How To Grind A Hss Turning Tool

[mikey]

Great posts and step by step Mikey....Except dissing on carbide again for home lathes (except for big, rigid, powerful lathes)...which is BS
Smiley Face here!
....Without going back and copying and pasting all the carbide info. and grades I've posted...straight up: The "good" carbide is stronger, harder, tougher and stays sharper many times over HSS
But granted, a common belt sander won't work on carbide....

I have to leave to run some errands right now but I'll respond to this when I get back.

 

[Tozguy]

I grind both HSS and carbide tools.
For carbide it is recommended in some cases to put a 45 deg bevel on the cutting edge to give it more strength. This idea is counter-intuitive after taking pains to get the edge sharp in the first place. But I buy the concept knowing how brittle some carbide tools can be and how hard some workpieces can be.
My question is about whether this idea can sometimes apply to HSS tools. A razor sharp HSS tool might be great for softer metals, but for the harder materials, that can be cut with HSS, would there be any advantage to honing a slight bevel on the cutting edge?

 

[mikey]

Great posts and step by step Mikey....Except dissing on carbide again for home lathes (except for big, rigid, powerful lathes)...which is BS
Smiley Face here!
....Without going back and copying and pasting all the carbide info. and grades I've posted...straight up: The "good" carbide is stronger, harder, tougher and stays sharper many times over HSS
But granted, a common belt sander won't work on carbide....

Chris, this thread is intended to help our newer members learn to grind a HSS tool. It is a skill well worth learning because it is a skill that is being lost. The industry has moved almost entirely to carbide tooling and almost nobody in a modern shop grinds HSS tools anymore. Who, then, will keep this skill going? Us hobby guys, that's who. For whatever reason we choose to use these tools, we have to grind them to use them and I wanted to give the newer guys a start.

Why not start a thread of your own? I promise not to come in and label something you said as BS.

 

[mikey]

My question is about whether this idea can sometimes apply to HSS tools. A razor sharp HSS tool might be great for softer metals, but for the harder materials, that can be cut with HSS, would there be any advantage to honing a slight bevel on the cutting edge?

Mike, I honestly don't know. I never honed a 45 degree bevel on a HSS tool. Maybe you can try it and let us know how it works. The hardest stuff I've cut with HSS is maybe 4140 and had no problems at all but there are much harder materials out there. Normally, cutting really hard stuff, or hard turning, is done with fast, rigid lathes using CBN inserts so that leave me out - my lathe isn't nearly fast enough or rigid enough.

The tool I use for 1144 or 4140 has slightly increased relief angles to improve penetration and more side rake to get the heat out of the cut, while back rake is usually left at the recommended angle for improved strength. I hone the edge sharp and the tool cuts well.

Which harder material(s) are you referring to?

 

[Tozguy]

The materials would be steels that are on the hard end of the range that HSS can handle (whatever that is).
It is a theoretical question because I don't have a turning project on the go. I have been roughing out some HSS tools with renewed interest, to have a variety of them on hand and be ready for 'anything'.

The Machinery's Handbook Pocket Companion has a section on grinding carbide tools. On p.229 it states ''....and it is good practice to bevel the edges of roughing tools at 45 degrees to leave a chamfer of 0.005 to 0.010 inch wide. This is done by hand honing and is done to prevent crumbling or flaking off at the edges when hard scale or heavy chip pressure is encountered.'' There is a bit of information in this book about grinding chip breakers on HSS tools but little else.

This idea of giving the edge a bit more strength at the expense of sharpness might also apply to HSS tools to some extent or maybe not. I know it applies to knives in that edge bevels will vary according to the use intended.

A more experienced person than I am, reading this, might have already been there and done that and have some clues for me. It is hard for me to believe that this has not already been considered somewhere and that no one can tell me if I am on the wrong track (which is probably the case) or not.

 

[BriancCc]

Here is a facing tool that I ground that is the least embarrassing of the group. I did this off the rest. It was the third of the night.

On the subject of back rake, I forgot that I'm using a tool holder that holds it at a bit of an angle.

(I had a difficult time getting a photo of this thing.)

 

[mikey]

This idea of giving the edge a bit more strength at the expense of sharpness might also apply to HSS tools to some extent or maybe not. I know it applies to knives in that edge bevels will vary according to the use intended.

On a HSS tool, you can bolster edge strength by reducing the relief angles. This provides a greater amount of material under the main cutting edge, thereby increasing strength. This is a compromise because cutting forces increase as a result. With many harder materials or materials that can potentially work-harden, the key thing is to get the heat out of the cut as expeditiously as possible and on a HSS tool, that means increased side rake and possibly back rake if finishing potential is also important.

For the really hard stuff, Rc55+, you won't be cutting that with HSS. You need CBN inserts, a rigid lathe and high speeds.

I don't make knives but many woodworking tools have a standard bevel and also a micro-bevel. This provides a very sharp cutting edge but with more mass backing it for strength.

 

[brino]

Great post Mikey, Thanks!

I'll be referring to this one often.

-brino

 

[llhots]

Fantastic post... Thanks! Much to learn about here.

 

[mikey]

View attachment 140589
Here is a facing tool that I ground that is the least embarrassing of the group. I did this off the rest. It was the third of the night.

On the subject of back rake, I forgot that I'm using a tool holder that holds it at a bit of an angle.

(I had a difficult time getting a photo of this thing.)

Brian, thank your posting a pic of your tool. This is exactly what I hoped to see - pics of tools. This allows us to provide suggestions for improving the tool if you are willing. What say you?

If you do want input, it helps to have pics that show the tool clearly. Look at the 4-shot series of the completed tool in my original post and take pics like that - that will be a big help.