Hand Tapping question

[A.K. Boomer]

What is the standard procedure for hand tapping? I was taught in metal shop as a kid that you go so far in and then back out a quarter or half turn then go in again and repeat, I just hand tapped my angle plate doing this and while reversing i back dragged the lead teeth of the tap and chipped some, yet there was no way i could have just kept going in the foreward direction cuz i woulda broke the tap, was this one of those "I had to do whatever it took because the material was so hard" examples?
I used cutting oil but nothing fancy...

[Ken_Shea]

A.K.
Sounds like you went a bit to far, when hand tapping hard material I always use some sort of appropriate tapping fluid and take it slow backing it out frequently and cleaning the tap threads of cut material prior to next tap.

On harder material, a little tip is to drill oversize just a bit, a few thousands can make a big difference in the ease of tapping and makes little difference to the final
result.

Chipping a few threads is better then breaking the tap.

EDIT:
Another thing is to always check the tap cutting edge for problems prior to tapping, they can get messed up pretty easy if one is not careful and you wont know it until it breaks and then we wonder why. Same goes for end mills, drill bits, I always give them a good once over before using them.


Ken

[lenord]

Hand Tapping

AK,

Also might want to make sure you have a good brand name tap. Hertel is about the bottom of my list. HF taps and the like are not worth it IMO.
Type of tap for the hole, coated or not, flutes etc. also need to be considered.

FWIW
Lenord

[Millman]

Handing.

Come on, AK, once you hand tap 2 holes; you see the "Feel" of the next hole. There's no big mystery doing the third hole. You will feel the crunchiness or stringiness of the material. By the way...how ya been? No hard and fast rules to tapping...hand or machine. Some will make you think otherwise..all in the FEEL.

[Your Old Dog]

My trouble was always not starting square to the hole and sinking the tap in not-plum. Made a jig to start them in straight.

I remove the tap from the hole at least 4 times and clean all the threads with a tooth brush and then put on more Tap-Magic and commence until done. This is time consuming but it works.

Like Ken said, I always go up on size in drill size over that reccomended. (I have the big set of drill bits with the Letter and Number drill sizes as well as fractional)

Slow, but it works for me.

[Millman]

YOD is right, harder the material; the larger the hole diameter. Strength of the bond is determined by the surface contact. No big deal.

[Spin Doctor]

YOD is right, harder the material; the larger the hole diameter. Strength of the bond is determined by the surface contact. No big deal.

Does that mean in diamond a 1/4-20 gets a .250 hole??? Also if one is using one of the so called "Gun Taps" that generate a continuous chip that gets pushed down the hole in front of the tap you must have a through hole. Otherwise the chips will build up in the bottom of the hole. Also in these cases you are better of to tap straight through. Backing the tap off will lead to chipped teeth on the cutting edge

[Rustybolt]

If you were tapping cast iron you're not supposed to use any tapping fluid. Just tap it dry. Still I don't think packed cast irion dust would chip a tap. maybe there was a hard spot in the casting , or some sand.

[A.K. Boomer]

You Guys make allot of sence, I should have went slightly oversize instead of going by the book, i had all the strength in the world and it wouldnt have hurt a thing, For the record this was a brand new tap that i bought from Fastenal (china) but i did have it totally centered and chucked up in a collet on my mill -- i used a wrench on my draw bar to go fore and aft and babied it in and out and removed it at least 7 times to clean all the chips out of the hole...

Now that i think about it maybe the collet was not such a good idea, maybe taps arent ground perfect and you want just a little forgivness?
Also going through the length of the spindle I will admit I lost the "feel" as Millman stated,(even though the tap was a 1/2 13) a short little hand tapper and using the mill spindle as a dead center would have given me back the feel for the elasticity of the material.

Thanks for the tips... When in doubt -- go a little oversize, when stupidity cost you either materials, tooling or limb the lesson will not soon be forgotten

[gizmo2]

Sounds like you're on the right track, boomer. Nah, you can't just keep going forward, you have to back her all the way out occasionally and clean out the crap. If the flutes pack up solid with material you will break the tap. And, as you can visualize, the smaller the tap the smaller the flutes so the more often it needs to be cleaned out.

Yup, you need to be able to feel the progress whenever possible. Several firms make a chuck for hand tapping in machine alignment. A shaft chucks up in your tail stock (or drill press) then you can spin the tool/tap by hand. The one I've got is by B-Square, and it has paid for itself many times over. If you need to chuck up the tap itself, just get the hole started straight, then finish the tapping by hand. Another useful idea is to buy your taps in sets. You will get a starter, a plug, and a bottom tap. Each has a different leade ground into them. Sometimes a started tap is the only thing that will get you going in tough material, but they are REAL easy to start crooked.

[BobWarfield]

Type of fluid matters too. I always use Tap Magic for tapping because it just seems to work best.

Sometimes its a good bet for cutting too, but I keep squeeze bottles like you get at the five and dime for ketchup and mustard that have kerosine and heavy sulfurized cutting oil. I also keep a can of WD-40. Aluminum seems to like WD-40 or Kerosene when cutting, for example.

Best,

BW

[JCHannum]

Country of origin matters also. China and India have yet to produce any cutting tools that are worth the money.

Buy good USA, Israel, European or Japanese taps. It is worth the extra couple of dollars.

And, a good tap can be tapped through without the need for reversing. That is what they were made to do. Watch a tapping head at work. You do have to have a place for the chips to go.

[Mcgyver]

no need for the reverse motion every 1/2 turn of so with CI if thats what you are tapping, this motion is to break the chip which obviously isn't there with CI. Like Millman says, its a feel, material, % engagement, tap material, sharpness and even geometry (number of flutes etc) all come into play.

I'm cheap and hate breaking anything. sometimes when using small little taps, the torque needed to turn it and seeing little tap twist causes the Scotsman in me to break a sweat. The trick i like to use in these instances is to alternate between a taper and bottoming tap, this greatly reduces the amount of material each has to remove.

[kap pullen]

Spin any way you want!

Does that mean in diamond a 1/4-20 gets a .250 hole??? Also if one is using one of the so called "Gun Taps" that generate a continuous chip that gets pushed down the hole in front of the tap you must have a through hole. Otherwise the chips will build up in the bottom of the hole. Also in these cases you are better of to tap straight through. Backing the tap off will lead to chipped teeth on the cutting edge

Yea, thats right Spin! Drill it .265 and put a bronze helicoil in. Stronger than the base material in c.i. and aluminum. That's what we send up in space.

Oh yea, you don' have to have a thru hole for a gun tap either. Just drill it deeper to allow room for the chips at the bottom.

Kap

[A.K. Boomer]

Good to know, the angle plate wasnt cast iron though -- it was steel, it had a case hardening to it but i removed that with a carbide endmill, then i had to cross drill though a pre-fab hole, this hole went through the same treatment that the outer parimeters of the angle plate did for hardening, i bet when i tapped through the cross drilled part of the hole is where the trouble started although it was still pretty tough everywhere else... Im also going to check out that tap chuck Giz is talking about, i do need to get something like it, thanks for the advise.