View Full Version : Cutting a keyway in a small dia blind hole

04-24-2005, 10:53 PM
I have been unable to cut a 1/8" wide key way in a 0.50 bore hub (1018 steel and blind) using a HSS parting tool blade held flat in the tool post of my 10" lathe. Although I have advanced the cut approx 0.002" with every stroke, the cutter deflects towards the center of the bore.
Any suggestions for making a stiffer holder
or using a different method would be really appreciated.
Thank you

04-24-2005, 11:26 PM
Maybe use a 1/8" center cutting endmill to mill the major section producing a sort of "U" shape then shave off the corners with the parting tool. JRouche

04-24-2005, 11:59 PM
I have had good luck using boring bars with the desired shape and size toolbit for cutting small keys, oil grooves,etc obiously it would have to be very small for your application. The principal is the same as what you are doing though so I'm not sure that it would work any better

04-25-2005, 12:40 AM
Try increasing the rake angle on the cutting face of the tool and make sure you have at least 5 degrees clearance angle between the tool and the cut surface.

I recently found this out cutting a square hole on a shaper. The sides of the tool had zero clearance, the face behind the cutting edge had 5 degrees clearance and the face of the tool had 30 degrees rake. I could advance the cut on the side with 5 degrees clearance, but could not cut sideways with the tool. If I had it to do again, I would put side clearance on all sides. The 30 degree rake reduces the side force deflecting the tool.

04-25-2005, 08:11 AM
Try using a narrower tool and doing the width in two (or three) steps.

04-25-2005, 09:10 AM
if you're using a parting tool, i doubt its the tool itself thats deflecting.. i'm guessing the parting tool is at least 1/2" x 1/8", probably thicker (1") outside the bore. i'm guessing you ground down only the part that fits in the hole.

sure its not sliding under the screws? or your turret isn't turning a bit? parting tools are usually tapered along their height and may be tricky to bolt down solid.


04-25-2005, 09:26 AM
as others suggested, sounds like something is hitting or rubbing. boring bar or make something out of drill rod would be my choice. btw, if you've not already done so, drill a small hole (design permitting) across the bore at the local where the keyway ends. Then you're not cutting a blind keyway

04-26-2005, 11:56 AM
Every one, Thanks for the insight.

04-26-2005, 05:46 PM
Put a stub shaft in the hole, drill a hole on the dia. with a 1/8" drill and clean up with your parting tool.