I see that there are a gazillion different kinds of taps and dies. Plug, bottoming, taper. H1 through H11+. HSS, Cobalt, TiN-coated whatever... Spiral flute, three flute, four flute....
For a home hobbyist, working mainly on small parts in brass and plastic and occasionally mild steel, what is an appropriate starting point? I don't really want to buy a whole big set of everything for $200 if it's mostly going to sit around unused. Right now all I've got is a couple of small hardware-store (Vermont American) pieces, nothing larger than 8-32; but last night I really coulda used a 10-24 tap, for a blind hole about 3/4" deep in a plastic shaft.
For through holes, or for holes which can have enough depth to accept the chips, I would use a 2-flute "gun" tap (spiral point) which chases the chips ahead of the tap, and thus does not require backing the tap up every half turn or so to break chips.
The taper, plug, and bottoming are best viewed as a set, with the taper being best for starting a thread by hand (it aligns with the hole better), the plug best for normal cutting, and the bottoming tap, as indicated by its name, for completing threads in a blind hole.
I would not consider the Vermont American ones worth anything other than to give to the guy who wants to borrow taps all the time.
I would avoid carbon steel, and consider HSS to be a minimum. For tougher steels, the Cobalt steel is better.
For some materials, the TiN (Titanium Nitride) coating reduces friction, and allows a tap to stay sharp a bit longer.
The 'H' numbers designate size, with the smaller number producing the tighter hole. I would probably use H2 or H3 unless a project calls for other clearances.
For my own purposes, as a starting set, I would suggest a couple each of HSS gun taps, H2 or H3 clearance, in the sizes which you are most likely to use -- for through holes. I tend to buy with the TiN coating. Those (in my mind) would be 4-40, 6-32 (the easiest tap to break in the collection), 8-32, 10-32, and 1/4-20. (Other people may work in a different scale, and need smaller or larger.
I actually have 0-80 through 1"-whatever, thanks (in part) to an eBay purchase of a really nice set (which actually runs 2-56 through
1-whatever, with taper (or starting), plug, and bottoming, plus the matching die in each size. It was an auction with no photo, but based on the description, I decided to take a chance. I've got lots of duplicates in certain sizes.
But while I have this nice set -- I use the gun taps most of the time.
Anyway -- as you discover a need for another size -- order it from someplace like MSC -- which at least in my area offers next-day delivery (shipping from PA to northern VA). If you need to tap blind holes, order the set of taper, plug, and bottoming. Otherwise, for through holes, order the HSS gun taps.
Note that when tapping with a tapping head by machine power, for some materials (e.g. aluminum and some plastics), a better choice is a "thread-forming" tap (also called a "roll" tap), which does not cut at all, but rather displaces metal from the root of the thread to form the crest. It produces harder threads in aluminum, and you don't have to deal with chips -- but you need different sizes of starting holes. (I have a few sizes of these for special projects.)
And -- you *really* need a set of number-size drills (#1-#60) to have the right size drill bit for tapping each thread. (For example, a
1/4-20 usually wants a #7 drill bit.) Fractional sizes are usually not close enough, and thus are either too large (resulting in weaker threads), or too small (resulting in excessive stresses on the tap, and likely breakage.)
And the thread-forming taps sometimes need a metric size drill for a proper fit, so the formed thread is complete.
Speaking of breakage -- while carbide taps will last longer in tough materials, they really *should* be used in machine-driven and guided tapping, not hand tapping, because they are very brittle, and a bit of side force on the tap wrench is likely to snap the tap off in the workpiece.
I know -- I haven't *really* answered your questions -- other than some general suggestions, and *lots* of conditions which might change your choices -- but *don't* use the Vermont American -- or any other carbon steel tap. (If it doesn't say at least "HSS", assume it to be carbon steel.)
I hope that I've at least given you some information with which to make your choices.
I tap both by hand and with a pair of different sizes of TapMatic tapping heads -- and with the latter, gun taps (or high spiral taps to pull the chips back out of the hole) are what makes sense.
Also -- be sure to use a threading lubricant for most materials. (For brass, you probably don't need any.) I keep Molly-Dee, TapMagic, and plain old high sulfur cutting oils on hand for threading, depending on the workpiece material.
The only tip I can add (and it's practically an obviousity) is that on more than one occasion I've gotten around not having a bottoming tap handy when I needed one by just grinding the end off a taper tap.
