Round-nosed lathe tooling?

[Harvey]

I need to produce some large-radius bends in some 5/16 x .035 4130 tubing and thought I'd do so by cutting some round-bottomed 5/16 wide grooves in one end of my Harbor Freight's sheet metal slip rollers. However, I can't seem to find any round-nosed lathe tool bits. Why is that?

Harvey

 

[Jimsehr]

It would take about 5 min to grind one out of high speed steel
or carbide.

 

[Bob Korves]

Make your own from HSS.

 

[BillWood]

You could grind your own maybe ? Or use a circular carbide insert ?

Have a google and look up Form tools.

https://www.google.com.au/search?q=...bFxMfYAhWHJ5QKHXu4AyIQ7AkIag&biw=1246&bih=615

at approx 2:24

 

[Dabbler]

I regrind those cementerd carbide tools for this sort of work. They don't work well as they come, and they are perfect for the kind of thing you want to do!

 

[Harvey]

Thanks, Guys, for your replies. I've seen blank tool stock before and always figured that it's intended for cutting custom shapes. However, I wouldn't think that a simple 5/32rad would be uncommon. Also, making something "by eye" doesn't seem (at least to me) to follow the machinist's "code of perfection".

Can a tool blank be formed with a "common" bench grinder or belt sander? The tool doesn't need to be perfect but I don't want to end up with something crappy either.

Harvey

 

[Glenn Brooks]

Harvey, yes, use a bench grinder and medium to fine wheel. A belt sander probably won’t give you enough control to properly shape the tool. Lots of videos and instructional threads on grinding HSS tooling out there. Just as in grinding drill bits, takes a bit of practice to make the correct shape. But it’s not a big deal to learn. Use a set of concave radius gauges to control the shape.

Glenn

 

[rgray]

Use a radius gauge. Compare your grind to the gauge to see your progress in making the tool.
No radius gauge? Poor man's/emergency 5/32 radius gauge...drill a 5/16 hole in some sheet metal and cut the hole in half.
Now you have a gauge.

 

[mikey]

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.

 

[Harvey]

Thanks Guys!

Harvey