Help with boring bar needed

[Sshire]

It was a fight with chatter on a 1” dia. by 2” deep bore with my Criterion DBL-202 head. Slowing down the RPM helped but I still had chatter no matter what speed or feed.
I know what the problem is: the brazed carbide boring bar was too thin for that depth.
Not interested in any more boring bars that I have to resharpen. I want to replace an insert and move on.

I’m considering an indexible boring bar ( a quality USA made product) and have these questions:

Let’s assume that 90+% of the boring is in aluminum or brass.
1. Boring bar material. HSS or Carbide?
2. Inserts. HSS or carbide?

If steel or cast iron is also a possibility, does that change the answers to questions 1 & 2?

I’ve looked at the Criterion bars and the A.W. Warner bars and HSS inserts. Any preference or is there a better choice than either.

 

[Tin Falcon]

Boring bar material. HSS or Carbide?

the real question here is how deep do your holes need to be.
the recomeded stick out for HSS is 2 1/2 timed the diameter of the boring bar. with carbide 7 times the diameter is ok carbide is stiffer .

Inserts. HSS or carbide?

HSS inserts will allow for better performance at lower speeds .
carbide is nice but it loves speed. High speed on a boring head can case vibration due to un balanced tool vibration is the enemy to a good finish.

IIRC the warner bars are lathe tools not boring head tools.

Not sure what product criterion offers.

Other option

$45 from Mesa tools

http://www.mesatool.com/products/boring-head-attachments/
Tin

 

[purpleknif]

Personally, I like HS bars because you can grind them to suit the application. It might be worth your time to get some "practice stock" and do some experimentation to see what effect different geometries have on the cutting action. Been doin' this for 30 years and still haven't found one tool that will work in every application.

 

[Sshire]

Purpleknif
Why would I need to grind an indexible boring bar?

 

[Sshire]

Tin
That"s the dilemma. A 2" hole would require a .8" (2/2.5) boring bar. Would be fine with a 1" hole, but not a .75 dia.

The other point. Everything I read says carbide need lots of speed, yet, I've bored many holes with my brazed carbide boring tools and have a great finish and I'm nowhere near the 2200 rpm max speed on the Bridgeport. (the 2J head does go to 3000 rpm but it's in the red zone on the speed dial and I'm not going there.)

Is this carbide speed thing for just for maximizing production and tool life in a heavy work environment, or does it have a noticeable change in the finish of the bore. I doubt a tool in my shop would get the wear in my lifetime that it would in a day or two of commercial use.

 

[Tin Falcon]

Published data is usually for best results under ideal conditions.
But we live in the real wold.

the other thing with boring bars is setting the correct angle .if the tip is tangent to the circle then there is more likelihood of chatter due to dig in . set the tool in such a way the defection of the tool causes a lighter cut not a heavier one and I was taught when boring to take a spring cut every couple of cuts especially if a bar is near its limits.
Tin

 

[Sshire]

The nice thing about the Criterion and a few others (Kennametal, etc) is the flat on the shank. The set screw on this flat insures that the angle is correct.

 

[petertha]

... from Mesa tools
Tin

Sorry of the thread tangent, but thanks for providing that website. Lots of goodies there & looks like decent quality. Do you have hands on experience with their tooling or more just providing a reference configuration for the boring bar question?

And best of all...

 

[Tin Falcon]

No hands on experience. these are made in USA by this guy he has posted here in the past he advertises in Home shop machinist magazine and his prices seem reasonable. I would not hesitate to place an order with him.

Tin

 

[lennardhme]

Would an Inline setup do the job ?
Unbeatable for accuracy & no flexing.
Leonard

 

[Sshire]

Leonard
Are you referring to a horizontal setup? Not sure but I'd love to know. Always interested in learning new things.

 

[Philjoe5]

[FONT=&quot]Stan,[/FONT]
[FONT=&quot]I’ll offer my own experiences with boring using a boring head with brazed carbide boring bars and boring bars with HSS or carbide inserts that are designed for lathe use. I’d say boring good non-tapered holes was my longest learning curve in machining. [/FONT]

[FONT=&quot]When I started out I did most of my boring on my X3 mill using import bars and boring head. For a long time it seemed like every boring bar I tried wouldn’t cut properly. I dreaded using boring bars (on the mill). I thought I was buying poor quality boring bars. The reason for my difficulties was I was using the stiffest bar that would fit in the drilled hole and consequently I was unable to set the rake of the toolbit properly. For ½” boring bars, it is usually unlikely I will get good results if I try to bore holes less than 5/8”. After, that size the thinnest boring bar can be used to increase the hole diameter up to about ¾” at which point the stoutest bars will work OK (my tools, my machines).[/FONT]

