View Full Version : Please help a newbie

08-06-2005, 10:38 AM
Guys, I am 57 years old and have been building things for a long time but no-one ever taught me the proper use of a tap.

I am having trouble with taps breaking. I know I need to go slow, back out frequently to clears chips, and I have been using WD-40 as a lubricant. I am trying to tap several 5/16-18 holes in 1/2" steel and am using the proper hole diameter (17/64). Can anyone give me a tip or two (tips for taps?)

08-06-2005, 10:44 AM
Perhaps you can go with 70% thread instead, ie a slightly larger hole. I use tap magic cutting fluid for tapping sometimes. If your braking taps, you might by applying sideway force on the tap. Also, before Wierdscience tells yah, Your taps good quality and sharp? Ie, OSG or Greenfield? http://bbs.homeshopmachinist.net//smile.gif
With that said, I unexplicidly broke one of my Greenfield taps and it shocked me, first one I ever broke. I must of accidently put sideway force on it.

Alistair Hosie
08-06-2005, 10:45 AM
Meincer it is very important to tap material straight with no wander of to the side I think this could be the cause of your taps being broken and as you say keep clearing the newly cut swarf Alistair

08-06-2005, 11:09 AM
What is your current procedure?

Are you using a proper tap wrench? If so, make sure you apply force equally to both sides of the handle. Applying force on just one side of the tap wrench handle (or using an adjustable wrench as a handle) will almost certainly guarantee problems.

A good tap wrench can help, too. I have some import (from India) tap wrenches that are pure junk because they hold the tap at a slight angle to the wrench. Strret wrenches are much better and not very expensive.


08-06-2005, 11:10 AM
I usually start holes by chucking the tap in the drill chuck or lathe, and turn it by hand to get a few threads started. Then I'm sure the tap gets started straight.
Also, there are three different starting configurations ground into taps, taper, plug, and bottom. If you're getting taps at the local home improvement, plug taps are all they offer. Taper taps have 7-8 threads leade and are easier to start, plug taps have 3-4 threads leade and are harder to get started correctly. If it's a blind hole then the taper probably won't give enough thread for a fair start, but for a through hole (or deeper blind hole) they're good. I generally start the thread with a taper, then switch to the (easier to replace) plug tap for the rest of the job.

Ian B
08-06-2005, 11:12 AM

Are the taps you're using HSS or high carbon steel? The HSS ones are more expensive, but worth every penny - they feel far less 'sticky' than the older HCS taps.


08-06-2005, 11:36 AM
reasons they break: dull tap, wrong tap drill size, jamming of chips or not started straight. to strart straight when free hand tapping an old trick is to use a guide - a one inch or so piece of metal with a flat bottom and a hole in it the size of the tap. hold it firmly against the work as you start the tap.

08-06-2005, 12:07 PM
I asked for the advice and I got it. Thanks so much for this forum!

I just ASSUMMED that the tap I got at my Ace Hardware was HSS (it was shiny and expensive). No, it is HCS.

I think I need to invest in a good set of HSS taps with all three types, not just plug.

I was aware of all the other advice I got here except this.

08-06-2005, 12:19 PM
carbon steel doesn't have to mean a crappy tap. all my BA taps are carbon and have served well and have never broken. the problem might be just a poorly made tap. Now most brand name taps are HSS so people assume the hss=better than carbon, but a crappy hss tap will be just as miserable to use as what you've got.

many/most of the sets you see in hardware stores are poor quality. the average consumer there isn't knowledgable and would't pay for brand name quality taps. I don't even know if the good stuff is availabe in sets, its made for industry stocking the tool room and is usually just bought per piece. - you will probably have to go to industrial supply places rather than the hardware store

[This message has been edited by Mcgyver (edited 08-06-2005).]

Forrest Addy
08-06-2005, 02:55 PM

There. Me feel better now.

That said. Hand tapping has becoem an art form fro some reason. I've been using a handy formula for tap drill size since I was 10 or so (ol' Dad taught me a lot).

Tap drill sia = nominal thread diameter - thread pitch.

Thread pitch = 1/TPI.

for 5/16" -18 5/16" - 1/18" - 0.257" tap drill size letter "D" is best and 17/64" is very acceptable.

Hand tapping free-hand should commence with a taper tap - the one with the long skinny tapered start. Apply balanced two fingered torque to both handle of the tap wrench when starting reversing the tap every 1/6 turn to break the chips. The tap will wobble at first then steady up. Check frequently for the tap's getting a square start with the end of a scale.

The long taper of the starter tap ensures the threads follow the axis of the drilled hole. If you free hand drill as well then a square hole axis might be problematical. Do your best.

WD40 is an excellent tapping agent.

Don't go any deeper than the first full thread. Finsh the hole with the plug tap starting carefull with the fresh starter tapped threads. Better yet finish the hole with a "gun" or spiral point tap.

08-06-2005, 03:07 PM
The first time you spend the money for a high-quality tap you'll wonder why you're spending so much. Then when you USE a high-quality tap, you'll understand. Personally, I like Hanson-Whitney taps, sold by Travers Tool Co. (www.travers.com) but there are a bunch of good brands.

WD-40 may not be the best lubricant for tapping steel, although Forrest knows a lot more about this stuff than I ever will. You might pick up a quart of "thread cutting oil" in the plumbing department to try. It's pretty cheap and a quart will last you forever. (If you can find a pint, so much the better.)

And all the stuff the others have said, especially be sure to statrt the tap STRAIGHT. I've got a Walton piloted tap wrench that was expensive, but it works great. (n.b. the cheap import imitations are worthless.) Or do as suggested, start the tap by holding it in the drill chuck until you've done a couple of threads, then switch over to a tap wrench.

