Line after turning

[farmersamm]

Might I suggest a custom grind for 1018, and other soft gummy stuff?



Works nice for crap materials. And.............it's not some screwball grind that's popular on the net. It's capable of .020 DOC, or slightly more. Great for the finish passes. It will give the same surface finish as low as 70rpm, or up to whatever you wanna run it at. I usually run at 400rpm. The rpm range is suitable for a wide variety of material diameters.

If you have the equipment, you can run at, what I consider, insane rpm.........using carbide. But for a more down to Earth approach, this works fine.

It's not a form tool. Set it with paper under the cutter(light shining on it), while putting it against the stock. You should be relatively "flat" against the stock,, but at an angle. The tool cuts with shearing action.

You will see some lines, but the alternative is a smeary cut, that tends to catch chips, when you use carbide on gummy stuff.

Anyways........it's an alternative for cold roll, and hot roll. Ya do what ya gotta do.

 

[boslab]

Use a right hand tool and turn away from the Chuck works on difficult materials, esp nasty stuff like nimonic.
Mark

 

[michiganbuck]

Likely you can look at your chip and tell the cutter/bit/insert is compacting the material, not pilling it away in shaves that equal your feed rate. Mild steel needs a very sharp edge, proper clearance, and rake angle that pulls the chip /material away..plus a suitable radius.
Likely a HSS tool bit will beat most inserts. Inserts made for aluminum can be OK for mild steel.
Most coated bote/inserts are not as sharp-edged as a not coated insert.

Node radius...A lathe guy shouldld node that a radius helped for a better surface finish.

Rake and Relief Angles

This page give rake and relief angles for turning various materials with high speed steel tool bits.

littlemachineshop.com

 

[CarbideBob]

Likely you can look at your chip and tell the cutter/bit/insert is compacting the material,

First thing I do is measure the chip thickness.
This gives you the CCR or chip compression ratio.
Big problem here is knowing what the uncut chip is since you are out on a radius and it is most certainly not the feed rate.
Bob

 

[michiganbuck]

If the feed rate is .010 pre-revolution a ribbon chip will be very close to that thickness for mild steel or aluminum, C shape or 6 shape chips(more desirable) will be a little thicker, chunky chips that seem greatly thicker are evidence of the material pushing back on/into itself before shearing off. This is common from a dull or not very sharp cutting edge. Mild steel and aluminum should shear off with little gain in thickness IMHO.
I think fingernail shaving sharp and with having a radius is best for mild steel and aluminum surface finish, Many coated inserts are not that sharp. Some insert may be that sharp and if so should also have greater side cutting-edge clearance than would be for hard steel or cast iron perhaps 8 to 10*. Very sharp and negative can be OK, but having side and back rake is often better.
Compacting the material also creates a lot more pressure so stresses all the machine attributes to increase problems so a possible influence to give a poor finish IMHO.
Yes this is not considering all the machine problems, but the Ops photo shows a reasonable length, stout part held between centers, and consistent finish end to end That should be a very stable set-up so I would consider first blaming the cutting tool.... IMHO

 

[chipss]

Ok, I'm a hobbyist with a wimpy little south bend 9 inch. Mudder, I'd recommend spinning it as fast as your machine can go if you're using carbide. Mine will do a good job at it's max of 1050 rpm with positive rake inserts which are needed as my machine has the rigidiy of a wet noodle. A couple passes to experiment with feed rate and it'll give you a nice smooth finish. *Unless of course your material perhaps is some unknown grade of scrapbinium.

 

[toughmudder]

A lot good informations....basic question: Regarding nose radius and sharpness, can i change those parameters with the grinder or the type of the insert must be changed?

 

[sfriedberg]

Regarding nose radius and sharpness, can i change those parameters with the grinder or the type of the insert must be changed?

If you have diamond grinding wheels, you can modify carbide inserts. However, that's not a common practice. People using inserts generally select and buy the appropriately sized, shaped and sharpened inserts. For example, I acquired CCMT32.51 and CCMT32.52 inserts for a highschool shop that machines primarily aluminum; the only difference is the nose radius.

You might be better off to switch to HSS cutters for this machine. You can sharpen HSS to a keener edge than a typical carbide insert, and you can obviously grind a HSS blank to whatever shape is most appropriate for a given job. You can also grind some shapes that are not available in carbide, like ones that do shearing cuts, discussed earlier.

 

[eKretz]

I think Bob means that the chip thickness changes depending on how much of the chip is being cut by the nose radius rather than by the flat edge. If it's a low DOC that can significantly change the chip thickness.

Easier to get a good finish by increasing speed than by farting around with anything else. If that's not possible, then alter your other parameters or consider the switch to HSS. If this is a working shop, switching to HSS might be the very last option I'd consider.

 

[michiganbuck]

Here is an old youtube showing a huge difference from one insert to another (no HSS in the test..OPS the first is HSS but taking a very heavy Depth of cut...and a few more HSS tools down the pike.

At about 4;37 - 4:55 look like the tail is wondering
(X) not a very scientific test because the kind of steel changes also. I give the test a C- ..darn could have been a good test.

(X) turning with and without using the tail...with using the tail there Is vibration, likely the parts were centered drilled in a different chucking. The grade goes down to a D+

Still, it was interesting,

I am surprised they would botch a test..I have worked with German cutting tool technicians and they were sharp. Robby( the ham radio guy) from Heller is outstanding.

Jump ahead to 5:26 - 5:45 - 6:17 if you get bored. big difference in sound also.

 

[john.k]

Usually the bulk cut goes OK ,problem comes when you need to take off a coupla thou.....and the cut balls up,next you know its a whole string of different diameters,and ugly as crap.

 

[eKretz]

Yeah, light cuts need WAY more SFM.

 

[Nmbmxer]

I use a tangential holder I got from Australia for finishing cuts on low carbon steels. I hog the material off using a generic CNMG then use the HSS for any light passes.

https://www.eccentricengineering.com.au/products/diamond-tool-holder/the-diamond-tool-holder?rCH=2