Models for grinding HSS Lathe Tools

[mickri]

I should have taken the tool bit out of the boring bar so you could better see the shape of the tool bit. It is small. 1/4" square by maybe 3/4" long The tool bit is at a 45 degree angle to the boring bar. Here is a rough sketch of the tool bit.



As you push the boring bar into the hole the front edge at the nose makes first contact.

 

[mikey]

Okay, I see now. It will still cut as I mentioned above. That grind is common on this type of tool but there are other variants. As long as it cuts, that's what counts.

 

[fitterman1]

Hi fellas, just lurking, haven't seen much mention of chipcutters and nose radii.

 

[mikey]

Do you mean chip breakers? What about nose radii would you like to discuss?

 

[fitterman1]

Yes, I call them chipcutters. Want to know how people form them, and how they size their nose radii.

 

[mikey]

I do not use chip breakers anymore. For me, they just aren't worth the time it takes to make them but others on this thread may have other opinions and I'll leave it to them to respond.

As for nose radii, I prefer them small. Most of my tools have a 1/64" to 1/32" nose radius on them. I prefer to use back rake and the edges adjacent to the nose radius to enhance finishes so I don't need a big nose on the tool.

What are your thoughts on nose radii, fitterman?

 

[fitterman1]

Same as yours, 99% of my tooling is carbide so I don't use a lot of hss.
Most tools I grind are form tools eg radius corner tool (int & ext) or a specific tool to get into a deeper corner than I could get into with an insert. I don't rough or finish with hss unless its a form tool.
Grinding of rakes are specific to the tool I'm making, generally I keep my side rakes to a minimum to give the nose more support underneath. I don't think excessive angles are necessary because my tool will be on center and so any rubbing of the work doesn't happen. This also minimizes the time spent grinding and wear and tear on wheels. Sometimes I'll grind a small 45 degree chamfer to clear the bore if its a smaller bore with a smallheaded form tool. All grinding I do is freehand and when it comes down to a radius on the nose, its done the same and then honed on a diamond plate to give it a nice sharp edge. Size would be in the vicinity of half to 3/4 mm, roughly the same as your sizes.
I have wheels in SiC, AO and diamond, grades hover around the 60 grit for the stone wheels to 80,100,150 for diamond. I have diamond plates upto a thousand grit for honing. I find a coarser wheel gets me there faster without too much heating. Used to use a belt sander for large drillbits (upto 2 1/2 inches) years ago, that was much faster than the grinder and I found it more accurate too.

 

[fitterman1]

Forgot about the chipbreakers, I have a couple tools with them only because I got them in a bundle. Personally I don't bother grinding them, just interested if others do.

 

[Downunder Bob]

I agree, I can't be bothered with chip breakers, I use a mix of HSS and inserts, some of the inserts have chip breakers, and so be it. None of my HSS have breakers I simply can't see the point. I have seen people spend hours trying to perfect a chip breaker, by which time the whole job could have been done, and they could be sitting down with a beer.

I also agree with Fitterman1 keeping relief angles to a minimum, especially on outside turning they're almost redundant, but do need them for internal work.

So far I have only ever used 60 grit AO and occasionally the Dremel for making a form tool, I don't have any diamond wheels or laps. I don't even have a decent bench grinder at the moment, only a small belt sander 1" belt and only 300W I do my roughing with an angle grinder then finish on the belt. I have bought a bench grinder, but have yet to set it up

My go to tool for HSS is the Eccentric tools Diamond tool holder so sharpening is relatively simple, I have a box of 3/8 HSS from my apprentice days, so far none of them have needed re-sharpening.

 

[mikey]

The great thing about HSS tools is that we can make whatever we want to do the job at hand. There is no right way or only way; as long as it works for you then that is what matters.