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Some help with boring bars

matt_isserstedt

Diamond
Joined
Dec 15, 2003
Location
suburbs of Ann Arbor, MI, USA
So getting around to selecting some tooling for my Mazak 10N lathe.

I have many questions, this being my first turning center, so go gentle on me here :)

It looks like the large diameter 1"+ bars using *NMG inserts are pretty common, I read the thread about the pros and cons of V- W- and C-.

http://www.practicalmachinist.com/vb/cnc-machining/cnmg-vs-tmng-vs-wnmg-263499/

I have some parts I'd like to try as the first ones which will have a 1" bore, leading me to smaller bars with positive rake tooling.

This set looks like what I could use (forgive brand, just trying to illustrate) to create the size.

404-1930A.jpg


However on ebay I see solid carbide shank bars with CCMT 32- inserts in the M&M tools store.

1 New 1 2" Carbide Boring Bar Takes CCMT 32 51 Carbide Insert 5 5" OAL Z617 | eBay

Coolant thru vs. solid carbide more rigid..CCMT vs. TCMT how to decide? Any pointers? I'm sort of inclined to get both and do my own testing unless I'm way far gone on what I should be using.

Also, my machine has 1-1/2" bores in the boring bar holders, is this typically a shouldered sleeve/bushing with clearance holes for setscrew?

(in concept...with geometry to fit my machine)

Used Boring Bar Sleeve Bushing 40mm Outside x 1 00" Inside Metric Standard | eBay


Thanks for any help, I think I understand the basics of manual machines reasonably well, but the details of the Mazak are a little fuzzy right now not having seen one fully tooled in action.
 
I would do the ccmt carbide with coolant through.

In several different sizes.

Be aware that they will hit the chuck jaws at the least opertune moment.
 
+1 on the CCMT inserts for boring smaller dia's. I have bought a few of those solid carbide bars from Ebay....they're okay for the price. Some of my guys are notorious for crashing them so I keep my costs down by puchasing el-cheapo's. Keep in mind that CCMT an CPMT inserts look identical and apear to fit in the same bar. CCMT goes in a SCLCR/L, CPMT goes in a SCLPR/L. The difference is the clearance angle of a CCMT is 7° and CPMT is 11°. Putting them in the wrong bar will allow the insert to move in the pocket and wholler it out fast.

Brian
 
Be aware that they will hit the chuck jaws at the least opertune moment.

Not on his machine. :D He can go to X0 with a drill and the adjacent boring bar will still clear a 12" dia part even though he has only an 8" chuck.

I usually use the bushings for 3/4" and larger boring bars. Anything 5/8" and under, I usually put them in a straight shank collet holder, which is stuffed in the boring bar socket.

You will likely need to mill or grind another set screw flat if using RH boring bars as the boring sockets have 3 out of 4 sides with set screws. The 'bottom side' of the boring bar holders are blank.

Try to run as much left handed tooling in the machine as possible. The machine is primarily designed to run LH tooling as the coolant ports will show. Running LH tooling will make the machine more rigid during a cut as the forces are pushing down on the ways--very helpful on this machine, not to mention, you do not have to stand on your head to index the inserts.

Small dia boring bars benefit from TPGM inserts vs CCMT inserts. The TPGM 221 and 321 have 3 corners and they are much less prone to chatter due (especially periphery ground) to the larger clearance on the backside of the insert. 1" and larger boring bars go with CNMG 432 inserts due to availability. I do not like WNMG inserts for general machining. They are great for production where you can optimize and keep cutting costs to minimum.
 
I personally do not like triangle insert boring bars. The 80 deg is a much stronger design. I always have less chatter and increased speeds and feed with a CCMT/CCGT boring bar. In smaller diameters I use solid carbide from Internal Tool or SCT. Accupro is decent too.
 








 
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