How To Grind A Hss Turning Tool

[mikey]

I have nothing to add but a thank you. I recently bought (5) 3/8" HSS blanks to get started on. I've tried some carbide and it worked ok but not a very good finish. I'm very new at this and like to run the lathe as slow as possible until I get a better feel for it. It had one HSS bit when I got it. I used it a few times and got a nice finish and then switched to carbide and could cut deeper but the finish wasn't as good. I feel like rpm is the main reason for that. I havea 6" and 8" bench grinders. I'm making some nice tool rests for the 6" and plan to use it for nothing but sharpening.
Your pics and descriptions were good. I really appreciate you sharing your time on this. That's why I like this place so much.

You're welcome. When you get that grinder set up, try making the tool I showed. It is a modified tool that will cut most common stuff while lowering cutting forces and cutting temperatures. If you reproduce it, it should rough well, size accurately and finish nicely. And you won't have to change your tool rest angle to make it.

Cutting speeds as we usually calculate them are starting points. Quite often, we need to adjust the speed to get the depth of cut we need (slower) or the finish we want (faster speed and/or slower feed). A good tool like that shown in the OP will let you cut deeper at higher speeds and will finish well at lower speeds due to the increased back rake. Give it a try and share it with us if you care to.

 

[Bob Korves]

I recently bought a large lot of tooling and got a box of HHS cutting bits with most of them pre-ground into many different shapes. They really point out the advantages to grinding your own bits. Thanks for your write up, it went along way to explaining the process.

It seems like every lot of old tools I get has a pile of already ground HSS tools that come as part of the deal, and also some NOS high quality HSS blanks as well. I clean them up, and then sort them into categories -- RH turning, LH turning, L & R facing, form tools, internal tools, blanks, and so forth. After cleaning and sorting them, I put them away by category, but first I give each one a close inspection to see how it was made and to speculate on what kind of material and job it was was ground to cut. If only those old tools could talk... Or if I could talk to the guys who ground them... Many of them are very carefully made, with obviously lots of time and effort invested into making them. Some were done on surface grinders or tool and cutter grinders, most by hand. I have so many that I almost never need to make tools from blanks, though I have plenty of those as well. I just find one that will do the job, or modify one that is close to doing the job, change relief and rake angles if needed, and make sure it is sharp. It takes far less time than making a tool from scratch, and just about all the tools I have were obviously made by talented machinists.

I got those tools for less than scrap value. They are useful, and work well after picking out the best one for the job and often making slight modifications. I also have carbide insert tooling, and I use that as well, it is tougher and can take higher feeds and speeds. It is also in dedicated holders, which makes them quick to get into play. The old HSS tools are usually the go to choice when I am doing more than simple turning or facing. Part of that is I want to see how the old tool made by someone who is now likely gone actually works, and honor his legacy. If only those tools could talk...

Most of the tools I make myself from HSS are fairly simple, no back rake, smaller side and front angles than what Mike is showing, often with chip breakers ground in, but then my lathe is bigger and more rigid (13x40) than many H-M guys have. Most of the HSS tools I come into are ground with angles more like Mike's work, and they work fine, but I do not push them hard.

I would feel quite limited with the few styles of holders and carbide inserts I have on hand, but they do the job for high removal rates and for harder and tougher materials. My HSS tooling fills in for the "other" work...

Thanks again for the great thread, Mike!

 

[Hukshawn]

If the tool works then it works - good for you! As you get used to the process things will be easier to control - it looks like you're most of the way there already. I can see side rake, back rake, good relief angles and enough of an end cutting edge angle to access shoulders. Nose radius looks to be about 1/64" and that will work great. Pretty tools are great and will come with practice but function is what counts and you've got that now - way to go!

the picture doesnt show it, but all of the angles you described in the first post are there. its a 3/8 tool, and i just didnt go as steep as you did. there is a good enough cutting angle to get into the shoulders. the top cutting surface is a mess because i dont have a very good edge to grind against. im using a pretty standard 4x36" belt/disc woodworking sander. i actually had to do that top cutting surface on the grinder. ive been keeping my eye out for a reasonable 1" belt sander. i like this bit now, i may refine it, make the angles a bit steeper to get into tighter spots without having to constantly readjust the QCTP.

