HSS Lathe Tools chipping, what might cause this?

The block is easier to grip, and most miter slots are far enough away from the grinder face to benefit from a block. The key part of the block is the ability to dial in two angles, the tilt and the face angle. Harder to hold a 7 degree tilt for edge relief in your bare hands than it is to seat in a block with a 7 degree groove. When doing your back cut, you'll end up hanging the block and bit over the edge of your grinder's table, the block provides enough of a rest to do this.
 
Ok. I can tilt the table and lock it in position. For these tools I had set the table to 15 degrees. So I "only" had to worry about keeping the tool flat against the table and parallel to the scribe mark. That was plenty hard enough for me...
 
pontiac428 said:
I really don't mean to ruffle feathers, but I need to point out that the grinding wheel leaves a flat, mirror-like surface, whereas the belt grinder flaps and jumps around a lot, leaving a heavily ribboned surface that is clearly making more work at the hone. I do my grinding with stones, so from the wheel to the hone there is very little sweat work. I gotta say, as cool as belt grinders are for knifemaking, they are not a good tool for lathe bits. A simple Delta carbide grinder would run circles around a belt grinder on lathe tools. A fixtured grinder, like the Deckel, will outperform the carbide grinder, stretching the gap between the belt grinder and tool grinders even further. Like I said, not out to cause any anger, but one tool in this lot has limited performance when it comes to grinding flats.
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You know I am saying this will all due respect but I have to disagree, Pontiac. A belt sander with a Pyroceram platen will grind totally flat faces with speed and control. It is far faster and cooler than a grinding wheel, even on a flat faced wheel. It comes down to the operator. Grinding tools is a skill and while some may feel that fixtures are necessary, I am not one of them. I alter tool angles often and I am more accurate and far faster doing it freehand, using only the table angle as a fixed parameter. I will grant that if you must have a given angle ground into a tool every single time then fixtures and dials work better for that but for lathe tools they are not necessary. More to the point, geometry can vary with material and application; there is no perfect geometry for everything and quite honestly, what is often accepted as a standard may not be optimal. If it were, I would still be taking 0.020" deep cuts on my little Sherline instead of the 0.050 - 0.060" I can actually take.

Lathe tool grinding is not hard but it does take some time to learn to move your hands. I assure you that some of us can produce perfectly serviceable lathe tools right off the belt sander and hone them with maybe only a few minutes with diamond stones. I can, freehand, remove the coarse grinding marks from a lathe tool in under a minute, smooth the faces in another minute and form the nose radius and polish the faces in under another minute with an extra-fine stone because I've done it hundreds of times and have paid my dues. And I am not alone.

I know you already understand this; anything that involves skill takes time to master.

I am suggesting to the OP to take that time.
 
OP, what is your intended nose radius, generally speaking? Are you intending to make the cutting point as sharp as possible or do you intend to grind (or hone) a small nose radius?

I don’t know very much about grinding HSS cutting tools (I usually use inserts), but my understanding is that it should have a small radius. You probably are well aware of this.

DEE0D2C0-490D-429F-A0EB-2BEBAB6353A5.jpeg
 
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I've learned the hard way (previously) that no radius is an invitation for breakage. For this tool I'm looking at putting in a radius of about 0.020-0.025" or so. Much bigger than that then cutting forces get high. Much smaller than that then the nose breaks. Mini-lathes don't have that much oomph, so I don't want to go to a large radius.
 
@mikey My take away from your reply to pontiac428 is that I'm messing up the grind. Consequently, the hone is taking forever. It is an art to hold the tool correctly for honing. I'm using a death grip due to fear of messing up, but that's counter productive. If I relax some, it surprisingly seems better.

The real problem is the grinder. It needs to be modified to work better. Whether it can be altered sufficiently to generate crisp edges without rocking remains to be seen. The current aluminum top plate is soft and catches the edges of the tool bit. I also need to increase the notch on the right side of the grinder to get a better top relief. The far end of the tool is hitting the housing and belt guard, limiting the top relief cut.

Don't want to blame the grinder, but this unit wasn't designed to do tool grinding. There are definitely compromises. Hopefully, enough of the compromises can be overcome to generate decent grinds. Got to think about a new table surface that offers enough support where it's needed. And a better more controllable way to hog out the notch.
 
WobblyHand said:
I think this really is my issue. The tool bit must be rocking a tiny bit as I'm pressing it in. Kind of need a press down action and push action at the same time while keeping your hands away from the belt. The aluminum surface I have on the grinder tool rest isn't helping me.

