New-to-me HF 7x10. Few Questions Re Set up and Tools

So I put together my lathe. It was not hard and I learned a lot about it. The finish is much better now than the first time I used it, even though I am sure that with practice and learning about set up I might be able to get even better finishes. Having said that, I do not expect miracles with this little guy but I am very pleased so far.
Question: the cutting tools are the HF carbide tips; what speed should I use for aluminum? I know that carbide cuts faster but I am wondering if I can use the same speeds than for HSS cutting tools.
The other question I have is how much you can shave each pass. I am cutting 6061.
Oh, the cutting tool is a hair low so I will need to shim it. I am thinking about buying a cheap feeler gauge, that way I can raise the tools little by little.

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Cutting speed for turning 6061 is about 500-600 sfm for HSS and about 2800 sfm for carbide. To get RPM, do a simple calculation: RPM = Cutting speed for the material in sfm X 3.82 / diameter of the work piece.

So, for carbide, 2800 sfm X 3.82 / guessing 3" OD = 3565 rpm. In other words, run it as fast as the lathe will go. If using HSS, you would run somewhere close to 600-650 rpm.

As for depth of cut, it depends on the quality, type of insert and the nose radius of the insert. Your lathe is not very rigid or powerful but it should be able to take a 0.030-0.050" roughing cut. You have to try it and see how the lathe responds. With a good HSS tool, I would guess you could take a 0.100 depth of cut easily if the tool is ground for aluminum.

EDIT: I just looked at your pics again and noticed that the tool is red. Not sure if that is HF inserted carbide or HF brazed carbide. If the former, see above. If the latter then it probably doesn't have a chip breaker and no top rake angles at all - it will just be flat. Brazed carbide tools typically are not that sharp as supplied and will cut much better if you hone the edges with a diamond stone first. They also do not usually come with a nose radius and a very small nose radius would be beneficial if this is the case so stone that on, too.

As for speeds and depths of cut with a brazed tool, I would slow the speed to a little faster than for HSS to start and see how the lathe responds; use as much speed as is needed to get the tool to cut well. Brazed tools with flat tops cut with much higher cutting forces so don't be too aggressive at first. I would go small with the depth of cut and increase a little at a time to see what the lathe and tool want from you. A good starting depth is 0.020" deep (0.040" off the diameter) and then go up from there in 0.010" increments. You will reach a point where the lathe will slow or chatter and that tells you the limit for that set of gearing when using that tool bit. You can either slow the speed, increase the feed or change the angle of the tool bit (turn it slightly more toward the chuck). This always works but you may find that your motor lacks the torque to handle deep cuts. That's okay; you've just learned the limit of your lathe with that kind of tooling.

Part of the fun when learning to run a lathe is sorting out how your tools work on your machine. Play with speeds, feeds and depths of cut. Be observant; watch it run, feel it run, listen to it and the lathe will tell you what it wants. You may not understand it in the beginning but eventually you'll tune into it and things will go much better. You are about to learn that a very small lathe like yours will cut with a carbide tool. When you are ready to go further, look into grinding HSS tools to really wake it up.
 
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Yes, those HB cutting tools are brazed carbide. I am turning a 2 inch aluminum bar and the speed is 1000 rpm. I ended up with a depth of 0.015" and the lathe was doing well. I noticed that at some point the chips were accumulating between the tool post/cutting tool and the piece of aluminum so the lathe started to slow down. I changed the tool and its angle and I stopped having that problem. Having said that, I needed to stop the lathe to clean the chips after each pass.
I cannot imagine how many little variables are for each material, cutting tool angles, etc. For now, I want to keep it simple. Having said that, I already have HSS blanks and a 30 min video to watch...

This is how much chips I get after each pass:

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I switched to this cutting tool (I do not know the name...) and I was not having many problem with chips anymore (let me know if I am still doing it wrong!):
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I noticed that the tip has some aluminum deposits. Is that common? I will look into honing my cutting tools though.
Another thing I noticed is that the top slide has too much play sideways even though I adjusted the gib strip. I bought a replacement (the original is bowed) so I will work on it.

Wilson
 
Aluminum tends to string like that with light cuts and slow feeds. This is due to the high ductility of the material; it bends but doesn't break unless encouraged to do so by either a chip breaker or taking a cut big enough to produce a really thick chip. In the latter case, a heavy cut and a faster feed rate produces chips instead of strings. I am not sure your lathe, with that tool, is capable of such a cut.

Cutting fluid really helps with chip evacuation, cutting temps and finishes. You still string but it won't pile up as badly on you. WD-40 works well for aluminum; just brush it on. Cutting fluid also reduces a Built Up Edge (BUE), which is that deposit you're finding on your tool. The mechanism behind how this occurs is somewhat controversial but you can look at it as a welding of the aluminum onto the tool. Accordingly, it can be really hard to get it off unless you grind it off. Trying to pick it off usually results in a chipped tool. Best to take a deeper cut, use some WD-40 and pick up your feed rate.

