Rake angles

Sorry Izzy - just re-reading my post and I didn't make myself clear on one point.

Your inserts will have some rake built in I assume - and you do mention this. I was referring to the actual cutting angles involved - so if you are just asking about 'inclinations' of the inset holder itself - then a "neutral" angle on the holder, will give you whatever 'rake' is built-in to the cutting tip of the insert...

You need rake to cut steel well - decide how much you want/need and adjust your insert holder angle accordingly, based on the tip's rake.

Regards,

IanT
 
Izzy said:
I honestly wouldn't have thought to check manufacturers websites! And honestly I'm only trying to make these inserts work because I have hundreds of them. My main reason for asking this question was because I made a facing tool to hold these at a neutral rake as a tester and I was getting quite a bit of chatter. I just used 3/4" cold rolled steel with an angle milled in and 6-32 screw to hold it. Tool was on center and just chattered horribly. I don't Wana spend a bunch of time on a boring bar and have it chatter like crazy too. I noticed the boring bars at work have a negative rake too why is that? Just better for boring or something more?
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I'm not sure that the steel used in the boring bars where you work are cold rolled steel. Chatter can have a number of causes and a flexible holder is one of them. Ordinary screws don't cut it either. Good insert holders and screws are expensive for a reason.

If your neutral rake facing tool chattered I would not blame the rake angle to start with. Continue to work towards getting satisfactory cutting with those inserts on ordinary turning and facing. Learn what it takes to get them to work before going to boring.

This is a general purpose beginner kit I use with similar inserts. Square shanks and neutral top rake. Note the extra screws because they are special.

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Maybe you could make a round holder for your inserts. Then, you can make adjustments to your rake angles by turning the bar in your holder. All the boring bars have seen include about 3 degrees of back rake and work well for me in stainless steel.

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Here's a drawing for a small boring bar I made may years ago to fit a bunch of surplus insert I have on hand. It came out okay, not perfect, did get the job done I needed it for.
 

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The type of steel and whether it is hardened or not will not change the flex characteristics at all. All steels, in all tempers, have about the same elastic modulus. If you want a more rigid boring bar, you must go to carbide. Edit: And/or go to a bigger diameter bar...
 
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Here's a picture of the boring bar I made to the drawing posted in my previous post. One thing you have to remember, you should cut the insert pocket with a tapered end mill that has an angle that matches the angle of the insert. That angle will be either 7 degrees or 11 degrees, depending on the insert style, TCMT or TPMT and all of it's variations. Ken

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@Tozguy I know the boring bars at work aren't crs that's just what I used for the facing tool. I would assume boring bars would be made out of a hardenable material to try an control flex/chatter as best as possible.
The tool I made looks identical to the tools you posted I'll take a pic so y'all can see what I came up with
Unfortunately the tip doesn't have any built in rake angles or chip breakers or anything like that just a nose radius and I measured 25° back clearance (I think that's what it's called)
@4gsr I like that boring bar and that's kinda what I was shooting for so I might just use that idea lol
 
Izzy said:
Here's a new design I just tried out, 10° rake. Seems to cut much smoother, chip isn't as hot either. View attachment 242411 View attachment 242412
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Okay, on TP_ style insert for turning tools, Angle one or the back rake is generally 0 degrees. The side cutting or the edge of the insert that is getting the cut, that angle is generally set at 5 degrees. That's why the TP_ insert has 11 degrees side angle to it. So you almost have it right. Since it is cutting, I wouldn't mess with it. Go for it!
 
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