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What is it/what is it used for? 5c Relief Grinder


New member
Going through my drawers and thinning out what I do not need.

Can anyone tell me what this is used for? It takes a 5c collet, the top pin is an index, only one hole. The front has what looks like a spring washer, so if you drive the screw in it cams up and drops.

Just trying to determine if I have a use for it.





Active member
It says right on the label what it's for. It's for grinding relief on cutters. The cam is what produces the relief. This particular device is going to give you axial relief on an end-cutting tool. It won't do anything about radial relief on side-cutting tools.

If you put multiple screws in the front index, you should be able to put relief on multiple flutes.

Oh, and if you're not interested in it, I would be.


Active member
One can circle grind as in just spin a cutting tool end round at the desired angle, then bring each flute end to a mark, to a finger or just eyeball to the center line and then radial relief (roll) each flute end to bring the radial relief grind action to just take away the circle grind to very small land and then wipe it out....often the angle will not match exactly straight so you bump a little more angle ( a half-degree or so) and to matches perfectly.
This sounds troublesome but is no trouble at all and goes very quickly.

Often one would go (grind) to just wipe out the circle land (to sharp) and then dial another .001 just to be sure old eyes were not leaving any circle land.

Some such devices have a cam to ride on that increases as you go down the cam so one might go from 10* to 15* or so..

As you go closer to the OD the axial clearance may not put on enough clearance. Say it would be good for 90* to 45* but getting to 70* it may not have enough clearance, so might heal drag..
We used to call that tilt and roll, think that is at about page 64 or so in the Cincinnati Tc grinder handbook.

XX nope it (tilt and Roll)is not in the handbook...darn

So consider if you put 10* on the end of a cutter by tilting a work head, then turn the cutter to be near adjacent to the OD you would have zero clearance there. diminishing clearance.. The same would apply to a cam action to the end.


New member
Thank you for the replies. So would it be used on a tool and cutter grinder?

I studied some cutter diagrams and now have a better understanding. Not really sure I need this fixture, I would be open to selling it.




I own this, thanks to Marco.
The amount (12) of various screw positions were slightly puzzling; but it doesn't index on each hole.

There is a stiff spring behind the 'index plate', just like a large lock washer. The indexing occurs at edge of that step, created by lock washer. As it turns, that spring pushes spindle in 'Z' travel. The index plate and spring are hardened, so there is little friction and smooth rotation.

Certain this will apply to fluteless and single flute (ie M.A. Ford etc) countersinks. I built a very unsophisticated jig once, based on 1/2-20, it worked on 3/8" to 1/2" cutters.

Putting 3 more 1/4-28 screws in during tests of the action, the single step can't/ doesn't engage. The 2 work independently, #1 is a stop, 2# uses the fine threads to control 'Z' travel amount against the spring (instead of a cam) which in turn relieves cutter.
The tapped holes offer differing travel by number of degrees from stop screw. ie 1st CW from stop is full, last CW from stop is least.

Dividing Amount of Travel by Degrees of Rotation equates to relief needed on C'sinks of different diameters. Haven't worked out how to best figure what that amount is. Once I do, a formula or diameter chart will have this in regular use.

Full travel is about .100, that'd be a damn big C'sink! Running screw in can reduce to 'Z' to 0.000 movement. 28 TPI produces 0.0357 per revolution.


Active member
Some/many of those will rotate with not any relief action so you roll/spin circle grind to one or many flutes.
Then you engage the relief action to bring each flute just up to a sharp edge.
For a single flute one might just grind on the cam action to bring that flute to sharp.