Please help me with threading a hole

seatlanta · Nov 17, 2007

OK, here's another beginner's problem.

I'm trying to make a set of toolmaker's clamps--you know, the ones in all the project books for beginners.

But I can't thread the 3/8 x 16 tpi holes. I drilled the steel bar to the correct diameter, but the tap goes in about 3/8" and then gets so tight I'm afraid to go farther.

I enlarged the hole by several sizes, and it was better, but I still couldn't get through the steel clamp arm.

I'm using one of those T-handle tap holders with a plug tap. The T-bar begins to flex as it gets tighter in the hole. I'm afraid I'll break the tap if I keep turning it.

I'm using cutting fluid, and I'm periodically backing out the tap to clear it.

Two questions 

Should it be this difficult when I thread a 3/8" hole by hand?

Do I need to buy a taper tap to get it started?

I'd appreciate any suggestions or tips.

Thanks.
James (seatlanta)

dfw5914 · Nov 17, 2007

What brand tap are you using?

Dr. Rob · Nov 17, 2007

...and it sounds dull.

Jeff B. · Nov 17, 2007

How old are the taps? Are they dull? Was the hole drilled straight? Most importantly was the tap started straight?

Peter Neill · Nov 17, 2007

...and check to see whether it's a left-hand tap.

Peter

Old Bill · Nov 17, 2007

Are you sure it is not a bottom tap? How many
threads are tapered?
Old Bill

Billy Boy · Nov 17, 2007

Tapping is tough, and breaking a tap in a hole can be a real PITA!

It's definitely best to be using a sharp high quality tap. Vermont American and Irwin taps that you can get at the Home Depot are both crap... with Vermont American being the bottom of the barrel.

The first thing I learned the hard way is that you want to go in for a turn and then back out for a 1/2 turn and then go in for another full turn. The back turn will cut the chip you have made and will allow it to clear much more easily that if you let it get long and stringy.

Also, if things are jamming up it can really help to pull all the way out, brush off your tap, blow air into the hole to clear things out, apply a new drop of lube and start in on it again. I said before that breaking a tap can be a real PITA, so I generally play it conservative.

Pretty much the game with tapping is chip management. When things jam up, it is almost always do to chips. Lubrication is also a big help. I never tap metal without it.

I generally use a taper tap for everything unless I really want to get close to the bottom of a blind hole. The taper tap starts a lot easier. If I'm going to bottom tap, I usually start with the taper tap, and once I've got things going, move to the bottom tap.

Hope this helps.

B

Carl Darnell · Nov 17, 2007

If you drilled a 5/16" hole the 3/8" tap should work. If the tap is dull or you are using a hard steel you have a problem.

I think the tap is dull.

matt_isserstedt · Nov 17, 2007

I'm wondering if you are hand-tapping, or better said, lining the tap up with the hole by hand (??)

If so, that's a losing proposition...yes you can get good at it over time..but there's a better way:

- with the machine that made the hole, drill press or mill, remove the pilot bit and install the tap. A drill chuck is just fine. I bring the quill down by hand, and with my other hand, rotate the chuck until the tap screws in as far as it is going to go with my hand strength. I coordinate the "downfeed" with light down pressure on the quill, nothing to be worried about as the tap will coordinate the "lead". Then release the chuck jaws and install your T-handle wrench and continue tapping until thru.

Also: whenever possible I use a spiral point "machine tap" (or gun tap) which sometimes has 2 flutes (sometimes 3) and is very difficult to line up by hand. The great joy is that you don't have to back it up when doing a thru-hole. You can use it for a bottomed hole but you have to leave some space at the bottom to dig out the chip string with a pocket screwdriver or better, dental pick. If you have to finish a bottomed hole, then a 4-flute "bottoming" tap is just fine and this can be guided by the threads already made.

Most all of the tapped holes I've ever made that didn't work out were because I started the tap crooked by hand despite due care. When I switched over to letting a drill press or milling machine spindle make the first few threads coaxial to the pilot hole, I've yet to have a problem.

boslab · Nov 17, 2007

taps over here come in sets of three, taper, second and a plug [used mainly to take a thread to the bottom, or nearly of a blind hole, through hole tapping as follows, drill correct tapping size hole, dip the taper tap into thread cutting compound [a kind of extrime pressure lubricant] wind it in about three turns, swarf will build up in the flutes and the cutting compound will melt, you can smell it, then back the tap half a turn, you should feel a resistance and feel that resistance disapear as the swarf shears and drops down the flute.
continue the process till the tap goes right through, the 3 turn is slightly different from billy boys but i find it ok for mild steel, i tend to go 1 and back a half with tool steel.
temaxol is a good thread cutting compound but i often use the green hand cleaner on ali [contains parafin and called swarfega over here]
buy some new taps, they are worth it.
mark

Troup · Nov 17, 2007

Does the tap have long chamfers, maybe four or more threads long - in other words, the sloping section at the entry end of each 'land' should have four threads of varying degrees of immature form. If not, yes, you do have to buy a taper tap, and best follow BB's advice and go for a good one.

His advice to "go in for a turn and then back out for a 1/2 turn" is indispensable for tapping by hand, so it applies perfectly in this specific case.

What a lot of home workshop people don't subsequently learn is that the opposite advice applies when tapping with a HSS ground thread tap under power. THe trick here is NOT to stop and back up until the thread in a blind hole is to depth, or the load comes off the tap in a through hole.

