But I've done this 1000 times

[RaisedByWolves]

Never discount the occult. Could have just been bad Ju-Ju. Nice tap guide there Charles. Mike

I do all of my fine work inside a pentagram made out of salt (Kosher salt mind you) to keep the heebie jeebies at bay.

Not sure how the spirits feel about this, but it keeps my co workers from bothering me for a few days after.

 

[Larry$]

Yesterday I power tapped 54, 6mm holes in a 7/8" thick aluminum casting. 90 rpm on the mill. 5mm hole. Full depth in one pass, new tap. 50 X 50mm grid on my new fixture plate. Worked great. Aluminum casting was a part from a junked out machine. Photos today if I remember the camera.

 

[RaisedByWolves]

9/16" bit for 5/8x11. 7/16" bit for 1/2x13. 5/16"bit for 3/8x16. 1/4"bit for 5/16x18. No. 5 bit for 1/4"x 20 Never had a problem. Use a 82 degree counter sink on the lip to help the tap start on whatever size hole and if your braking taps buy new American made ones. Use lub. or spit when tapping. Use 4 flute taps.

You were doing good until that last part.


I only learned from this board after doing this for 35yrs about changing the drill dis for a deeper hole.

Never did this but it does make sense if your going past the 1.5x the dia rule in steel or 2x for aluminum.

We use primarily gun taps.

 

[rwm]

I am always learning here. I did not know it was possible to break a 5/16" tap???

 

[Larry$]

I did not know it was possible to break a 5/16" tap???

You aren't trying hard enough! I suspect the major causes of broken taps are: not getting them started straight & cheap taps. Power tapping on the mill is so much faster and has worked great for me, ... after I got good sets of spiral taps.

 

[GeneT45]

You aren't trying hard enough! I suspect the major causes of broken taps are: not getting them started straight & cheap taps. Power tapping on the mill is so much faster and has worked great for me, ... after I got good sets of spiral taps.

Probably over 20 years ago I broke a tap off in a project I had significant time and dollars into. I added to the cost by destroying an utterly useless Walton tap extractor (has anyone *ever* had one of those work? - I think they're worthless) followed by a couple of carbide drills (which are normally successful). After that I took up a study of tapping. I learned a lot, but the takeaways that really mattered are: use a high quality tap (not Irwin or Vermont American, or whatever is being sold at your local big box store) and get it started straight. Quality wrenches or tap holders are probably third on the list. I then went about 20 years without breaking a tap, until I tried tapping #2-56 x 3/8" in 17-4 PH. I forgive myself for breaking those (yes, multiples...).

GsT

 

[RaisedByWolves]

Probably over 20 years ago I broke a tap off in a project I had significant time and dollars into. I added to the cost by destroying an utterly useless Walton tap extractor (has anyone *ever* had one of those work? - I think they're worthless) followed by a couple of carbide drills (which are normally successful). After that I took up a study of tapping. I learned a lot, but the takeaways that really mattered are: use a high quality tap (not Irwin or Vermont American, or whatever is being sold at your local big box store) and get it started straight. Quality wrenches or tap holders are probably third on the list. I then went about 20 years without breaking a tap, until I tried tapping #2-56 x 3/8" in 17-4 PH. I forgive myself for breaking those (yes, multiples...).

GsT

Snake oil. I have had better luck breaking them up with a punch or chisel.

Last tap I broke was a 2mm ……something thread in a tiny aluminum RC heli motor mount. The whole mount weighed less that 2 grams and took me hours to make.

I got that one out with the battery acid and alum method and it worked great.

That was due to being cocky and wanting to power tap to start the tap, but not thinking how much momentum the mill had over that time tap.

The momentum carried it all the way to the shank and snapped it clean.

The hole even still had threads after the acid trick.