Double end boring bars

[Batmanacw]

I honestly have never used one yet.



I am aware of the basics of clearance and rake, but does anyone use these with cemented carbide? The bits are not offset so tipping the bar a bit would add clearance as would running above center a bit.

I recently bought a bunch of 60⁰ angled cemented carbide tools brand new in the box. I don't have a nice carbide grinder so I was looking at ways to utilize them for internal threading without radically changing the sharp factory grind.

Because the square hole in the bar is on center, if you hold the bar on center it would automatically cause the edge to be above center. Would that be enough to give a cemented carbide tool the clearance it needs? A slight tip closer to center would also give more clearance. Both situations would cause a negative angle cut.

Just considering the best use of this type of bar.

 

[woodchucker]

I use these a bunch having a 9" lathe, I use mostly HSS. I generally don't use the brazed unless absolutely necessary, but if I am going to use brazed, then I have room to use a bigger bar, which is what I would do, and continue with HSS. I generally use the biggest bar I can with the least amount of stick out.

edit: and I generally cut above center internally to clear the bottom, but I always put a steeper relief on an boring bar tooling.

 

[mickri]

These are my go to boring bars. I only use HSS tool bits. For general boring the tool bit is ground kind of like a left hand tool bit. Of course it depends on whether you are boring a blind hole or a through hole.

 

[epanzella]

I have a set of these but rarely use them. The minimum bore is just too big with these bars.

 

[benmychree]

For threading, a tool needs to be on center, for just boring this not critical, but it does effect cutting efficiency; I do not use double ended boring bars, if they are used, they should use the cutting tool on center, this causes the need to use boring bars significantly smaller than the bore diameter, this is why I promote the use of Bokum boring bars, they have clearance angles that provide adequate clearance while they are mounted on center, also having provision for sharpening without altering cutting geometry.

 

[Batmanacw]

I do have a few of that style of boring bar but none big enough for a 3" deep bore.

 

[woodchucker]

I do have a few of that style of boring bar but none big enough for a 3" deep bore.

hmm, what is the diameter of the bore?

 

[Batmanacw]

hmm, what is the diameter of the bore?

It's really a moot point. I have a Kennametal top notch boring bar coming. I can get inserts for $6 each locally.

I was just considering the use of what I have laying around.

The bore would be just over 2" and 2.75" deep.

 

[woodchucker]

so this is what I have. The one at the bottom is a 5/8 endmill modified for boring. Currently it reaches 2 1/4 , and if I pushed it out, it would easily reach 3"
I'm not sure why some of you think these are horrible. They are prone to vibrate in the smallest bars.. but what isn't? As you get larger it gets much better.
The 3/4 bar doesn't deflect in my 9 inch lathe. I am sure if I were to use it in a big lathe on big bores, it might. But my largest bore has been 3 inches.

edit: I guess I should have checked before I said easily 3"... easily 2.5", 2.75 would be dicey.

 

[Batmanacw]

so this is what I have. The one at the bottom is a 5/8 endmill modified for boring. Currently it reaches 2 1/4 , and if I pushed it out, it would easily reach 3"
I'm not sure why some of you think these are horrible. They are prone to vibrate in the smallest bars.. but what isn't? As you get larger it gets much better.
The 3/4 bar doesn't deflect in my 9 inch lathe. I am sure if I were to use it in a big lathe on big bores, it might. But my largest bore has been 3 inches.

edit: I guess I should have checked before I said easily 3"... easily 2.5", 2.75 would be dicey.

View attachment 484135

I'm more looking at specialty tools like threading and cutting grooves in double ended bars.

I've got solid carbide bars up to 3/4" for standard boring and facing.