diy boring bar with carbide inserts rake angle question

Cipher said:

My lathe boring bars have different negative radial rake angles, that's why i am more confused about than i should be. ; )

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I intended to comment on this and forgot. If you are using CCMT inserts in your lathe boring bars then the SCLCR bar and insert configuration has positive rake geometry. It is intended to be used with zero radial rake when positioned in your boring bar holder. Inducing negative rake with these bars defeats the purpose of the geometry.

Of course, they are your bars and you can use them as you choose but I just wanted to make sure you were aware that while inducing more positive radial rake is a common practice with solid boring bars, it is not a recommended practice with inserted bars. This is mainly because the cutting edge will then be out of position when you do this but also because you reduce the clearance angle under the insert and that leads to rubbing and consequently, chatter.

I see my error now. I was confused about adding up the angles of the insertholder and the insert itself. My inserts have positiv rake, my holders negativ, that will result in somewhat neutral...
HSS is not really a option for me, since i'm not allowed to make too much noise where i live (not heavy grinding). However since it would be a very simple way to start, i will go for a 3mm round HSS toolbit and a simple holder, just like Stefan Gotteswinter showed on youtube. These bits should be simple and small enough to be ground with a dremel tool. And if I mess up dirlling a few holes and tapping one of them, oh well...

4gsr said:

Here's drawings to a couple of boring bars I drew up many years ago. Never did build them, good reference information.

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Whats with the tilted part in the drawing? Im having trouble reading that.