tapping very small blind holes in copper

[rschultz@asc]

hello this is my first time using this site n i am looking for help. i am using a milltronics rw15 machine. i am currently working on copper that is roughly .5 inch thick. drilling and tapping many holes at 0-80 and 2-56. i am breaking taps repeatedly and not sure what i am doing wrong. i have drilled the holes .040 past the tap depth and have tried pecking and cant get anything to work.

[rschultz@asc]

i forgot to add i am using a floating tool holder and have a strong stream of coolant flowing. i am also using a forming tap.

[Caprirs]

What size are the holes after drilling? If you're using a H2 or H3 tap, the 0-80 should have a hole about .055" and the 2-56 should have a .078" hole.

What rpm are you running the spindle at?

[DSIF]

Just my 2 cents. You need to drill deeper because .040 is not enough-and floating tapping heads are not too great at holding a specific depth. Also,copper is gummy. Make sure you have enough velocity on the tap so it will not grab and break. Coolant may not be the best lubricant for copper. You might try manually putting Kingsford lighter fluid or kerosene in the holes before you run the taps.
Dan

[rschultz@asc]

What size are the holes after drilling? If you're using a H2 or H3 tap, the 0-80 should have a hole about .055" and the 2-56 should have a .078" hole.

What rpm are you running the spindle at?

a chart i have for taps says .052 and .073 for 50% thread.
i am running my machine at 500 rpm

[thedave]

I would check with the manufacture on hole size. Forming taps use different drill sizes than cutting taps. I learned the hard, expensive way.

[RICHARD ZASTROW]

Just for $h*ts & giggles, try spraying your tap with "Pam" cooking spray. I remember using it to turn copper rolls where there was copper buildup on a PCD insert.

Also, thedave is correct, forming taps require larger holes.

Dick Z

[ebrewste]

+1 on the different hole size. Here is the first hit for a Google search on form tap drill chart. Worth printing out.

Form Tap Drill Chart

[SORCHEROR]

can you rigid tap in that machine?should use solid tap holder,and form taps drill size is bigger than normal taps,plus for copper coolant is good,try a good tap fluid

[rschultz@asc]

thanks guys.. i appreciate all of your help and believe for now i have found a solution. i am using a rigid tap holder and i set the machine to reverse at the same rate as the infeed rather than 2x. its working so far and thanks again.