Boring bars- How do you setup and use them?

[HMF]

Hey Guys,

If you wanted to use a boring bar on a lathe and/or mill.... to bore a hole in a round bar of mild steel...

1. How would you set it up (indicate it)?

2. What speed and position would you use?

3. Would you use coolant or not?


Any videos that have been made that show the process as YOU envision it? (In other words, whose methods YOU agree with?)

Thanks!

Nelson

 

[aametalmaster]

You mean set up a boring head? I like running at lower speeds for bigger cuts and faster for the last few thousands...Bob

 

[olcarguy]

I believe u need to clarify what you want to know. There is a difference between using a boring head and a boring bar. Normally a boring head is moving when doing the cutting and the work is stationary. With a boring bar it is normally opposite.

 

[HMF]

Ok, I am dumber than I thought.

First, what is the difference between a boring head and a boring bar? The boring bars I have seen look like round pieces of metal, and that is what I was originally thinking of.

Second, how would you indicate and set up each one?


Thanks,

Nelson

 

[aametalmaster]

A boring head is used when the part doesn't turn like a cylinder in a car engine block. The block is bolted to a table and the boring head has to be adjustable to take the depth of cut. It has a top and bottom part that slides on a dovetail. It also turns as the part doesn't. Like this part where the piece is held in the tool post and the cutter revolves around it...Bob

 

[aametalmaster]

Here is a pic of the head itself mounted in my lathe spindle...Bob

 

[olcarguy]

a boring bar is held in the tool post and cuts are adjusted using the cross slide

 

[Tony Wells]

Some confusion may come from the industry habit of referring to automotive engine cylinder and portable boring rigs as "boring bars".

Most common use of a boring head with integral adjustment via a screw and dovetails is in a milling machine where the work is stationary. Can be used in a lathe, as Bob showed, where again, the work is not rotated.

More often, the term "boring bar" refers to a single bar of round construction that holds either a carbide insert or a square hss tool. Many have a flat to align the axial position. The insert is mounted on the business end in a manner to present the cutting edge to the work. Most have the ability to face the bottom of the bore, so the insert is presented with a 5 deg typical front relief angle. Of course, this means that the bar needs to be aligned parallel with the lathe bed ways. It's not as critical as needing to be indicated dead on, but should be close. Most of the time I eyeball along the bar and the rear way from above. I have seen people run the tailstock ram out and sort of pin the bar against it, forcing the bar to be parallel to it. This is far more important, critical in fact, for threading bars. That is another thread in it's own right.

Setting the height is a little trickier. You could run the cross slide to the back side of a piece of bar stock and use the old 6" scale trick. You could use a dead or live center as a pointer of center to visually compare to. You could use a pair of calipers or a depth micrometer to measure from a known diameter down to the edge of the insert.

Leave no more bar outside the holder than required to reach the depth of the bore you are working. Use the largest bar you can get into the hole. Set the bar above center. Below will drag on the heel. Above also compensates for flex as the bar is pulled down by cutting forces.

Above all, get a devibe bar!!

 

[HMF]

Wow...there is a great amount of information in this thread.

In order to get the boring bar properly centered both for depth and height with respect to the work, is there a way to dial it in, i.e., use a DTI to maintain dead center, and if so, how would you do it?

Thanks,

Nelson

 

[Conrad Hoffman]

Man am I a dummy. I just finished boring something about 5 min ago on the mill. Used a standard 2" boring head. Lacking a suitable boring bar to mount in the head we just stuck in a two flute end mill and cut with one side of it. Pretty conventional.

On the lathe I mount the boring bar in the boring bar holder for the QCTP and bore the rotating part. Again, pretty conventional.

Nothing in this thread is what you think of when you think boring! It never occurred to me to put a boring head in the lathe and do the OD of a part.