boring bar insert style question

I use WNMG and TPG inserts at work ( od and id ) I have a large bar at home( 1 1/4)that uses tpg and smaller ones that have cnmg .

The wnmg is great for roughing and tpg for finishing ( no chip breaker).
The problem I have with the cnmg is, my bars leave very little clearance between the bar and bore for chips.

So I am looking at Dnmg or Dcmt or tnmg.

I already have a turning holder and inserts for tnmg. But with either diamond I would also have to buy inserts.
4 edges with the dnmg seems better but are there disadvantages?
The tnmg holder I'm looking at seems to have more side clearance.(3/4 dia bar)

My 3 hp lathe doesn't really push the wnmg properly on od so that is out.Not looking at serious hogging anyway. Just would like to make more chips and less strings.

Any opinions on these or should I just stick with tpg.

Dave

If you're having this much of an issue with neutral rake tooling, go to positive rake inserts.

I like to use an Iscar E-SDUCR 10-2. It's always left a great finish for me. I've not had any problems so long as feeds/speeds/carbide grade was appropriate to the application. There's plenty of clearance between the cutting edge and bar for chip clearance. ISCAR Cutting Tools - Metal Working Tools - E/S-SDUCR/L : 3601954 - E-SDUCR 10-2

These "super positive" inserts are killer:

ISCAR Cutting Tools - Metal Working Tools - ISO-Turning - Int. 60deg Triangle 91deg Approach - TPGT-SP

Naru, The diamond is one I am looking at. Seems to have a lot of clearance around the shaft for deeper holes for the chips.Is there a disadvantage to the double sided inserts compared to the single side.

We have an od tool at work with that insert. works fine but when someone that doesn't really belong on the lathe used it they blow out the whole end.
Maintenance shop, what else can I say. Most of the problems guys are gone now.

One good reason for the tpgs. they are dirt cheap. That and seldom have optimum set ups as far a grip on the part.
I grind a radius on the shim so a broken edge doesn't take out the shim too.

Dave

winger said:

Naru, The diamond is one I am looking at. Seems to have a lot of clearance around the shaft for deeper holes for the chips.Is there a disadvantage to the double sided inserts compared to the single side.

We have an od tool at work with that insert. works fine but when someone that doesn't really belong on the lathe used it they blow out the whole end.
Maintenance shop, what else can I say. Most of the problems guys are gone now.

One good reason for the tpgs. they are dirt cheap. That and seldom have optimum set ups as far a grip on the part.
I grind a radius on the shim so a broken edge doesn't take out the shim too.

Dave

Click to expand...

If by double / single you mean Neutral / Positive, I'm sure there's a list out there since I wouldn't claim to know all of them, but..

Neutral Pros / Cons:
P: Flip the insert for extra cutting edges
P: Faster material removal rates
P: Deeper maximum DoC's
C: More tool pressure causes more deflection on smaller parts or pieces with stickout
C: surface finishes on light passes
C: Less availability in smaller sizes

Positive Pros / Cons:
P: Better surface finishes on light passes
P: Better chip control on lighter passes
P: Lower tool pressure
C: Less cutting edges
C: Lower maximum DoC
C: Less availability in larger sizes

Those are just what comes to mind for me, others may know more or even disagree with what I've listed above. I would never recommend you use positive tooling for everyday heavy turning as the cutting edges (especially on DCMT) is very fragile. You CAN take relatively hefty cuts with a DCMT32.1 insert and it'll do fine, but if you accidentally bump the cutting edge into anything or touch into the part too hard/fast, you'll likely break the edge. They're definitely not an all-purpose insert, but for finishing passes or thin parts where deflection is a larger factor, they perform very well. As far as cost goes, they, just like many other inserts can be expensive. The inserts I use are $11/ea from McMaster-Carr, granted I'm not burning through inserts like a large production shop.

I ordered a bar for tnmg since I already have inserts and a 5/8 bar with dnmg and 2 different inserts (for steel and aluminum).

Dave