08-06-2005, 03:37 PM
Just from a bad experience I had,,mike the drill bit. Some of my nonUSA bits are a few thou under the marked size. Check the book for the decimal size for fraction size. Jim

Tin Falcon
08-06-2005, 04:06 PM
Lots of good advice here. I am not the expert but have been around and have done some short run production tapping. I will pass on some additional advise from the factory rep at greenfield tap and die.
1) Use Moly Dee Tapping fluid. It extends the life of your taps and lab tests show that it reduces the torque required for tapping therby reducing breakage. It is a little pricey (about $10.00 a pint) and is available at MSC. www.mscdirect.com (http://www.mscdirect.com)
2) Pay the extra for coated taps. Again this reduces required torque and extends tool life.
Again this advise is from a tool salesman.

I have used the moly Dee at home and in a a pro ' shop it works well and does seem to reduce required torque.
Aso two flute taps are stronger than 4 flute. one machinist I worked with hated 4 flute taps for this reason.
Usual disclamer!!

08-06-2005, 05:14 PM
If you're not doing a lot of tapping in many different sizes, it's probably better to buy a good quality tap as you need it, rather than buying a set. I find that I need only about 5 tap sizes, and almost never do I use the dies. I don't buy taps at the hardware store, I buy them from a machine shop, and I buy the ones they use. Yamawa has been good for me, and I do not like any tap that has a mottled looking finish on it.

I'm starting to make alignment blocks out of plastic to use for hand drilling and tapping. If you drill and face them on a lathe, the hole will be aligned perfectly and they're quick to make. In use, the block will hold the tap straight and also let you get a feel for how you might be pushing the tap sideways as you turn it. The block will lose it's flat contact to the workpiece if you do that.

I've also started to use a small cup for cutting fluid. Now it's just a quick dip of the tap in the cup, no more squeezing a bottle or pulling a trigger to get some cutting fluid on the tap. This means I'll keep the tap lubed more often. The cup I made from a pvc end cap and a flange of some kind. It's been awhile, I don't recall if I had to machine the parts to fit, but in any event the solvent cement sealed it. The flange is the base, and the end cap I drilled a 3/4 inch hole into for filling and dipping a tap through. I don't bother with a lid of any kind for it, though a rubber stopper might be a good idea. It's very stable and doesn't spill easily.

Something else I find with tapping is that as you reverse the tap to break chips, it can get stuck easily. I find that if you then turn it forward another quarter turn or so, then reverse again, that it results in the chips breaking off more easily. There's a certain amount of forward turn before reversing again that results in the easiest tap removal. This is something you just have to experiment with.

08-06-2005, 06:51 PM
I have a *lot* of trepidation about disagreeing with Forrest about anything, but perhaps those of us with far less experience and less "feel" for tapping are better off with a more, er, robust tapping fluid than WD-40. I've done waaay better with sulfur oil (1 gal. Mobile Gamma = lifetime supply) than with anything else, especially that mouse milk from tapmagic.

I also tend to drill the hole in the mill, remove chuck, insert center, and tap in place to insure correct alignment. This does take longer than doing it right the first time the other way, but sure beats doing it over.

Good job, meincer, in getting that response from the resident "New Hand" columnist. 8)


08-06-2005, 07:06 PM
Here is another idea for you to have a look at, these little thing-a-me-bobs keep the tap at right angles to whatever your tapping. This might be a solution to your problem.


reegards radish

08-06-2005, 07:08 PM
Mouse Milk, Now thats an image I will never shake.

Your Old Dog
08-06-2005, 07:28 PM
I was busting taps left and right until one guy posted this. "In my experiance most taps are busted due to not going in straight"

I got hyper critical about going in straight and have not broken one since. I suspect if you really are having that much bad luck you have the same problem.

It helps me to eyeball the tap to get it as perpendicular as possible and I hold the wrench in two hands. I make the first few revolutions very slowly and very deliberate. I generally take 1/2 turn in, 1/4 out, 1/2 in, 1/4 out...... Then, after I've made about 2 or 3 full turns I remove the tap and clean off the debris and start it back in again.

I guess if you're going in no more then 3 times the diameter of the tap it's about right. Any more and you'll likely have trouble again. I use Tap Magic but confess I think it messed up the paint on my lathe after much use.

[This message has been edited by Your Old Dog (edited 08-06-2005).]

08-06-2005, 07:34 PM
I've tried to have conversations with the nice people down at the local ACE hardware store to convince them that they are way behind the times in much of the machinist type items they carry. "You should sell spiral or gun taps instead of those old plug type" Hah.

Greg C.

Tin Falcon
08-06-2005, 09:34 PM
A tap guide either shop made or comercial could also help.

08-07-2005, 01:23 PM
I started using a tapping wax and found that works really well. Had to tap 6 blind holes freehand to repair a backhoe solenoid the other day. Less messy than the oil and tends to keep the chips stuck to the tap,which is useful for blind tapping. The stuff I have was made by Castrol. I use it for all my hand tapping.

I've used the Bridgeport for power tapping 1/4 through 3/8. Drill hole, replace drill with tap and plug it through. Through holes
only, of course. Anything smaller, I'd want to use a tapping head.

Guides are useful, but you can do it freehand with a little practice and attention. It's easier with the larger sizes; I wouldn't try a 2-56 by hand. Maybe 4-40, 6-32 is generally OK.

08-07-2005, 01:38 PM
<font face="Verdana, Arial" size="2">I think I need to invest in a good set of HSS taps</font>

...and a can of "Rapid Tap".