How To Grind A Hss Turning Tool

[Wreck™Wreck]

I drafted the above sometime in September of last year but due to chronic laziness and honest busyness, I only just now put the final touches on it. There have been numerous discussions about tool grinding, carbide vs HSS and so on recently and that got me off my butt. It is my sincere hope that this helps someone get over the hump and learn to grind tools. Most of us don't own big, rigid, fast or powerful lathes. We own hobby lathes, typically in the 10-11" class with max speeds of 2500 rpm or so. For those lathes and smaller, HSS is usually the best tooling option and we can further modify those tools to enhance the performance of your lathes even more.

I hope this gives you a start.

Mikey

Excellent job, you have way to much free time however, this is a good thing I suspect.

 

[mikey]

Hi all ,New member here and also new to the lathe hobby. I have a HF 7x10 I got from a friend at a great deal. I followed this thread and tried my hand at grinding some keystock to the tune of the first post. Came out fine on my second try. Did a few more for practice and now ready to try on some HSS I ordered.
Thanks to Mikey for making this easy to follow and a great tutorial.
The cutters I have are the inserts and the HF carbide on the red arms. I don't seem to get a nice finish cut on cold rolled steel. Its ok on aluminum which is easier to cut.
I did have a question though.
Why remove so much material on the first cut of the side? Is this for all around cutting or for specific materials?
Thanks again,
Solman

Hi Solman, and welcome to the HM community to you, too. I'm really glad to see that you tried grinding tools from keystock. In my opinion, that is the fastest way to learn tool grinding. It does take some time to learn how to move your hands and to clarify the various tool angles in your head; keystock is the best way to do that.

The answer to your question is more complicated than it seems. You actually don't have to remove so much material from the cutting side of the tool. The Brits often use a knife tool as the default turning tool and that tool has a straight cutting side - NO angle. The side we're discussing is called the side cutting edge and the angle it is ground at is called the side cutting edge angle. A knife tool has a side cutting edge angle of zero.

In times past, turning tools were oriented with the shank of the tool perpendicular to the work. In this position, the side cutting edge angle gave the user the proper LEAD ANGLE for that particular tool. To be clear, the side cutting edge angle = the lead angle when the tool was perpendicular to the work. Roughing, facing and finishing tools all had their own side cutting edge angles and when oriented perpendicular to the work the lead angle that resulted was appropriate for the function of the tool. For example, a roughing tool has a shallower lead angle vs that of a finishing tool. This shallower lead angle allowed a roughing tool to take deeper cuts without chattering. The larger lead angle of the finisher allowed for a much finer finish but it would chatter more with deeper cuts. The reason lead angle influences the potential for chatter is that cutting forces increase as more of the side cutting edge comes into contact with the work; the more contact, the more potential for chatter but with shallower depths of cut we get better finishes. If the above is true then angling a roughing tool so that its lead angle is the same as a finisher should improve the finish, right? If you do this, you will find that a roughing tool will finish just fine.

So, tool shapes in the past reflected the way the tools were used. That is why there were roughers, facers and finishers. Nowadays, with the much greater mobility of our quick change tool posts, we can use any shape that gives us the strength we need and we simply adjust the angle of the tool to suit our purpose. The tool in the OP is one such shape. It has enough mass in the tip to rough, it has enough clearance to face into a shoulder and then face out and it can finish very well with the right lead angle. We simply angle to tool to allow it to perform each of these functions.

Now, if you take a turning tool - a knife tool or a general purpose tool - and you perform roughing, finishing or facing functions by changing the tool post angle to suit, you will find that the lead angle that works best for the particular task is very nearly the same as the old time tools that were oriented perpendicular to the work. Interesting, eh?

So, the tool shape is not critical provided it is strong enough for the task and allows access to shoulders if that is important to you. Keep in mind that we are talking only about tool shape here. The actual geometry of the tool is another matter. Roughing, finishing and facing tools cut with different parts of the cutting edge and this is greatly influenced by the rake angles. The strength and efficiency required for these different functions is influenced by the relief angles. And the rake and relief angles are influenced by the material being cut.

