How "sharp" should HSS lathe tools be?

Ok guys, I get the point... gotta learn grinding now. Guess I'll add this to the already steep learning curve.

I do have a couple of 6" grinders that I'm in the middle of replacing the wheels with a range of grit, plus an El Cheap-O belt grinder that I'll also try. Re-watched This Old Tony and Blondihacks vids on the subject, it seems obtainable to get at least as crappy results with my tooling that I am already working with.

What I find interesting however is pretty much everybody grinds the same general shape (the "10 degree everywhere" profile), and my stupid set doesn't have anything close to this shape! Why my set doesn't even have this basic starter-shape is beyond me.

Even tho I'm sure my set is the "junk" Chinese or Indian HSS, I'll probably flip one end around and try grinding my own just for the experience. Once I get a little more experienced with what I'm doing, I'll invest in some better grade HSS blanks. Wish me luck!
 
Keystock is cheap to practise with too. Doesn’t cut worth #### but you can use to get the hang of the angles if you’re short on HSS.
 
You do NOT need to learn to grind tools. With a 11" lathe, you have enough power and rigidity to use inserted HSS and carbide tools. f you need advice on which tools to buy, I suggest you buy David Best's book and listen to him.

On the other hand, if you want to optimize what your lathe can do then HSS is a very good option. As you go along in this hobby you will find that there is no perfect tool. Sometimes brazed carbide is the ticket for the material you have to cut. Sometimes it will be inserted carbide and sometimes HSS is the way to go. You have to try and see how each cuts to know when to use which tool. Those who tell you they only use one kind of tool, at least in the hobby world, are missing something. In order to have the option of using HSS, you have to learn to grind tools. More on this below.

So, to answer your question, your tool should be as sharp as you can get it. Mine slice paper like a finely honed kitchen knife. Lots of opinions on whether or not to hone but in my experience a honed tool holds an edge much longer, cuts more accurately and produces much better finishes.

As I said, you should learn to grind lathe tools. Just because a tool is made from HSS does not mean it will work well for you. What makes a tool work well is it's tip geometry. I don't mean just the shape, although that matters, but more the angles of the three faces of the typical turning tool. You can go here for a simplified discussion of these angles and how they are ground. You will find that each material group you work with will favor different angles. Plus, you can further modify those angles to improve the performance of your tools once you figure out how this grinding thing works. The Model Tools thread has everything I know about tools in it. It might be long but it's free and will tell you quite a lot about the subject. You might invest the time at some point.

I also own an 11" lathe, an Emco Super 11CD. It is a small lathe but is rigid for its size and has 2 real HP. My HSS tools easily outperform carbide on this lathe so I prefer HSS about 90+% of the time. You will find the same to be true, especially when you need to do tight tolerance work.

zippyslug31 said:
Ok guys, I get the point... gotta learn grinding now. Guess I'll add this to the already steep learning curve.
Click to expand...

There are some guys who were in the same place as you when we started the model tools thread. Some of them can now grind tools as well as I can; I know because I've held their tools in my hands. I don't know of any of them who, having learned to grind a good tool, regrets the time it took to learn it.
 
Most of the time I use carbide on the lathe and HSS M2 or carbide on the mill. Sometimes I prefer HSS tools on the lathe for a better result. For coarse threading in steel, I use a HSS tools because threading inserts are pretty brittle and snap off. For parting I use carbide. For parting thin materials close to the chuck, a 1.2 mm HSS parting tool.

On a lathe, rigidity is super important. You should keep the stickout of the tool as low as possible. Try to keep the tool above the tool post, don't turn the top slide out of the tool post. You must tighten the gibs to minimize play without causing extra wear.
Another point are cutting forces. The smaller the nose radius, the lower the cutting forces. If you cut to deep, the tool will dig in and the finish is bad.
I can see the nose radius of the tool so it must be big and the stickout can be decreased.

The more RPM, the more heat you put in the cut. That makes the metal softer resulting in lower cutting forces, better finish and longer tool life. But if you overheat the tool tip, it will soften the tip. A thicker cut will also put more heat in the material. There is a balance between a good surface finish and tool life.
It all depends on your lathe, material to cut, setup, cutting tools, feed and speeds. When using inserts, the manufacturer gives some directions of how to use the tools. Using HSS, the only direction I have is the cutting speed 30 m/min for steel.
You have to respect the limits of your lathe and setup. On my bench lathe, I can't move the material at the rates an industrial lathe can. As a result, I can't always get the same shiny finish as you see on YouTube.

