-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
Models for grinding HSS Lathe Tools
- Thread starter mikey
- Start date
What a great thread. Has to be up to being close to #1. Absolutely fabulous information and instructions. Mikey is great and describing the process and is very modest in in his presentation. I would like to know what he has forgotten. To all the posters you also are a great asset. All are very willing to encourage the NOOB and seasoned participents who want to expand their skills without be negative. As far as I am concerned this it by far the best forum on the interweb. I feel honored to associated with you all. Thank you. Now off to try my hand with some tangtung bits.
- Joined
- Dec 20, 2012
- Messages
- 9,422
Hey Vac, a belated welcome to HM! Thank you for your kind words but to keep things in perspective, I learn best from my mistakes. If I seem to know something, it means I screwed up ... a LOT!
All the stick waxes are about the same. Search Amazon for "stick wax lubricant" and pick the cheapest option. You don't need a lot; just a few seconds of application with the belt running will do ya'.
By the way, Tantung bits can be a challenge to grind. Some M2 is easier and will work for most stuff.
- Joined
- Nov 14, 2016
- Messages
- 3,007
Ok, I'm still digesting this. I've started to ask a question several times, but then thinking it through I find the answer is actually somewhere in what you have written, either specifically or readily implied.
I keep thinking if a sharper angle is less work for the machine, then why not more. Obviously there must be a point where to much is too much, and I keep coming back to an answer only to read through you posts again and see this.
Considering how often I seem to see this angle in your tools, that explains a lot.
At least on our end it seems like the very simplified summary is shallower angles are easier on the tool (less need to sharpen) while the steeper angles are easier on the machine (cuts better, with less force).
One item that seems to have only been briefly touched on is tool size, larger being more rigid, smaller being cheaper and easier to grind. I'm not seeing anything to suggest the tool size has much effect beyond that. What works well on 1/4" will probably work even better on 3/8" or 1/2".
The trade off seem to be cost, and grinding effort, vs stiffness and tool durability. Does that pretty much sum up tool size?
Perhaps some minor fine tuning needed based on the tool flex, but a bigger tool doesn't seem to result in a larger, less agile contact point, it just has more material backing it up.
I've been using 1/4" tooling all this time and when I was playing with aluminium and brass that seemed fine. Steel seems to be more of an issue, so I've bought some 3/8" blanks to try out to see if the additional rigidity helps on these harder materials. Nothing too fancy just 12L14, and some hot and cold rolled.
I'm going to carve one of the 3/8" blanks into a square tool and see how that goes.
I keep thinking if a sharper angle is less work for the machine, then why not more. Obviously there must be a point where to much is too much, and I keep coming back to an answer only to read through you posts again and see this.
Considering how often I seem to see this angle in your tools, that explains a lot.
At least on our end it seems like the very simplified summary is shallower angles are easier on the tool (less need to sharpen) while the steeper angles are easier on the machine (cuts better, with less force).
One item that seems to have only been briefly touched on is tool size, larger being more rigid, smaller being cheaper and easier to grind. I'm not seeing anything to suggest the tool size has much effect beyond that. What works well on 1/4" will probably work even better on 3/8" or 1/2".
The trade off seem to be cost, and grinding effort, vs stiffness and tool durability. Does that pretty much sum up tool size?
Perhaps some minor fine tuning needed based on the tool flex, but a bigger tool doesn't seem to result in a larger, less agile contact point, it just has more material backing it up.
I've been using 1/4" tooling all this time and when I was playing with aluminium and brass that seemed fine. Steel seems to be more of an issue, so I've bought some 3/8" blanks to try out to see if the additional rigidity helps on these harder materials. Nothing too fancy just 12L14, and some hot and cold rolled.
I'm going to carve one of the 3/8" blanks into a square tool and see how that goes.
- Joined
- Dec 20, 2012
- Messages
- 9,422
Let me say that there is no magic number for any angle. What works for me may or may not work for you. I tested every single angle on each of my tools and found what I think is the optimal angle for a given material but to say those angles are correct is just plain hubris. The 15 degree angle thing is just something I've observed; it is not a rule or anything. Let me illustrate.
When I was trying to optimize my threading tool, I ground 10 separate 1/4" tool bits with relief angles from 8 to 17 degrees (zero rake) and cut 10 separate 1/4-20 threads in 12L14 steel. Under 10X magnification, I looked at edge wear and how clean each thread was cut; all subjective but it is what it is. I found that as the relief angle increased the threads got cleaner and cleaner until I hit 16 degrees. What seemed to happen is that I began developing edge wear and that showed up as more burrs, and 17 degrees was worse. 15 degrees cut clean threads with a nice finish and the edge held up really well. I have since cut threads in brass to semi-hardened steel with that 15 degree tool and have gotten really good results and no significant edge wear. I normally only give the top of the tool a few strokes with a diamond stone from time to time and haven't had to re-grind a tool for well over 10 years now. So, 15 degrees is not magic; just tested and found to work well for me on my lathes in my hands.
As long as your tip geometry is good, tool size is not a major factor. This is especially true for softer materials. In harder stuff, like higher carbon and tool steels, you will probably see a better finish with the larger tool size. I don't know if this is a resonance thing but I suspect it is. I use 3/8" bits because they are stiffer and cut better for me vs 1/4" tooling, and I tested them pretty exhaustively. I can also use the same tools on my Sherline or my 11" lathe. It takes me 2 minutes to grind a 1/4" tool and under 4 minutes for a 3/8" tool. It takes 8 minutes for a 1/2" tool but without any gain in performance so I don't use them.
I suggest you grind identical tools in 1/4" and 3/8" blanks and see which works better for you. Its the only way to tell, and once you know it then you know it and nobody can tell you different. The same applies to your tool geometry. Test it yourself so that it works well for you and ignore what anyone else tells you to do, including me.
I am always leery about sharing tool angles. This is why my initial post in this thread said that these are my tools used on my lathe; it is right for me but it may not be right for you. This whole thing isn't about duplicating my tools. It is about learning to design and grind tools that work for you. I hope that is clear to everyone because the last thing I want anyone to think is that I'm some tool grinding guru or that my way is the only way; I'm just one of the guys.
You know you're the lord of the angles... 
I've tried a few changes, though not under a microscope. I find 15 works well for most things so far, of course, most things amounts to all of three things that I happen to have in the shop, so it's far from exhaustive. And it plays to my lazy streak, I don't have to adjust the table angle!
I've tried a few changes, though not under a microscope. I find 15 works well for most things so far, of course, most things amounts to all of three things that I happen to have in the shop, so it's far from exhaustive. And it plays to my lazy streak, I don't have to adjust the table angle!