Oh, and I've busted a lot fewer small taps since I got myself a "spring loaded center" (mine has a pointed end and a straight body which can be grabbed in a lathe tailstock chuck or a drill press chuck. It's used as shown in the seventh photo on this page:
I try my best to resist the temptation to use small taps freehand and usually take the trouble to set up and use the spring center. I can't remember where I bought mine. I just tried but couldn't easily Google someplace selling them using that name, but if you have a lathe, "designing" and making one yourself is practically a no brainer.
Took one more shot on Google and found a page showing exactly the spring loaded center I'd bought. It's a page from a company in India, so I probably bought it from someplace which sells cheap imports, like Horrible freight:
Now I do remember that the shank OD was a smidgin too large to make it into the 3/8" tailstock chuck on my little lathe, but there was plenty of wall thickness so I turned it down to fit.
I noticed they also make a "tap guide" which might be worth thinking about. Looks like it'd work pretty well on holes which are normal to flat surfaces:
You don't say what kind of plastic. But for many kinds of plastic that do not form chips easily, "thread-forming" taps are the answer.
I don't bother with hardware-store taps anymore... first of all it's getting harder and harder to find a hardware store that even has taps (I know a couple exceptions in my area but I'm afraid that Home Depot will drive them out of business... damn I hate it that Wheaton Lumber is out of business now, just as a OT anti-Home-Depot rant), and then they're overpriced and often not appropriate to the work at hand. I just order from MSC and they arrive the next day.
For small taps I use a disk, about 1-1/4" in diameter x 3/16" thick, with a hole through the center for the tap shank and a set screw in the edge. Place the disk low on the shank, near the threads, and tighten the set screw. Hold the upper part of the tap shank in a slightly loose drill chuck or collet to keep the tap vertical. Turn the disk with your fingertips to feed the tap into the workpiece. Either the set screw will slip or you will "feel" when the tap isn't cutting. I'm sure it's saved me from breaking many taps.
Missed the original post so may be barkin up the wrong tree here...
To add to the notion of thread forming taps...on many plastics (like poly and some acetal..the non brittle ones) you don't even need to tap. Most screws and bolts will act as self tappers/self thread formers. To do this you generally need a reasonable chamfer at the opening of the hole to get things started without a battle.
Don, as usual, gave outstanding advice. FYI, they sell sets of the common sizes that also include the proper sized drill bit in a stand. It is very handy to have the drill bit and taps together like that. That might be a good starting point and then add more exotic sizes as needed.
I myself like to home in on the term "hobbyist", in as much that if you are required to wait a day or two for a needed item, no big deal. (As opposed to the business end, time is money!)
In general terms, buy what you need, but get the best quality possible. (budget, etc).
Getting down to specifics, you should attempt to identify the type work you are doing, because using more 'precision' tools than actually needed only adds to cost. That is, a class 2 fit is usually considered 'standard'. Hence to buy taps/dies intended for class 3 or better fits may be counter productive.
Granted the many variables do exist, but unless you are involved in something really esoteric, keep in mind the concept "keep it simple".
Yes -- though I would start with a plug tap instead of a taper (starting) tap, as that would produce more complete threads as you approach the bottom -- unless you grid a *lot* off the tip. :-)
That is a useful one -- and I have one (which came in a machinist's toolbox which I bought -- either from an eBay auction, or a local estate sale. I think from the former.
It is best when you have just drilled the hole and the workpiece is still clamped to the drill press or mill table. Otherwise, you have to set it up on center again.
Usually -- if it is going to be more than two tapped holes, I set up the appropriate TapMatic tapping head in the drill press. For fewer, I will usually hand tap -- or in the lathe, I will use the tailstock center to steady the back of the tap wrench (a T-handled ratcheting one, not the bar style for that.)
Agreed. Remember to make the spring-loaded point reversible, with a male center on one end (for the larger taps) and a female center on the other end (as the smaller taps tend to have a male center on them.)
Can you explain "class 2" and "class 3" fit? I understand that I can purchase taps in various degrees of oversize, e.g., H2, H3; but I don't know what the "normal" one to get is.
I am not, generally speaking, doing precision or demanding work. An example of two things I recently had to do: needed to tap an 8-32 blind hole in a piece of brass so that I could screw a wire to it (using a crimp terminal) for electrical grounding; needed to tap a 10-24 blind hole in the end of a
1" acetal shaft in order to bolt it to a piece of metal.