I marked the face and then partially honed it with a coarse grit. The black parts are near the edges.View attachment 336260
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I think you know, but just to be clear I've cropped just the cutting tip from the above picture:

RoundedTip.jpg
There appears to be far too much rounding to be honed away (see arrow). Unlike Mikey, I can't freehand grind. I think your 100 grit belt is making things worse. It is pretty aggressive and may be 'grabbing' the tool bit as you make contact with the abrasive. That could tend to roll the tool bit and result in the problems above. I use a moderately worn 120 grit Blue Zirconia belt but most of my tool bits were ground on a 6" bench grinder before I got the sander. The convex surfaces left by the round grinding wheel make it easier to register the tool bit on the honing stick.

I think the tool bit above needs to be reshaped on the belt sander or bench grinder. Use black marker and go back and forth between the machine and your medium hone. That should show visually whether the new-ground surface is getting rounded over or not. (HSS is really pretty cheap!)

Also, I don't think you've said what kind of belt grinder you are using? A 1 or 2 inch? Hopefully not something like a 6X48.

Craig
BTW, your photos are pretty darn good. It is very difficult to photograph reflective metal and smartphone cameras generally get thoroughly confused about what to focus on.
 
Yes, there's too much rounding to take off honing. I have to both modify my technique and the table surface. It's an 1/8" aluminum plate screwed to the underlying table. The aluminum tends to grab when sliding the bit on the surface. Been caught by it before. Going to remake the surface out of a piece of scrap 1/4" plate steel. While I'm at it, I'll extend the right side so I can get more support especially when grinding the critical top face.

This is a 2 x 48 belt sander with no disk sander. The platen is cast steel and an integral part of the unit. It makes it tough to modify. Like I said previously, it was never designed to grind lathe tools. So I have made some minor mods to enable this. It seems there is still room for improvement.

Thanks for your comments on the photos. It is tough to take these photos. Spend a lot of time setting up the pictures. If one puts a a new surface close to the desired surface the camera will then tend to focus on the correct object. (The close stuff, not the background.) Have to fool the autofocus algorithm.
 
WobblyHand said:
@mikey My take away from your reply to pontiac428 is that I'm messing up the grind. Consequently, the hone is taking forever. It is an art to hold the tool correctly for honing. I'm using a death grip due to fear of messing up, but that's counter productive. If I relax some, it surprisingly seems better.

The real problem is the grinder. It needs to be modified to work better. Whether it can be altered sufficiently to generate crisp edges without rocking remains to be seen. The current aluminum top plate is soft and catches the edges of the tool bit. I also need to increase the notch on the right side of the grinder to get a better top relief. The far end of the tool is hitting the housing and belt guard, limiting the top relief cut.

Don't want to blame the grinder, but this unit wasn't designed to do tool grinding. There are definitely compromises. Hopefully, enough of the compromises can be overcome to generate decent grinds. Got to think about a new table surface that offers enough support where it's needed. And a better more controllable way to hog out the notch.
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No, the point I was trying to make in my response to John/Pontiac428 was that a belt sander is, in my opinion, almost ideally suited to grinding lathe tools. I've used bench grinders for years for that purpose and it won't come close to a belt sander that is properly set up. I've tried Baldor tool grinders, too; they work but are very slow compared to a belt. For drill and end mill grinding, I won't even get into a thread where Pontiac or C-bag are discussing stuff because I'm an idiot when it comes to that but lathe tools, that I have some experience with. John already knows I have a great deal of respect for him and his opinions. Its just that I disagreed on this one point.

As for your belt sander, there are two things a good belt sander needs to grind lathe tools. One, an adjustable tool rest to grind the angles you require; it is best to make this tool rest from steel to prevent sticking and dragging (as you've discovered). It must also provide adequate support on the right side of the sander to allow you to grind your rake angles. Two, it needs to have a flat platen so you don't grind curves into your tool. The best fix for this is a ceramic glass platen commonly known as Pyroceram. Trying to grind tools on a steel platen that is even slightly dished is an exercise in frustration.

Honing is something you have to do to get better at. It is actually harder to learn to hone a tool than to grind it, or at least it was for me. If you think about it, you ground three flats on your tool with your belt sander. Now you simply need to hone those flats with your stones. The key is to understand that you are trying to keep those flats flat while also trying to remove grind marks.

I will concede that if the tool face is not flat then it is harder to make it flat but I assure you that it is possible because I used to do it all the time when I was learning to grind and hone lathe tools. The trick to it, if there is one, is to work at making each face flat because it is the intersection of those flats that does the cutting. If the faces are not flat then they will not precisely intersect and the tool will not cut. That really is all there is to it, intersecting flats at angles that you choose to grind.

As for technique, keep your hands soft and your wrists locked. Do most of your cutting on the pull stroke; if you push, you will be more likely to roll an edge. Use gentle pressure and let the stone cut; excess pressure causes your hand angles to change. Use the coarse stone to flatten the face and once it is flat, do all you can to keep it flat. The goal when stepping up through the grits is to simply remove the grinding marks left by the media before the current one while maintaining the flat surface your working on. Concentrate as you move so you don't rock the tool; when I hone, nothing else exists except the flat on that face.
 
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