The reason that second tool seems to work better has to do with the lead angle of your tool. See the side of the tip where the cutting is taking place? That edge is called the side cutting edge - pretty imaginative name, eh? Okay, engineers are not known for originality. ;)

Anyway, that side cutting edge is at an angle, called the side cutting edge angle. The angle of your tool's edge is canted back a bit more than the typical brazed tool and is actually angled similar to what a good HSS side cutting edge angle is. At this angle, the edge tends to cut or shear a chip rather than plow (like the typical brazed tool does) when you take a light cut. What also happens is that the chip follows a path that is perpendicular to the side cutting edge of the tool so chip evacuation is a bit better. That is why the chips don't seem to pile up - the cutting forces run perpendicular to the side cutting edge and the chips will flow along that path, perpendicular to the angle of your side cutting edge. Make sense?

Don't get too hung up on this stuff for now. What I wanted you to know is that that side edge angle on the tool is NOT how a brazed tool is usually used but it will work better for you on a light lathe taking light cuts so use it.

The other thing to note is that the tool has a very sharp corner at the nose. That is, it has no nose radius and this is typical of brazed tools. It will work better and definitely finish better if you stone a tiny radius at the very tip. Just use a diamond stone and round the nose just a little. I think you will be surprised at how much better the tool both cuts and finishes.

So, my suggestions to you are:
  • Get your tool on center height - get it precisely there, not close. I know other guys will tell you to go higher or lower or whatever but trust me, center height on a small lathe is where you should be.
  • Sharpen the tool edges with a diamond stone. Follow the angle under the cutting edges (called the relief angles) and hone them evenly. Then flatten the top of the carbide insert, then put a tiny radius at the tip of the tool.
  • Angle your tool (the one in the picture) slightly toward the chuck to rough and slightly toward the tailstock to finish. See what happens to your ability to take heavy and light cuts when you do this, and notice what happens to the finish.
  • Use WD-40 for all cuts. It helps.
  • Take bigger/deeper cuts to rough and lighter cuts to finish.
  • Play, have fun but be observant. See what happens when you vary depth of cut, speed and feed and see if you can fine-tune things to get what you want.
  • Learn to grind HSS tools. For your lathe, this will easily outperform those carbide tools.
I've been doing this for what seems like a very long time but I still enjoy watching a chip peel off exactly the way I want it to, and I still take pleasure seeing a fine finish produced on a piece that comes in on size. I no longer think much about what I'm doing to get these results but I can tell you that it is exactly what you're doing now - paying attention to tool angles, sharp edges, cutting fluids, speeds/feeds/depth of cut and so on. Basics, Sir, basics.
 
Thanks, mikey, for your reply. I forgot to mention that although the tool and the aluminum I was turning were not hot, I used wd-40 and helped with the chips.
I have feeler gauges that I’ll use to center my tools as you are suggesting.
I watched a video from old tony yesterday about grinding now I have an understanding of the basics for tool grinding; now it’s the time to practice!
 
I think I saw that video, too. One of the guys posted it up here. I really liked the computer graphics that made things a lot clearer for the new guys. Have fun!
 
I avoided HSS tools for a long time because I was intimidated by the idea of hand-grinding them, but when I finally bit the bullet and tried it, my first effort resulted in a usable tool bit. No fancy chip breaker or the like, but it cuts metal just fine!

I just ordered some HSS and cobalt blanks from Victor to grind some more. I'm reserving the cobalt ones for situations where tool wear during a job would be problematic.
 
Thanks, homebrewed.
So I am trying to set the tool height and it turns out that the tool is sitting higher than the center of the lathe chuck. What do you do on that situation?

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There are a number of reasons why you want the tool to be as close to the center as possible. If it is too high, the cutting tip of the tool may not contact the work so you will have poor cutting action. If you then push the tool in harder, it could grab and, at the least, stall your lathe. Worst case, you could break your tool or break/bend the work when it tries to climb up the tool. Finally, if you are facing, an off-center tool will leave a "nub" in the center of your work. Also, If your tool is too high this will make it difficult to get the tool to the center of the work (w/regard to facing). It looks like that's what you got going, from looking at your photo.

I use the classic machinist's ruler method to set the bit on-center with the work. Gently pinch the ruler between the work and tool. If the ruler isn't exactly vertical the tool needs to be raised or lowered -- if it nods toward you, raise it, away then lower it. It seems remarkably sensitive, at least with the size of stuff I work on. Larger-diameter rods will have lower sensitivity, but that is OK -- they are more forgiving if the tool isn't exactly on center.

Of course this method won't work for square/hex/etc profile stock. I have some short (~4 inch) pieces of 1/2" drill rod I use for tool set up purposes. After all, once the tool height is set correctly it should be good for whatever you put in the chuck.
 
because I was intimidated by the idea of hand-grinding them

When I was in high school doing machine shop for the first time... I still remember us going over slides of diagrams on how to grind all the angles. But from what I recall, it went over our junior heads so we just grinded a quick simple tip and it SEEMED to do the work for us just the same. LOL!
 
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