Tapping questions

Steve,

Well sure small taps are eayser to break than big taps...

DUH Oil makes a difference and so does getting the chips out of the hole. Lube the hole and the tap.. for EVERY hole... every time you back the tap out CLEAN it.

I don't strictly follow the 1/4 turn rule, but it's a good place to start, depends on the materila i'm tapping... you tape enough holes and you ga\et a 'feel' for whats right...

As for how many holes.. well lets see, the last locomotive I built had close to 600 5-40 tapped holes, about 200 of which were 'blind' .. Uh.. I did then all with the same plug tap and also bottom tapped the blind ones.. Material varied, CI, AL, Steel, Brass, Potmetal...

No taps are NOT self aligning, they tend to folow the hole, but if you go crooked the tap WILL cut crooked... Thats why at a bare minimun use a tapping block.. even better is a tapping fixture... I've build a really inexpensive one, go here for pictures and a how too.

--.- Dave

First, the KRAPP at the local hardware store (Vermont, etc.) are totally awful, brittle high carbon garbage, often with molded threads. The $6 and up taps from a regular machine shop supplier are a world away from that stuff.

a VAST difference. And, it isn't just plain oil, but special stuff with high-pressure lube compounds that improve the cutting action.

Thousands, but you can't get that at hand tapping speeds. I have a gadget with clutches and gears called a tapping head that allows me to tap holes at

600 RPM (I don't trust myself to go faster). I can do hundreds of holes in half an hour with that. I use a tapping fluid appropriate to the material. I use mostly spiral-flute taps, they remove the chip up the hole like a drill bit. You plunge all the way in in one shot, then back out, and you're done! (I do this on a CNC milling machine, but it can be done on a drill press, too.)

There are also things called thread drills, that drill and thread with one tool. If you have a drill press, and the work fits on it, this will make sure the tap follows the hole on axis and on center.

And, 1/4-28 is a stronger tap than 1/4-20, as the thread root dia is larger.

No, they were NOT! See above. I know what Ace carries, as I have had to use theirs on occasion when I needed a tap right now.

There is a tapping guide that will align the tap normal to a surface, but if the hole isn't normal to the surface, it won't help any. You may have to align by feel. Taps will break REALLY easily with a side load, which is what develops if the tap is started at an angle to the hole. Taps are definitely NOT self-aligning, do not assume they will line up. If you get one started off axis, you can back up and re-start, and get it into closer alignment, but it takes a sensitive feel for the load on the tap.

Jon

If you don't have blind holes get a spiral point tap. (Even the cheap ENCO imports are not too bad.) You should be able to tap all of the way thru without ever having to backup. Use the right drill size. Use cutting oil.

You don't say what material you are using. On mild steel you should get at least around 100 holes on one tap. You do have to have it aligned correctly.

If you are currenlty using one of the hardware store taps you will be really surprised at the difference a resonably good tap makes.

Ray Spinhirne

Backing out 1/8 turn will not do much if anything, you want to break off the forming chips with the next flute around the tap, back off 1/2 turn for a 2 flute tape, 1/3 turn for a 3 flute tape, etc. How far you can thread before backing out depends on a lot of things (that means I am too ignorant to know the answer) and I usually go on feel, but generally 1 complete turn forward then back to break chips for 1/4 or bigger taps. I am more cautious with small taps or when breaking the tap would be a big problem rather than a minor annoyance.

Oil makes a difference. 1) it extends tap life, sometimes dramatically, 2) it reduced the torque needed to turn the tap, which reduces the chance of breakage 3) it improves the threads, less tearing of the crests.

small taps will break more than big taps. The only time I broke a 1/4" tap was when I knew I was forcing it to much.

Alignment is important, and it get more important as the hole gets deeper. On the one you broke I suspect the tap was not aligned with the hole and was cutting farther and farther off to the side as you went deeper until it couldn't stand the torque and snapped. If you are not pressed for time you can use the drill press to guide the tap straight in. Clamp the work to the table, drill the hole, replace drill bit with the tap, start tap by hand turning the chuck, carefully switch to a tap wrench when you need more torque. Repeat for each hole

Carl

If you using a drill press or mill with the part clamped, you can use a tap guide. After drilling you put the tap guide into the chuck. It has a spring loaded point which goes into the countersunk back of the tap handle. Bring the chuck down enough to keep the point into the handle, while turning the handle. The tap will then go straight down into the hole. Since there is no side movement, the tap shouldn't break.

Wayne D.

============== Assuming this is not a troll.

Taps are not self aligning, and if you start a tap crooked, it will stay crooked, with the taking a deeper and deeper bit as it goes into the hole before it breaks. Another good way to break a tap is to start it crooked and then force it sideways to straighten it up. If you start a tap crooked, the only cure is to drill the threads out and restart the tap straight.

You will quickly save enough money to pay for a tap guide in the cost of broken taps and ruined parts.

The simplest tap guide is a block with close fitting holes to guide the tap. This can be off the threads or the shank. A block that guides off the threads is quicker to make, but a guide off the shank may be more accurate. Shanks are standard for the various size taps. A tap guide block was a traditional apprentice project. see:

The next step up is combination tap wrench and guide. These are nice, but expensive, and in my experence don't offer much if any improvement over a block.

The next stup up from this is a hand tapper, which is a product shop item. The big benefit is the protection to applying a side load to the tap.

The depth [percent] of thread is critical. 75% is good enough for almost all uses. Higher percentages increase the pullout or stripping torque only marginally, are much harder to machine and tend to break taps. If you tap 1 diameter [1/4 thick for a 1/4 hole etc.] with 75% depth of thread you will break the fastener before you pull the threads out.