I have a lot of inserts and test under what conditions, material and material sizes they perform the best on my lathe. Also the HSS tools are tested. Nevertheless, I have some unknown steel types that give a marginal finish. I have marked them by the letter M.

I use CCGT060204 inserts for aluminium. They not always give a glossy finish but the finish is good enough for tight tolerances. If I can't find find a HSS tool or carbide insert that gives a good finish, I use this CCGT060204 insert as a last resort.

In the past 10 years, I have managed to get a better surface finish with less effort so don't give up.
 
The angle that you approach the work with makes a huge difference, As well as speeds/feeds.
 
Newbie question: when buying HSS tooling, is M-2 not enough of a guarantee of good quality steel?
 
AlfromNH said:
Newbie question: when buying HSS tooling, is M-2 not enough of a guarantee of good quality steel?
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The short answer is NO. Not because M2 isn't a good alloy, but more so because many offshore manufacturers either misrepresent their products, and/or cheat on the composition. If you buy reputable brands from reputable dealers M2 should be sufficient for almost anything being done in a hobby shop. Most of my older HSS tooling is M2. The newer tooling is M35. In all probability I don't really need the M35, but it was what was available at the time, and the price was such that I couldn't refuse it.

Here's a link to an article on the Wikipedia website explaining the different grades of HSS and their most common uses.

en.wikipedia.org

High-speed steel - Wikipedia

en.wikipedia.org en.wikipedia.org

Just as important as the tool material choice are the speeds and feeds, they're run at. Here's a link to a speed and feed calculator on the Little Machine Shop website.

www.littlemachineshop.com

Speeds & Feeds

The premier source of tooling, parts, and accessories for bench top machinists.
www.littlemachineshop.com www.littlemachineshop.com

Many on this site are advocates of carbide tooling. I'm not one of them. I do use it on occasion but find HSS tooling is more than sufficient for 90+% of the work I do. Carbide is nice when working with some grades of tool steel, but in almost all cases HSS will accomplish the task. It might be at slower speed and feed rates, but this is supposed to be a hobby not a production situation.

I'm a bit old school in that my time in the industry was from the 1980's to the early 2000's. Carbide was just coming into its own in the 80's and was advertised as the end all and be all to the machining industry. While it was good for some situations it still had some drawbacks. One of those drawbacks was interrupted cuts. Many an insert was trashed trying to repair shafting with keyways, sheaves, gears, and pulleys with set screw holes, and plates with through holes that needed modifications.

Things have improved substantially since then, but the cost of carbide tooling has also increased dramatically. While the price of a single carbide insert may compare to the price of a similar size HSS tool blank in most cases the HSS blank (if used and maintained properly) will far outlast the insert. The nice thing about HSS is that it can be ground to almost any shape you can think of. A blank ground for right hand turning can be reground to make a snap ring groove, left hand turning tool, threading tool, or almost any other profile in a matter of minutes. When the job at hand is finished it can be reground for its original purpose. A single tool can be resharpened to its original profile dozens of times and repurposed nearly as many.

As Bart Simpson would say: That's my story, and I'm sticking with it, I didn’t do it, nobody saw me, you can’t prove a thing, and the photographs are altered.
 
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@projectnut thanks for the detailed reply. Like the OP, I thought I'd be better off starting with a known quality of lathe tooling so I bought a small set from LMS.

I do intend to learn to grind my own, the lathe and mill I got recently came with a cabinet full of tooling. This is the drawer of lathe bits, the PO was very creative in grinding his own. I hope to eventually be able to look at each and decipher what it was for, its quality, how useful it is to me, etc.

Lathe Tooling.jpg

edit: sorry, not trying to hijack the thread...
 
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I was pretty hesitant at first to grind HSS. I quickly found out however that it's not all that hard. And best of all, if you don't like the edge or it's not cutting well, just a quick touch-up or adjustment on the grinder and try it again..
A sturdy tool rest(?) on your grinder is your best friend here.
I bought a toolbox from a retired machinist, containing a batch of used HSS. I was very surprised at the variety of angles, shapes & radii I found in there. No doubt each was for a specific job or cut.
 
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