Y'all Ain't Gonna Believe This One

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Global Moderator
Staff member
H-M Platinum Supporter ($50)
Feb 8, 2014
Yesterday I was looking for a reamer in a box and found a 1/4 inch solid carbide spotting drill in the bottom. So I put the drill in my countersink rack.

Today I broke a 5/16-18 tap about 5/8 deep in a part, a brand new OSG spiral flute. This of course was the last operation on a matched pair of parts. :mad: So first try the normal stuff to get the tap out, needle nose pliers, tapping on it with one of my broken bolt removing punches. Nope, it was stuck tight. OK, probe around a bit with a carbide scribe to remove any loose pieces on top, and blow out with the air hose. Then try a carbide cone burr to see if I could plunge into it. I got a little way, at least I had a good center divot. Then I tried a 1/4 ball carbide burr, it only went down a little ways but did give me a nice wide starter center for something.

Then I thought of the spotting drill, chucked it up, and started chewing on the tap. About 500 RPM, a lot of pressure, and mist coolant. It was going through it fast enough that I thought the drill was being pushed up into the chuck, but I actually managed to DRILL the tap out with the spotting drill. This would not have worked had I not prepped the operation with the carbide burrs to give the drill a good center to start in, the drill bit would have just walked sideways and shattered.

This tap used to be about 5/8 longer

This is what the tap used to look like. I like these for blind holes, they pull the chips up rather than packing them into the bottom of the hole.

One drill flute came out fine

Chipped the other flute a bit when the tap broke up in the hole and caught the lip.


H-M Supporter - Gold Member
Staff member
H-M Supporter - Gold Member ($25)
Jan 31, 2016
Jim , I'm in at work now , and that is most of the machining I do now-a-days . We blow filters thru super heated extrusion dies and they constantly break the grade 8 bolts in the dies . I have to pick up the holes and get a good spot for drilling these out with either cobalt or sending an endmill down thru them . I then have to chew out the remaining threads in the holes . I use high hook taps and most of the time I get lucky . Sometimes I don't , and snap ! I break out the carbide ball mills and go right thru the taps . I have the spotting drills also but they tend to walk more than the ball mills . These holes go from 6-32 and up to 1/2-13 . They keep me busy ! ( but not tonight ) ;) We also have the edm's when needed .

+ 1 on the exo-taps .......................best taps made !
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