How To Grind A Hss Turning Tool

[mikey]

Just to make sure I understand you, don't cut such a sharp angle on the right side of the cutting tip? let's call that right side face a 45° to the adjacent side. you'd like me to go as shallow at 80°. am I understanding correctly?

Yes, exactly. If you take the side cutting edge and rotate it so it is vertical, then draw a line about 10 degrees below horizontal and grind the end cutting edge angle to that line it will give you a lot more mass backing the tip so the tool can sustain heavier cuts. See the OP for grinding the second flat if this is not clear.

A tool shaped like the above will take a cut as heavy as your lathe can handle without breaking the tip off.

 

[Hukshawn]

Got it! I will readjust.
You seem to like this tool for most general machining. how do you alter for various needs/materials? I think you mentioned previously all you do is change the rake angles. can you specify? and reasons. I'm actually learning a lot here.

 

[mikey]

I'm having trouble with my laptop. Hope this goes through.

This is a tool I share with others because it works for most things. I also use material-specific tools with the same general shape but with relief and rake angles that suit each material group. My stainless tool is different from my tool steel tool, etc. Each tool has relief and rake angles that are intended to reduce cutting forces or accommodate a characteristic of the material.

If you have time, read the articles I linked to in the original article. It will tell you what each angle on the tool does and how you can modify the tool to do what you want. For example, if you work with stainless steel you will find that it has a tendency to work harden due to high temps in the cut. Stainless likes more aggressive relief angles to cut well but if you also increase side and back rake the chip clearance is better. Since most of the heat in a cutting operation is in the chip, the faster you get the chips out the lower the cutting temps are and consequently the less work hardening occurs. In other words, you can use your tool angles to make the tool do what you want it to do.

Another example is aluminum, which tends to get hot when cut and then it gets "gummy" and can weld onto the tip of your tool. My tool has increased relief angles to penetrate faster and it has large (40 degrees!) rake angles to get the heat out of the work fast. As a result, I don't have any issues with chip welding. I also add more back rake and a more generous nose radius to improve finishing potential and my aluminum tool leaves a mirror finish, even on roughing cuts. This tool is amazing in aluminum.

The rationale for these tool angle changes is explained on page 5, post 137 of this thread:
http://hobby-machinist.com/threads/turning-tool-and-facing-tool-questions.36687/

As you learn how each material likes to be cut you will be able to adjust your tools to accommodate them. You just need to know what each angle does so you know what to change to get what you need.

Don't underestimate the value of cutting force reduction. You only have 3/4HP, which is not a lot of power. By prioritizing cutting force reduction your tools will enable your lathe to make cuts it may not be able to make with a standard tool. That is the beauty of HSS lathe tooling - you can modify it to extend your lathe's capabilities while enabling you to machine stuff more efficiently.

 

[Hukshawn]

I don't have a clear protractor, I have a machinists protractor/ruler, but that was cumbersome. so I winged it. but it's about 75°. but my back rake angle to the side is much steeper than I intended. I actually screwed up and flipped the bit over and did the other side...
But this is a hefty tool. lots of meat.

 

[mikey]

Yeah, you got it. Add a bit of nose radius and you should be good to go. That tool will now take a heavy cut without you worrying about the integrity of the tip. Have you tried it yet?

 

[Hukshawn]

Ya I didn't hone it or do the radius before I took the picture. It works well. I took a quick pass on whatever I had in the lathe. A 1" bar. With the angle I had the tool set in the QC it didn't leave as nice of a cut as the other bit,but it swollowed a 3/16" thick pass without killing the lathe. And I had it at 1400 rpm. Fast but not very strong. But by that point I only has 1/2" of marterial left after previous test passes. It distorted the thin piece but still cut well. So, I'm satisfied. I've really learned a lot about tooling here, mike. This was one portion of the hobby I was really trying to understamd and improve but just using reading material wasn't cutting it... so to speak...
thanks for sure.
Shawn

 

[mikey]

You're welcome, Shawn. You learn fast and I'm sure that in time tool grinding will come second nature to you. Keep us posted, okay?

 

[schemer]

Hey Mikey,
Great informative thread on tool grinding. What I would like to know is, what brand/model belt sander is that you are using?
Thanks

 

[mikey]

Hey Mikey,
Great informative thread on tool grinding. What I would like to know is, what brand/model belt sander is that you are using?
Thanks

Thank you!

I am using an old Craftsman 1/2HP 2 X 42" belt sander. I can't even remember when I bought this machine. Its over 15 years for sure, maybe more, and it is absolutely reliable. They are still available as a somewhat anemic 1/3HP version nowadays. I have one of these weaker sanders and I can completely stop the belt when grinding a tool so I cannot recommend it for tool grinding. They are sold by Palmgren, Dayton and others.

You would think that anything from Sears is basically junk but this is one of the more intelligently designed sanders for tool grinding. The reasons I say this is because the platen is easily replaced with a piece of angle iron to which a piece of ground steel can be attached. To this, a glass liner can be adhered and the whole thing shifted back to allow the glass liner to run even with the front of the two wheels. The right side of the platen is entirely exposed; there is no sheet metal in the way, and this allows full access to the belt for grinding the rake angles on a tool. This access thing makes most belt sanders on the market (except for the 2 X 72's) unacceptable to me.

This sander also has a chassis that is flat so a template with holes to angle the tool rest is easy to attach. The tool rest is simple to fabricate and allows for angle changes in seconds without tools. If you're interested in more on this sander, see here: http://www.machinistblog.com/modifying-a-craftsman-2-x-42-inch-belt-sander-for-tool-grinding/

The belt tracking mechanism is simple and precise. It does not allow the belt to drift unless the tension spring gets weak and this is only an issue if you're grinding huge back rake angles. If you can't tell, I love this tool!

I've been looking for a replacement or substitute grinder for years and haven't found one that satisfies my needs. The two things I mentioned - ability to attach a platen and have the right side completely accessible and the ability to attach a tool rest template - are important to me. If anyone spots something like this, let us all know.

 

[RonWB1957]

Timing is every thing. I need to learn to grind my own HSS bits. I need to find out how to grind a bit for cutting the recess in a medallion. SO how do you guys grind the tip to allow clearance when cutting the recess? Is the tip still centered on the diameter ?