need help with a holder to shape some 3/8 tool steel

[BigSki]

I'm scratching me brain, trying to come up with a way to hold a chunk of carbide steel in front of the grinding wheel in a way that I can rotate it back and forth in order to put a 3/16 radius edge on it. The reason- I want to cut a few small diameter bending dies for some 3/8 brake line material for a new cage for the 1/6th Jerp.

My cheap skate idea is to make a plunge cut with the tooling steel, I only need to make 2 dies. I only have access to a lathe at the moment, so I'm trying to work with what I have right now. I'll be cutting into free-machining brass. I can design something real quick in Solidworks and print it, I'm just not so sure that I want my fingers next to a grinding wheel going 3600 RPM and having the plastic tool holder break!

Any ideas/feedback would be appreciated.

[SMR 510RR]

How big is the piece of tool steel you are using? I have always ground stuff like that by hand. Just make sure to keep a cup of water to dip it in every once in a while so you don't burn your hand off!

[Etype R]

5c collet, and holder.

[BigSki]

3/8 square stock.

[BigSki]

More thought and some time with a pencil and a sheet of paper sketching the geometry that I needed to achieve, a design came to life. Once I thought it could work, I spent a few minutes with Inventor and made the 3D model. The holes on the bottom will lock onto a pin that's on the tool rest on the grinder, the holes are in 1/8 increments and start from the tangent edge of base. This will allow me to increase the radius of the arc that the tool swings on.



The slot is exactly 3/8" so the tool steel fits nice and snug, then there's a 4-40 hole on the side that will allow a thumb screw for any adjustments that need to be made.



The whole thing is .750 in diameter, the locating pin holes are 1/16. I'm thinking that this would work, but tell me- what thinkith ye?

[SMR 510RR]

If its plastic it will melt, its going to get hot as hell while you are grinding on it. You should also relieve the back side, I just tilt the rest a few degrees and do it by hand. As long as the piece is a few inches long you don't have a problem holding onto it. At least rough it by hand and then put it in that for the final pass to get a perfect shape on it.

I also don't think having the pin in will actually be helpful really. If it is sandwiched up against the wheel its going to be hard to actually grind it, its easier if it is free to move around.

This may be helpful: Grinding Your Own Lathe Tools

There are also tons of videos on youtube showing it done on a bench grinder by hand.

[BigSki]

Thanks, but I need to grind a near-perfect arc on the steel so I can use it as a plunge cut cutter. The ability to swing the tool holder back and forth at a fixed radius from the face of the grinding wheel is what I need to accomplish.

[JeepinDoug]

Take a piece of 3/8 diameter carbide and braze it upright on to a stick tool shank. The you can grind hook and relief clearance on it.
I usually drill a hole at 5 degrees off tangent to the shank plane.
Mill part of the drilled hole away and then braze the carbide in.
This gives you a natural front clearance, then all you need to do is grind your hook and set your centerline.
Keep your rpms really low, form tools create alot of load.