Could use some info on Taps

[Mike W1]

Some of you fellows obviously know lots about machining and tools. I DON'T!!!

Only need to deal with the few sizes of small ones I own which are 6:32, 8:32, 10:24 and a 10:32 I have need of. They've been purchased at a small hardware store and selection was pretty limited.

I store them in small pill bottles and foolishly did not save the factory labels but did record the tap size and pilot drill sizes at least.

It didn't even take me long to figure out there must be another type tap than I have as I always had to drill the hole a little deeper so as to be able to thread my hole clear thru. Apparently I need what Wilkopedia refers to as a bottoming or plug drill. I "think" the ones I had were marked NC though it's possible it was NF.
I haven't a clue what those 2 terms mean though.

Perhaps some of you can enlighten the unknowing a bit. Wasn't having much success finding anything real useful on my google searches. The ends do have a very definiite taper but I can't say which of the lower 2 in the drawing they might be.

 

[Brad]

I'm no expert but here I go anyway.....

Start with a taper tap. Once it bottoms out switch to a plug or bottoming tap. The plug and bottoming tap will thread far closer to the bottom of the hole. Don't start with them because that taper is what helps get the threads started.

For stuff like tapping a Lee mould for a set screw I have no problem with hardware store taps. If I want soemthing for steel that will be used a fair amount I go to MSC and spend a little more.

Lubricant makes tapping much easier. Again for Al like a Lee mould I have done them dry or with a little WD40. For steel I really like the Castrol Moly Dee. It wasn't cheap but my gosh a quart will last me a few lifetimes.

NC and NF are National Coarse and National Fine.

This should help a bunch.


Google tap drill chart, lots of them out there. I should print one and have it laminated to keep by the tool cabinet.

 

[Mike W1]

Thanks. Was just snooping on evilbay and found an inexpensive Irwin which is the brand I'd been getting so think I'll order it. I should have thought harder,fine and coarse, makes sense but the abbreviation didn't click for me. Saved the little chart to my desktop.

 

[Brad]

Irwin is fine for light use. I own more than a few of them. It is a matter of need. I'm not a shop needing to tap 100 holes a day.

Mike, I'm no expert either. I have learned a bunch by using Google and the hobby machinist forum.

 

[Ian]

If you need a bottoming or plug tap (two different degrees of the same thing) to finish threading out a blind hole, take an extra one of your inexpensive hardware-store taps and break the point off about two threads ahead of where the taper peters out, then grind the tip square.

I'm familiar with four tap tapers: Starting taps, taper taps, plug taps, and bottoming taps. Most of the hardware-store variety are taper taps.

Here's something I keep bookmarked:
https://www.newmantools.com/taps/taptech.htm

 

[Mike W1]

I just bookmarked that page along with this one. May have another question or two after I do some more reading.

 

[Jeff Michel]

Just a suggestion, do not "save" money on an inexpensive tap/tap set. Buy the best you can find and take care of them, throw them away when they get dull if you can't or don't know how to sharpen them. Never tap without a lubricant, kerosene works well in aluminum, any "Tapping Oil" will work on steel, I like sulfur in mine (steel only) but it can create a stain. This are pretty delicate, be careful. I break the chip every half turn and clear frequently. Use a tap guide or mount the tap in your drill press or milling machine, starting a tap straight, by hand is not easy and if not started straight, the results can be bad to horrible, crooked screws to broken taps. I keep holes in aluminum to about depth of thread of 75% in steel 50%, any more your really straining the tap and your not gaining anything in holding ability. If your interested, there is a book titled "Drilling and Tapping" it's in the "Workshop Practice Series" the series is aimed at the hobbyist with limited resources and experience. It will take all the mystery out of tapping and set forth all the guidelines to do it successfully. I've broken two taps in 35 years of poking holes in stuff and both would of paid for all the resource books and taps I've used since. Just my thoughts, others will have different, good luck.

 

[smokeywolf]

Mike, for through holes you want a 2 flute, spiral point tap (above 5/16" 3 flute). For blind holes you want a spiral or helical flute tap. Whenever and wherever you can, try and stick with Cleveland, Guhring, Reiff & Nestor, Union Butterfield brands.

When tapping high carbon steels, stainless, titanium and other exotics and high nickel alloys, drill at least one size over the typical (75% thread) tap drill size.

Use a tapping fluid, cutting oil or wax when tapping.

Don't try to use a wrench to grab the square base of the tap. Buy an honest-to-goodness tap handle.

 

[smokeywolf]

Jeff Michel knows what he's talking about. All good advice.

 

[Bret4207]

To expand on something Smokey Wolf said, suggested drill sizes are just the nominal sizes to use. You have to feel your way along sometimes, especially if you don't own really good drill bits. I don't, and I often have to get the tenths reading mic out and find the next size up in either fractional, letter or number size to get the tap to thread without breaking it or not being able to tap it right. I've run into a few odd alloys at various times that required me to go to the big city or get on line and order a really good tap too. The difference between an Irwin or Vermont American and a Cleveland is night and day.

