Solid Carbide Boring Bar?

Ray C

Ray C

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Folks,

Curious to know if solid carbide boring bars with index-able inserts significantly improve performance over traditional steel?

Even when adjusted as short and rigid as possible, traditional bars tend to make the entry hole slightly larger resulting in a tapered hole. This is expected and known behavior. Does anyone have true experience with solid carbide boring bars and if so, all other things being equal, how much improvement do they bring to the table vs traditional bars? I'm mainly concerned about deflection.

I need to bore a 17mm hole and would like to make it slightly minus sized by 0.03mm. I searched around and could not find minus sized 17mm reamers and I'd like to avoid buying a 17mm reamer and grinding it myself.

Any thoughts?

Ray
 
I assume you are speaking of boring in the lathe, Ray. If so, then I'd like to offer an opinion.

I no longer use steel boring bars on the lathe unless I have no other option. I prefer solid carbide Micro 100 bars for tiny holes and solid carbide inserted carbide bars for everything else. The key reason for this is as you stated - reducing deflection.

Carbide inserted bars have a constant diameter so you can use only as much extension as you need to minimize deflection. The material itself has the highest modulus of elasticity of all the available materials and this further reduces deflection. A 1/2" carbide bar should fit in your hole and that gives you a depth capacity of about 4-5" while still being able to hold pretty tight tolerances.

I have noticed a few things that need to be attended to with these inserted bars:
  • Bar geometry matters and a positive lead bar may work better for you in that the geometry helps alter force vectors from radial to axial compared to a zero lead bar. When tolerances are tight, this matters.
  • The nose radius you choose is really important, as you know. I have found that the largest nose radius I can use on a 1/2" bar is 0.008". This allows a finish pass of 0.003-4" deep; any shallower and the cutter deflects due to excessive radial cutting forces. At 1/2 the nose radius, the insert cuts accurately and clean in most materials.
  • You cannot pause or stop on entrance to the bore; doing so causes vibration at the entrance and may be an element in causing bell mouthing as you noted above. Maintaining speed on entry also reduces the chances of chipping the insert.
  • The boring bar holder matters with any bar but especially with a carbide bar. I have found that using a holder that holds the bar circumferentially instead of with set screws that bear directly on the bar produces the best results. An example of this type of holder is the Aloris 4D. This type of holder provides the greatest amount of rigidity in the set up, improving accuracy and finishes.
Hope that helps. I have found that solid carbide bars are the best choice for boring, at least for me.
 
I had an appropriate imperial sized reamer re-ground to 14.1mm at a total cost of £50 including purchase of the MT2 shank reamer.
 
Another vote for solid carbide boring bars. I bought a half dozen insert type Circle brand bars a decade or more ago, Way less chatter, tighter tolerance on bore, and you can have way more overhang than you can with steel before you run into pushoff, flex issues. For really tiny stuff I use Micro solid carbide bars.
 
I regularly use Iscar MGC 06 and MGCH 08 solid carbide bars, rigidity and damping are very good, even when operating at the greatest possible extension from the clamping screw(s) or holder
 
Problem solved... I remember having a boring bar that worked really well but took slightly odd inserts so, I set it aside. Well, it took an hour of digging but it finally turned-up. After that, I went thru the dead carbide bucket and found an insert that had one usable edge left. Bingo, it worked fine. I snuck-up on the diameter and got it really close then, finished-off with an adjustable hand reamer.

BTW, the insert was a TPGB 221 and the holder was a Shars 404-1981 1/2" 95 Degree TBBN/S. This is a really sweet bar and that 95 degree attack angle hits the hole and stays put without pushing away. I recall using these inserts in some bars that took a TCMT 2151. They fit fine and the inserts perform really well during their short lifetime. The flat edge is very fragile but, they cut almost like HSS. I might switch back to these for a while. Maybe rough-out with a 2151 and finish with the 221.

Ray
 
Ray C said:
Folks,

Curious to know if solid carbide boring bars with index-able inserts significantly improve performance over traditional steel?

Even when adjusted as short and rigid as possible, traditional bars tend to make the entry hole slightly larger resulting in a tapered hole. This is expected and known behavior. Does anyone have true experience with solid carbide boring bars and if so, all other things being equal, how much improvement do they bring to the table vs traditional bars? I'm mainly concerned about deflection.

I need to bore a 17mm hole and would like to make it slightly minus sized by 0.03mm. I searched around and could not find minus sized 17mm reamers and I'd like to avoid buying a 17mm reamer and grinding it myself.

Any thoughts?

Ray
Click to expand...
16.97mm = .6681 in. .668 reamers are availible.

Sent from my SM-G955U using Tapatalk
 
My go-to bars are all solid carbide Kennametal bars. I have several from 1/2 inch to 3/4 inch diameters.

The smaller ones take the TPG 221 inserts.

-Bear
 
While standard steel bb typically limit you to about 3:1 stickout, maybe a little more on a heavy machine and very sharp edge, solid carbide easily doubles that. Sometimes you can get more. Lots of people do, on both counts, but if you really need to eliminate the bell-mouthing and cut the chatter, those are standard parameters. I believe 8:1 is considered the limit for plain solid carbide.

However, there are alternatives. Many mfg offer de-vibe bars, and there are several approaches taken. Some are hollow and have a tension rod through the center that has a set screw bearing against it so you can tune the bar to be out of the natural harmony of the chatter. And other than solid carbide, there are less costly options. Several of the regular suppliers offer "heavy metal" inserted bars. See here for some explanation:

http://www.naeco.net/NAECOMET Tungsten Based HEAVY METAL BORING BARS & Tooling.htm

I've used several styles, and achieved as much as 10-12:1 with not too much trouble getting them to perform. Had a 4" bar that was nearly 48" long that I loved because you almost couldn't make it chatter. Too heavy though. But it did work, and was not carbide.
 
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