First time parting not too good

[janvanruth]

A video in the thread that 'great white' linked to in post #2 explains it in terms of the relationship of the pivot point to the tool/work piece interface. I found it very enlightening. And a neat tool, also.

Tom

the video, especially the animation sucks
watch the animation in regard to centerhight

 

[randyc]

Tapping a hole in the cross-slide allows installing a 1/2 diameter steel rod directly under the toolpost. The cutting forces are then transmitted directly to the cross-slide and the carriage. There is no "rocking" and "tipping" of compound or cross-slide. The capability of thelittle 8 x 18 lathe when working hard-to-machine materials went up by 100%.







The shortcoming of this "fix" is that movement of the compound is limited, although it's simple enough to unscrew/remove the support rod and restore full compound travel. With the support removed, rigidity is diminished and chatter returns during heavy cuts using the compound.

 

[janvanruth]

draw a circle
draw a line going from the centre out and beyond the circle
that is a centreline
now draw a line perpendicular to the centreline outside the circle
that is the line of force
now explain why the force would change with the changing of the turning movement of the circle

you wont be able because there is no difference

the reason for having the cutoff tool on the back is speed of working
in stead of having to change the tool for a cutting off tool and reversing the lathe all you do is crank the backtool towards you
offcourse the tool will be upside down otherwise it wouldnt cut
and as the cuttingtool holder only serves one purpose it will be much more rigid than the compound that has to serve more purposes

a cuttingtool with no top rake will never be drawn into the piece be it high or low
only a cuttingtool with a positive rake on the top can be drawn into the workpiece

rigidity is the key to parting off

 

[janvanruth]

I tried parting off a 1" piece of cold rolled steel. Extremely noisy. I cut in about a 1/8 in and it grapped in and stalled then blew the fuse. I was feeding so slow aswell. Its a 10x22 lathe
I had watched you tube video's and read about how difficult it can be.
This is what I was using. It is tapered and the top has a bevel on both sides.

View attachment 94564

how do you mean a bevel on both sides?

 

[higgite]

the video, especially the animation sucks
watch the animation in regard to centerhight

The video that I referenced doesn't have any animation. It's not the same video that Henrymac referred to earlier.

draw a circle
draw a line going from the centre out and beyond the circle
that is a centreline
now draw a line perpendicular to the centreline outside the circle
that is the line of force
now explain why the force would change with the changing of the turning movement of the circle

you wont be able because there is no difference

the reason for having the cutoff tool on the back is speed of working
in stead of having to change the tool for a cutting off tool and reversing the lathe all you do is crank the backtool towards you
offcourse the tool will be upside down otherwise it wouldnt cut
and as the cuttingtool holder only serves one purpose it will be much more rigid than the compound that has to serve more purposes

a cuttingtool with no top rake will never be drawn into the piece be it high or low
only a cuttingtool with a positive rake on the top can be drawn into the workpiece

rigidity is the key to parting off

In your example, the pivot point would have to be on the center line of the spindle for the force and the reaction to that force to be the same in both directions of rotation. The pivot point on a tool post/cross slide combo is below the center line of the spindle. Direction of rotation and tool orientation do make a difference in that case. The video that I referenced does a good job of explaining it.

Tom

 

[coolidge]

Gunrunner you need to order a set of these for the Z axis hand crank. Bill did you just spit coffee on your monitor? :rofl:

View attachment 253356

 

[mikey]

Deleted

 

[janvanruth]

The video that I referenced doesn't have any animation. It's not the same video that Henrymac referred to earlier.


In your example, the pivot point would have to be on the center line of the spindle for the force and the reaction to that force to be the same in both directions of rotation. The pivot point on a tool post/cross slide combo is below the center line of the spindle. Direction of rotation and tool orientation do make a difference in that case. The video that I referenced does a good job of explaining it.

Tom

the pivot point could indeed be beneath the centre line, it depends upon the setup whether it is or not
but in turning upside down it would be exactly the same distance above the centre line using the same kind of setup
so no difference at all

 

[higgite]

the pivot point could indeed be beneath the centre line, it depends upon the setup whether it is or not
but in turning upside down it would be exactly the same distance above the centre line using the same kind of setup
so no difference at all

As much as I hate the cliche', I'm afraid we will have to agree to disagree. I'm done.

Tom

 

[janvanruth]