Hard Starting Taps - What gives?

Great posts and advice for this common problem. I have heard about gun taps, but after all the raves I will try them as well! One thing I learned about spiral/plug/bottom taps is to buy good quality ones. Most if not all the hardware store stuff is cheap quality. If you can buy from a fastener specialty store or machinists supply you will get better quality steel and "ground" taps (better), not "cut" taps (cheaper). I did this and it has made a world of difference. A little more in price makes the job easier and is a bit more insurance against a broken tap. Also having the drilled hole, especially in steel, a bit more on the generous side than the tight side will help. LMS has a good chart for tapping clearances, etc.

I see a reply from Frank Ford. If folks haven't been to his HomeShopTech site you have to go. It is fun, informative and fabulous. Thanks Frank.

rd2012
 
I use a battery powered drill to tap.
It makes alignment easier, and the tapping is done in a few seconds.

I use Hitachi green lion drills with real jacobs chucks- they have little runout and more than enough torque.
I have drilled 12 mm holes in structural steel with these.
The drills (I use 2) are very expensive, but extremely good.
They paid for themselves in 8 days, 7 years ago.
I just put new jacobs chucks on them, after lots of use.

Down to 4 mm in size.
I dont snap taps due to the drill.

I also like spiral flute taps, but machine taps also work well.
I use chinese good quality taps - industrial.
I import china stuff direct from hong kong and china.
 
Pmedic828 said:
I am attempting to tap some small holes in medium steel. I am using a HSS hand tap turning the tap with a tap wrench. The problem seems to be too small a hole when I look at the charts for drill size vs tap size for specific size. I think that the last hole I attempted was a 1/2 - 13. I drilled the 27 / 64 inch hole in the steel plate and attempted to start the tap. I was using a plug tap. I started the tap and after 1 revolution, it wouldn't turn any more. I used tap magic on the tap and in the hole. After seizing the tap, I carefully backed it out and changed to a taper tap of the same size. This also would not turn after 2-3 revs. I bored out the hole to a larger size and after increasing the size of the hole I was finally able to turn the tap and cut threads. The two mating surfaces seemed to mesh well and were tight. The taps were also new and purchased from a quality machine shop supplier. These were not Chinese taps.
One other question - What does H1, H2, H3 on the taps and how do they differ? I think that it is the tightness of the threads or something like that. Can someone explain what is meant by the different grades to a novice. Thanks.
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Okay I had to look up your question about plug taps. I always called them a bottom tap for blind holes. You need to use a regular tap first then finish with your plug tap. Make sure your tap is started staight with the hole. I have used a drill press or a drill block to start my taps. I am not sure about the "H"s. I know there are usually three fits for threads. Usually one would find them on "Go" "No Go" thread gages. One end of the gage the thread is real tight and the other end is loose or on size. Good luck
 
So there are no one else using spiral flute taps, except for hanermo2, you guys don't know what you are missing......I overlooked them for many years due to the cost, but after I used them I haven't touched my regular taps...............
 
metalmole said:
So there are no one else using spiral flute taps, except for hanermo2, you guys don't know what you are missing......I overlooked them for many years due to the cost, but after I used them I haven't touched my regular taps...............
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I use both spiral point (gun) and spiral flute taps at work & at home. One must be careful with spiral flute taps as they aren't as strong as a straight flute tap plus they can start a "new" thread in the hole if you do not start them correctly in a hole that already has threads.

Correct tapping fluid/oil selection is a must too.
 
I love gun taps. Do not confuse spiral flute taps with spiral point or gun taps. Spiral flute are generaly used for blind holes to remove chips as you tap. I would not use one unless you had a special reason to use it as they break very easy and are expensive. Gun taps cost double or triple a hardware store tap but are worth every dime.
ALSO, if you are tapping "Medium" steel, (is that medium carbon steel) For harder materials it is often customary to drill oversized tap drill holes. It is easier on the tool and opperator and the strength of the thread is stronger than the fastener anyway.
 
"I don't always break taps, but when I do I break spiral taps"

They break easily when coming out.
 
The following comes from Wikopedia regarding H limits which simply mean loose fitting or tight fitfing threads. It's sort of a floating scale because a large inside threaded hole requires a large H number (like 9) for a tight fitting thread. As you can see tightness or looseness of mating parts has little to do with the difficulty of the tapping operation only the finished fit.

"The way in which male and female fit together, including play and friction, is classified (categorized) in thread standards. Achieving a certain class of fit requires the ability to work within tolerance ranges for dimension (size) and surface finish. Defining and achieving classes of fit are important for interchangeability. Classes include 1, 2, 3 (loose to tight); A (external) and B (internal); and various systems such as H and D limits."

Tapping difficulties occur when the wrong tap is selected for the material used and improper lubrication along with incorrect chip breaking. Taps can stop dead or break when chips fall into the threads. Spiral taps and shooting {gun) taps work best in softer materials and will seldom stop or break.
 
Jeff in Pa said:
I use both spiral point (gun) and spiral flute taps at work & at home. One must be careful with spiral flute taps as they aren't as strong as a straight flute tap plus they can start a "new" thread in the hole if you do not start them correctly in a hole that already has threads.

Correct tapping fluid/oil selection is a must too.
Click to expand...
WOW I guess I am in the minority about spiral flute taps. I use them for power tapping in a tapping head and hardly ever break one....with one of my tapping heads I can tap 10 holes drilled the correct size with a spiral flute 3/8-16 tap in 60 seconds !!! If the tap is a good brand, and sharp it wont break because it cuts and doesn't bind.......
 
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