HSS Lathe Tools chipping, what might cause this?

[WobblyHand]

Here's a few. Gee, I didn't do a very good job on this tool. Un-doctored photos.




Looking at the last photo, the cutting edge (as used) has damage for 2mm out of the 5mm edge. (From the tip, then 2mm to the right.) I don't think that damage was present when I was done honing.

Looking at this with a critical eye, there's clearly stuff to fix. On my part, I will try to grind a new square bit from the same lot (no quenching of any sort) and maybe from some cobalt steel (also no quenching).

 

[Mitch Alsup]

I do not see chipping, what I see is the aluminum has welded itself to the tip of the tool.
A bit of WD-40 should eliminate this problem. {hint: machine aluminum wet}

 

[WobblyHand]

@Mitch Alsup agreed, there is a tiny bit of aluminum on the tip. The other stuff is a break. I wish I could take high resolution microscope photos, but that is out of my grasp. For what it is worth, the aluminum was wet and slinging WD40.

 

[brino]

As you can see above, there is lots of interest in finding a solution.
What a great group!

This is a 2" diameter piece

so cutting aluminum with HSS I'd want to be about 110 sfpm.
For a 2" diameter, that's about 210 RPM.

Are you cutting close to 210 RPM?

I don't have any spare 3/8 square HSS tool bits in stock, but I have 5/16" (Cobalt-6 Sheffield) and 1/4" (Eclipse H5 England).
I would send you one for comparison (no charge) if you PM me your address.

-brino

 

[WobblyHand]

So I ground two new square tools, one from the same lot of HSS and a second from piece of 5% cobalt steel. Haven't got to honing them yet. My belt grinder needs more modification to better make these tools. After I put on a finer grit belt, I found I had difficulty touching up the top relief cut. The reason for this is the belt grinder structure is in the way of where the tool needs to go. Basically, this particular belt grinder is being asked to to things it never was designed for. So maybe I have to grind my grinder...

Here are all 3 tools. The new ones have not been honed yet. You can see the on the top relief where the belt only partially hit the surface. On the other faces, the fine belt did remove the gouges of the coarser belt. A few more photos.

 

[WobblyHand]

As you can see above, there is lots of interest in finding a solution.
What a great group!

so cutting aluminum with HSS I'd want to be about 110 sfpm.
For a 2" diameter, that's about 210 RPM.

Are you cutting close to 210 RPM?

I don't have any spare 3/8 square HSS tool bits in stock, but I have 5/16" (Cobalt-6 Sheffield) and 1/4" (Eclipse H5 England).
I would send you one for comparison (no charge) if you PM me you address.

-brino

Yes, lots of good insightful responses. There's a lot of helpful folks here.

I was cutting faster than 210. Maybe 800, mmm, 900? Sooooo, that's something I can fix!

As you can see, I do have some cobalt, and at least 20 more pieces of HSS from that lot. I have one weird piece of Mo-max, but that has an odd grind on it, so that one's a last resort. So for the moment, I'm all set, but thank you very much for the offer!

Really need to make a settable articulated holder for honing these guys. Keeping the hone flat is a problem for me. My forum name is Wobblyhand and let's just say it's apt.

 

[mikey]

Let me say that you have ground some really nice tools! I'm not sure if I could have done them better and that's the truth.

I honestly don't know how you're managing to chip an edge unless that edge is not sharp. It is NOT your tool grinding but it may be your tool honing. Each plane on the tool tip - side and end cutting edges and the rake angles - must intersect precisely. You cannot get this from grinding; it must be honed that way. Try honing and looking at it under your scope.

Otherwise, I got nothing.

 

[markba633csi]

Hi Wobbly: One problem with your grind is shown here in your pic: The face of your tool should be flat or slightly concave, not convex. Looks like the tool would be rubbing too much. Normally we would use the face (as opposed to the side) of the grinding wheel to do this. Hard to do properly with a belt. Also, I don't see sharp knife-like edges there, I see dull, roundy edges. Small things, but they make a big difference
Your geometry looks fine, you just need to finesse it a bit more
-Mark

 

[WobblyHand]

@markba633csi some of what is seen in the photo is an illusion. I had a tough time getting the right lighting on all three tools. That said, I think there's some problem on the top edge, as you say. You are seeing incomplete tools. No honing or prep was done, just raw off the belt sander. I can see a burr on the cobalt tool. I need to do better on the belt. I have an aluminum table and sometimes the tool digs in rather than sliding. Perhaps that's causing some of the rotation. Maybe I'll replace the surface with steel. Since I have a mill now it won't be that hard to do.

 

[WobblyHand]

@mikey, flattery will get you nowhere
I think I am messing up the edge with my grind, and hosing the edges with honing. I really do have a devil of a time doing the honing. So much so that I've been looking at diamond disks today.