DIY extra length 16mm drill bit

[bob ward]

I needed an extra long 16mm drill bit for a one off job recently. I'm sure someone sells them but I couldn't readily find them and they are probably too expensive for a one off. The drill bit I wanted to use is a reduced (1/2" 12.7mm) shank and in crude terms I put a 1/2" hole in the end of a piece of 16mm bright round and used loctite to glue the drill into the extension

The trick of course is to make sure that the extension ends up being concentric and straight with the drill bit, I'm making a 200mm long hole through a block of aluminium.

Holding the 16mm bright round in an ER32 collet in the headstock I first drilled a 12.5mm hole to the required depth. Lacking a proper 1/2" reamer to give me an accurate 1/2" hole I used a 1/2" drill bit as a reamer with surprisingly good results going by the "pop" test - when I pulled the drill out of the extension it made a pop sound which to me means the hole is a good fit. I added some bearing mount Loctite and the extra long drill bit was good to go.

Its a slow drilling/pecking process of course once the flutes are buried in the hole. I was clearing the drill every 10mm, I wanted to stay well away from overpacking the flutes with swarf.

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[KBs PensNmore]

Hi Bob, in image 2006, your aluminium block is sitting in a steady, what is the round thing, and how is it attached??
Kryn

[BaronJ]

Hi Kryn,

Its a spider ! Basically a tube with four bolts supporting the work.

[bob ward]

The end of the block has 4 tapped holes as part of the design of what I'm doing, I used those holes to connect the steady adaptor to the block. The steady adaptor is a repurposed old hub from the scrap pile.


Hi Bob, in image 2006, your aluminium block is sitting in a steady, what is the round thing, and how is it attached??
Kryn