Using boring bar in boring head

[Alberto-sp]

Hello. I have a boring head like this one



I have been using the borings bars that came with it with not bad results. No perfect, but not bad. I tried to cutting a regular thick boring bar, looking for more rigidity and to being able to change the insert. It is the one on the top of these pictures



The results weren´t good. It looks like the cut is off centre or something, not sure. And maybe is something to do with the boring bar. Not sure if you can see the exact position of the insert, but it isn´t close to the axis of the boring bar.

I could try with another boring bar, like this one



But before cutting it, I´d like to know your opinion.

Thank you

Best regards

 

[mmcmdl]

The insert doesn't really have to be " on center " but you need to have clearance on the bar . Most likely what you're running into .

 

[Cadillac]

From what I see that insert edge is destroyed flip it. Then like said above you need clearance on the backside of the insert. To use that bar you either need to grind some off the bottom side of the bar, rotate the bar so the edge is cutting not the bottom of the insert. Or you have to use that bar on a hole with a bigger radius.

 

[RJSakowski]

The boring bar you show is meant for use on a lathe where you can adjust the height via the QCTP. The flats don't permit rotation of the rake angle as do the brazed carbide inserts. Additionally, the location of the cutting edge above center means that you have a negative rake. Looking at my insert cutting bar, it has a built-in negative rake which adds more negative rake. While this isn't a problem on the lathe, a boring head in the mill can't adjust.

 

[matthewsx]

If you’re having trouble with the rigidity of the bars that came with your boring head have you tried replacing with solid carbide?

John

 

[ChazzC]

I’ve used these boring bars with good results:

https://a.co/d/99plgsw

 

[RaisedByWolves]

That insert is indeed trashed, but OP, are you sure the tip of the insert is what's cutting?

It almost looks from the pics that the side or back edge of the insert may be either cutting or rubbing.

An endmill works well for most situations, either in stock form or custom ground, they are considerably stiffer than the criterion bars.

 

[homebrewed]

Something else to pay attention to is the specified minimum starting-hole size for your boring bar. A smaller hole virtually guarantees that the tool will rub rather than cut.

 

[Alberto-sp]

Thanks for all your help. Yes maybe that was the problem. Trying to cut a too small hole. Thanks you!

 

[MrWhoopee]

While we're here, I will point out that the brazed boring bars you received with the boring head require substantial grinding in order to make them suitable for use in a boring head. As received, the cutting edge is well above the centerline of the bar. When you rotate the bar to put the edge on center, the top surface presents a negative rake which results in significant deflection and poor finish. Here's a picture of before and after grinding, and this is just to get to a neutral rake.