Precise Radius Grinding?

[Otokoyama]

Is there any jig or technique available for grinding the leading corner of carbide boring bars to a precise radius?

Thanks.

[Rich Carlstedt]

I do it freehand.
I drill a hole near the edge of a thin piece of steel ( .062 i.e.) with a drill having the radius desired.
Then i grind awaythe edge to expose the radius gage I just made.
Then i use it to check my progress on the carbide when using the diamond wheel.

If you have one of those slow speed grinders (name?) they work great for this.
The only other methods i know are dressing a diamond grinding wheel with the radius ($$$) or using a tool and cutter grinder
rich

[WhiteTiger]

For very small radii, the bonded diamond discs and a dremel type tool have worked well for me, since it allows you to do the work right up close. Also works nice for cutting back the top of dulled indexables.


Tiger

[Otokoyama]

My hands aren't steady enough to do this freehand. I suppose to do this right I'd need to get an Accu-Finish Series One, though their information doesn't indicate that precise radii are readily achievable.

[DareBee]

You could fixture your boring tool inserts in a "Harig" fixture to do this job.

[Otokoyama]

The Harig fixture certainly looks good, though at 2x to 3x the Accu-Finish price.

[DareBee]

I am not familiar with "Accu-Finish".
I have not tried one in person but "Suburban" makes 1 that accepts a 5C collet in the center in addition to the V-block, it looks to be a really nice unit.

[One of Many]

Originally Posted by Otokoyama Is there any jig or technique available for grinding the leading corner of carbide boring bars to a precise radius? Thanks.

How precise does it need to be? Inside radius, or outside?

Most inspection is done with a radius gage set. Not likely that anyone would check it much closer than that.

If this radius is not a standard, then I could understand the need to custom grind one. I just get them close on the wheel and then hand hone them in with my radius gage and a magnifier to fit. Viewing the fit using a back light against some white paper or wall helps define the match.

If it is a standard size radius. An insert type boring bar with the radius already done would be the cheaper route. Grinding houses would be the next cheapest, compared to buying the proper equipment to swing the radius and grind the angles in one setup. The accu-finisher that I use is still a hand operation.

Otherwise make your own rig to set the cutter in the proper position and swing the fixture to get the radius center point in relation to a diamond wheel. The clearance angles need to be set in this fixture also. You couldn't use silicon carbide because they break down so fast, it won't hold the radius during the swing.

For outside radiuses, I use a tapered dremel stone. Again, get it close and then run the stone up into the proper radius with a little draft in the sides, so it blends well.

DC

[Rich Carlstedt]

White Tiger
I wasn't aware of the Dremel bonded diamond wheels..that is something I have to look into.

Otokoyama
I forgot to mention that I have a tapered radius diamond hone (stick ).
its good for larger radiuses, like 2mm +, and using it on the cabide upside down, it gives a natural relief to the cut edge....the only problem is that you have to sneak up to the desired radius.
Rich

[Otokoyama]

This is for a "typical" cutting radius, such as 1/16" or 1/32". When I try to do this by hand using a radius gauge, the resulting edge just doesn't cut cleanly. I've thought of making a grinding fixture that can be attached to my 2-wheel diamond carbide grinder, but if something already made is available, I would just as soon save the time.