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I have found that the smaller and less rigid the lathe, the better a rear mounted tool works.
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Turning from the rear on Sherline lathe.
- Thread starter fcs
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I have found that the smaller and less rigid the lathe, the better a rear mounted tool works.
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Mikey,
Just out of curiosity, When you bore something on your lathe do you invert the boring bar and work towards the far side of the part?
Eric
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I think I may have to try it that way. I was making a fixture this week with a wide/shallow opening in it using a short boring bar in the normal way. I kept crashing the bar into the bottom. I did the same thing when I used it too. If the tool were on the back I could have seen where the end was.
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Somehow I missed the gist of your post - you're crashing the bar into the bottom of the bore? Are you not using a carriage stop? If not, you should. It is hard to make a bore to a precise depth without one.
I also happened to look at the Sherline site for the first time in maybe a decade and noted that they have tool posts for rear mounting turning tools and parting tools back there. I suppose that was the inspiration for the OP.
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No carriage stop. I was watching the edge of the cut on the back to see where the tool was in the front. I eventually accomplished what I needed but it was loud at the end.
What form of carriage stop do you use/recommend?
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I have an angle iron bolted to the front of my lathe base that allows me to use a shop-made stop that is quite rigid. The lathe is buried right now but I'll try to get a pic when I can.
Sherline sells stop rods that go in a 1/4" hole drilled in most current headstocks. You can also drill your own hole. That would be the easiest way to implement a stop. Regardless of how you do it, a stop is a really important accessory when precision boring.
Sherline sells stop rods that go in a 1/4" hole drilled in most current headstocks. You can also drill your own hole. That would be the easiest way to implement a stop. Regardless of how you do it, a stop is a really important accessory when precision boring.
Not to question experience vs. theory (even inert placebo pills can work miracles), but I've puzzled over this "turning from the rear is more rigid" idea. Why!?
So, at the risk of beating a dead horse:
First, we note that it's generally advisable to "choke up" on the work with your tool and the tool post, vs. adding longer lever arms that contributes to flex.
So, if the tool post binding (i.e. the bolt to tie it to the cross-slide) is considered a hinge of sorts, then turning from the front puts downward pressure on the tool-post edge closer to the work as well as closer to the lathe's ways, enhancing rigidity similar to that "choking up", and a lifting force from the rear, which adds no rigidity (but that edge is farther from the work and the ways anyway).
On the other hand, turning from the rear puts downward pressure on the rear of the post (farther from the work, and farther from the bed ways, tending to reduce rigidity vs. if it was closer, i.e. not choking up) and a lifting force (adding no rigidity) from the closer edge (again, the opposite of choking up).
In this overly-simple and naive picture, the front mounted tool post seems superior (and consistent with centuries of practice). Where does this purportedly go wrong?
(I deleted a "P.S." that included a mistaken presumption.)
So, at the risk of beating a dead horse:
First, we note that it's generally advisable to "choke up" on the work with your tool and the tool post, vs. adding longer lever arms that contributes to flex.
So, if the tool post binding (i.e. the bolt to tie it to the cross-slide) is considered a hinge of sorts, then turning from the front puts downward pressure on the tool-post edge closer to the work as well as closer to the lathe's ways, enhancing rigidity similar to that "choking up", and a lifting force from the rear, which adds no rigidity (but that edge is farther from the work and the ways anyway).
On the other hand, turning from the rear puts downward pressure on the rear of the post (farther from the work, and farther from the bed ways, tending to reduce rigidity vs. if it was closer, i.e. not choking up) and a lifting force (adding no rigidity) from the closer edge (again, the opposite of choking up).
In this overly-simple and naive picture, the front mounted tool post seems superior (and consistent with centuries of practice). Where does this purportedly go wrong?
(I deleted a "P.S." that included a mistaken presumption.)
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Yes, but from the back only, since the cut-off tool post doesn't work on the front. It went fine in brass and smaller leaded steel.
Hmm. Looking at the post, I'm not sure I see a limitation that would have prevented a post (different design) from mounting the blade for use at the front.
I'm not disputing the notion, just confused as to why it's "better". And if it is better, why hasn't generations of lathes simply spun the spindle in "reverse" so tools can be conveniently mounted for cutting in the front the other way?
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