(Blind holes are tricky, there are other caveats which I won't go into here)

Even using a drill gun, it's entirely possible to tap successfully provided the tap is good enough and you hold it square and true.

I would never try this with a cut thread tap, or a cheap HSS tap.

I've noticed that some metalwork tutors grew up in an era when taps simply were not strong enough for this to be viable, so they don't always give up-to-date information, even to trade inductees.

jim rozen · Nov 17, 2007

1) what size hole are you trying to tap?

2) what cutting fluid are you using?

3) what kind of tap are you using.

Answer those three questions and the solution
to your specific problem will become a good
deal more obvious.

Jim

Hans B · Nov 17, 2007

The basic procedure is as described by Billy Boy.

Indeed tapping is chip management based on your experience which develops a feel for these things.

Go forward until you feel resistance, (don't go until handle bends), then back off slowly because you are breaking off the chip. (Certainly make sure your tap is straight with the hole.)

Continue this process until you are through.

Good luck.

Hans

rke[pler · Nov 17, 2007

Run the tap in until it stops, then check the tap for squareness to the work. If it looks pretty square check the hole for squareness - if a tap is getting increasingly difficult to turn that usually means that it's doing more and more work, meaning that it's not going exactly the same direction as the hole but at an angle to it.

If you can try drilling the hole and starting the tap both in the same fixture, even if it means driving the tap a little bit with the drill. Once in hook up with a tap holder and tap the rest of the way by hand. Use a decent lube and break the chip frequently by turning the tap backwards a couple of flutes every full turn or so.

seatlanta · Nov 18, 2007

Thanks for all the suggestions. I'll try to answer the questions you've asked:

Hole size? I first made a 5/16" hole. When I had problems, I redrilled with an S drill to make it larger. Still didn't work.

Cutting fluid? I'm using Grizzly cutting/tapping fluid.

Right or left hand tap? It's definitely a right-hand tap. I don't own any left-hand taps or dies.

Brand of tap? I don't know. It's part of a set from ENCO or MSC. Probably an Asian import.

Procedure: I drilled the holes with a drill press, removed the workpiece and started the tap by hand. I tried to keep it square, and as it began making threads, it looked square.

I did back out 1/2 turn after each full turn. But getting a full turn was almost impossible. It was more like, turn it about 10 degrees and reverse it, then try again for another 10 degrees. A full revolution took many steps. I couldn't get a full, smooth turn. As I turned the tap, it wouldn't move, then it would jerk forward.

How hard is the steel? I don't know. It's a piece of bar stock from a scrap pile.

============

After reading all the replies, I'm wondering if my low-cost set of taps and dies could be the problem.

Maybe I should buy my taps (and dies) one at a time, one project at a time, and try to get better tools.

More questions:


About how much should I pay for a good 3/8" RH tap?

What's a good brand?

Thanks again for all the replies and suggestions.

James (seatlanta)

Frank Ford · Nov 18, 2007

As a recent middle aged newbie myself, I can tell you for CERTAIN that ANY tap sold as "carbon steel" is nearly worthless, and almost enough to put you off metal working. That, as far as I know, includes all tap-and-die-sets.

The simple switch to ones called "high speed steel" will change your life, for sure. Use some appropriate tapping fluid, and add to that, the "spiral point" and you're in range of great tapping success for "through holes." Blind holes are a bit more challenging.

As to brands, well, I'll leave that to the more experienced - I'm not sophisticated enuf to tell the difference.

split tenth · Nov 18, 2007

Get yourself a good eye loupe and take a good look at the cutting edges. You will be surprised at how dull a cheap tap can be.If it doesen't look sharp don't even think about using it.I've gotten into this habit and have avoided disaster a few times.

Lumberjack · Nov 18, 2007

Some of those asian taps can vary somewhat in size... try to measure it and compare to what it should be. I might be a little bit large.

Otherwise, when tapping screws up...

I often find this.

1 Tap is not square/alinged with the hole, mostly when doing it by hand in hurry.
2 Wrong cutting geometry for the material (incl. dull).
3 Wrong cutting fluid for the material.
4 Wrong size/tolerance of hole/tap.

This is NOT a guide to how to tap but rather where I first find any fault when it has started going bad... Things do get wrong as 1 = Bad practice, 2 = Hmmm... ohh did I get THAT tap..., 3 = None? 4 = Oops what size did the hole Acutally get, what the heck is this for a junktap?
But I still want to say that even If everything isn´t perfect, you still should get a threaded hole.
Three critical things for not getting the tap through is undersized hole/too large tap, missalingment and dull tap. (Fluid can be.)

RAS · Nov 18, 2007

In addition to the good advise already given, I would suggest that you make a 'tapping block':

This will help to ensure that the tap is started square with your drilled hole.

RAS

Joe Henderson · Nov 18, 2007

Did you have any trouble driling the hole? You can test the hardness with a file. If it files easily then it should drill and tap well. If the file does not take a good bite then the mystery metal is hard and will not tap well.

As matt mentioned eariler, gun or spiral taps are the easiest to use as they push the chips ahead of the tap. Cleveland or Greenfield taps are good. You really do get what you pay for in taps.

Please help me with threading a hole

Plastic

Stainless

Hot Rolled

Aluminum

Stainless

Hot Rolled

Hot Rolled

Titanium

Diamond

Titanium

Titanium

Diamond

Aluminum

Diamond

Plastic

Hot Rolled

Hot Rolled

Hot Rolled

Stainless

Aluminum

Similar threads