On the drill bits, good drill bits are the same as good taps vs cheapies. If you're like me and own a lot of Harbor Freight stuff and a little good stuff, you have to learn to measure the drill bits because "Quality Control" in China. India, Pakistan, etc is ore of a suggestion than a fact. Drilling a hole that turns out to be undersize is one degree above drilling one that turns out over sized!

If you go to my "Shop Tips" posts, I outlined the basics of running a tap and die that I've learned through instruction in machine courses, reading and through the school of hard knocks and broken taps. http://artfulbullet.com/index.php?threads/shop-tips.113/

 

[Ian]

Bret nailed it on tolerances. Smokeywolf nailed it on % fit and drill selection. You need to measure your drills and make sure the points are centered so they drill as accurate a hole as drills can. Mic your drills, and mic your taps. All the fitement stuff is discussed in great detail in the link I provided, pretty technical for the layman but it pays to dig in and try to understand it. Studying basic thread forms and fit helps with tapping operations, you need to have a solid concept of minor, major, pitch, and class of fit before getting too deep into it or you'll have sloppy fits.

 

[KeithB]

If you don't have a tap drill guide just remember that for UN (Unified National) 60 degree thread forms the proper drill size is the nominal diameter - one thread pitch.

Ddrill =Dnominal -1P Example: For a 1/4-20 UNC internal thread Ddrill = .250 - 1(1/20) = .250 - .050 = .200 Most drill guides recommend a #7 (.201), I use 13/64" (.203) for steel and AL and a #5 (.2055) for SS.

Formula works every time for 60 degree UN threads (and 60 metric also but remember metric threads have pitch stated directly, unlike UN threads which use threads per inch).

 

[RicinYakima]

For gunsmith work, I have been very satisfied with Brownells best quality, most expensive, small drills and taps made in USA.

 

[Mike W1]

The more I read the dumber I feel. Every drill/tap table I've seen shows the 10:32 as NF and 10:24 as NC. Seemed to make sense as as 32 would be finer in my mind than a 24. So I hit the hardware and buy a 10:32 3/4" set screw along with a 10:32 with larger end as well as a 10:32 nut. The 3/4" one works fine in the hole of the mold and the nut will also thread on easily. But not on the one with the large end. It's the same way trying the mold's hole. Lay 'em together and the threads seem to mesh perfectly as well as diameter. Has me stumped to say the least.

Is there such a thing as 10:32 NF and a 10:32 NC? Visually I cannot see any difference in these 2 screws.

All I really want to do here is get a "bottom" type tap and finish the hole Lyman did at factory but sure as heck don't want to screw up anything that's there. If there really is a 10:32 NC tap as well as a 10:32 NF tap I'd guess that would be a problem. The bottom taps I've seen on ads have said NC when they bothered to list that at all.

Crude picture of what I bought attached. A little edit to add. Just looked up some nuts and they seem to be NF which makes me think that my mold hole might be NF and did find taps that were marked NF. Thinking that might be the way to go.

 

[Ian]

Coarse is coarse and fine is fine. #8 and #10 are both commonly available in 32 threads per inch pitch (fine), my first guess was you had a #8 set bolt and nut, and a #10 cap screw. If you bought out of parts bins, the parts could have been switched. The threads will mesh, but the #10 won't go in a #8 hole. There's such thing as a #12x32, but very rare. Are you sure the cap screw isn't METRIC?

 

[Mike W1]

At this point am not sure of anything other than the mold hole is 10:32. The metric's are on the other side of the aisle in that store but that doesn't mean some knothead didn't put something back in the wrong place. If I can talk mama into a trip over for supper might try another out of the bin and this time see if their stuff is designated NC & NF. Not gonna make a 45 mile round trip today unless she wants to eat over there. Usually not too hard to talk her out of the kitchen though.

 

[Mike W1]

Apparently that cap screw was metric! New 10:32 fits fine but didn't find whether they're NC or NF.

 

[Ian]

I deal with it all the time. #$%%^#$&# coon-fingering mechanics mixing up stuff in my parts bins. Grrrrr.

 

[KeithB]

10-32 is fine thread (NF). 10-24 is the coarse thread size (NC).

 

[Bret4207]

If you don't have a tap drill guide just remember that for UN (Unified National) 60 degree thread forms the proper drill size is the nominal diameter - one thread pitch.

Ddrill =Dnominal -1P Example: For a 1/4-20 UNC internal thread Ddrill = .250 - 1(1/20) = .250 - .050 = .200 Most drill guides recommend a #7 (.201), I use 13/64" (.203) for steel and AL and a #5 (.2055) for SS.

Formula works every time for 60 degree UN threads (and 60 metric also but remember metric threads have pitch stated directly, unlike UN threads which use threads per inch).

Never saw that before. Thanks!