Need Help on Gun Drilling....!

[Thiyaggu]

Hello all,

we have a problem with the gun drilling process at the Swiss turn

The Part is about 150mm long & ø 3.5mm which we are processing in swiss turn, & it has a thro' hole of ø1.8mm.
Due to the smaller diameter, we planned to drill from both sides for about 80mm deep.
And we are using a Single flute Carbide Gun drill.
The material of the part is SS455
But unfortunately, the drill is not matching at the center of the part always it has offset.
Below are the Parameters.

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[Waznik]

I am new here, how do you create a post ?

[DMGFANUC]

The Part is about 150mm long & ø 3.5mm which we are processing in swiss turn, & it has a thro' hole of ø1.8mm.
Due to the smaller diameter, we planned to drill from both sides for about 80mm deep.
And we are using a Single flute Carbide Gun drill.
The material of the part is SS455
But unfortunately, the drill is not matching at the center of the part always it has offset.

shouldn't gun drill follow whatever is there... your pre drilled hole

[Thiyaggu]

Pre-drill we do max. up to 12mm

[OldSchoolProgrammer]

I don't know what sort of work holding setup you have, and you didn't specify the direction and amount of offset, so I'm kind of shooting from the hip here. A setup with a spring loaded retractable locating pin might work for you. The pin would be pushed down by the face of the part on the first operation, but would enter a drilled hole when you turn the part around for the second operation. If you are currently using two different fixtures, the second one with a locating pin must be oriented very precisely.

Some shops get completely away from a gun drilling machine and use a vertical milling machine with high spindle speed capability. They use a center drill and a stub length drill to start the hole, drilling down only about one and a half diameters deep, then finish with a gun drill rotating it at just a couple of hundred RPM, not revving the gun drill up to optimum speed until the gun drill is one diameter deep in the shallow starting hole. A second fixture is designed and built with a locating pin and features for to indicate for positioning and orienting it with great accuracy.

[deadlykitten]

hy align the long drill, use it after a pilot hole, and don't turn on high pressure coolant too soon

main trick is into alignmnt, such as small tools, may simply be missalingned because of the force used to mount/dismount them, thus be sure that tool mounting force is gentle enough to keep previous alignment ...

for specific details, if you are still interested, pls share some photos with machine cabinet / kindly