Boring bar centering

[Ian q]

Hey Guys

Does anyone have any methods to quickly and accurately center a lathe boring bar.

Ian

[specv]

face a piece of stock, xxxxm it up, then scribe a line on it with the insert. you will be able to see it plain as day.

[Jack Mitchell]

The method is included in your holder. The set screws will lock onto the boring bar flats which allows zero deflection.

If by chance you are using a boring bar without flats, then I can't really say outside of building some sort of locational centering tool.

 

Regards, Jack

[Guest]

If it is a round bar with no flats, place it in a grinding vise true it up with an indicator and grind a flat on it. I do this with Circle bars all the time.

 

Problem permanantly solved.

[Trevor Bailey]

Ian's method is quick and down and dirty. Depends on what you are doing with the bar will determine if you should cut permanent flats on it. Sometimes with hard cutting material, you may need to rotate tip off center to help with vibration, flex, etc...

[Charlie Pierson]

You could face off about .003 and check the shape of what is leftover in the middle of the stock.

It should completely flat.

If there is material left in the shape of a cylinder , your bar is below center.

If there is material left in the shape of a cone , your bar is above center.

 

cp

[MCam Newbie]

The xxxxm & scribe method works well. Also, the top surface of the inserty in the bar should be parallel to the X axis travel.

In my experience, it is better to run a boretool set about .010/.015 above centerline of spindle rotation, unless you must face to spindle centerline, in which case you would want to be right on center.

The reason is that if the tool is loaded enough to flex, an above center tool pushes down, making a lighter load, whereas a bar on center, if deflected, will pull more chip, loading the tool further. Sometime, the increasing load will cause catostrophic tool failure, especially if initial deflection is caused by a dulling insert. An extyernal tool, set at or below center, for the same reason. If you have trouble picturing what I descrine, draw a circle, a aline thruogh center, and a paralell line on eaithr side, Tool deflection will be perpendicular to the cutting edge, more or less,

Note that pressed inerts, with edges square to the top face, are set into the holsers at an angle, so that side clearence is obtained, giving a negative tool rake. These inserts will not have top surface paralell to X axis, but those tools almost always have flatts on the tool shanks by the mfg.

I have seen people place a scale between the insert tip and an O.D., (machine spindle stopped. Hey, one never knows ....) And move the slide in towards the o.d. until scale is held there. It should be 90 degrees to the plane of axis travel. This will get you quite close, if not exact.

Lastly, build a duplicate of the tools mounting on the turret, basicly locating on the same surfaces on your fixture the turret will. Make sure the base of the fixture holds the toolholder in the same planes, relative to X asis novement plane, as when on the tool turret. Get a tool that is on center in the machine, place it into your fixture, and on a surface plate, get the distance to tool centerline from the surface plate. Face a piece of bar stock to that length, and bolt a flat piece of stock to one end, covering half the face on the bat, overhanging on one edge.

You can now mount a tool to your block, face up or face down, and have a surface you can pass under, or over the cutting toi to check height.

I have done this for Mori Seiki lathe with block type holders, and Hitachi Seki lathes with V taper holders. In the latter case, I bough manually acctuated recievers from the Mfg. and built my tooling around them. These centering devices allowed the machinist to set tool with extremely accurrate results, without stopping the spindle to find centerline. We used drop indicators for tools requiring exact centering, when required, to insure no "nub" at centerline. (Yes, I know they are "xxxx", but the ruckus that word caused on an incoming parts inspectiuon report, sent along with the parts to review due to such a flaw ....... Well, we'll just say that on two coastlines memos flew into in baskets, the buck goty passed, again and again, until the official sanctioned term for raised metal at centerline of turned parts, as deemed politically correct and sexually non-offensive by corporate lawyers and acceptable to the board of directors, is now "Nub"

I kid you not, this really happened! We LOAO for a couple months over it, but we all say "Nub" now!

Unless we are discussing things some might construe as being sexually offensive, as boys are apt to do from time to time ...... But then we are not refering to that raised material at enter line, I can assure you.

[MCam Newbie]

Sorry all my postings are so brief .... Shy, I am.

[Guest]

Sometimes a cogent thought just cannot be wrapped up in 3 sentences.

 

[Ian q]

Sorry for my delay in responding to all the great input, but I was out of town for a few days. Anyway, I will certainly give these suggestions a try and thanks a bunch!!!!!

Ian