# Drill and Tap



## jbwilcox (Jan 2, 2008)

I read about drilling and tapping for screws. What is that and how is it done? What type of equipment is needed? 

When i put on a coupler i usually just drill a hole and screw the screw in. It seems to work. 

Should i be doing something different? 

For modeling work is there certain sizes of drills and taps that would be best to have on hand? 

Thanks 

John


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## Semper Vaporo (Jan 2, 2008)

Posted By jbwilcox on 08/20/2008 10:29 AM
I read about drilling and tapping for screws. What is that and how is it done? What type of equipment is needed? 
When i put on a coupler i usually just drill a hole and screw the screw in. It seems to work. 
Should i be doing something different? 
For modeling work is there certain sizes of drills and taps that would be best to have on hand? 
Thanks 
John




Very much depends on what materials you are using. 

Plastic deforms easily so drilling a hole and forcing the screw in just deforms the plastic to create the internal threads in the plastic. The plastic pressing back on the screw just helps to retain the screw in the hole. 

A tap is used to cut and remove material to create the thread shape. Some screws have a slot or groove in the side of the threads that help CUT the threads ("self-tapping") instead of shoving and compressing the material around the hole. 

Some materials don't take to forcing the screw in as well as others. Plastics and woods do fairly well, but most need a hole to start the screw in... kind of depends on how strong the material is against splitting instead of compressing out of the way of the body of the screw. Metal usually doesn't deform well and the threads of the screw may give way and you end up with a smooth shaft in the hole instead of a threaded screw in a threaded hole. 

If you drill the hole in the plastic too large then there may not be enough material left to deform and make the threads. Drill it too small and you risk splitting the plastic. Drill it the right size and use a "Self tapping" screw is the easiest, but using a tap to cut the threads is "best" (arguable, based on personal preferences). 

Just like you need differnet drill sizes to match your screws, you need different taps to match them also. Different threads per inch, different thread types (not all threads are just a "sawtooth" shape), etc. There are many "standard" sizes, so you don't need a huge set of drills and taps, unless you are really into selecting the absolutely perfect match for the materials and purposes they are to be put to. Attaching a coupler to the bottom of a coal car, okay, drill a hole slightly smaller than the size of the "self tapping" screw and assemble them. Attaching a brass nipple to a brass steam chest that needs to handle 60lbs of Steam pressure and not leak nor work loose and you need to "CUT" the proper threads so it won't leak or fall apart.


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## Les (Feb 11, 2008)

Mr Vaparo has pretty well covered the main features. Be advised that there are charts that list the size of the screw (say, #4) the thread pitch (40) which is a commonplace 4-40 screw. Next to it is the 'Tap Drill' size column listed, (I can't remember the drill size) that's the size drill for leaving an optimum amount of material for the tap threads to cut away. Last is a column marked 'Body Drill'. That's the size you want if you want your #4 screw to slip right into the hole, as when you want a pivot. 

Now the good news is, one can buy a complete set of #4, #6 & #8 tap drills, taps, and body drills for a very reasonable sum. One can also get other sizes as needed, even smaller, down to 00. (Double Ought). (Again, I forget the actual sizes but they're close to eyeglass screw sized--at least the 00 is). One can get a tap wrench with the better sets, which is indespensible. I bet MicroMark would have what you need. You can also get metric sizes and threads. DO NOT MIX THEM UP IN YOUR WORKBOX. You won't like the results./DesktopModules/NTForums/themes/mls/emoticons/crying.gif 

Lastly, armed with the above sizes on your tap-drill chart (what they're called) you can then get matching dies for cutting threads on rods, and lo, everything will fit together! (So long as the numbers match). i.e. a 4-40 tap will cut a threaded hole that, after running a 4-40 die onto the proper diameter rod(also on the chart) you can screw them together. And so on. Of course, you'll need a die wrench, quite inexpensive, to set the dies in to use 'em. 

One final note: get some good thread-cutting fluid. I use Kroil. There are other brands out there, including pastes. Use some kind of lubricant. 

Also note that, if you drill a hole in a piece of plastic and force in a sheetmetal (self-tapping) screw, you might, after a greater or shorter time, find a stress crack in the plastic. 

Les W. (Ret'd tool & die maker)


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## Guest (Aug 20, 2008)

Where do we get the good or great drill and taps? 
Seen cheap ones and just don't trust makers toady, the set for all I know is made in China./DesktopModules/NTForums/themes/mls/emoticons/crazy.gif 
Toad


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## Les (Feb 11, 2008)

Posted By Ole Toad Frog on 08/20/2008 7:24 PM
Where do we get the good or great drill and taps? 
Seen cheap ones and just don't trust makers toady, the set for all I know is made in China./DesktopModules/NTForums/themes/mls/emoticons/crazy.gif" border=0> 
Toad




That's a good question. My idea would be to find a machine tooling supply house. I have a catalog if I can lay my hands on it, where I order my stuff through my son's workplace. That way I know I get 1st class, American-made tooling. But it's not cheap. 

A fair question to pose is, would you use an offshore tap/die enough to justify the difference in price? I happen to be picky about the quality of the threads being cut, so in my case, it's the expensive stuff. And with care, it'll last a good long while in home (non-production) use. Like maybe a lifetime. 

So just Google 'taps' 'dies' etc and find a major supply house. Not Micromark, they're infested with Chinese stuff. 

Les


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## John J (Dec 29, 2007)

Some taps will tell you what drill bit to use. Some times it's on the tap it's self or on the packaging. 

Once I know this I buy two of the proper drill bits to go with the tap. Then when I am done I take masking tape and tape the proper drills to the tap. That way they are alwasy together.


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