Boring and turning alumimum: insert shape

Hi

I'm a novice working on a 19" 7.5hp manual lathe.. most of my work has been turning, facing and boring (3" plus holes) with ferrous metals. This is not a production shop, so insert life per $ is not a big concern for me. I've been using CNMG tooling and have had good results in steel and iron. I would like to get into machining aluminum, and boring smaller holes, so I'm looking at buying some new tool holders and inserts. Most of my boring will be straight bores and tapers, but I need the flexibility to do some internal shoulders too.

I have some uncoated CNMG inserts that I have used for turning and facing aluminum, and the results are decent, but not great. I'd like to improve this too as I look at smaller boring bars for both aluminum and steel. My understanding is that positive rake inserts should really improve my results on non-ferrous metals. Grinding more rake into HSS certainly helped on my old small lathe. I am looking at boring bars for either CCMT/CCGT or TCxT. I have a few questions:

1. Am I right in choosing these inserts for non-ferrous, and will they also be suitable geometry for boring small holes in steel (1 to 3 inch)? Is there another insert I should look at? I'd prefer to just have one set of bars.
2. Is there any practical difference between the C and T shapes? T gives me an extra point per insert, and they are about the same price around here. My thought was the triangle should also get less clogged with its own chips.
3. Are these also good choices to use if I buy some turning holders? I'd like to improve my OD finish on non-ferrous, so if I'm buying a bunch of inserts for boring, it would be nice to kill two birds.

Thanks!

Well you don't give details, liker diameter range and length of bore...So there are lot so variables.
For sure positive inserts and uncoated are where you want to go.

My personal boring favorite 10mm or so and up to 2" depth is the Sandvik "Coro-Cut MB E12-48-07R
This is a magic boring bar that has solid carbide inserts that screw on the end and are located with a three sided face spline.
The choice of inserts for the bar include grooving tools for various widths, plain turning inserts and threading inserts...Sort of the Swiss Army Knife of boring tools.
Turning inserts work well in steel and non-ferrous materials as well.
Bar is solid carbide so works well even at long extensions and is quite rigid.....Through drilled for coolant.

Be aware that this stuff ain't cheap!!!!!!!!!!!!!!!!!!!


Cheers Ross

CCMTs are great for both boring and turning. You would want to use polished "up-sharp" inserts on aluminum and you can use them on brass and bronze if your machine is stiff (won't pull the machine into the cut due to positive rake). I suppose for a 1" hole you will want a 2xx size. With up-sharp inserts the tip is fragile, and the triangle shape does not help that situation. CCxx give the sharp edge more support. If you are concerned about economics, my guess is the CCxx robustness would make up for only having two tips versus three on a triangle. If you are really worried about economics, you can buy a Dorian face mill that uses the obtuse CCxx corners that you can't use on a lathe. I can make an up-sharp CCMT insert last about forever on a manual lathe unless I screw up. I can also use them to put on a fine cut to finish, e.g., a bearing seat in steel, if I am careful about surface speed.

rklopp said:

CCMTs are great for both boring and turning. You would want to use polished "up-sharp" inserts on aluminum and you can use them on brass and bronze if your machine is stiff (won't pull the machine into the cut due to positive rake). I suppose for a 1" hole you will want a 2xx size. With up-sharp inserts the tip is fragile, and the triangle shape does not help that situation. CCxx give the sharp edge more support. If you are concerned about economics, my guess is the CCxx robustness would make up for only having two tips versus three on a triangle. If you are really worried about economics, you can buy a Dorian face mill that uses the obtuse CCxx corners that you can't use on a lathe. I can make an up-sharp CCMT insert last about forever on a manual lathe unless I screw up. I can also use them to put on a fine cut to finish, e.g., a bearing seat in steel, if I am careful about surface speed.

Click to expand...

Excellent info, thanks. I had thought about the lesser support on the T inserts, but discounted it as it's not exactly a D.. but if using sharper inserts (than I'm used to with steel), it's good to know that it's a problem before I went buying T.

I'm currently keeping my eyes out for a decent turning holder to use the obtuse corners on CNMG, and it's good to know they make face mills for that too.

I think I'll grab a couple of SCLCR bars to start with and talk to my local rep about some up sharp inserts. I think the 3xx size will go as small as I need to bore for now, and I can still buy a 1" square turning holder to use them.

Thanks!

I personally like the Triangle inserts for boring on an internal boring bar as you can get them 90 degrees to the face to make smooth bores in the bottom.
find an uncoated one, zero rake with a huge sharp edge. insert sizing is depending on depth of cut and feed required. many inserts out there, just depends on the exact job needed.
also coolant is your friend to prevent chip welding.

if you want three corners and strong insert you can go with a wc??. they have 80 deg corners and come in polished or steel grades.

CNGP?

From My past experience with smaller HP. lathes,I have found my best results on most materials,comes with an 11 degree positive insert.The ccmt is a 7 degree insert,and a fair choice,but if if all conditions are correct,such as speed,feed,and correct tool orientation,there can be a noticable difference in finish with a CPMT,DPMT,WPMT,or even a low cost TPG,as all are 11 degree inserts.I have noticed that the 11 degree inserts seem to be a little bit more free cutting,though the rigidity of the machine also plays a big part in the equation.Due to the high cost,and sketchey avaliability of most 11 degree inserts,I would have to reccomend going with a TPMR,wich is just a TPG with an added chip breaker.I have not ran a small machine for quite some time,but even with my 15hp cnc lathe,I am partial to the 11 degree inserts,when I have the need for a positive insert,mainly for close tolerance finishing or any soft non-ferrous material.My main OD. turning inserts on my CNC are WNMG430,WNMG431,WNMG432.With my 20 horsepower turret lathe,my most used insert is a CNMG642,or CNMG643.,because I will often remove 1/2" plus material per pass,even on steel,though both of my machines have high pressure coolant systems.With my CNC,for boring,I have a host of solid carbide bars from 1/4" to 1-1/2" diameter,all of wich use 11 degree positive inserts,though I do have a few larger neg. rake bars that take CNMG inserts,for jobs that require a high material removal rate.Both of my machines just love high tool pressures with negative inserts,and the finish and accuracy shows it,but in my experience,tool pressures can really raise hell,with trying to get a good fit and finish on a small lathe that is not real rigid,not to mention the heat problems that the tool pressure can create with the work piece,on a small machine that does not have a steady stream of high pressure coolant aimed at the work piece and insert.I believe that more rake can in many situations,create less tool pressure,resulting in less heat,and work piece deflection.I have talked to friends that use inserts with as much as 20 degrees of rake on high speed swiss type cnc machines.I havent always had all this fancy equiptment to work with,and truly believe that a good machinist should be able to study the job at hand,along with the readily avaliable equiptment and tooling,then with a little skill,luck,and the grace of God, get the job done,and done right,even if it means bringing a file and emery cloth to the table,and I can remember the days when I had ground a HSS tool bit so many times,that I could no longer hold on to it.Having all the toys just makes life a little easier,and a little less taxing on the noggin.