Machining an internal concave bevel

[RaceDiagnostics]

How would you put a concave radius, say 4mm into this internal edge. I was thinking about trying to grind a bit of hss steel for the job but I normally use inserts and my hss grinding experience is non existent.

How would you do it?

 

[Maker]

Carbide button insert?

 

[Misterg]

What diameter is the hole?

I think a 7° clearance / 3.175mm thick button is good down to ~27mm diameter, but you will likely have to grind quite a bit of the tool holder away.

If it's just a one off, and the radius isn't too critical, I think I'd be tempted to free hand it with a boring bar.

 

[m_c]

8mm ball end mill.

For what you're trying to achieve, I'd probably do most of the work on a milling machine with a rotary table.

 

[RichardM]

What machines do you have, what material is the part made of and could you show a cross section of the part?

 

[RaceDiagnostics]

Lathe and die grinder.

It's mild steel, 15 mm thick and id is 100mm.

 

[RaceDiagnostics]

I'm thinking perhaps tie down the die grinder with small ball end carbide tool to the lathe and bring up to the workpiece. What could go wrong?

 

[RaceDiagnostics]

Tried out my method on a test piece.

8 mm carbide ball.

Freehand with the grinder.

High spots taken off with this stone just held in hand.

Finished off with 150 then 400 grit.

That's good enough.

 

[Kram]

Looks good!

I'd clamp a radius bit in the tool post and use just one of the cutting edges. I've done that with cheapy radius router bits for alu

I also made a ball turner attachement, which can do it but is more effort to set up.

 

[RaceDiagnostics]

Tried clamping the router bit in the tool post but the results are worse. Guess the router bit really needs to be spinning to get a good radius.

 

[RaceDiagnostics]

Looks like I made this overly complicated.

I had a go at shaping a bit of HSS.

Worked perfectly.

 

[addjunkie]

Looks like I made this overly complicated.

I had a go at shaping a bit of HSS.

View attachment 517132

Worked perfectly.

View attachment 517133

Its called a form tool, if you go too big you can end up with chatter.

You must be a proper bloke engineer over thinking it!

 

[Maker]

Tried clamping the router bit in the tool post but the results are worse. Guess the router bit really needs to be spinning to get a good radius.

View attachment 517130

That's a carbide burr not a router bit, it doesn't have nearly enough chip clearance for what you're trying to do. The router bit Kram shows probably only has two cutting edges.

 

[RichardM]

Form tool and stone the cutting edge.

 

[oldbikedavey]

Might be able to wangle that with my Holdridge Radii Cutter, maybe.