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Finding original centre using cutting broach only??

NEW65

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Nov 17, 2010
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Hi Chaps.
My query is:
Why is it necessary to file a worn hole? If a cutting broach is pushed tightly into a worn hole it will automatically position itself on the unworn side and will stay in that position. Gradually broaching the hole out will form the new hole with the original centre? Surely? You would have to use the pin vice to achieve this of course.
I would like your views please?
Thanks
 

Schatznut

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Sep 26, 2020
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Hi Chaps.
My query is:
Why is it necessary to file a worn hole? If a cutting broach is pushed tightly into a worn hole it will automatically position itself on the unworn side and will stay in that position. Gradually broaching the hole out will form the new hole with the original centre? Surely? You would have to use the pin vice to achieve this of course.
I would like your views please?
Thanks
Seems to me that the broach will find the path of least resistance and tend towards the center of the hole. By nibbling the side opposite the wear, you are in effect moving the center of the worn hole back towards where it was when it was unworn.
 
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disciple_dan

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Mar 10, 2016
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I think the broach would want to cut at the point of least resistance. In that case, it would be tight on the unworn side but cut at the two points of the smaller worn side causing it to drift to that side. Just a thought, Danny
 
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shutterbug

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I do exactly what you are describing. I use the correct size reamer unless it's a really big bushing, and lower it slowly while allowing it to nibble the edges until the hole is round. You have to make sure the plate is clamped tightly in the proper position for the hole, and then watch it while you nibble. If the plate moves even slightly you have to reposition it and start over.

EDIT: Ooops! You were talking about a broach, not a reamer. In that case you have to file the hole in the opposite direction so when the broach "finds" center it will be in the center of the hole. Otherwise it will take the course of least resistance, and your hole will be off by 1/2 of the wear.
 

bangster

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What Shutterbug said. :thumb:
 
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