Boring Head-Bar Set-up

RandyM

Mr. Deliberate
H-M Supporter Gold Member
Joined
Apr 12, 2011
Messages
3,417
I just recently for the first time used a boring head in my milling machine to bore a hole. This act has me wondering about some things about boring heads. The bar has no flats at the mounting end and is held in the head with a set screw. This allows for the cutting tip flat to be in any 360 degree position relative to the offset motion of the head. Though the operation of the task worked quite well, it has me thinking this through a little more. What I did was visually (by sight) set the cutting tip flat parallel to the head offset motion with the cutting edge outward of center.

Questions:

Are there set-up techniques for proper cutting tip orientation of the boring bar to the boring head?

What is the proper angle of the cutting tip to be set at?

Though I used this set-up to bore an ID, has anyone turned an OD this way?
 
Hi Randy,

Others with more experience should have better answers but after having used a boring head two whole times now, I'm reasonably sure you want to set the angle of the cutter to have a rake similar to what you would use to cut the same material on a lathe. I read that a boring head can be used to cut a circular boss, but either the boring head must be solid and your machine must have reversible tool rotation (the head doesn't thread onto the shaft), or you have to find a left-handed boring tool to fit the head.

Walt

Edit/ Hmm, I see that you were asking how to set the tool angle and I didn't address that at all. I just eyeball it to be at right angles to the work piece, but I'm only making light cuts in aluminum and that may not be good enough for your purposes. /Edit
 
Last edited:
I've seen a boring head used to turn a boss in the shop i work at by some of the older guys. one said he was "cutting the other side of the hole":thinking::nuts:.
Any way, setting the angle isn't all that tricky. the rake should already be there on the bar and then eye balling the point is good enough...
However, when i finally get my OWN set, i plan to mill or grind a flat that will orient the point to the ideal position every time.
 
Start out with the top of the tool parallel to the slide on the head, this will give you zero degrees back rake on the tool. If you are cutting non-ferrous metals like aluminum or brass, you may get a better finish by rotating the boring bar slightly to get a little back rake. Sometimes rotating the boring bar a bit one way or the or the other can also help get rid of chatter, so a flat is not necessarily a good idea. When sharpening a boring bar, grind on the end only to maintain the form and keep the point sharp. A very slight radius can be stoned on it to improve surface finish, but too much will cause chatter. If you do encounter chatter, anything that upsets the natural resonance of the bar will kill it, try changing the speed, feed or even adding a rubber band or a couple of O-Rings to the bar to absorb the vibrations. Boring bars work equally well for bores or bosses, i.e. inside or other side of the hole. :)

Tom
 
Last edited by a moderator:
I'd say you're only limited by your imagination. I've used them both outside and inside I've even used it for broaching. Like Tom says your material makes a difference, along with the tool you're using. Sounds like you're on the right track and thinking beyond.
dickr
 
When I align the bar in a boring head I take a small, long, fairly straight scrap of metal (you could even use a nail) and hold it against the flat face of the cutting surface on the boring bar. This helps me to see the angle the cutting surface is in relation to the boring head.

Hope that makes sense,

-Ron
 
Guys c'mon!!! A boring bar used in a boring head needs to have it's cutting edge on the centerline if you expect to hold tolerances using the dial. Period. The cheap (flat-less) brazed boring bars are not suitable as purchased. Most of the time, if you orient the top of the bars cutting edge parallel to the slide motion of the head, the cutting edge will be so far above center, you might as well drill the hole. Put the cutting edge on center, and your cutting with so much negative rake, bar spring and chatter will make boring with the head a nightmare. You CAN modify these bars with a little work, but you have to grind away a good bit of carbide. I really like the (more expensive) HSS bars, or bars made by grinding an old endmill.

Bob
 
Guys c'mon!!! A boring bar used in a boring head needs to have it's cutting edge on the centerline if you expect to hold tolerances using the dial. Period. The cheap (flat-less) brazed boring bars are not suitable as purchased. Most of the time, if you orient the top of the bars cutting edge parallel to the slide motion of the head, the cutting edge will be so far above center, you might as well drill the hole. Put the cutting edge on center, and your cutting with so much negative rake, bar spring and chatter will make boring with the head a nightmare. You CAN modify these bars with a little work, but you have to grind away a good bit of carbide. I really like the (more expensive) HSS bars, or bars made by grinding an old endmill.

Bob

This really deserves a "how-to" with pictures. I'm not sure I'm following what you mean by the "top of the bars cutting edge". Is that the flat portion of the carbide? What is the best process for doing this? It seems easy on the lathe. Also could you throw in there what are reasonable DOCs that can be taken with a boring tool of say 1/2" dia x 2". Is there a formula?

Barry
 
Guys c'mon!!! A boring bar used in a boring head needs to have it's cutting edge on the centerline if you expect to hold tolerances using the dial. Period. The cheap (flat-less) brazed boring bars are not suitable as purchased. Most of the time, if you orient the top of the bars cutting edge parallel to the slide motion of the head, the cutting edge will be so far above center, you might as well drill the hole. Put the cutting edge on center, and your cutting with so much negative rake, bar spring and chatter will make boring with the head a nightmare. You CAN modify these bars with a little work, but you have to grind away a good bit of carbide. I really like the (more expensive) HSS bars, or bars made by grinding an old endmill.

Bob


Granted, I may be easy to confuse at times :eek: but I'm with Barry on this one. I don't quite understand what you are recommending. You say that "needs to havie it's cutting edge on the centerline if you expect to hold tolerances" but you also state "Put the cutting edge on center, and your(sic) cutting with so much negative rake, bar spring and chatter will make boring with the head a nightmare.". Those two statements seem to contradict one another.

Pics, or maybe just expanding on this a bit would be a great help.

-Ron
 
According to Criterion, the cutting face of the bar needs to be aligned with the center of the bore:

ScreenShot119.jpg

The center diagram is the desired orientation. Note also that the face of the cutter is perpendicular to the point of contact.

When the face of the cutter is on the bore centerline it will allow the depth of cut adjustment of the head to produce accurate cuts. If the cutter face is not on the centerline the doc adjustment will be off, as shown here:

ScreenShot120.jpg

I "think" this is what Bob is referring to.

ScreenShot119.jpg ScreenShot120.jpg
 
Back
Top