Radius Knurling.

[John Hasler]

I just see him honing the front flat, but watching more closely I see that front relief comes from his having cut past the center line on the mill. That should also have provided a bit of flank relief if I am visualizing the geometry correctly.

[whateg0]

Taps also have no back relief. I've always wondered if they would work better if they did, but cutting them would be hellish, I would think.

Dave

[whateg0]

That should also have provided a bit of flank relief if I am visualizing the geometry correctly.

Nope. Recall, that flank is part of the surface left when he turned the shape initially.

Eureka tool is the machine I was thinking of earlier for cutting that back relief. I think I'll add that to the list of things I want to make!

Dave

[John Hasler]

Cutting past the center line will have made the angles where the turned shape meets the face slightly acute. The flank angles lack face relief, though.

I think it just wasn't very sharp. Having seen his (I don't claim I would have thought of this the first time either) I think that if I were to make one of those tools I'd come in perpendicular to the long axis of the tool with a large diameter end mill so as to leave the face concave. That would make it easier to hone a good edge onto it.

[whateg0]

Cutting past the centerline does in fact leave an acute angle on the face, but remember, the shape of the cutter doesn't change. It just moves where it cuts that width further back. So, radially, a "X" from the CL, the tool width is the same. The benefit is that it has rake, which is completely different from back relief, and tends to provide a better finish. Think straight router bit vs spiral bits.

Dave

[armscor 1]

My Australian made Taps I just measured have a definite back relief.
The imports do not have the relief.
You get what you pay for.

[Harold_V]

Taps also have no back relief. I've always wondered if they would work better if they did, but cutting them would be hellish, I would think.

Dave

Yes, that's true, and I thank you for the comment, as I didn't even think of them when I posted.
Taps, like drills and reamers, are most likely tapered slightly to reduce contact, but I don't know that to be true. If I can remember to do so, tomorrow when I return to my shop I'll measure one with wires to see if it tapers. It's obvious with twist drills, and I can't tell you the number of chucking reamers I've modified by regrinding. We were expected to provide about two tenths taper with the reamers.

[BadDog]

Lathe change gear door thumb wheel knurled.

Nice. Well beyond what I've accomplished.

[John Hasler]

I found a discussion of the grinding of taps that calls what I think you mean by "back relief" "radial relief", which makes more sense to me. What I called "back relief" I guess would be more properly described as "flank relief".

I can see now that Clickspring's tool has no radial relief as machined: the intersection of a plane perpendicular to the axis of the tool and one of the teeth is a segment of a circle. Cutting past the centerline does not change this, though it adds flank relief.

I see what Harold means: he could have added a bit of radial relief in the small part of the tool that actually cuts with his file.

I still say it wasn't very sharp, though. Look at the image near 5:31 where he seems to have finished honing it.

Thank you. I learned something about tool geometry, though I will probably never actually make any rotary tools.