How "sharp" should HSS lathe tools be?

[great white]

I started out grinding my own hss tooling. Was decent, could do the jobs I wanted to with acceptable results.

Tried a carbide insert tool and haven’t looked back.

I will still grind a hss blank if I need a special profile tool though.

I also part with hss tooling. Not that carbide won’t part, I find the hss more effective and more importantly; more forgiving if everything isn’t exactly perfect. I also find carbide parting tools very limited in depth of cut. The ones I’ve tried you essentially get the length of the insert for the cut and not much more. I usually use the carbide cut off tool for grooving instead of parting.

 

[JPMacG]

I believe that nose radius is the parameter that most affects surface finish. Not just radius, but the smoothness of the radius. I inspect the radius with an eye loupe looking for high spots and burrs and keep stoning until it looks perfectly smooth. As long as their is relief, the angles are not critical compared to the nose radius. Admittedly, I am just a beginner.

Today I was getting a terrible finish on mild steel. I spent 5 minutes working on the radius and the same tool then produced a very nice finish. No change to the angles. Same with HSS boring bars.

 

[Huub Buis]

Newbie question: when buying HSS tooling, is M-2 not enough of a guarantee of good quality steel?

I use HSS-M2 tooling because, as far as i know, HSS-M2 is the hardest HSS without cobalt. HSS M35 contains 5% cobalt. Cobalt is a "heavy metal" and inhaling the dust is very unhealthy.
I do use HSS-M35 drills but do not reground them but thrown them away when they become dull.
If you don't reground drills, HSS-M35 drills are "cheaper" to use because they last very much longer than HSS-M2 drills.

 

[Huub Buis]

I also find carbide parting tools very limited in depth of cut. The ones I’ve tried you essentially get the length of the insert for the cut and not much more. I usually use the carbide cut off tool for grooving instead of parting.

I use a SPB32-2 holder for SP200 inserts as parting tool. In my standard setup, it will part 50mm diameter steel. My 1.2 mm HSS parting/grooving tools are used on small diameter bars that will be parted off near (0.5 mm) the chuck

 

[great white]

I use a SPB32-2 holder for SP200 inserts as parting tool. In my standard setup, it will part 50mm diameter steel. My 1.2 mm HSS parting/grooving tools are used on small diameter bars that will be parted off near (0.5 mm) the chuck

I'm using a 10" atlas, so I'm also limited as to how much "stick out" I can use compared to the rigidity of the lathe....hss is much more forgiving on my atlas with greater "stick out".

 

[Huub Buis]

I'm using a 10" atlas, so I'm also limited as to how much "stick out" I can use compared to the rigidity of the lathe....hss is much more forgiving on my atlas with greater "stick out".

To part off 50 mm a stick out of 26 mm will do.
My mini lathe also is 10" and I have part of 45 mm 42CrMo4 steel on it. I have used a (1.2 mm) 3/64 1" HSS parting blade for a long time but switched to a SPB26-2 holder (can't find a 3/64 blade any more). On both my lathes, to part off, I have to place to tool upside down and reverse the spindle direction otherwise the tool will dig in during parting.
I find parting of aluminum more difficult than steel because of the chip welding. I always use lubrication when parting off.

 

[great white]

To part off 50 mm a stick out of 26 mm will do.
My mini lathe also is 10" and I have part of 45 mm 42CrMo4 steel on it. I have used a (1.2 mm) 3/64 1" HSS parting blade for a long time but switched to a SPB26-2 holder (can't find a 3/64 blade any more). On both my lathes, to part off, I have to place to tool upside down and reverse the spindle direction otherwise the tool will dig in during parting.
I find parting of aluminum more difficult than steel because of the chip welding. I always use lubrication when parting off.

I built a solid plinth to mount on the cross slide. Parting without chatter and “grabbing” was nearly impossible with the top compound installed.

The plinth was a night and day difference.

Parting actually became enjoyable once I had the rigidity sorted. Truth be told, my top compound is now usually sitting in the drawer and I use the plinth for all my tooling. The rigidity it adds makes mist things much easier. If I need to cut an angle or bevel, then I’ll install the top compound and remove it when done the task.

Parting with the insert tool was certainly workable, but I find the HSS cutter just works better for me.

Seems like the carbide eventualy wither jams, diggs in or otherwise has a problem and then it either snaps the carbide or the holder the carbide is in. I just don’t have those issues with the hss.

But at the end of the day, whatever works for ya is what works for ya. For me, it‘s the hss parting tool.

 

[Provincial]

To part off 50 mm a stick out of 26 mm will do.
My mini lathe also is 10" and I have part of 45 mm 42CrMo4 steel on it. I have used a (1.2 mm) 3/64 1" HSS parting blade for a long time but switched to a SPB26-2 holder (can't find a 3/64 blade any more). On both my lathes, to part off, I have to place to tool upside down and reverse the spindle direction otherwise the tool will dig in during parting.
I find parting of aluminum more difficult than steel because of the chip welding. I always use lubrication when parting off.

Parting in reverse on the Atlas is not recommended because the chuck threads onto the spindle and the forces can unscrew it. The spindle on the 10" Atlas is actually quite rigid, and flexing of the spindle is not the limiting factor.

 

[Huub Buis]

Parting in reverse on the Atlas is not recommended because the chuck threads onto the spindle and the forces can unscrew it. The spindle on the 10" Atlas is actually quite rigid, and flexing of the spindle is not the limiting factor.

It is not the flex in the spindle, but the flex in the tool post that gives trouble when parting off.
You are right, if the chuck threads into the spindle, you should not reverse the direction of rotation. You can place the parting tool upside down at the back of the workpiece, that has the same effect (cutting forces are upwards).

 

[StevSmar]

I appreciate everyone's links and details on how to grind

You may also want to consider a tangential tool holder. Only one angle to grind.

Eccentric Engineering makes a popular one and they also have a grinding jig that sets the angle up for you.