Models for grinding HSS Lathe Tools

ttabbal said:
So not like the normal HSS where you don't want to let it get too hot? Do I need heat protection to grind this stuff? M2 gets pretty toasty at times while grinding.
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As Bob said, HSS can get hot without concern. What I meant is that the high Tungsten content of T15 takes more pressure to grind it. Once you cool it, it seems to get even harder so getting it to cut again takes even more pressure before it starts to cut again. I use Vasco Supreme bits that are T15 and they are superb bits but grinding them is a bit of a chore. Once I get the belt cutting it well, I don't let up until I have to. Don't worry; it isn't alien steel and you grind it like any other cobalt tool. Just use more pressure and you'll be fine.
 
mikey said:
As Bob said, HSS can get hot without concern. What I meant is that the high Tungsten content of T15 takes more pressure to grind it. Once you cool it, it seems to get even harder so getting it to cut again takes even more pressure before it starts to cut again. I use Vasco Supreme bits that are T15 and they are superb bits but grinding them is a bit of a chore. Once I get the belt cutting it well, I don't let up until I have to. Don't worry; it isn't alien steel and you grind it like any other cobalt tool. Just use more pressure and you'll be fine.
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Hmmm... I could swear I heard somewhere not to let the tool get too hot when grinding to avoid messing with the hardening/tempering. By "don't let up until I have to" do you mean till it's hot enough to burn you? Or do you hold it another way? With M2 I've just been dipping it in water perhaps more often than needed to keep it cool. Mostly to keep my fingers unburnt, but also to avoid getting the bit too hot. Sounds like that part was not needed. I'd still prefer not to burn my fingers too much though, that's what welding is for. :)

I suppose I could use welding gloves, but that seems dangerous around spinning things. I think I'd prefer using a jig of some sort to hold the bit if it comes to that. As usual, I'm probably overthinking it and need to just go fire up the grinder.

I have 36 grit ceramic belts, and wax lube for them.
 
I would just dip the tool if the tool gets too hot to hold and not worry about it. The advice about not getting the tool too hot usually comes from wood turners. Many of them used carbon steel tools, although HSS is much more common nowadays. In any case, dip it. There is some concern about micro-fracturing but I haven't noticed any degradation in performance from dipping my tools.

I hold the tool bit with my bare hand but I use a glove on the other side, the one next to the belt. I know I shouldn't but I've been cut to the bone too many times not to. When using AO belts, the tool gets really hot because the belt doesn't cut efficiently but ceramic belts cut so fast and cool that I don't need to dip the tool, even though I do in between faces. Your results may vary so if it gets hot, just dip it and cool it. There are no rules when grinding other than to do it as safely as you can. Personally, I think that you should do what works best for you and ignore bozos like me.

T15 is harder to grind. It takes more pressure to get it up to the temperature where the belt starts to cut well so once I get the belt working well, I keep it up until I'm either finished or close to it and then I look at where I am. If I need to further, I go further but I don't dip it unless I can't hold onto it due to heat; that's rare.
 
HSS tools, including the higher cobalt versions, were developed specifically for good high temperature hardness. They quickly replaced high carbon tooling when users learned how heat tolerant they are. Don't get me wrong, you can burn them up, but you will have to work at it. The heat of grinding the tool is not an issue. Dunking it in cold water can cause micro cracking, like Mikey said. Only cool them enough to get them ground. It is a good idea not to leave stress risers in the finished tool. Some blue, brown, or purple color on the tool after grinding does not give problems when you use the tool.
 
Okay, it's been a few days and I hope you guys have had a chance to determine if you understand this tool angle and tool mod stuff. I just re-read it and there is a LOT there. I wrote it so I do understand it but something tells me that a lot of you do not. It's okay, I totally get it. Unfortunately, I don't know how to make it simpler than I did. Tool geometry is the key to lathe tool performance and if you want to grind high-performance tools then you need to understand this stuff. If something is not clear, then ask.

The other way you can do this is if I just give you the angles. I know that most of you should be able to grind a tool to specs by now. So far, I have given you the tool angles for mild steel, brass, aluminum and stainless steels. Not much left to cover - just the harder steels - but rather than just give you numbers, I would prefer we take a look at these steels and work out a design that one or some of you can grind and test. It really is simpler than it looks.

Heh, heh, so if you want a tool to cut tool steel or higher carbon steels then this is how you get it. You jump in so we can uncover confusion points and clear them up. Then pick a material and lay out the characteristics we need to accommodate. Then we'll design a tool together, meaning you choose the tool angles and I'll guide you but I will not tell you. If someone is willing to grind it up and test it, we can tag along and make suggestions for improvement and that would be an incredible opportunity for all of us.

We do not have to do this if you are not so inclined. However, it is the only way to have me there to look over your shoulder to make sure you're going in the right direction. So I will leave this to you and you guys can decide how you wish to proceed.

By the way, I talked this proposal over with Bonehead before I wrote the above message. His reaction was really interesting because his default is "snarky" but not tonight. He said that he has come to enjoy the responses and questions that have come up in this thread, many of which he had himself when he was learning to do this. He especially enjoyed seeing the tools that you guys have ground and sincerely congratulates you all. I again tried to get him to join the forum but he just flipped me off when his wife wasn't looking! In any case, with regard to my proposal above, he said, "Good idea. How else they going learn?" Seven Pidgin English words in a row is a lot for him so, with his approval, my offer stands.
 
I have to admit, I want to meet bonehead. Sounds like a fun guy. If I make it out there, I'm buying you both a beverage.

I don't have anything harder here. But I like the idea. I kind of went that way with cast iron. I ground up a T5 bit but haven't cut with it yet. I'll add a pic just for fun. It's a basic 15 degree square tool with about 10 degrees back rake. I was lazy and didn't want to reset the table angle. :D

Have to really push that T5 into the belt..

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Toldja' that T15 needs some pressure to cut. The edge holds up for a looong time, though, and it will handle CI well if you get the angles right. You certainly have the grinding down, Travis - good for you!

We're more likely to catch Bonehead in Vegas - he goes there so much he should file for residency in Nevada. He tells me he enjoys gambling but I suspect he is just trying to keep his wife occupied so she stops nagging him.
 
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