I've got to bore a 3/4" diameter closed end hole 2.5" deep in 1" diameter titanium 6AL/4V rod using a 9x20 lathe. I'd like as nice a finish as possible, with a corner radiused 1/64" or less.

My current plan is to first 1/4" cobalt drill to depth, then 47/64" cobalt drill to depth, then finish with a .360" minimum diameter boring bar (5/16" diameter shank) with C2 insert.

Can anyone suggest a better approach to creating this closed end hole?

Available are carbide and "heavy metal" boring bars. The carbide bar is somewhat more expensive, though finish greatly outweighs tool price.

Can anyone provide information on wich type of boring bar, carbide or "heavy metal", might be best?

Thanks!

You should use carbide! Have fire extinquisher on hand also!

Your plan of action will work just fine. I machined quite bit of titanium during my time as a tool maker and you have to push high speeds and very light cuts in order to et in the realm of titanium fires. Think Unimat lathe type of speeds and feeds. With your 9-20 lathe you can spin it slow enough and take decent cuts so that the titanium isn't hair fine and sparking as it is machined. Make sure to use coolant and not kerosene. Water soluable oil works well.

Safe your scrap for the camp fire next summer. Don't breath the fumes.

I did get a fire extinguisher.

I will be using Castrol Syntilo 9913 as a coolant.

Is carbide the best boring bar in this case? The "heavy metal" is supposed to help with vibration. Basically I'm looking for the boring bar with the most resistance to chatter.

Please tell me more about the titanium fumes. :confused: I didn't know anything about this.

No worries about fumes during machining, you won't be running any kind of production that'd cause probems, but if you play with the chips and a campfire, be wary of those fumes.

Yes carbide. High speed steel will wear very fast and lose it's edge. Even carbide wears and loses it's edge faster than when cutting regular steels.

Haven't machines TI in awhile. But I have machined it. I havn't ever heard of it lighting up???

I've machine Mag before and it does light up! But its more of the "pull it out of the machine and throw it into the sand box and roll it outside" kinda fire. Although I have never lit it up machining ;)

Does TI light up and keep burning on its own or is it the chips???

edit:
come to think of it we welded TI at my old job and the fumes are toxic had to use either Vacuum box or flood gas it in a realy well ventilated area. Dont recall lighting any up into a bonfire.

Yes it burns if the chips are fine threaded. As the chips get thicker, it becomes harder tolight them off. A fine light cut will produce a thing long chip that will light easily with a match and burn fiercly. It has a very bright flame too.

Thats something I didn't know! wounder why it never lit up welding it???

i wouldn t run the boring bar to fast , because if you work harden it , not much is going to touch it , lots of oil , keep it cool and don t take to light of cuts nor too heavy
carbibide is the way to go , the sharper the better , titanium is funny stuff i ve had it melt pretty badly around drills , sometimes it s like cutting butter other times like cutting a grinding wheel , overall if you ve cut tool steels or stainless , work titanium the same
take a look at this site
http://www.suppliersonline.com/propertypages/6-4.asp#General

Regarding the actual boring bar, I do intend to use C2 carbide inserts, but have the choice of bar materials, either carbide or "heavy metal". Does anyone have any experience that suggests "heavy metal" might be better than carbide for any purposes?

if expense isn t the issue carbide is the best , , if you use a steel bar snug it up , +.1 on the overall length to reduce chances of chatter , even if you have to sharpen the insert tip do it , i know that idea will make a lot of guys cringe , but use it as a last resort , i really don t think you will have any problem if you use a carbide bar , keep the feed and speed to the sfm recommended by the manufacurer , i recently worked on a lage piece with a bore size of 1.5" +-.0002 , it ran like crap i had to grind the boring bar ( solid bar no insert ) a couple of times till i found that sweet spot , it cut beautifully , i know i ran it at 160 rpm but i think 1 in/min and lots of cutting oil , no coolant

Thanks, carbide it is!

good choice , heat is the enemy , the sharper the insert the less friction you will have to deal with

The reason to use the carbide bar is that carbide will not flex as will a "heavy metal bar"!

I've been running lots of 6Al-4v on a HAAS SL-30 for the last couple of months.
On the HAAS I've been sticking to PVD coated inserts & of coarse Cobalt Drills.
I've been successful using the following SFPM & feeds.
Coated Carbide ...160 to 175 SF (Positive Rake PVD coated)(PVD coating stays on
Un-coated...125 SF sharp edges better)
Drills...40 to 50 SF
Ruf Passes ~.10 doc @ .005/.008 ipr
Fin Passes ~.01 doc @ .003/.005 ipr

Good luck & you'll get the hang of it quickly