Boring Machinest Question

[Al_The_Man]

I aquired a nice little boring bar in some equipment I purchased, I picked up the inserts, and tried it out on a pulley bore I needed.
Here is the problem, It is a Carboloy bar, and states on it 'Minimum Bore .812", Which I assume I should be able to run the tool down a .812" bore just skimming?
I mounted the bar with the tool tip on centre, the bore is at .85", The bar has flats top & bottom so the angle of the tool is I assumed set by this?
As the tool enteres the cut, the bar profile behind the tool starts to rub badly.
I entered the tool dimensions in AutoCad and subscribed a circle, .812 diameter with the tool tip on the circle horizontal quadrant.
The Lower quadrant of the circle does not extend far enough to clear the bar profile, hence the rub.
Is there something a green machinist is doing wrong here?
Al.

[HuFlungDung]

Al,
You can cheat by running the bar a little above center. This has no ill effect unless you are taper boring.

Sometimes, you have to modify the tool a wee bit to make it fit, such as mill a little bit off the back side of the bar, opposite the insert tip. Or, go to the next size smaller bar, but this can often cause more vibration trouble if working at the limits of overhang to do a given bore.

[DareBee]

Judging by your picture and my experience with boring bars; I am wondering if that bar has the wrong insert in it.
By wrong I mean thickness.
It is not normal for the carbide to sit that high above the top of the seat pocket.
This would greatly reduce min bore size as the center lines are askew.

[Mcgyver]

my bride would say all machinist questions were boring....when i first saw it I thought it just needed to be rotated a bit, so there was negative rake and more clearance, but I like Darabee's answer better - as it is, I can see why it rubs, there is no front clearance here unless it was one large dia bore.

[msomerville]

darebee has a point that is one big insert for a boring bar that size.

[Al_The_Man]

You all may be on to something, I did a bit more work with the geometry in AutoCad, and for a .812" bore to clear, the tool tip would be required to be .03" above centre.
I took the bar into a local tool supply and this is what they sold me as the correct insert.
I will go back and see them with the evidence.
Al.

[ajl6549]

Originally Posted by DareBee Judging by your picture and my experience with boring bars; I am wondering if that bar has the wrong insert in it. By wrong I mean thickness. It is not normal for the carbide to sit that high above the top of the seat pocket. This would greatly reduce min bore size as the center lines are askew.

I agree, I looks like the insert is to thick

[Al_The_Man]

Thanks guys, I just got back from the tool supplier, the turkey had given me the wrong inserts.
The proper ones are flush with the top of the insert mount.

Al.

[ViperTX]

Pic Al....show's a pic of the good insert.

[Al_The_Man]

This worked.
Al

[Willbird]

The guy must have smoked his lunch to drag out that first insert hehe. Thats a weird looking sucker.

Bill

[justCNCit]

yeah when you look at the two the first one sure looks funny.