Spring Cut Off Evolution! An Easy to make design + the PLANS

[winkys workshop]

>>One problem that many may not consider is the axial position of the cutting edge from the tool-post centerline which induces a rocking couple that I believe is a big problem on lightly built machines that lack rigidity.

You hit the nail on the head.

[Toolmaker51]

re post *8. Only limitation seen, won't the extended front will interfere with substantial diameters or mid-point in a bar? Winky's puts the motion above and behind, long the accepted arrangement.

re chip ejection, I use the hollow top ground variety most often as well. According to sense of touch, sight and sound [in that order] binding occurs that instant before chip breaks off. That depresses tool tip, deepening the cut into unreleased material...
Avoiding the nub that remains, can addressed grinding a shallow angle on the 'right' side that will penetrate it on the part side first.

All in all, my parting usually goes to some depth in proportion to diameter [bigger = less depth] and finish via horizontal band saw. It's one off production, of pump sleeves and slip rings, again silicon bronze. The investment in time - materials - and reinstalling a critical pump make it sensible.
When possible we also part off in a different sequence; boring ID a bit deeper [blade width] than part requirement. That greatly reduces penetration from outside; with both sides concentric, part breaks away predictably.

[CanBeDone]

A few observation: The second tool works on smaller stock and or when the lathe is in back gear (very slow). If you are in the US I can ship you the first two if you want... you can keep them. .

Thanks, Winky, but I live in New Zealand, so that is out. It would have made a nice research project, comparing a number of different designs and establishing what really makes a parting off tool effective.

[CanBeDone]

[QUOTE=Toolmaker51;197288]re post *8. Only limitation seen, won't the extended front will interfere with substantial diameters or mid-point in a bar? Winky's puts the motion above and behind, long the accepted arrangement.
/QUOTE]

Not on my machine, since I consider parting off from a bar of not more than 25 mm diameter. That gives me more than 100 mm free space below the bar to put the toolholder into. But if I needed to frequently part off rings from a 100mm tube, that would be an entirely different kettle of fish.

My key question remains, however: Why does Winky have great success with one toolholder, and when he builds a second one to the same design, why does it fail? Or, to put it in a much broader perspective, Why do we have such a great variety of toolholder designs, not just for parting-off tooling, but also for form tools and even "simple" clean-up operations, and why do so many of them produce poor surface quality cuts? Not under all circumstances, of course, but I experience it again and again, and hear others complaining about it as well. So it is not just my incompetence as a machinist, because sometimes I do produce mirror-like surfaces, but not always. And always is what I want, predictably, whenever I try it.

And Winky's admission of a "Failure" has triggered a chain of thought that might lead to a much better understanding of how to design a toolholder that predictably produces a mirror surface. Last night I had success designing a test rig that I can build given my resources, and that would give me the measurements I need to decide where Winky's builds failed. - That is if I can convince Winky to ship his "Failures" to New Zealand, together with a new toolbit of the same design he uses, so that I can get an idea of what is going on. Obviously, I will reimburse you, Winky.

Another if: to generalize from what works on my lathe to what works on any lathe, I would need access to another lathe, preferably one that is very different in capabilities from my own. Since that would involve physical traveling in a Covid affected world, I would want to restrict this lathe to be somewhere in the Waikato.

[Toolmaker51]

Interesting prospects. I did not consider 1"/ 25mm as your maximum. The physics of cut off make a mirror finish unlikely. Some materials have more potential, but very limited in respect to metallics. The only mirror or close specification I recall on any print would be O-ring grooves, as the seal has trouble when surface roughness keeps it from moving into it's seat.
I'm glad about so much participation the subject pulls in, there is no hard and fast guarantee in grooving and parting.

[uv8452]

Dear CanBeDone,
"The standard explanation adds a third argument...." I have learned a fourth and practice it: Since it is resonance, I reduce the cutting speed.
Ulrich

[Floradawg]

This is the second version of my spring cut-off tool. This design moves the point of flex toward the point of cut which makes the tool retract more under load. The concept is fairly easy to understand (see part one) but the amount of flex and where it flexes is a bit of a guess. I've used the tool at various speeds, feeds and diameters and it seems to be fairly forgiving. I like it!

I think version 2 is less rigid than version 1 because it is not welded. Even though there is an interference fit, the slot is very shallow and just the screws can't prevent flexure.

[DIYer]

Thanks winkys workshop! We've added your Spring Cut Off Tool to our Lathe Accessories category,
as well as to your builder page: winkys workshop's Homemade Tools. Your receipt:

Spring Cut Off Tool by winkys workshop

tags: lathe