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Boring bar and drill selection

Howardd

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#1
I need to bore a few 1 1/2" dia blind holes about 2" deep in brass. The bottoms do not have to be perfectly flat. I was thinking of drilling to about 1 1/8" diameter and then using a boring bar. I am not considering buying a 1 1/2" drill as I want to get experience in using a boring bar.
For the drill bit which is better 118 or 132 degree time?
I was thinking of getting the Aloris adjustable chip breaker boring bar but am open to suggestions for other bars.

Thanks

Howard
 

Bob Korves

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#2
I need to bore a few 1 1/2" dia blind holes about 2" deep in brass. The bottoms do not have to be perfectly flat. I was thinking of drilling to about 1 1/8" diameter and then using a boring bar. I am not considering buying a 1 1/2" drill as I want to get experience in using a boring bar.
For the drill bit which is better 118 or 132 degree time?
I was thinking of getting the Aloris adjustable chip breaker boring bar but am open to suggestions for other bars.

Thanks

Howard
118 or 135 degree drills will work, but they will need to be modified so they do not dig into the brass. A small axial flat below the cutting edge needs to be ground onto the drill bit.
Most boring bars will work, but it will also need to be positioned for a neutral rake, and not cutting below the lathe center axis.
 
Last edited:

Wreck™Wreck

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#3
Twist drills will screw themselves into free machining 360 brass WHEN a smaller pilot hole is drilled first. There is no reason not to spot first then drill to size in one operation then finish by boring.

In order to minimize the drill point angle at the bottom of a blind hole begin with a drill size slightly larger then the minimum diameter that the boring tool will fit into, beware of the lack of chip evacuation however.