Shars D-Bit Grinder

[Hugh Currin]

Let me start a new thread related to this one..

So I purchased a Shars “Universal End Mill Cutter Drill Bit Grinder Sharpener”. While far from Universal it seems to be a decent D-bit or Single Lip cutter. Here’s a pic of the suspect:

I’ve done some reading but just starting to use the machine for real. Thus I have questions. :-)

I disassembled the lower portion of the work head for clean up and to ream a hole in the center of the rotating table. I figure this will be needed to grind a radius. I have some ideas for this but first..

I’d like to grind a lathe threading tool. Something like the pictures below.

It just has a 60 degree included angle with, say, 5 degree relief on left and right faces. Let’s leave the top flat, no back relief. Extra credit for the radius shown on the right hand side. How would you grind this tool using a d-bit grinder? Note, on the Shars you can’t rotate the “table” far enough to grind the right hand face as the head interferes with the wheel cover and/or the wheel.

I’ve come up with two alternatives each having drawbacks. The first depends on a square 5C collet and it’s ability to rotate the tool. Set the “tilt” to zero, the “rotary table” to 30 degrees, and the tool flat to the “table” (5C rotation=0). Now rotate the 5C 5 degrees and grind the left face. Next rotate the 5C -175 degrees from original zero and grind the right face. But, I understand you should grind into the cutting edge and the right side is backwards. Probably a touch up with a diamond stick would fix this , at least for HSS. However, I don’t see a way to grind the radius with this set-up. Also on the Shars you can only lock the 5C rotation at specific points, and 5 degrees isn’t one of them.

The second scheme is to set the “tilt” to 5 degrees, the “rotary table” to 30 degrees, and the tool flat to the table. This will work for the left side face. For the right hand face, the “tilt” is reset to -5 degrees, and the “table” to -30 degrees. The back side of the grinding wheel is used to grind this right hand face. This scheme doesn’t require a square 5C collet, the lathe tool holder could work. But I’m hesitant to grind on the back side of the wheel. Also the graduations for tilt don’t go negative.

I think we can get the radius with this second scheme but in two parts. Just swing the “rotary table” through an arc using each set up for part of the radius. (Here one has to set the center line of the rotary table to go though the center of the radius to be ground.) Note there are no “rotary table” stops to prevent going too far.

I suspect there are better ways. I’d be real interested to know how you go about this.

Thank you.

[rklopp]

I've used your first method but on a round-shank tool. I think I did half the radius at each setting, swinging from 60° to 0, and having to tweak the depth of grind to get the radii to blend. Not easy.

[Hugh Currin]

rklopp:

Thanks for the response. I concur with the "Not easy" comment for grinding a radius. Nice to hear I'm not completely in left field though.

With side rake I don't think the geometry is there to grind a tip radius. Flipping the tool, other than 180 degrees, would move the center point of the grind radius off the rotary center line. You'd have to re-set the tip radius center, or as you say tweak the depth of grind. Very doable but not easy. If the blank were split (ground down to 1/2 the thickness), thinking your round blank, it would work.

Even harder if the tool wasn't symmetric, i.e. the tool tip not on the blanks center line. Then you would have to re-set the center point after flipping it.

I just ordered a 1/8" wide straight CBN wheel from Shars. My plan is to mount it further from the spindle, likely requiring a new arbor. This should give better access to the back side of the wheel. We'll see.

Thanks again.

[rklopp]

I am not a big fan of grinding on the back side of the wheel.  Not easy to dress and not really designed for that use. YMMV.

[Hugh Currin]

Like grinding of the side of a regular grinding wheel. Not a great thing to do, I agree.

I've read some and found references from "go ahead, don't worry about it", to "never". I understand the side of wheels aren't designed to be used, that a part being ground can dig into the wheel, or excessive side pressure can causing it to explode. That is reported to be a very bad day. Thus, I never (or hardly every) touch the side of my standard bench grinding wheels.

What I want to do with the D-bit grinder is a little different. First the motion into the wheel is controlled rather than freehand and the depth of grind is very small. Similar to a surface grinder where they do side grind. Also, the CBN wheel I've ordered is an aluminum disk with a thin coating of CBN on the periphery. I don't think these are likely to explode. I believe CBN and diamond wheels need no dressing as such.

Alternately, it would be possible to use two thin dish wheels back to back.

May have started an interesting discussion though?

Thanks.