Trepanning (drilling): What is trepanning?
This tool maker explains "trepanning"
"a surgical intervention in which a hole is drilled or scraped into the human skull, exposing the dura mater to treat health problems related to intracranial diseases. It may also refer to any "burr" hole created through other body surfaces, including nail beds. It is often used to relieve pressure beneath a surface. A trephine is an instrument used for cutting out a round piece of skull bone."
Now used in metalwork as well.
In medicine, the trephine is simply a saw that cuts a hole in bone, typically the skull. AKA "burr holes"
The word bore can be used interchangeably with trephine. At least that's how we use it in medicine.
Unfortunately, the word "bore" has a very specific meaning in the metalworking world. It refers to the hole forming method done with a boring bar on a lathe or with a boring head on a mill. Referring to a trepanning operation as "boring" will cause confusion.
Take a look at the flywheels on this engine...
Each flywheel is cut from the solid. The process of removing the material between the hub and rim to form the web is called trepanning.
Last edited by mklotz; 08-30-2019 at 04:17 PM.
Home Shop Freeware
Thanks guys. Not wishing to contradict or confuse I quote from page 1051 of the 28th edition of Machinery's Handbook (which some refer to as the world's principal reference work for metalworking) .....
Cutting a groove in the form of a circle or boring a cutting hole by removing the center or core in one piece.Shallow trepanning is also called face grooving can be performed on a lathe using a single-point tool that is similar to a grooving tool but has a curved blade. And the paragraph continues for a further half page stating in passing that trepanning is probably the most economical method of producing deep holes that are 2 inches and larger in diameter.
Hope this is helpful.
Kind of...Trepanning for metal work [not the medical boring of skulls] is a face operation. Simultaneously, the bit bores the ID of a recess, turns OD of what will become a boss [or slug if penetration is 100%] AND faces bottom of resulting recess. And commercial bits look exactly as Bony describes; a curved cutoff blade. Trepanning uses less horsepower/ amperage for resulting hole size than a twist drill or spade drill, less chips, and often a usable slug of remaining material.
A trepan can be shop made; 4130 type mechanical tubing, a shank for toolpost or tailstock and the cutters. Easiest, probably is brazing carbide tips into areas cut away for chip clearance. A hole in top of tube makes a port into the 'reservoir' for coolant. End mill shanks, or HSS drill blanks work in a pinch, just grind sides for back clearance as a cutoff tool, and the top to form a cutter, with minimal rake. It won't run in a machine or setup that is not rigid and stable.
They are kind of [barely] like a combined endmill & flycutter, but far more akin to annular cutters [hole-saw on steroids] like steel workers use. Effortless holes that no-one could push an equal sized drill bit. Consequently a carefully made cutter with a leading edge smaller and ahead of the finishing bit is not impossible.
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