Turning from the rear on Sherline lathe.

[mikey]

You should try parting from the front. It will be educational for you, especially in brass.

 

[zondar]

You should try parting from the front. It will be educational for you, especially in brass.

Well, I can't at the moment. But again, why have centuries of lathes done it the standard way if it's so clear that the rear (or from the front spinning it in reverse) is better? I also don't see why "because it's a small lathe" makes a difference either. More rigid should be more rigid regardless.

I don't know, maybe it's actually something other than rigidity, or maybe it will remain a mystery of the universe.

 

[mikey]

But again, why have centuries of lathes done it the standard way if it's so clear that the rear (or from the front spinning it in reverse) is better? I also don't see why "because it's a small lathe" makes a difference either. More rigid should be more rigid regardless.

Parting from the rear has been done for maybe the last 75 years or so, maybe more. It actually began in the UK, I think, and mainly on the smaller lathes that were available at the time. Seems that they were looking for a better way to part on small lathes because parting from the front, the standard way, sucked. It still sucks and if you try it on your Sherline lathe you will discover quite quickly that it sucks. The same degree of suckage exists for many, many other lathes out there that are much larger than a Sherline, so much so that many guys take to using a hacksaw or bandsaw rather than part on their lathes.

Now granted, not all lathes have issues parting from the front but a good many do, and the older and more worn out the lathe is, the more likely you are to have issues.

 

[zondar]

Ok, I'll take your word for it. But I'll keep wondering about it anyway. Puzzles like this tend to gnaw at my mind. Like why only parting tools, even, vs. all tools? There's probably a hint to the solution in that.

One thing I do like about the rear parting tool is that I can leave it on the back and another tool on the front simultaneously. That's convenient.

Thanks.

 

[WobblyHand]

Parting on my mini-lathe used to be terrible, mostly since I didn't know about tightening up all the adjustments. Now it's tolerable, but not good. I wouldn't want to part 1045 steel or stainless on it. Eventually will add a rear parting tool.

Even on my 10 x 22 lathe, parting is not a pleasant experience. The compound is not rigid enough to resist the parting forces. I could literally see the deflection. Of course, I am machining bigger parts than on a mini-lathe, but the last parting of a steel mandrel made me give up and go for a hacksaw. Was not fun.

I designed a rear parting tool for the 10 x 22 mounted in a steel plinth. Will receive the steel block soon and hope to be machining it by next week. From the lessons learned, I will make one for my mini as well.

 

[mikey]

Ok, I'll take your word for it. But I'll keep wondering about it anyway. Puzzles like this tend to gnaw at my mind. Like why only parting tools, even, vs. all tools?

Don't take my word for it; try it and come to your own conclusion.

And the improved rigidity applies to all the tools you mount back there.

 

[EricB]

Joe Martin wrote in The Sherline Accessories Shop Guide that "cutoff tools work better inverted, because they have a tendency to lift rather than dig in" (read flex). That makes sense to me. It doesn't affect precision because the dimension you are working toward is zero.

 

[zondar]

Don't take my word for it; try it and come to your own conclusion.

And the improved rigidity applies to all the tools you mount back there.

It's not a matter of seeing, it's a matter of trying to understand the mechanics of it.

One more Q: If it's better for everything, why don't all lathes just put everything in the front, tools upside down, and spin the lathe "backwards?" Minor convenience, e.g. seeing the tool tip slightly easier, over superior rigidity? Just a long-standing convention from back in the days when all lathe tools were basically hand-held gravers?

 

[zondar]

Joe Martin wrote in The Sherline Accessories Shop Guide that "cutoff tools work better inverted, because they have a tendency to lift rather than dig in" (read flex). That makes sense to me. It doesn't affect precision because the dimension you are working toward is zero.

So now I have to puzzle over why one tool "lifts" and and others "dig in." Thanks for setting me up with another week of obsessive mental torture. Lol.

 

[WobblyHand]

It's not a matter of seeing, it's a matter of trying to understand the mechanics of it.

One more Q: If it's better for everything, why don't all lathes just put everything in the front, tools upside down, and spin the lathe "backwards?" Minor convenience, e.g. seeing the tool tip slightly easier, over superior rigidity? Just a long-standing convention from back in the days when all lathe tools were basically hand-held gravers?

I don't know exactly how to do this (easily) but one could install several sensors on the cross-slide, the blade, the tool holder, ... and instrument the cut dynamics. Bet you would learn a lot from it!