[McMaster]

Hello,

I would need a tooling to make round bottom holes. Diameters varies from 24mm to 45mm. Depths from 250mm to 350mm. Is going straight to round bottom drill bit a no go? I was thinking drilling maby first with a standard drill and then have two different diameter holders one for smoller holes and one for bigger ones. With a possibility to change the head for different diameters. Would this approx. 300mm hanging length require heavymetal/carbide holder or would it be ok with normal steel holder?

How would you go about it?

[ToolHIT]

Hi McMaster!

The best option I can think of is to use a standard drill to rough out the bore and then come in with a Internal Spherical Boring Bar (on a Lathe) or Ball Nose End Mill (on a Mill) to finish the bore to have the round bottom you need. It sounds like you would be running this on a Lathe so an Internal Spherical Boring Bar would be the best option but a Ball Nose End Mill could also work.

A Carbide or Chatter Free Bar would be ideal at the 250mm-350mm Depth, a Steel Bar would just not be rigid enough and would likely chatter. A Steel Bar can go 3:1 or 4:1 Length to Diameter, while a Carbide Bar can go 8:1 Length to Diameter and a Chatter Free Bar can go anywhere from 10:1 to 14:1 Length to Diameter based on what the bar is tuned to.

Hopefully this helps!

Mike