problem since you say that you can keep things centered on your lathe. . Taper and plug taps are designed to help you avoid thread misalignment, but you still have to be very careful.

You also say that you usually use both a plug tap and a bottom tap - that is very good technique. . I would say that it is never recommended to start the threading with a bottom tap. . But with appropriate technique, it can be done - depending on how brittle the material is.

Many people tend to bypass the taper tap, and start with the plug tap, followed by the bottom tap when that is appropriate (blind hole).


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