how to use taps

[mudd turtle]

I have 2 sets of tap and dies. I don't know a thing about how to use them. How do you know the right size hole to drill? Then what is the right size tap or die do you use? Are there books I can buy that will tell me everything I want to know about their use? Would some of you help enlighten me. mudd turtle.

 

[paulvallandigham]

Most any home supply, or hardware store has a plastic coated chart, pocket sized, that give you the right size tap to use for the size hole you want to drill, and vice versa. You probably can find this on line, if you google Tap and dies. Sometimes hardware store give the charts away because they put their own names on them.

 

[bioprof]

Here's a web site that has a chart that shows what size drill bit you need for different sized taps.
[url] http://bobmay.astronomy.net/misc/drillchart.htm[/url]

 

[bob243]

Here is a chart online.. Link

 

[Geraldo]

I found this for you. It covers the basics and has some decent pics.
[url] http://www.diynetwork.com/diy/tl_metalworking/article/0,2037,DIY_14390_2270183,00.html[/url]

Tha main points are to make sure you the tap is squared up with the hole when you start. Use oil, and back up the tap now and then to clean the tap. If tapping a blind hole, use the regular tap first, then use the bottom tap to finish. Don't force anything or you'll be testing out a broken tap extractor.

 

[Zonie]

Geraldo, thanks for the link. It is a good starting place but I think I might like a few bits of information to it.

Each thread size requires the correct size "tap drill" so that it doesn't remove too much material or too little. Use one of the thread charts to determine the correct drill.

While you can use just about any oil to lubricate the drill bit for drilling, there are special thread cutting oils available at the hard ware stores that should be used when tapping a hole or cutting threads on a rod with a die.
These oils usually have a high amount of sulfur in them which keeps the cut metal from sticking to the tap/die.
The oil is cheap and to use some other regular oil (which won't work well) is asking for a broken tap.

When your tap starts cutting you should pay attention to the amount of resistance you are getting. Any time this resistance starts to greatly increase, unscrew the tap at least 1/2 turn to break the chips in the hole off, then run it back in and proceed with cutting some more threads.

Assuming we are talking about making threads for a existing screw you will need to first measure the outside diameter of it.
There are standard sizes of these screws. The smaller ones are designated by numbers and the larger ones by fractions of an inch.
If your thread diameter measures .112 it is a #4, if .125 it is a #5, if .138 it is a # 6, if .164 it is a #8, if .190 it is a #10.
The fractional sizes are pretty much self explanatory.

Each of these thread sizes will have either a course thread or a fine thread. This is a measure of the number of threads per inch.
Assuming you have some taps, the easiest way to figure out which thread series (fine or course) you have, try to mate it up with the threads on the screw. The correct thread tap will match the threads on the screw exactly.

Hope this helps a bit.
zonie

 

[Geraldo]

Good points, Zonie, especially about the 'feel' of the tap.

In addition to using the right drill/tap, you really need to have the hole in the right place, generally on two axes and the hole must be drilled square to the part. If you're off on one axis or the other, or have the hole drilled at an angle, whatever you're doing won't line up correctly.

The only way to learn is to do it, but I would suggest starting with some scrap steel to get the feel of it. That way you're only out a few bucks if it all goes wrong.

 

[bob243]

That brings up something I learned unintentionally :redface: If your drilling through and are part way on the breech plug, watch out for drill bit deflection, it will cause you hole to become enlongated because the bit will want to push away from the breech plug. I started using "screw machine" drill bits which are about half the lenght of a normal jobber bit. This helped out quite a bit.

 

[ChrisPer]

Bob243, do you mean drilling a tang bolt on a breech, or drilling the barrel to thread for the breech plug? I just bought a 14.5mm stepped drill bit and tap set to thread a barrel for a plug the first time and don't want to screw it up!

 

[bob243]

No, drilling for your touch hole or drum on the side of the barrel, depending on how it lines up it is possible your location will be right on the end of the breech plug. If this is the case then when you get through the barrel and half or so of your drill bit is drilling across the front of the breechplug it is going to want to push away towards the front of the barrel. This will cause the bit to start making the round hole you just drilled oval. The shorter the bit you use the less it will bend.

I havent tried drilling and taping for a breech plug yet. I probably wont attempt that till I get a lathe.

As far as a tang bolt, usually your fine, but I like to start the hole using a center drill, it helps keep your bit from walking before it starts the hole.

 

[dlemaster]

bob243
I would recommend you pull that breechplug before you drill. Then you won't have to worry at all about an out of round hole. Then you can dish out and polish the cut out in the breechplug which will help slow down accumulation of fouling and rust in the cut out.
More than likely you going to have to remove the breechplug to tap the barrel anyway

Regards, Dave