gun drills keep breaking!

[slidingheadfred]

hi, i would be greatful for any help at the moment, i am trying to drill a 6.5mm dia hole horizontaly in en1a material to a depth of aprox. 95mm on a citizen l32 machine using a gurhring gun drill with coolant holes, sorry cant remember drill spec. but have been given spindle speed of 3427rpm and a feed of .1mm/rev straight in, no pecking cycle.
This seems to work on the back end (T3500), but on the front end (T2400) it will make three or four and then break the drill with no apparent warning.
currently using high pressure coolant through both drills T35 & T24.

Thanks for any help in adavace.

[RICHARD ZASTROW]

Is this a true gundrill or some kind of coolant fed twist drill or? What I refer to as a gundrill usually has one flute off-set so the point is at 1/4 of diameter.

There are the cutting edge and two carbide pads that guide the drill thru a bushing and then thru the hole the tip cuts. Sometimes a shallow hole is drilled as a "start hole" because the point is eccentric and can't start a hole without guidance.

There are modified geometries to this basic form.

The speeds are usually high and feeds very small. Chips must curl into small "ice cream cones" that curl into themselves and break free. The high pressure high flow coolant then flushes the miniature chips past the drill shank and out of the hole.

If the chips do not break they will become stringy, wind around the drill body and the drill will break.

Hope this helps.

Dick Z