What Taps do you buy?

[Tin Falcon]

The discussion about broken taps got me thinking. What kind of taps do you use? 4 flute hand taps are great for breaking. Unfortunately that is the only kind I have ever seen illustrated in text books.

I tend to use spiral point taps for through holes.The chip is pushed in front of the tap and out the bottom. For blind holes I use spiral flute the geometry pushes the chip up and out of the hole.

Yes these are considered gun taps, for powered applications. I use these by hand all the time. I do use a tap guide. Somehow I have managed not to break a tap in a long time. I think tap selection has a lot to do with it as does the correct tapping fluid for the job.
Tin

 

[rake60]

All of my taps are spiral point.
I have at least two of every size and one is ground flat to use as a bottom
tap. Grinding a small tap is a tricky thing. It's very easy to get it warm
enough to ruin it.

 

[Lew Hartswick]

AGrinding a small tap is a tricky thing. It's very easy to get it warm
enough to ruin it.

Not if you buy high speed steel ones. Thats all I'd buy.
...lew...

 

[compound driver]

HI

Il echo that HSS taps are a good choice for most materials. Spiral point are for high speed tapping and not needed for hand tapping unless your going onto some of the exotics and even then there not always an advantage.

Taps break for two reasons. clogging with swarf increasing the torque effect and side loading on the tap.
The first is easily cured by backing the tap out half a turn every turn. This one is simply good tapping practice.
Second keep the tap verticle and avoid bending the tap over. This breaks more taps than anything.

Proper lubrication is all important. In cast iron tap dry, in mild steel use a good grade of cutting oil designed for reaming and tapping. In aluminum use parrafin or kerosine. Copper use either tallow or cows milk. Brass again dry. Phos bronze can bennefit from using a drop of almost any cutting oil. Aluminium bronze a mix of lite oil and way oil helps a bit but its still a sh*t to tap.

Selecting a tap for the job is also important. Always buy taps in sets of three NEVER as just one tap. The order of use is first, second, and then finish with the plug for bottoming and ending.

Drill sizes should be thread core minus a few thou. LBSC in his works in model engineer listed drill sizes that were slightly larger than the recomended drill by a few thou. This certainly eases tapping and has so little effect on the root or tops of the threads as to be unimportant.

if a tap look blunt replace it and if it looks like its lost a tooth replace it.
If you do break a tap in non ferouse a bath of salamoniac will rust the broken tap out in a few days or a week with HSS. If the work is non criticle heat wise softening the tap some times lets you drill the break out. The other option is to have the tap spark eroded out this is the best option I know as it does not effect the work.

One old trick is to take the broken tap lay spring wire down the flutes wiring the spring wire on using half a dozen turns of coper wire and inserting the tails of the spring wire into the flutes of the stuck tap section. This will let you wind the tap out if its in any way loose in the thread.

Cheers kevin

 

[Lew Hartswick]

HI
Drill sizes should be thread core minus a few thou. LBSC in his works in model engineer listed drill sizes that were slightly larger than the recomended drill by a few thou. This certainly eases tapping and has so little effect on the root or tops of the threads as to be unimportant.
Cheers kevin

I think that approach may give a tighter fit than necessary. A 70% thread
will give a strength greater than the screw if the taped hole has a screw
diameter or more depth. Most of the tapping charts are for a 70% thread.
Now if you get into thread forming that is another game entirely.
...lew...

 

[compound driver]

Hi Ian

I tend to agree with you on some points but given the discusion was about avoiding breaking taps HSS is the better option. Cant ever remember breaking an HSS tap but a few CS certainly.
yes carbon steel is fine for most jobs, and preferable in cast iron.

Most days for either work of traction engines I go all the way down to 18 BA
and have to say i cant remember the last tap i broke. Care and practice is a lot of it with saving taps from an early grave.

if your finding HSS taps pricey give these people a try "Horley drill services". Superb range of tools from milling cutters to almost any drill bit you could dream up. Plus if you need a special reamer they will make it for you in a week or so. prices are superb as well. Before you ask i dont own stock but i wish i did the amount i spend in there. They also ship worl wide.

Cheers Kevin