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Turning small diameter taper using tapered end mill


Nov 3, 2019

I had to turn 20 degree internal taper to hole where smaller diameter was 8mm and upper 10mm. I didn’t have small enough boring bar so I used tapered end mill. Of course it didn’t come to my mind that due to having spiral flutes it tends to pull it from the tailstock and that’s what happened. It pulled the drill chuck from the morse taper and ruined the part. Fortunately end mill was ok. So the question is, is there any way to do this taper with this setup? If smacking the drill chuck harder to the tailstock and feeding super slow, would there be any chance to succeed in doing this?

Thank you in advance


Jun 24, 2019
Make a boring bar from a HSS blank. Not that hard to do.
Drill to depth, at the smaller size, then set the compound.
Test an aluminum blanker, and measure the best way you can.
Adjust and continue.

Step away from the tailstock.............


Dec 13, 2002
Benicia California USA
Endmills should never be chucked by a drill Chuck!
The D reamer is likely best solution.
If you wish to run the end mill then hold it in a tool holder on the cross slide. Indicate to be centered with the spindle,
plunge using the “Z” or turn the compound parallel with the “Z” (alla Europe) and plunge using the compound.
Cheers Ross


Jun 23, 2002
Vancouver BC Canada
Hi corn:
If the numbers you gave in your first post are correct, this thing is only 2.747 mm deep.
That's only 0.108".
This is a dirt simple thing to single point bore with the compound slide set over 20 degrees and a hand ground cutter or a standard endmill used as a small boring bar to poke in your tapered hole.

Even if you actually meant 20 degrees included angle and only 10 degrees per side, it's still only 5.671 mm (0.223") deep, also dead easy to do.

So no D bit grinding needed (although it's a perfectly viable way forward and is recommended if you have lots to make and want to be efficient).

Moving on to your desire to do it with the tailstock...you've already experienced the failure mode and there is no realistic way to make it bullet proof.

Two problems:
One is the one you experienced, pulling the taper(s) apart...the other is sucking in the cutter when the pull force takes up the backlash in the tailstock spindle and breaks off the cutter.

As a safe alternative, mount and center the cutter in the toolpost and feed in with either the carriage or the compound slide, depending on whether the carriage has backlash or not.

But as others have already advised, by far the least fucking around though, is to grab a 1/4" endmill in the toolpost, line up one of the cutting edges to be on center, swing over the compound to the correct angle and go to town.
Getting everything set up shouldn't take you more than 15 minutes unless you need to make a holder for the cutter.
Turning it also shouldn't take you more than 15 minutes unless you need it super accurate.


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