Is my new boring bar OK?

T

tigtorch

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I ordered a 3/8" carbide insert boring bar from http://www.cdcotools.com/ and just received it. It looks like it is well made but when when I used it (after setting the height of the cutting edge properly) I noticed it was chattering even with a very small cut in 12L14. The bar is round with three flats and these flats establish it's stance in the tool holder. This looks very wrong to me but I am a novice, is this angle correct, or should I complain? (see photo)
)carbide.JPG

carbide.JPG
 
That does not look right to me either, don't you have a holder that has a hole in it that you can set the boring bar into.? I don't see how you can cut with that angle on the insert.
 
Could be a bunch of things... It's just like regular cutting bits; sometimes you need to keep tweaking different positions, bar angles, speeds and feeds before you find the magic spot. Does one of the flats provide a neutral angle? Try that. Also, what kind of insert is that; coated or not coated? TiN and TiALN tend to squeal less. Raw carbide is the noisiest. Was it 1 or 2mm radius? 1mm (pointy tip) will cut quieter. Generally, it helps to use the least amount of the bar as possible. The longer the bar, the more room there is for vibration to set up.

Ray
 
My only boring bar holder has a bigger hole. What else would three machined flats be for other than to use to clamp in a tool holder?
 
It's not the boring bar, it's the holder. That boring bas should be fit to a holder with a thru hole as said earlier.

"Billy G"
 
BTW: There could be a case for using an angle like that. If you're boring inside a small diameter hole, you'll need all the relief you can get. As the hole diameter increases, it becomes more like normal cutting and you won't need such a downward angle.

If you want to use that in a holder with a hole, you could make a sleeve for it with a slit down the side.


Ray
 
I have used boaring bars that sat at an angle before. Just drop it alittle below center. In outher words Eyeball the center at the angle the tool sets
 
As I said, I am a newby. I have successfully held small round boring bars in a regular tool holder before. It seemed plenty rigid and I have more regular holders than boring bar holders (I actually only have one 1/2 inch round boring bar holder). The fact that this bar had 3 flats, 90 degrees apart lead me to beleive this would allow the cutter to be aligned properly if one of these these flats were clamped parallel to the lathe. What is the purpose of these flats that don't seem to be aligned with the cutter at all?
 
The angle shown in the picture is a valid angle for very small diameter holes -especially if you had an insert with little/no relief. The angle you use also depends a lot on the style insert you use. Inserts are available with positive, negative and neutral relief. Also, folks commonly hold bars with a split sleeve. The other day, I had a deep bore with a skinny, short bar and I could only hold it in a regular holder that had a V-notch in the base but, I could only get two screws on it. Made a terrible racket at the start but got quiet when the hole opened-up a bit. That's the way things are sometimes...

Maybe you'll come to like it once you experiment -maybe not. I have some boring bars that I'm not crazy about but, I keep them around...

Oh, often times when I bore, I run the lathe in reverse and cut on the other side. It's easier to setup the cut and spot-check inspection is easier to see. That could very well be another advantage for having those flats positioned where they are.

Ray
 
Tig, I would agree with you that those flats imply that they are clamping flats for use in a standard tool holder to orient the tool as the maker intended. If so, then this bar was meant to be used with a negative radial rake. That produces very high tangential forces so unless you have a really rigid lathe you will get chatter. Personally, I would send it back and buy one with a neutral radial rake.
 
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