# New boring bar



## precisionworks (Jun 6, 2009)

This is the 1" bar that uses CNMG-4xx inserts (currently on sale at MSC)






Look just to the right of the insert to see the coolant through channel





Back end of the bar is tapped for 3/8" NPT, which makes it easy to add a ball valve & an air fitting





First step in setting up any new bar is to level the bar to the lathe bed. The lathe bed was precision leveled just last week.





Next, the insert needs to be set to centerline height +0.010". I use a shop built gage with a piece of precision ground flat stock for a reference surface. A height gage can also be used.





Finish directly off the tool. Insert is a Mitsubishi CNMG-432SA medium finisher, DOC at .001", speed at 306 sfpm, feed at .0015 ipr. Air pressure set to 50 psi. Material is black pipe, which doesn't finish as well as some other materials.





Finish after touching with a maroon Scotchbrite pad





The fine finish inserts will be here Monday (CNMG-431F), which will do an even better job.


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## Mirage_Man (Jun 6, 2009)

precisionworks said:


> First step in setting up any new bar is to level the bar to the lathe bed. The lathe bed was precision leveled just last week.
> 
> 
> 
> ...



Would you mind explaining in a little more detail what you're doing in these 2 photos? I don't understand how you're "leveling to the bed" with a combination square? Unless you're just using it as a level? How are you holding the "reference block" to get it's edge .010" above spindle center?


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## darkzero (Jun 6, 2009)

Mirage_Man said:


> Would you mind explaining in a little more detail what you're doing in these 2 photos? I don't understand how you're "leveling to the bed" with a combination square? Unless you're just using it as a level? How are you holding the "reference block" to get it's edge .010" above spindle center?


 
I'm curious to know as well. How would one level the boring bar or other tool to the bed? Shimming the tool in the holder? I understand the reason for leveling the lathe but what is the importance of leveling the tool to the bed & what is the effect if it isn't leveled?

Sorry, another beginners question. I always see pictures of the compound set at an angle rather than set at 0 (parallel to the ways) even when not maching an angle/taper. Is this so there's no risk of the compound moving? Can that even happen under high force causing the compound screw to back out?


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## precisionworks (Jun 6, 2009)

Any level could be used to set up the bar, as the top (or bottom) surface of the bar needs to be parallel to the lathe bed. Some tool holders have set screws that lock down on the upper or lower flats, so a level isn't needed. The Aloris holder doesn't use that method, but uses clamping screws instead.



> How are you holding the "reference block"


The reference surface is supported by a post that rests on a flat bar that straddles the bed. All three parts are welded together. The surface grinder was used to set the height of the "boring bar end" at centerline + .010", and the other end is set to centerline +/- .000"

The centerline gage is used often. Whenever inserts are swapped from one brand to another, height is checked. Also when a new tool is put into a holder. Most machines (except CNC) don't have a way to check center height, and a gage is worth the time it takes to build.


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## Mirage_Man (Jun 6, 2009)

precisionworks said:


> The reference surface is supported by a post that rests on a flat bar that straddles the bed. All three parts are welded together. The surface grinder was used to set the height of the "boring bar end" at centerline + .010", and the other end is set to centerline +/- .000"



Cool. How about a picture showing the whole thing in place?


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## precisionworks (Jun 6, 2009)

> what is the importance of leveling the tool to the bed & what is the effect if it isn't leveled?


Every boring bar has a different design, but all of them are set up using the same two steps. The first step, leveling the bar, establishes the angle at which the insert meets the bore. Negative inserts, like the CNMG, slope downward. Leveling the bar sets up the insert at the correct angle to remove material.

Say that you didn't level the bar, but only set the cutting tip to correct height. It would be easy to have the tip angled upward, giving no clearance behind the tip (rubbing). Or to have the tip angled too far downward, reducing the support behind the tip.


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## darkzero (Jun 6, 2009)

precisionworks said:


> Every boring bar has a different design, but all of them are set up using the same two steps. The first step, leveling the bar, establishes the angle at which the insert meets the bore. Negative inserts, like the CNMG, slope downward. Leveling the bar sets up the insert at the correct angle to remove material.
> 
> Say that you didn't level the bar, but only set the cutting tip to correct height. It would be easy to have the tip angled upward, giving no clearance behind the tip (rubbing). Or to have the tip angled too far downward, reducing the support behind the tip.


 
I see now, thanks Barry.

And how about the purpose of the compound angle?


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## wquiles (Jun 7, 2009)

Thanks much for the photos and explanations - learned something new today


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## precisionworks (Jun 7, 2009)

> how about the purpose of the compound angle?


It's more personal preference than anything else, but there is one big advantage to having an angle ... the slide becomes a super fine adjuster when only tenths need to be taken. Some people go so far as to calculate how many tenths (on the radius) per mark on the dial, which varies with the angle.

FWIW, most production machines I've seen have an angled compound.


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## precisionworks (Jun 13, 2009)

> How about a picture showing the whole thing in place?


In the Compression Collet thread, there's a photo with both a turning tool & the boring bar being set up. The gage is used every time an insert is indexed, and every time the brand of insert is changed - there is often a small variation, which will really mess up a boring job. (Pun not intended )


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