My belt sander runs at 3450 rpm. I get my Aluminum Oxide belts from an ebay seller called Barbkat. Most sanding belts have a shelf life of about a year so buy only what you can use quickly. If the belts get old the adhesive in the splice gives out and the belts can snap. I usually buy 5 belts of 24 grit to shape and 80 grit to fine sand the bit and then hone from there. I try to make tools in batches and grind up a bunch to use the belts while the splice is strong. Last time I ground tools I think I made 10 of them. Then I don't buy belts until I need to grind again.

im surprised, i would have assumed some other belt material other than aluminum oxide, it tends to dull faster than others. especially on tool steel.
i deal a lot with sanding belts, but with wood. my stroke sander in my basement shop is 6"x168". and the drum sander is something like a 10' piece of 3". cant say ive ever had one snap.

if youre able. im interested in seeing some other types of common tools youve ground for various uses.

 

[mikey]

Thank YOU, Bob. It helps for the guys to know how other experienced machinists make their tools. The more we share, the better it gets for all of us who use them.

 

[mikey]

the picture doesnt show it, but all of the angles you described in the first post are there. its a 3/8 tool, and i just didnt go as steep as you did. there is a good enough cutting angle to get into the shoulders. the top cutting surface is a mess because i dont have a very good edge to grind against. im using a pretty standard 4x36" belt/disc woodworking sander. i actually had to do that top cutting surface on the grinder. ive been keeping my eye out for a reasonable 1" belt sander. i like this bit now, i may refine it, make the angles a bit steeper to get into tighter spots without having to constantly readjust the QCTP.



im surprised, i would have assumed some other belt material other than aluminum oxide, it tends to dull faster than others. especially on tool steel.
i deal a lot with sanding belts, but with wood. my stroke sander in my basement shop is 6"x168". and the drum sander is something like a 10' piece of 3". cant say ive ever had one snap.

if youre able. im interested in seeing some other types of common tools youve ground for various uses.

This is the first of many, Hukshawn, and in time your tools will look exactly the way you want them to. The main thing is that they cut well for you.

When looking for a belt sander, see if you can find one that uses a 2" belt and has a solid but replaceable platen so you can add a glass liner to it. It needs to be at least 1/2HP to grind tools. I would avoid the typical 1" sanders because the platen is usually mounted only on one end and WILL move when you apply pressure to it. Aluminum Oxide belts work great on my sander. I can get maybe 3 - 4 tools fully ground before I have to change the belt. Maybe the wax stick lubricant has something to do with extending belt life; I think so anyway.

The Square tool is just one tool. It is ground with angles that I found to work with most stuff - steel, tool steel, stainless, aluminum, and plastics. It also cuts brass like butter, even though the top rake angles are there. I came up with this tool after literally hundreds of experimental tools and it has proven to be a very good general purpose tool, at least good enough that I decided to share it on this forum.

My personal tools look very much like this one. If I showed pics they would look the same because the angles are the main thing that differentiate them and you cannot see a 2-3 degree angle change in a pic. I did show some of them here: http://hobby-machinist.com/threads/turning-tool-and-facing-tool-questions.36687/. See post 153 and you'll see three pics; a knife tool, a tool steel cutter and my aluminum cutter. The first two were very old tools and the last was a few months old; have a look.

I can tell you that each tool works very well.

• My knife tool will put a mirror finish on any face I use it on and will also produce whisper-thin cuts on thin work pieces with very little deflection. It is one of my favorite tools and if you need a facing tool I highly recommend you consider making one. The one shown is for softer stuff; I also have one for hard stuff. They have replaced all the facing tools in my drawer. The details for construction are in the third part of the article from MachinstBlog I posted earlier.
• My tool steel cutter can take a 0.200" deep cut (0.400" reduction in diameter) in 1144 semi-hardened steel on my 11" Emco lathe, and then take a 0.001" deep sizing cut and produce a fine finish. That's a healthy cut in semi-hardened steel and the lathe doesn't even slow down. I mention this because I initially made this tool to work on my little Sherline lathe, where it takes a 0.04" deep cut in 1144. That may not seem like a deep cut but on a lathe as small as a Sherline it is very good. It will also take a 0.050" deep cut (0.1 reduction in diameter) in mild steel while leaving a pretty good finish on the part.

This tool is ground with slightly increased relief and rake angles to reduce cutting forces and temperatures and most of the heat goes out with the chip. As a result, very little work hardening occurs so that very small sizing or finishing cuts can be taken after the work is roughed in. A tool ground to the angles found in a typical angle table will not be nearly as capable of doing this.​

• My aluminum cutter looks weird because the belt was being displaced on the platen due to the extreme back rake angles I use. I found out that the reason the belt moves is because the tensioning spring on my belt sander is weakening after all these years so the belt can move. I haven't been able to track down a replacement yet as this grinder is out of production. Anyway, this tool will take a 3/8" deep cut in aluminum and then produce a mirror-finished fine cut on the part. Due to the increased relief and rake angles, the tool cuts with little force and has not ever developed a built up edge.
  
