Rounding toolbits

[Sshire]

Reading many posts, etc about grinding hss toolbits, most say to round over the tip. I have diamond laps but need a bit more detail about the rounding over. Freehand? Toolbit in a vise?
Rudy Kouhoupt mentions "rolling the bit between fingers"
Any hints would be much appreciated.
Thanks
Stan

 

[gbritnell]

Hi Stan,
I sharpen my high speed bits in the prescribed manner for the material I am cutting, brass, steel, stainless etc. To make a nice smooth finish cut I take the tool and put a small radius on the tip of the tool. The larger the radius (within reason) the smoother the cut. The best way to associate this to cutting is if you has a sharp tipped tool and you were cutting with a coarse feed the finish would something like a very fine thread. Now put a radius on the tool and use the same feed rate and it would smooth out all those fine points. I use my diamond hand hone and just work it around the corner of the tip letting it rest against the front clearance and then onto the side clearance. It doesn't take much to smooth out the cut.
Most carbide inserts can be purchased with varying radii on them for the same reason as putting them on a high speed tool.
gbritnell

 

[Anko]

Hi

Is a common practice to grind a radius in the tip of the tool, because a pointy tip will wear off quickly and will leave tools marks, a round tip will resist better and depending on the radius will leave more or less cutting marks..

But for smalls thread cutting you will need a very pointly tip, it depends on the purpose of the tool

the grinding metod is not critic, by hand or helding the bit in a vise to get more control, I made a rougth grinding close to final shape, then I finish the tools edges with a belt sander, and the radius on the tip is made in the belt sander too, all by hand

but if you have a vise or fixture to make precision grinding will make the job easyer, then just make a small pases on the belt sander and you got the tip rounded

hope to help

Saludos

 

[Tin Falcon]

I assume you mean hand honing a nose radius. a good oil stone is preferred over diamond.
Here is a wood mock-up i did to help visualize
a top view showing the rounded tip

and a more 3-d view of the tip

1 hold the side of the cutting edge against the stone

then drag and lift at the same time

then continue the motion by dragging and pushing down

Rock and drag back and forth until you get the radius you need . hone the top, end, and side, of the cutter smooth first before doing your radius.

Hope this helps
Tin

 

[steamer]

Wot Tin Said!

Additionally, a polished tool will cut a polished surface....spend some time honing that edge to a mirror finish...and watch what happens.... ;D

Dave

 

[Sshire]

That was a huge help!
George. Great explanation of why I should do this
Tin. I'm a visual guy and the "brown stuff" bits are fantastic. For the first time someone has explained how to round over
Anko. Love the sander idea. I'll use it
Steamer. Got it thanks a bunch

That's what is so great about HMEM. Someone who is just beginning gets very comprehensive answers from people who have been doing this for a long time and are willing to share.
Thanks again
Stan

 

[Tin Falcon]

Stan: honing a nose radius by hand gives a lot more control than with a sander or a grinder. that is unless you are doing a radius tool then use the grinder or belt sander to pugh ouit then finish hone. .
Once you get the feel of doing this yo can rough out a nose radius on a grinder . after the faces are ground turn off the grinder and do a couple of quick swings on the grinder.
A grinder will leave a hollow gind . so when honing the the cutting edges just worry about the cutting edge and the heel and do not worry about the hollow. if you are not hitting the heel you are changing the cutting angle.
Hope this helps.
tin

 

[Sshire]

Tin
I did understand your demo about hand "rolling" the radius.
The curved hollow grind I'm real familiar with after sharpening wood chisels and hand plane blades for years. Those are all done on a slow speed Tormek with the wheel running through a water bath. The combination of the water and slow speed keeps the tool very cool. Would the Tormek have any advantages in sharpening hss lathe toolbits?
Best
Stan
(BTW USAFR ret Msgt -27 years)

 

[Tin Falcon]

It would certainly have the advantage of keeping the tool cool . also not having to take the tool off the stone and putting back will reduce faceting.

(24 years New jersey National guard 6 army 18 Air with a fighter wing)
Tin