Shars D-Bit Grinder

[currinh]

I suggest grinding your 60-deg flanks first, using the lathe tool attachment, and include your side relief in those two steps. Make all angle settings using the pivots. The spin indexer has other purposes, it is not used to include relief in square bits. I mean, it can be, but it's not prudent. So you place your flanked and relieved 60-deg tool in the lathe bit fixture, top side up. Center it and set the point just a touch over center on the pivot indicator mark (shop mod) sighted below the tool tip. Then set the back tilt to 5 degrees. Free the yaw pivot, and work the infeed as you radius the tip by yawing it back and forth into the wheel. Pivot all the way until the tool flanks almost touch the wheel, both sides. Did I mention you're using the proper cutting face of the cup wheel? Sorry. Only use the face. There's more than 180 deg of tool presentation available at that position on the face of the wheel.

You can accomplish a ton of operations on the Sheckel (Shars-Deckel!) tool grinder. You can make fixtures to expand the possibilities. The only problem is there is no guidebook, so it's up to you to break the code and make it work for you.

That all makes sense. I think the head hits the wheel or guard before I can get the second face ground. Same on swinging to get the radius. Maybe the lathe tool holding fixture would allow more motion, I haven't tried this but will. It would be possible with a modified fixture.

I have reamed a hole in the center of the rotary table to align the tip of the tool. I found a setting gauge for the Quorn that fits into this hole using a micrometer head. That should allow accurate set-up for radius grinding as you mention. Just need time to make one.

I agree these machines can do a lot more than D-bits. The videos from Stefan Gottenswinter that pushed me over the edge to order one.

Thank you for the help.

 

[currinh]

I too have the Shars grinder. I have to admit I haven spent much time with it.
If I had mire experience maybe I would have a better handle on it.
I keep telling myself I’m going to sit down and devote some real time to learn all the accessories and it’s basic functions.

I agree. I also need to spend a lot more time experimenting. We're now traveling so don't have access, but soon...

Thanks.

 

[currinh]

These things take some getting used to and making a few jigs. They can actually grind the flutes on end mills quite nicely as well as the ends. A two flute is easy enough by just copying the angle on a new one. 4 flute, it is easiest to just grind out the center. The nose radius on your threading tool is a lot quicker to do free hand. There are very good videos on line.

Yep, likely quicker to do freehand. But I'd sure like to know how for similar tools where the radius really does matter. I haven't found a good video on grinding a radius. Which ones where you thinking of? I've seen a few but they seem to skip steps, like setting up the offsets.

Thanks.

 

[dbb-the-bruce]

I think your method is similar to my first. It would work but not reasonable to grind the radius on the tip. A method to cut radius would be useful for more than this tool.

The machine as designed (certainly for my Deckel, and likely for any clones) is for single lip / D bit. So it's pretty much impossible to do a square nose radius (the tool you are trying to do) because you can't get to the second half of it without flipping the bit over and even then the rake would have to be 0.

For the tool you asked about (and probably most other similar, non-round, nose radius tools) grinding the nose on round part of the wheel is fine. You will get a slightly concave face or "hollow grind" but it's not going to matter. If you want to get rid of the hollow you can always flatten the ends of it with a few light strokes of hone.

The swing of the arm or rotary joint will give you a smooth radius. Stopping at the sides could be done with the rotary stop (at least on one side, I haven't really sorted out how both rotary stops used together and what the range of rotation is), or it could be done (carefully) by eye using a marker or dykem to make sure you don't go too far stopping just shy of hitting the full side angle that you already ground.

The longitude bar rotation stop would be used to control the rake angle on the nose. Getting an exact rake angle on the nose would be a bit of a PIA because it depends on how far out the bit projects from the head, but small angles should be pretty easy to do.

I've done similar calculations and I think it would be possible, but it's been a long time. A bunch of vector manipulations. But from your results it doesn't seem to help much. With the dials on the Shars it would be hard to get any closer than a degree or so. I don't think I could measure those differences anyway.

I thought about commenting on this but considered it pretty obvious in the post. Yes, for using the dials and indicators on the machine and for the precision you are likely to obtain, there is no need to even bother with anything other than your target angles. It takes a pretty large rake angle to make any real difference. BTW - this also applies to the nose - and it's why a lot of people here recommended grinding the nose by hand - it would be quicker and good enough for the kind of work being done.

This method grinds one face into the edge and the second away from the edge. I've heard you should grind into the edge but don't know how important it is? May depend on the material?

Thanks for the help.

It is preferable for the grinding surface direction to be "into" the face of the edge being worked as it won't produce any sort of bur on the edge. However as you note, if you have to grind the other direction on a hard tool material there isn't going to be much if any bur produced unless you are grinding REALLY aggressively - which won't be the case here. Also it is common to lightly hone edges when looking for a very fine surface finish on softer metals. Any bur can easily be honed away.

Anyway, I'm sure you will get it done. Don't over think it. The only angle that needs to be really close on the bit you are describing is the 60 deg thread angle and you can get that by flipping the bit over. For what it's worth, it's not that hard to grind the 60 deg angle by hand and compare it to the fishtail gauge you use to set it up. Even using the grinder you should check the angle against something rather than rely on gages on the machine. So far, all of my HSS lathe bits are ground by hand.

The Deckel/clone will allow you to do other grinds that are hard or impossible to do by hand. (touch up side flutes on a mill for example)

Have fun!

 

[gerritv]

The manuals all seem to have a lsightly different way of describing the grinding of features. In some cases additional features that would apply to all these grinders. And sometimes just better wording or pictures/drawings.

Should it be avoided on other cutting tools (like carbide)?

I'm not sure, the goal is to avoid removing the sharp corner of the grining surface.