Bushing with Drill ?

[marc hildebrant]

Group,

All of the bushing discussions that I have seen talk about the use of broaches to make the bushing a circle again for the new bushing to be installed. Is there a reason that people do not use a simple drill instead ? You could clean up the hole with a smoothing broach ?

Marc

[Bob Tascione]

Hi Marc,
The problem with using a regular drill is that they can deflect easily which will lose true center. Some clocksmiths use shorter stub drills with success but better control can usually be obtained by filing opposite the worn side of the hole and then broaching.
Hope this helps Marc,

Bob

[marc hildebrant]

Bob,

Thanks for a clear, straight forward answer. Makes sense to me.

Marc

[david pierce]

Marc,
Bob is correct about the drill drifting. I spent several years in a tool and die shop and 22 years in a general machine shop. I know from experience that the only way to correctly deal with a hole is to first drill it undersize then bring it up almost to size with a single llip cutter and finally size it with a reamer. If extreme precision is required the hole can be reamed slightly undersize and lapped to the final size. The single lip cutter can be a boreing bar used on a lathe or a boreing bar used in a boreing head with a verticle spindle milling machine. If there is only a small amount of metal to be removed the broach will work fine. If a larger hole or a new hole is required the plate to receive the hole can be centered and fixed in a face plate and drilled bored and reamed. If a verticle spindle machine with X-Y movements is available the operation is a little easier.
David Pierce

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