[FONT=&quot]I’ve had much less trouble boring on the lathe and I suspect that is because with autofeed I can run the boring bar slow enough so it doesn’t climb over the work, and chatter. It’s harder for me to do that on the mill feeding with the quill.[/FONT]

[FONT=&quot]With my tools and machines I seldom take a cut greater than 0.015” on the milling machine or the lathe and I now seem to be getting quite acceptable (to me) bores.[/FONT]

[FONT=&quot]Once I got this all figured out, I went back to those boring bars that I thought were poor quality and they work just fine.[/FONT]

[FONT=&quot]FWIW,[/FONT]

[FONT=&quot]Phil[/FONT]

 

[Sshire]

Thanks Phil. I hear you.
I really hadn't had any problems on the mill until the 2" deep hole with, what I considered, too thin a bar. Just looking for a solution when those arise.
I too, can't get a great finish with the quill feed, but now, with the power feed on the Bridgeport's knee, I can run it really slow. A thing of beauty.

 

[kvom]

My boring head takes 3/4" shank bars. The steel bars I own have a flat that aligns the bar via set screws, and they use triangular carbide inserts. I can use these bars on both the lathe and mill. I don't have chatter with these bars at 2" depths.

I had both a brazed carbide bar and a grindable HSS bar, and both are now in the "never used again" department of my shop. One issue with both of these is that the shanks taper down to allow smaller than 3/4" holes to be bored. My insert bars are constant diameter and thus need a 3/4" or larger starter hole.

 

[cncjunior]

Hi Stan,

If I may add my two bits worth here and agree with Tin, Kvom, and Philjoe5 for their various points. I used to use the brazed on carbide bars that came in a kit of 7 or so that would be in a round holder sticking straight up. They aren't the greatest as Kvom said about the tapered bar.

The one thing I want to say is that back rake angle and side relief angle are important. When custom grinding brazed on carbide and HSS these play a big part. With carbide inserts, the holders and insert combination will give different back rake angles. Typically for steel it would be negative-negative ( my shop uses the steel insert for brass ). For alum. you want to use positive- positive back rake.

The insert makers will tell you to use triangular inserts for boring bars as they have the least side force due to geometry. Side force is the force that pushes the cutter away from the material and can contribute to chatter.

A question was raised about productivity and carbide inserts. Generally the speed and feed of the inserts is set so that it will have a life of about 15 minutes in the cut. 15 minutes doesn't seem to be that long of time and yet that is a lot of material being removed when you look at a surface feet per minute of 1400 -1600 in steel where in comparison HSS at best conditions is about 100.

The question about turning with carbide is the rpm. Carbide does cut best at the higher rpm range. Will it cut at the lower range---yes. The only thing is that the insert might chip with too low a speed. How low well I can't really say. The older brased on carbides had a surface speed of 300-400 so I would say that that might be your lower limit for modern day inserts. Just a guess.

To throw a monkey wrench into the mix, something that my shop has discovered about machining cast 316 stainless steel is that ( counter to insert technology ) is that a positive back rake works the best in terms of cutting and surface finish. Sometimes, experimenting with different angles pays off.

Daniel

 

[lennardhme]

Stan,
In line boring bars are available commercially, but if you have a few hours, dead easy to make. Google for availability or plans, or if you have problems finding info I can email you.
Basically, a bar between centers on the lathe driven by a dog as usual.
The bar has a HSS insert set at @ 40degrees. The cylinder is setup on the lathe cross slide [ a good model eng. lathe will be dovetailed for such work- or make a plate ]with the bar going through the cylinder. Simply set the crosslide going at the slowest speed, after each pass adjust the bit out till the desired bore is reached.
I have several bars for different bore sizes with collars on to hold the cutting bit. I use a different bit for the finishing cut. A jig can be easily made to set the cutter diameter.
leonard

 

[Sshire]

Thanks, guys for all the extremely valuable info. I have a 3/4" indexible bar for the lathe and it cuts beautifully. Certainly the stiffness is the main factor.

I'm now pretty committed to getting ½" shank, carbide tooling with both carbide and HSS inserts. Lots to play with. As I said, the shallow bores are no problem. It's when it gets to a depth of 2" or so that the "thin" brazed carbide bars don't work the way I want them to.

Leonard. I did remember what you were referring to. I've watched videos of that process. On a long bore it would seem to be the best way to approach it.

 

[Forestgnome]

Solid carbide bars are real nice at reducing resonance. I rarely use anything else. Just a hint, if you start resonating and it makes waves in the work, you need to cut those waves out before it will stop resonating. So changing speed, feed, etc, may have little effect. The way I do it is by cutting deep at a snails pace for one pass.

 

[Sshire]

Thanks for that tip. I would have just reduced the speed and it wouldn't have helped. That's what is great about forums. You get a whole lot of info from people who know what they're doing.