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Boring and turning alumimum: insert shape

Miles B

Plastic
Joined
May 21, 2017
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!
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
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
 

rklopp

Diamond
Joined
Feb 27, 2001
Location
Redwood City, CA USA
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.
 

Miles B

Plastic
Joined
May 21, 2017
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.

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!
 

BT Fabrication

Stainless
Joined
Nov 3, 2019
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.
 








 
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