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Producing half (or 2/3rd) round holes

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Andrew Tinsley	27/04/2021 19:22:32
1817 forum posts 2 photos	Just came across such a hole in a piece of kit I am working on. Just wondering how one would produce such a hole, presumably some form of broach? Andrew.
JasonB	27/04/2021 19:38:29
25215 forum posts 3105 photos 1 articles	Yep
Andrew Tinsley	27/04/2021 19:44:26
1817 forum posts 2 photos	Thanks Jason, Interesting looking broach. Is it a home brewed version? Andrew.
Simon Williams 3	27/04/2021 19:54:30
728 forum posts 90 photos	I've played with a square broach, and that follows the lead of the round pilot hole. The broach cuts equally (provided it enters straight) so the hole ends up on the same axis as the pilot hole. But this "D" broach is a different animal. How do you determine that the circular segment of the finished hole is co-axial with the OD of the work piece? On the face of it the flat surface of the "D" doesn't cut, so the material removed is one sided, as shown by the swarf. That means that the centre of the "D" moves sideways as the broach enlarges the circular segment. Or have I got it wrong, and it's actually very simple?
JasonB	27/04/2021 20:18:34
25215 forum posts 3105 photos 1 articles	Yes, home made cutter. Broach hole first, mount on arbor or in this case the engine's crankshaft to turn the rest, see here
Andrew Johnston	27/04/2021 21:37:46
7061 forum posts 719 photos	This type of hole is common on electrical components, such as connectors, that fit in panels. Panel holes are normally punched, although I use the CNC mill, or handraulic methods, for small volumes. That leaves a fillet in the corners, but it only needs a couple of licks with a file to remove the fillet. Andrew

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