6061 + Carbid Help

[spartan2381]

First let me start by saying I'm new to this and fumbling my way around. I have some 6061T6 bar stock and I'm trying to get a good finish on it with carbide inserts. I'm not sure where to start with spindle speed, power feed rates and insert selection. I have tried various spindle speeds from 460 up to 2,000 rpms. The carbide inserts are the silver ones that come in the precision matches set (CCMT/CCGT 300 Series). I have also picked a few inserts from Shars. Any help on speeds, feed rates and insert selection would be greatly appreciated.

Inserts from Shars:

1. CCMT 32.51 EF YBG202 - https://www.shars.com/ccmt-32-51-ef-ybg202
2. DCMT 32.51 EF YBG202 - https://www.shars.com/dcmt-32-51-ef-ybg202
3. WCMX 32.51- https://www.shars.com/wcmx-32-51-carbide-insert

Toolset from Precision Mathews:


6061 Finish:


Power Feed Chart:

 

[Firstram]

That's a lot of stick out, are you using a live center? The rule of thumb is no more than 3x the diameter without outboard support.

 

[spartan2381]

That's a lot of stick out, are you using a live center? The rule of thumb is no more than 3x the diameter without outboard support.

Yes, I'm using a live center. The diameter of the stock was too large to go through the headstock so I was turning it down.

 

[rabler]

Depth of cut is important to getting a good finish with carbide. Too shallow is often the issue, try to take at least .020”. Feed rate anywhere around .002-.004. SFPM around 300 or more. These are off the cuff numbers, there are better references available. Also, I started with Shars inserts and found a significant improvement going to name brand inserts.

@davidpbest on this site has a book on carbide inserts for the lathe which I recommend.Searching this site for lathe finish or similar will turn up extensive posts with lots of suggestions.

 

[Watchwatch]

What Rabbler said.

Take a look at Mikey’s mega thread on HSS lathe bits. HSS will give you much better results on your lathe.


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[ErichKeane]

If you have an Android phone, I'd suggest the app FSWizard for your speeds/feeds!

One thing to beware of (as Rabbler said!) is that Cabide doesn't like to be run too 'low' on speeds, or feeds, or depth of cut. With Carbide you have to be within a certain range of the 'speed/feed' given by the manufacturer, or it'll give a crappy finish.

HSS on the other hand can cut reasonably at much lower speeds/feeds/DOC and is way more forgiving. For HSS, the charts are essentially "Max" values instead of "You must be close to this" values.

I found with my small lathe (1.5hp 10" logan) that I just didn't have the HP for the right DOC/S&F to run carbide reliably, and I think most small lathes do not. Even now that I have a 15hp lathe, I still run HSS since I don't have the speeds available.

 

[pontiac428]

+1 for FSWizard and another for HSS. Grind up a finishing tool out of HSS with the right rake for aluminum with a nice radius, and you'll not be worried about speeds and DOC. Save the carbide for 304 SS, nobody is going to wear out lathe tools on aluminum.

 

[spartan2381]

Great advice from everyone and looks of it I have a bunch of reading to do on some of the threads mentioned.

I know HSS is easier to work with but have heard grinding tool shapes is a leaning curve all in its own. With that said are there any recommendations on where to buy pre-ground HSS? I need to look at Mikey’s mega thread but does that also go into how to grind as well?

 

[ErichKeane]

Great advice from everyone and looks of it I have a bunch of reading to do on some of the threads mentioned.

I know HSS is easier to work with but have heard grinding tool shapes is a leaning curve all in its own. With that said are there any recommendations on where to buy pre-ground HSS? I need to look at Mikey’s mega thread but does that also go into how to grind as well?

The ebay pre-ground sets are pretty good, and reasonably priced for what they are: https://www.ebay.com/itm/143882772192?

That said, grinding bits is EASY. I find the general tutorials to be a little too complicated for what is a pretty simple operation. Even a pretty darn poorly ground one will do a surprisingly good job! There are 3 faces you have to grind, only 1 of which is meaningful to the cut. The "Front" (toward the material) and "left" (or "right") just need to be ground for 'clearance' so that they don't rub on the material.

The "top" just needs to be ground at an angle that makes the 'point' be sharp-enough for the material you're cutting. From there, you just polish it with a stone of some sort, and set a level of 'nose radius' that your lathe can cut, will last some time, and that leaves a good finish.

Note that lathe cutting for a smooth finish is essentially just cutting a 'thread' along the length, so the nose radius wants to be enough so that the overlap causes it to be flatter/smoother.

 

[DAT510]

It looks like the inserts you listed were all MT's (CCMT). From your picts I can't see the cutting edge clear enough to tell.... But. for 6061, if you are using carbide, you'll see better performance with a Sharp (Almost Razor Sharp) cutting edge. You might take look at GT's (CCGT), they're designed for cutting AL and are have much sharper cutting edges vs CCMT inserts.

On lower power lathes, CCGT's can also be good at cutting steels when you have less power. They are also better at shallower depths of cuts on steels than the CCMT's. That being said, with the sharper/thinner cutting edge, you have to be careful as the CCGT inserts are more susceptible to chipping on harder materials.

I've personally had good luck with ISCAR CCGT 2-1-AS inserts. I get almost a mirror finish on 6061 with them.

Here's a closeup of the CCGT ISCAR insert.