Chip breaker and finish relationship question?

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dml66
Posts: 41
Joined: Fri Apr 29, 2022 8:21 am
Location: SW Washington State, Steelhead Country

Chip breaker and finish relationship question?

Post by dml66 »

I want to make certain I understand the relationship, if any, between the turning operation being performed such as roughing, semi-finishing, finishing etc., and the cutter's chip breaker.

With respect to HSS cutters, the video pat1027 was kind enough to share in another post, the author shows how to add a chip breaker to a hand ground cutter on one hand, but adds that he doesn't seem to care for doing so for a number of reasons.

When looking at insert cutters, it appears the suitability for a given level of finish is tied to the chip breaker.

Just to throw a wrench in the gears, viewing a Blondiehacks YouTube video on the topic of finishing, seems to point to the cutting edge profile, or it's roundness, as the driver of finer versus more coarse finish. My takeaway is the more round a cutting edge is for a given feed rate, the more the spirals are averaged out resulting in a finer finish.

The only way I can wrap my head around how a chip breaker might affect the level of finish is by imagining that if chips, which are at least as hard as the piece they came from, are allowed to grind on the piece, they may cause roughness. If they are broken up they should fall away from the workpiece. I really don't know, just guessing.

Figured I'd ask the experts here 🤔.
David2011
Posts: 178
Joined: Wed Apr 24, 2019 3:18 pm

Re: Chip breaker and finish relationship question?

Post by David2011 »

First, I'm no expert; my successes are the result of trying until I get what I want. I made a tool many years before I saw Quinn's "Blondihacks" but this tool confirms what she says. I ground this specifically for making some parts from 1018 steel. It doesn't have a chip breaker per se but it does have proper relief angles and a suitable top rake. The cutting edges are sharp with both the sides and top honed with a hard Arkansas stone. The nose has enough of a radius that it feels rounded to the touch. The edge to the right of the nose is set up so that it is nearly parallel to the machined surface so it skims a much wider area than most tools. It doesn't leave ridges like many tools. For a sense of scale, this is a 1/2" tool blank.
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HSS Bit for Mild Steel Cropped.jpg
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