Never broke a tap before. Just broke two in about 5 mins!

[devils4ever]

As the title states, I've been very careful when tapping and have never broken a tap before today. I was threading a 1/2" piece of 1018 steel with a 1/4-20 spiral point tap. I used a guide to keep alignment and prevent breakage. I was only 2-3 threads in and snap! I was able to get out the pieces out without too much trouble. On attempt 2, I clamped the guide to the piece to prevent any lateral movement. Same thing happened again!

I had no more spiral point taps left, so I used a spiral flute tap and started on the other side and was successful. Very strange. I wonder if I hit a hard spot or something?

 

[matthewsx]

I’d say you were lucky, you got them both out

 

[Nutfarmer]

The quality of steel can very a lot now days. I have come to the point of not trying to even machine the last inch of a hot rolled bar because of hard spots.

 

[benmychree]

The quality of steel can very a lot now days. I have come to the point of not trying to even machine the last inch of a hot rolled bar because of hard spots.

Perhaps because of the sheared ends?

 

[FOMOGO]

Could have just been flawed taps, or as said, funky steel. If that's your first occasion to break a tap, I'd say your doing something right. Mike

 

[devils4ever]

There were both quality taps. One was Widia and the other was Hy-Pro from MSC or McMaster-Carr.

Luckily, it was only a few threads in so it was easy to get out.

 

[Mitch Alsup]

I never tap anything without using heavy cutting fluid.

Were you using cutting fluid or Tap Magic ?

 

[woodchucker]

what size drill bit did you drill with?
Very odd, the spiral flute is a weaker tap than a spiral point.

 

[devils4ever]

Yes, I was using Tap Magic and a No 7 drill bit.

 

[Bi11Hudson]

As a rule. the tapping-drill charts were devised for maximum thread depth in moderately hard material. From the reference to a Nr 7 drill, I would say you were cutting 1/4-20 threads. Unless I need full thread depth (seldom) I will use the next larger drill. ie. For 1/4-20 I will use a Nr 6 wire size. Or, quite often in the field, the fractional equivilent.

For very hard steel, I am careful to use a new or nearly new tap in addition to the oversized drill. Most of my projects these days involve softer materials such as aluminium, brass, or zamak. But the tap sizes are so small that an oversized drill still pays off. When the tap drill gets below a millimeter (Nr 60) size really does matter.

Then there is the matter of starting the tap true to the hole. In smaller sizes, that becomes a serious issue. 1/4-20 screws are large to me, 2-56 is my nominal midrange. When I do work with larger sizes, I tend to be overly conservative of torque. A 1/4-20, to me, is tough. A 5/8-11 is a tree for strength. Should you be working the other direction, over-torquing a small tap would be easy.

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