In addition, the size of the lathe matters. Where a larger lathe can rough with shallower relief and rake angles, a smaller one requires greater rake and relief angles to produce an equivalent depth of cut. The reason for this is that different geometries produce different cutting forces so the tools used on a big lathe should differ from those used on smaller lathes. This is the key advantage to HSS tooling - we can change the geometry to suit the purpose and the lathe.

The bottom line is that shape is not as important to understand. Find a shape that suits your needs and go with it. Spend some time understanding what the relief and rake angles do and learn to use them to your advantage. Until then, try the tool in the OP. It will keep you turning until you find your own design to meet your needs.

I hope I explained this to your satisfaction. If not, let me know and I'll try again.

Welcome to HM, Solman!

 

[mikey]

Excellent job, you have way to much free time however, this is a good thing I suspect.

Thank you. Wreck! Yup, retirement is a very good thing!!!

 

[solman]

Mikey
Thank you for the clarification

 

[markrf555]

Thanks, Mark, and welcome to the HM community! That grinder is going to make things a lot easier for you to grind good tools - it came out really nice!

The Sherline lathe is an excellent lathe. I love mine and use it a lot, despite having a much larger one in my shop. Like all small lathes, it is limited in its power, rigidity and speed, and the key to unlocking every bit of the potential in that lathe is your tooling. With the wrong tool or tool shape, the lathe will balk and fight you but with the right tool it will perform with great precision and will take cuts that will surprise you.

Spend some time grinding some tools from mild steel keystock until you are comfortable with grinding. Those practice tools won't hold an edge long but they will cut. When you feel that you have a handle on the material in the OP, try one in HSS. I think you'll be pleasantly surprised at what your little lathe can do. Show us your results if you've a mind to - I would be interested in seeing them.

Again, welcome to HM. This is a wonderful community and you'll learn a lot from the posts here. You'll learn even more by asking questions; there is no other forum that is as open and helpful to beginners than this one.

Yes love the Sherline, it was my first lathe and came with a nice set of HSS cutters and there is alot of information on them included. I have some experience (self taught) on grinding HSS wood turning tools so tackled the HSS lathe cutter but as I said need to learn the appropriate angles and shapes, but don't know until you do! I'll post some pics of my cutters this week when can get back in the shop and out of work. I will post my mistakes too.

Also thanks Solman, the belt sander was a great learning experience and project. Commercially avail ones (2x72") are $1000-2000 and didn't want to drop that, so built mine mostly from scratch. got the wheels (plastic not metal) and several other parts for it from an Ebay co that is great and priced right, then made rest of stuff and got an old 1hp elec motor from a motor shop here in New Orleans. I have a total of about $250 in it, anyone wants the plans or help, shoot me a message or email. I can also do a thread on it. very proud of it and works like a charm. think using Mikey's great tutorial and some jigs and plywood push stick (great idea btw), will be able to really dial in some cutters!

 

[markrf555]

Mark, Thats a sweet sander you made . I have a Kalamazoo 1x42 which runs at half speed and I like it, but yours looks much better for knife making.

THanks. I also got a Kalamazoo 1x30 but needed a big dawg, so made that one. Will post a thread on it, cuz was pretty easy to make and saved a ton of cash doing it.

 

[mikey]

think using some jigs and plywood push stick (great idea btw), will be able to really dial in some cutters!

Looking forward to your result, Mark. BTW, 3/8" square bits work better on the Sherline if you have them. Your belt sander will make short work of it for sure.

 

[markrf555]

Looking forward to your result, Mark. BTW, 3/8" square bits work better on the Sherline if you have them. Your belt sander will make short work of it for sure.

Yes I ordered Sherline's 3/8" tool holder and will get some 3/8" HSS blanks for it. I quickly learned the importance of quick change when using that lathe for my first big machining project. everytime I had to change the cutter had to realign and center. took me 7 hrs to cut out the rigid alum risers for my harley, but they worked! Will prob machine a few 3/8" holders for it or a 4 way holder, pretty simple design

 

[N2XD]

Matt,
Could you send me more information on your belt grinder? Thanks


John

 

[Dan_S]

One thing I would add, is buy a range of HSS too blank sizes. When I first started, I only used 1/2" square blanks and it was really frustrating, because it took forever to grind a new blank. Today I keep a 1/8", 3/16", 1/4", 3/8", & 1/2" square blanks on hand, and choose the appropriate size for the task at hand.