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Boring Bar Sings
- Thread starter epanzella
- Start date
- Joined
- Feb 8, 2014
- Messages
- 11,144
I have noticed a big difference in brazed carbide turning tools. The junk ones I buy from HF will chatter even after properly grinding them, the Kennemetal ones I have don't seem to have that problem, even after several sharpenings. I suspect it is the steel they use for the shank.
If that is a new import boring bar, maybe it is the bar material. Just a thought.
If that is a new import boring bar, maybe it is the bar material. Just a thought.
- Joined
- Mar 31, 2014
- Messages
- 607
I know what you mean, I bought one similar and it does the exact same thing unless I put something under it to stiffen it, maddening...!:angry:
Edit: for the past few years I've been using solid carbide boring bars and they are wonderful, the one in the picture I've used so much you wouldn't believe it, I just give a little touch up on the diamond wheel.
http://www.maritool.com/Boring-Grooving-Threading
Last edited:
- Joined
- Jan 22, 2014
- Messages
- 578
Got some good tips here if the need arises. I even have a baseball-size lump of Duck Seal leftover from my pellet gun target box... :thumbsup:
- Joined
- Apr 8, 2013
- Messages
- 1,982
Those are the only ones I have. I'll see if I can locate some with less radius. Thx.
Try a 3/8 HSS round bit. Grind it to a D on the end and angle the bottom and opposite side away from the cutting point. Turn the tool post 1* so it doesn't drag the side of the bore and cut away using the compound or longitude drive. I was surprised at how well a 1/4 bit cut for me recently.
Dave
Dave
- Joined
- Dec 20, 2012
- Messages
- 9,422
That bar is a zero-lead, negative rake bar with a large nose radius - 0.0015? I personally find these negative rake bars great for hogging a through hole but for boring to a shoulder in a hole that has to be accurate and have a nice finish I prefer a positive-lead bar with a neutral or positive rake insert and a smaller nose radius so I can take a smaller finish pass and still have a reasonable finish. I also prefer a flat-topped insert instead of a chip breaker.
As the others have said, this singing thing is a result of the harmonics set up by the radial and tangential cutting forces acting on the tip of the bar; the large nose radius and the negative rake insert angle are largely responsible for this. Damping the bar may help but it won't address the cause of the issue.
Assuming you are not inclined to buy another bar, my suggestion is to use an insert with a maximum 0.007" nose radius and use a holder with a round hole so you can rotate the bar in a positive direction (clockwise, looking toward the tip of the bar) as far as the edge angle of the insert will allow without rubbing. Take roughing cuts of the nose radius + 0.001-0.005" and finish cuts at about 1/3 the nose radius. Use cutting fluid and feed at a rate of about 50% of the nose radius in IPM for roughing and about half that for finishing. If feeding manually, rough fast enough to produce coils instead of chips and finish at half the roughing feed rate. I also suggest cutting only on the infeed and moving the tip away from the wall as you retract; if you have a positive cut with a reasonable DOC on the infeed you don't need a "spring pass". Finally, be sure you do not hesitate or slow down your feed on entrance to the bore; this can cause chipping or mircro-fractures of the tip and mess with your accuracy.
The other thing you can try is to use a smaller bar with better tip geometry and nose radius and cut the bore with that. I know we should use the largest bar we can but getting the job done is more important right now and lighter cuts with a smaller bar might work better.
Best of luck!
As the others have said, this singing thing is a result of the harmonics set up by the radial and tangential cutting forces acting on the tip of the bar; the large nose radius and the negative rake insert angle are largely responsible for this. Damping the bar may help but it won't address the cause of the issue.
Assuming you are not inclined to buy another bar, my suggestion is to use an insert with a maximum 0.007" nose radius and use a holder with a round hole so you can rotate the bar in a positive direction (clockwise, looking toward the tip of the bar) as far as the edge angle of the insert will allow without rubbing. Take roughing cuts of the nose radius + 0.001-0.005" and finish cuts at about 1/3 the nose radius. Use cutting fluid and feed at a rate of about 50% of the nose radius in IPM for roughing and about half that for finishing. If feeding manually, rough fast enough to produce coils instead of chips and finish at half the roughing feed rate. I also suggest cutting only on the infeed and moving the tip away from the wall as you retract; if you have a positive cut with a reasonable DOC on the infeed you don't need a "spring pass". Finally, be sure you do not hesitate or slow down your feed on entrance to the bore; this can cause chipping or mircro-fractures of the tip and mess with your accuracy.
The other thing you can try is to use a smaller bar with better tip geometry and nose radius and cut the bore with that. I know we should use the largest bar we can but getting the job done is more important right now and lighter cuts with a smaller bar might work better.
Best of luck!
- Joined
- May 12, 2014
- Messages
- 164
The 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?
Hi,
The material might be too hard to machine ? Do you know what it is .... Internal grinding ?
What is your finished size your aiming for ? Can you use a reamer ?
You have gotten a lot of good input here, I agree with using a smaller nose radius, tool height won't change much. turn (rotate part) as slow as you can, physically hold the boring bar some times this can stop the resonation and get you over the line
Anyway let us know what worked
dd
Hi,
The material might be too hard to machine ? Do you know what it is .... Internal grinding ?
What is your finished size your aiming for ? Can you use a reamer ?
You have gotten a lot of good input here, I agree with using a smaller nose radius, tool height won't change much. turn (rotate part) as slow as you can, physically hold the boring bar some times this can stop the resonation and get you over the line
Anyway let us know what worked
dd
- Joined
- Apr 8, 2013
- Messages
- 1,982
Thx, boys, all good ideas. I take away from your input(s) that the substantial nose radius and the negative rake can add up to significant down force on the cutter. I don't have inserts with a smaller radius but I can do something about the 15 degree negative rake. I'm making a round holder with set screws that will allow me to set any rake angle I want. I just quit to watch some TV with the general. Three more holes to tap and I can try it. Tomorrow is another day.