Being as the bar uses a carbide insert I didn't think of running it slow. I tried all the speeds my G4003G will produce between 360 and 1400rpm. It will go down to 70rpm so I'll give that a try. Thx.Have you tried running the lathe as slow as it will go? It will take longer to bore the hole,but might stop the singing.
Sometimes when I can't get a wide cut forming tool to not chatter,I turn the lathe over by hand and feed the cutter in until it smooths the cut up. This always works,but not the thing for your case. But,something to keep in your bag of tricks.
So that bar is for heavy cutting loads. I tried DOC's .005" to .040" @ .001" to .004" /revolution in steel that machines fairly well. The bar is only 3/8 diameter and I'll need about 1 3/8 penetration. Should I have been making heavier cuts than that? The singing didn't seem to get better or worse with any combination. I tried 360 to 1400 rpm.You purchased a negative rake bar that is machined to the correct angle for its intended use - heavy cutting loads. The inserts typically have little to no clearance angle under the cutting edge, which makes them stronger and allows you to have 6 cutting edges per insert instead of just 3. The clearance angle required to prevent rubbing is achieved by holding the insert at that negative rake angle the machined flat holds the bar at. The manufacturer did not make the bar wrong; you bought the wrong bar for your application. Sorry.
See title above .... BLJHBThe boring bar pictured below sings like a canary and I can't seem to stop it. It bores "OK" but although I can't feel the chatter with my fingernail in the bored surface I can see the herringbone. I've got a project coming up that requires boring to a square shoulder that has to seal against 40,000 psi and I know if that bar is singing now when it gets to that shoulder it's gonna dance. I've tried lots of feed/speed and tool height combinations with no luck. The machine is a Grizzly G4003G and it parts like a champ so I know it's rigid. My other bars cut great but won't fit in a .458 hole. It sings with the amount of projection shown in the photos and that is approximately the depth I'll need for the project. The bar looks to have 15 degree negative rake built into it via flats on the top & bottom. If the rake angle is the problem I can make a holder that will allow changing the angle. Any thoughts?
So that bar is for heavy cutting loads. I tried DOC's .005" to .040" @ .001" to .004" /revolution in steel that machines fairly well. The bar is only 3/8 diameter and I'll need about 1 3/8 penetration. Should I have been making heavier cuts than that? The singing didn't seem to get better or worse with any combination. I tried 360 to 1400 rpm.
The speeds & feeds I quoted were with the bar in it's normal position with the neg rake. I didn't go heavier than .040 doc because it's only a 3/8 bar. Your post did make me realize two things. Although the bar didn't cut well with the original insert, I have replaced that one with the same ones that I use for the rest of my insert bars which are for external cuts. This may be a contributor. The second thing you made me realize is that although this bar cuts great at zero rake I tried it in a one inch hole, not the .458 hole that I'll be using it in on my project. It's possible that I won't have sufficient clearance in the smaller hole. I'll have to try it in some scrap. At lest with the adaptor I made I can use any rake angle I want including the factory angle. Thx for the help.The bar is meant for heavier cutting loads when used in its normal configuration. It will not work the same when turned to a zero-rake position because now you have very little clearance under the edge and the insert may rub at some point. What this point is, I don't know - you'll have to try it.
Let me try to clarify this clearance thing. I copied this off the net:
View attachment 77892
You can see how both a positive and negative rake insert have the same clearance angles under the cutting edge when their respective bars are held in the holder as intended. What you have done here is to rotate the negative rake bar so that the top of the insert is now flat but as a consequence the angle under the edge has all but disappeared. The bar will cut, no doubt, but how deep you can go before the lower part of the insert rubs and causes chatter is not clear.
My advice is to be conservative so you can finish your bore. By conservative I mean roughing cuts at NR + 0.005" or so. If your nose radius is 0.015", then a reasonable roughing cut would be 0.020" and a reasonable finishing cut would be 0.005". If it does not rub and the cut goes well then I would stay with that and not push it. The reason I would personally not push it is because rubbing will affect accuracy and finish and I cannot tell you when the rubbing will affect the cut.
I hope that clarifies this for you.
The second thing you made me realize is that although this bar cuts great at zero rake I tried it in a one inch hole, not the .458 hole that I'll be using it in on my project. It's possible that I won't have sufficient clearance in the smaller hole. I'll have to try it in some scrap. At lest with the adaptor I made I can use any rake angle I want including the factory angle. Thx for the help.