HSS or Carbide inserts fot lathe turning????

With a little practice you'll get the hang of grinding hss. Just make sure you have enough relief and your cutter is on center. Get yourself some 12L14 steel to turn, it's easy to cut and gives a good finish. When cutting mystery metal from a scrapyard anyone can have problems even a pro.
 
It sounds like you have a number of things going against you so you may want to stop, back up a few steps and start over. First of all, the pins you are cutting are likely hardened, probably even too hard for carbide, so get yourself some known steel for your project. The next thing you need to do is put those carbide inserts away. Carbide inserts work best on a rigid lathe with lots of power, not a light lathe like the one you are using. You may get away using the occasional brazed tip carbide tool because they are sharper, but not inserts because if you try to push the lathe hard enough to make them work, it will either chatter or stall, both of which will chip the insert.

Leaning how to grind a HSS bit is a basic skill every machinist should possess. HSS is inexpensive, versatile and extremely forgiving for the new machinist and if you make a mistake and burn one up, all you have to do is resharpen it. It sounds like you already discovered my video on sharpening HSS turning and facing tools. You should also check out the one on cutting speed and RPM and the ones on drill sharpening as well. The more you practice, the better you'll get, but first you need to get some steel you can cut.

Over the next few weeks I'll be making some very basic lathe videos that should help you get started without getting frustrated.

Tom
 
Just another data point. I have a little 7x14 and use both the HSS and the set of carbide tools from LMS.

The angles on HSS tools are *kinda* important to get perfect results but pretty forgiving to make a good enough finish. A few degrees doesn't make that much difference. The biggest things to make for a nice finish is the honing after grinding and the radius of the cutter. A grinder leaves a pretty rough finish on the tool. Getting the edge nice and sharp with a hone will improve things a lot. Small lathes generally don't have a very fine feed so if the tool is too pointed, you end up cutting what is effect a very fine thread rather than a smooth surface. A larger radius will even them out a bit and hide that. You can also rotate the tool edge more parallel to the axis so it takes more of a shearing cut.

I find myself using the carbide inserts more than the HSS for most things. Mainly because I start playing around and spend all my time sharpening trying to get a perfect edge instead of working on the project. It leaves a good enough finish as long as I plan my cuts and don't try to take really fine finishing cuts. The carbide doesn't work well if you are trying to take a couple thousandths like you can with HSS. The edge is not that acute because the carbide is too brittle to grind that finely. It is a lot more pleasant to cut with at at least 4 or 5 thousandths per cut. I don't have enough power to really get the most out of them like taking advantage of the chipbreaking. It works a bit but no where as well as when you can power through and drive the chip into the chipbreaker.

I also have a selection of brazed carbide tools. They are not really very sharp out of the box. A little quality time with a diamond hone and they cut well but not as convenient as the insert tooling.


General guidelines for both:

With a large lathe you can ignore some things as you have power to spare. On a small lathe, it takes a little more finesse.

Choke up on it. Don't have any more tool extended than you really need. The closer to the toolpost, the less it will flex.
If it is not cutting well, don't be afraid to re-position the tool, change the spindle speed, or change the feed direction.

Play with the materials before you go to make parts out of them. Avoid mystery metals until you get more experience. I can get some free metal at work that they use over in the materials lab. I can turn it but it looks like I have tied it to my bumper and driven around town for a few weeks with it dragging. Some materials you just need to stay away from until you have the experience to deal with them. What little I have had to do with hardened steel was pretty easy to solve. Put the grinder on the toolpost and have at it. Either that or anneal it so it is soft enough to work. If it is case hardened, you can cut through the hardened surface to soft steel that can be turned. Generally I stay away from it. To really turn it well, you need power and high grade carbide or ceramic tools. Otherwise work it in it's soft state and then harden it once you are done. Unless you work with it often, it is much more expedient to just get new material that is annealed than to mess with it.
 
Good points. One thing that gets me is.... There are left hand and right hand, The tool post swings around as does the compound slide. So why have all these variances? I'm so new to this that I have green grass coming out of my ears. I like it very much (machining that is) and have wanted to do this type of work since I shot competitively which I no longer do. I'm back into being a gear head, something that I've always loved and have a motorcycle now. There are tons of things I can do with this lathe( within it's limits). I did grind another tool bit and noticed that it cuts better when the lead screw is engaged going from left to right instead of right to left.
 
Well, much of it is that metal is not really as homogeneous as you would think. It has chunks of impurities and uneven distribution of particles. It has a grain much like wood, but a bit different. It has uneven hardness due to how it was cooled or from things like welding. It has layers due to processing like being rolled. It's structure changes by motion such as metal fatigue. As the cutter hits these differences, it changes the way it cuts. It is also a little anisomorphic. The grains are not exactly the same in all directions. They may be a little stronger along their length than their width or vice versa. We are used to it and expect it in wood because we can see the grain. In metal it can surprise you since it is not visible.
 
If you can post a pic. of your tool bit I'm sure you'll get lots of pointers on ways to improve your grind. Also feeds, speeds and depth of cut all come into play.
 
Here's some pics.. I picked up several honing stones at an estate sale today. My cuts still look horrible and I'm hardly taking big bites. I really thought the carbide inserts would be the cats meow. The tool grinding is making me want to put this thing in the corner. Like I said. The compound swivels and the tool post swivels.... That makes no sense to me. Too many variables. It's embarrassing.

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These are 3/8" HSS. If I try and put the tool post at any angle it just chews the metal and chatters. Hardly any feed. YUCK!!!! That's not what I really said, but you get the idea.

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Kinda fuzzy but it looks like you have the side relief backwards in that first picture. The line running down the front of the tool is leaning left and it should be leaning right. The cutting edge should be the first point to hit the work but it looks like the first thing to make contact is the portion below the cutting edge. In that first pic, leave the cutting edge about where it is and grind the bottom of the tool until that front line is leaning the other way about 10-15 degrees. I'm sure the big guns on this site can spot some more things that are less than perfect but having the heel rub the work is a total deal killer.
 
Your tool isn't cutting because you don't have any clearance under the cutting edge. Without proper clearance, the side of the tool will rub and the cutting edge can't do its job. Watch my video again and pay attention to the part about clearance angles because they are very important. The tool you are grinding is intended to be used perpendicular to the work, not angled as you have it.

The following pic shows the angles you need to have on your tool bit for it to work and shows the side and end relief (clearance) angles that I am referring to. Just don't use the back rake angle it shows, just leave it at zero.

Tom

Toolbit.gif

Toolbit.gif
 
Ok.

So let's go over the basics now.

Is the tip of the tool at the lathe center? You can check this by pitting a dead center in the tailstock and making sure the tip of the tool that will e doing the cutting is RIGHT at the tip of the dead center.

Are you using the leadscrew-carriage-feed to feed or turning it by hand?

Are the crosslide and cross feed smooth but tight? Meaning, can you lift up and down on the tool bit when it is mounted?

I need to mention here, that there is a PERFECT possibility that the metal your are working on is not an easy one to learn on.

It looks like your work is about a half inch in diameter. (Yes?)
If so your rpm should be around 500 RPM (or more) depending on your steel.

I would try light cuts for now until you get things more normalized.


Bernie
 
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