You also mention brass. Thread-forming taps work great in brass and acetal. The one exception is when you are tapping plastic and the shape of the piece you're working won't handle much radial stress, e.g. tapping a big hole in the end of a narrow rod, when the work will have a tendency to split.
Hmm ... we could use a bit of clarification here. Advertised where? My subscriptions to both HSM and MW have lapsed a while back.
If you mean tapping heads -- my experience is with two styles by TapMatic. The smaller one is the style with an adjustable torque limit clutch, and the larger is one with an adjustable overtravel instead.
Either size uses two "rubberflex" style collets by Jacobs to hold the tap centered, and a pair of steel plates adjusted by a hex key from the side. (They are both threaded onto a single screw which is left-hand thread at one end, and right-hand thread at the other, so they move symmetrically.) I think that the same chuck is present on at least some tapping stands.
The smaller one ("30X" IIRC) handles from very small taps (say
2-56) up through 1/4".
The clutch in this should be adjusted so it just does not slip, in the workpiece material in current use, with a brand new tap. When it starts slipping, the tap is dull enough so it is time to replace it, so it does not break off in the next workpiece. The cost of a new tap is a
*lot* less than the time lost to remove a broken tap. (I would suggest that you put the tap aside for hand use in less demanding workpiece materials, if it hurts your sense of thrift to discard a tap which still
*looks* new. :-))
The other, a 40-something, I think (I forget the designation suffix) has no clutch, but instead has an adjustment at the tap end of the body, which moves the tap farther towards the release point of the dog clutch which disengages the tap to stop threading (once the drill press or milling machine spindle reaches its own preset stop.) The benefit of this is when tapping fairly shallow blind holes, as normally the tap will move an extra 1/8th or 3/16" of an inch before releasing once the spindle travel stops.
This size is for 1/4" to 1/2" taps, so breaking taps with torque is less of a problem than with the smaller ones. (6-32 is really the most fragile tap for its size, thanks to the extra-coarse thread pitch, resulting in a smaller minor diameter.) I've broken several 6-32 taps over time, but only one 0-80 -- all when tapping by hand.
I've read reports of the Procunier tap heads being better, but I have no personal experience with them, and I have had very good luck with the TapMatic ones. The smaller one came from an eBay auction, the larger I got at a metalworking club meeting -- both for quite good prices.
Now -- if instead, you were talking about the tapping stands, in which the tap is guided while being hand cranked -- I've never used one of these. Normally, hand tapping works well enough for me if I don't need to do a lot of them (and for three or more, the tapping head gets installed in the drill press -- if the workpiece will fit on the drill press table.)
Note -- I *have* used gun taps in an hand-held variable speed reversible drill motor, 10-32 and 1/4-20 at least, with care to not apply any side thrust. Don't let the motor get up to speed. Set the speed limit as low as you can mange. Start the tap into the hole, and then just give a "blip" on the switch. Increase the length of the blip until you are far enough in, then switch to reverse, and use full-time contact to back it out.
I've even used (prior to getting the tapping heads) a drill press to start a tap. Drill pilot hole, loosen chuck, replace drill bit with tap, blip power on, and just as the spindle is slowing to a stop, feed the tap into the workpiece. This usually gets it well enough started so you can then loosen the chuck, and put on a bar-handle tap wrench to complete the job -- or if you have enough spindle travel, put a center into the drill chuck and use it to guide the back of a T-handled tap wrench with a ratchet.
Classes of threads: Distinguished from each other by the amount of tolerance or tolerance & allowance specified.
Generally speaking, a class 2 fit is described as "free running", whereas a class 3 fit has a slight drag (by hand). A class 1 fit is pretty sloppy.
For the work you describe, good technique and using the proper size tap drill along with good quality machine taps (H2) should yield good results. Of primary importance in tapping is to drill the hole deep enough to allow for the tip of the tap and also room for the chips.
Thanks, Don for all the great information on tapping heads. Very informative, as I've never used one and had some questions.
The thing I asked about is called a tapper, I think. As you described it has a number of chucks for holding various size taps in a vertical spindle and a crank handle running horizontally on top. It sits on a base and has a column similar to a drill press. They sell for 100 - 200 $.