Chamfering the pilot hole with the tap, possibly with a drill the nominal size of the fastener, will remove any burrs allowing the guide to set flat, and assisting the tap to start. Go deep enough so that the burr that is kicked up by the tap will be below the surface of the part.

Generally in the United States taps come in 3 "nose styles" taper, plug and bottoming. It can be helpful to start the hole with a taper tap, and if a blind hole finsh with a plug or bottoming, depending how deep you need the threads in the hole. If you have a through hole, a gun or "chips ahead" tap works well. These also come in taper, plug and bottoming "nose styles." The taper will be easier to start.

The style of tap wrench can ge critical. I find that the style with two equal handles to cause less tap breakage than does the type with a chuck and a sliding T handle because you can more easly avoid putting any sideload on the tap. see: good

Tap lubricant can be critical. see: ?PMAKA=505-2011&PMPXNO=940682&PARTPG=INLMK3?PMAKA=325-5965&PMPXNO=5830166&PARTPG=INLMK3?PARTPG=INSRAR2&PMAKA=825-8140&PMPXNO=940175?PMAKA=505-1979&PMPXNO=944158&PARTPG=INLMK3 There are many other suppliers. Google is your friend.

Unka' George [George McDuffee]

------------------------------ Watch out w'en you'er gittin all you want. Fattenin' hogs ain't in luck.

Joel Chandler Harris (1848-1908), U.S. journalist. Uncle Remus: His Songs and His Sayings, "Plantation Proverbs" (1880).

found a couple spare tap holders, the 2nd one I had someone turn down a little, which now are "drill press accessories".

If the work needing to be tapped can be brought to the press I tap it on that. Turn the pully by hand.

My main tip that keeps me from breaking taps is backing them ALL the way out at least twice. I then try to get the cruft out and put the cutting oil in the hole, then on the tap and then apply more as I think its needed.

Unka, great idea on the tap guiding block.

i

I tried something today. I used my drill press

for HAND tapping. I used the spindle and chuck as a tap guide. I drilled a appropriate sized hole for a 1/4-20 tap. Then I chucked the tap in the chuck. Then I lowered the tap into the hole with the pedal, and use the chuck key as a wrench and hand turned the chuck. The tap nicely went into the metal. I think that it is a good space saving and money saving solution for most tap sizes that I would encounter.

Having that foot pedal for two handed operation, is very handy.

I may try to make a little collar with three handles that would screw into the collar to hold on to the key holes on the chuck. I think that it would be perfect for hand tapping, along with the pedal.

I am thinking about buying McMaster items 5081T51 and 62385K61 to make that.

i

Using the drill press works well for me, I just hand turn the pulley (This is the only time its ok to use a drill press and wear gloves).

Clamp to the table or in the vise and lower the spindle. Once its bitten in ok, I just tighten the spindle lock a bit (so it doesn't pull up hard but still goes down) and that frees the other hand if I need it.

Sounds interesting. I also tried tapping a 1/2"-13 hole (with a 29/64 drill bit) with the same setup. It was straightforward, but required obviously more effort. I will try to make a collar with handles instead of using chuck key. I think that this will be my default tapping setup from now on.

i

I generally use a piloted tap wrench in the drill press. A piloted tap wrench looks like a regular T-handle tap wrench, but is drilled axially to accept a steel rod. This rod is clamped in the drill press chuck, forcing the tapping operation to proceed on axis.

The price has risen since I bought one: .

It's quite well made, and strong. The smaller model is .

These piloted tap wrenches are expensive, but far cheaper than a tapping stand, and will work on anything one can drill on the drill press (or mill) in question.

Large taps usually are center drilled in the wrench end, and one can get spring centers intended to go in the drill press, with the spring point riding in the center hole in the tap, guiding the tap while one uses a straight tap wrench to turn the tap. T-type tap wrenches also often have a centerdrilled hole at the top.

The spring-center guide is here: . This works for smaller stuff, but the forces involved in tapping big holes causes the wrench to pop out of the spring center, so I hardly ever use this guide any more.

Joe Gwinn

On Tue, 20 Mar 2007 21:05:53 -0500, with neither quill nor qualm, Ignoramus22126 quickly quoth:

Nah, pop the lid on the belt housing and drill a couple small holes in the top pulley to insert a hand crank. Or find a splined shaft which would fit in the pulley hole and build a hand crank that way.

I picked up a hand tapping unit for $50 at GunnerWorld(tm) when I was there so I'm set.

-- Love the moment, and energy of that moment will spread beyond all boundaries. -- Corita Kent

I've tapped with a drill press for years, too. On the Powermatic, if you set the spindle speed high before you start tapping, it's much easier to rotate the chuck by hand (for small taps). I also release the tap from the chuck and remove the tap by hand to avoid any thread pullout.

Great list of products, Unca George! I can add but little to it. Brownells' sells a nice little tapping block similar to the OMW except the shank holders fit individually into the block.

Taprite Kit (tap guide), item # 357-001-000 $27.15

Bob Swinney

Joe, thanks, I think that I can use my drill press chuck to hold taps directly, and turn the drill press by means of handles such as McMaster item 62385K21. I tried that yesterday, with a 1/2-13 tap and the chuck key, it was not as nice as with handles, but it worked. Thank you for looking them up for me. McMaster has something similar for a little less, though MSC's model seems to be better designed for drill presses.

i

Does it work ok for you? I think Ive got another one now in one of the lots I brought home that remain unsorted.

Gunner

"Liberalism is a philosophy of consolation for Western civilization as it commits suicide"

- James Burnham

My drill press is tall, it is not convenient. I will buy handles for the chuck.

Sounds nice!

i

to avoid any

Good idea on setting speed high for easier tapping. Thanks a lot. Once I am done with my setup, I will post pictures.

i