Dedicated Morse Taper Center Drill Holder

The pandemic has allowed me the luxury of more time to pour over some of my machinist books. While reading Machine Shop Know How – The Tips and techniques of master machinists, I came across a very enticing project to make a dedicated center drill holder for my lathe tail stock.

Machine Shop Know – How by Frank Marlow

I started with a 3MT To 2JT Tanged End Drill Chuck Arbor purchased from Amazon for about $12.

Prepping the MT Jig

The center drill I selected to be used in the dedicated Morse taper fixture measured in at 0.248. I put the jig in the tail stock and used my relatively new collet chuck to center drill the jig with the collet holding the tool piece. Next the jig was drilled on the JT end just undersized and then finally finished out with a reamer. Again both operations were performed with the collet holding the tool pieces. I had to purchase a custom reamer for this and made the error of buying an exact fix reamer (0.248) which made the fit too tight for the first fit up. (Facepalm). I then ordered a reamer .001 larger (0.249) which after being reamed fit perfectly into the Jacobs taper end of the fixture.

3 Morse Taper to 2 Jacobs Taper Drill Chuck Arbor
Drilling the MT to JT fixture to accept the center drill
Final reaming of the MT to JT fixture to accept the center drill

Adding a set screw

The text states to grind a flat on the center drill bit that will be used to accept the flat of a future set screw. This is best done on the surface grinder since the bit is hardened.

After the center drill holder was properly reamed to accept the center drill tool bit I drilled and tapped the Jacobs taper to accept a #10-24 set screw.

Drilling the MT to JT fixture to tap and add a set screw
The MT to JT fixture successfully tapped to hold a #10-24 set scew to secure the center drill in place.
A dedicated MT center drill holder

The finished product came out well! I slapped the dedicated MT center drill into the tail stock and put a center indentation in a piece of scrap stock. The center bit did move a little more inwards before fully settling and bottoming into the reamed out hole and the set screw subsequently had to be lightly retightened. Otherwise all was well.

It works!

This is a simple tool but one that will add efficiency to the shop. This will be a pleasant addition to my lathe toolset.

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