Round-nosed lathe tooling?

[benmychree]

If I were to grind a round nose tool, I would use HSS and use a radius gauge like @rgray said. I would mark the top of the blank with a Sharpie and scribe a line to define the shape and then grind it on a belt sander. In my opinion, a belt sander is the ideal tool for lathe tool grinding. Set the tool rest at 12 degrees to give you adequate relief so the tool cuts instead of rubbing and hone the top to remove any burrs.

Use a slow speed and feed manually. This tool will have a LOT of surface contact and will chatter if you go too fast.

12 degrees is quite excessive and would result in a weak cutting edge; 5 deg. would be more than enough, unless you were using Armstrong style tool holders, in that case, it would not be enough.

 

[mikey]

12 degrees is quite excessive and would result in a weak cutting edge; 5 deg. would be more than enough, unless you were using Armstrong style tool holders, in that case, it would not be enough.

A matter of opinion, perhaps.

 

[benmychree]

A matter of opinion, perhaps.

A matter of opinion, perhaps.

No, a matter of fact; I speak with over 50 years working at the trade.

 

[mikey]

I certainly don't have that kind of experience in the trade but I do have an interest in HSS tool grinding. It has been sort of a pet focus for me for the last 30 years but I grant that I am not in a production environment. Still, I've ground a bunch of form tools over the years and have found that 12 degrees works well on a round nose tool like this (as opposed to the 8-10 degrees that is normally recommended). If the nose radius was narrower, I would increase the relief angles to 15 degrees to lower cutting forces even more to reduce chatter potential and improve finishes.

As I said, a matter of opinion.

 

[Dabbler]

hey, we all do what works of us. A matter of how you use it as much as how it is made!

 

[pds65]

I was looking for inserts like this and Kennametal has some inserts, also micro100 has half and full convex radius bits, too but @ $40 for something I can grind from HSS blanks, I think I'll try that first too as Jimsehr mentioned above

 

[petertha]

I'm going to be faced with this exact same situation making steel rollers for a mini tubing bender. It will see both imperial & metric tubing +/- their particular OD tolerances. From what I've read, a good finish & dimensional accuracy on the radius groove is somewhat important. The other issues (depending on the bender design) is not just making one roller wheel, it may have to be a matched set.

I've had moderately decent luck making simple hardened parts out of O1 tool steel just using torch & (oven) tempering. If I turned a dedicated cutter disc looking profile from O1 tool steel, I could make the appropriate cutting diameter + relief angle + hold-down hole in one turning operation. Or maybe even get fancy & also turn an edge relief on the upper lip. That just leaves a tool holder which could be a blank of steel, tapered on the business end & threaded hole for fastener. I'm not sure I would trust it to make the entire groove in one plunge operation if it large-ish radii, but the groove could be roughed out with parting tool & this tool reserved for final finishing.

General idea sketch shows a 0.375" cutter disc x 3/16" thickness with 6-32 button head bolt. I'm not sure how far you could scale it down before the fastener gets too tiny. At that point I guess break out the cutter grinder machine LOL

 

[Bob Korves]

I'm going to be faced with this exact same situation making steel rollers for a mini tubing bender. It will see both imperial & metric tubing +/- their particular OD tolerances. From what I've read, a good finish & dimensional accuracy on the radius groove is somewhat important. The other issues (depending on the bender design) is not just making one roller wheel, it may have to be a matched set.

I've had moderately decent luck making simple hardened parts out of O1 tool steel just using torch & (oven) tempering. If I turned a dedicated cutter disc looking profile from O1 tool steel, I could make the appropriate cutting diameter + relief angle + hold-down hole in one turning operation. Or maybe even get fancy & also turn an edge relief on the upper lip. That just leaves a tool holder which could be a blank of steel, tapered on the business end & threaded hole for fastener. I'm not sure I would trust it to make the entire groove in one plunge operation if it large-ish radii, but the groove could be roughed out with parting tool & this tool reserved for final finishing.

General idea sketch shows a 0.375" cutter disc x 3/16" thickness with 6-32 button head bolt. I'm not sure how far you could scale it down before the fastener gets too tiny. At that point I guess break out the cutter grinder machine LOL

That tool looks like a likely chatter producer on steel due to the large radius. Find or make one that is really rigid, and then mount it as rigidly as possible.

 

[petertha]

That's what I suspect/fear too Bob. The commercial tool I have with round carbide insert has a milled pocket. I thought about adding that recess feature on tool holder but I'm not really sure how much the that might be contributing to stabilizing the cutter. It might have more to do with cutting edge repeatability? My only experience with this tool is making the valves on my radial engine. It was also roughed out & then the circular cutting tool made the final tulip shape. But the difference is I could creep in on it so minimized all that lip contact which is where chatter rears its ugly head.

I thought about a mini Radii cutter which is a way better way of making these profiles... but not at these small diameters.

 

[T Bredehoft]

NO one has addressed the difficult part of the cut. removing most of the material.

Use a cut off tool to remove 80% of the metal