Producing half (or 2/3rd) round holes

[Andrew TinsleyParticipant @andrewtinsley63637]

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.

[Andrew TinsleyParticipant @andrewtinsley63637]

[JasonBModerator @jasonb]

Yep

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks Jason,

Interesting looking broach. Is it a home brewed version?

Andrew.

[Simon Williams 3Participant @simonwilliams3]

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?

[JasonBModerator @jasonb]

Yes, home made cutter.

Broach hole first, mount on arbor or in this case the engine's crankshaft to turn the rest, see here

[Anonymous]

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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