• One tool I didn't include in that post was a roughing tool for mild steels. This guy is a workhorse. I haven't pushed it to see what it can do but I have taken a 0.200" deep cut in 12L14 with it and it cut without a whimper. Tool angles are standard except for slightly increased side and back rake angles to reduce cutting forces and temperatures while still retaining strength under the cutting edge. It looks like the pic despite being about 10+ years old. Anytime I need to turn mild steel, this is the tool I use. It was intended to be a roughing tool but it sizes and finishes like a general purpose tool - pretty useful.

​

My tools are just everyday tools like yours, except that they have all been modified to reduce cutting forces and temperatures and improve penetration. None are ground to the angles in a grinding table. When I say that they reduce cutting forces, this translates into extending the limits of the lathe. A very small lathe, like a Taig or Sherline, will double its cutting capacity before running into chatter issues with these tools. When I say you should consider modifying your tools (and there is enough info in the links provided in the OP), I wasn't kidding.

 

[Bob Korves]

(snip)ive been keeping my eye out for a reasonable 1" belt sander.(snip)

Harbor Freight (Princess Auto?) has a very cheap one that does the job OK. Get the one without the disc sander, belt sander only...

Edit: I see Mike does not like the cheap HF 1" grinder, and I understand why. He is using it to do roughing work while I will only use it for touch ups and finishing. It is pretty worthless for hogging anything, and yes, the platen is soft. I have not had the luxury of ever using a powerful narrow belt sander...

 

[Bob Korves]

Thank YOU, Bob. It helps for the guys to know how other experienced machinists make their tools. The more we share, the better it gets for all of us who use them.

Knowledgeable, perhaps, but experienced, not so much... Just an old codger playing with machines for fun. I had a lot of exposure to metal working in the work I did for 40 years, so some of it comes through osmosis, but actually doing the work is another thing altogether. You can watch a million YouTube videos. but will not learn many of the important details and work flow choices until you have your hands on the controls enough times. That said, I have no idea how hobby machinists learned enough in the old days before the internet and YouTube (and Hobby-Machinist!) and other sources available today to keep from hurting themselves. Machining is not really something you can learn from a book, without some hands on coaching and mentoring to get you safely started down the right paths. Making tools is one of those skills. I would never show my first attempt at making a HSS tool...

 

[mikey]

Knowledgeable, perhaps, but experienced, not so much... Just an old codger playing with machines for fun. I had a lot of exposure to metal working in the work I did for 40 years, so some of it comes through osmosis, but actually doing the work is another thing altogether. You can watch a million YouTube videos. but will not learn many of the important details and work flow choices until you have your hands on the controls enough times. That said, I have no idea how hobby machinists learned enough in the old days before the internet and YouTube (and Hobby-Machinist!) and other sources available today to keep from hurting themselves. Machining is not really something you can learn from a book, without some hands on coaching and mentoring to get you safely started down the right paths. Making tools is one of those skills. I would never show my first attempt at making a HSS tool...

Regardless of what you say, Bob, you have my respect. You have helped me and many others here on HM and you've earned it.

Yup, I'm one of those old goats that started messing with tool geometry before there was an Internet. I've mangled many a tool bit, I can tell you that! Heck, I went to college when the newest high tech thing was a room-sized computer that used key punch cards.

 

[AR. Hillbilly]

You're welcome. When you get that grinder set up, try making the tool I showed. It is a modified tool that will cut most common stuff while lowering cutting forces and cutting temperatures. If you reproduce it, it should rough well, size accurately and finish nicely. And you won't have to change your tool rest angle to make it.

Cutting speeds as we usually calculate them are starting points. Quite often, we need to adjust the speed to get the depth of cut we need (slower) or the finish we want (faster speed and/or slower feed). A good tool like that shown in the OP will let you cut deeper at higher speeds and will finish well at lower speeds due to the increased back rake. Give it a try and share it with us if you care to.

Will do. It may be a spell. I haven't finished the rests on the grinder yet. The grinder works well but the original rests are flimsy junk. These will be fairly large and very rigid rests with easy adjustment.
My work has kept me fairly busy lately and the dear wife wants some kitchen repairs done before I get much more shop time.

 

[mikey]

Happy wife, happy life - her first.

We'll be here when you have the time.