Etch a sketch them and blend with a file. No fancy jigs necessary
I agree with this approach. . When turning shapes for pens you never want severe curvatures (such as small spheres).
I do a lot of this mildly-curved shaping on my metal lathe. . For some I use the cross feed at a couple of different angled settings and then round the resulting unwanted "ridges" using a file or coarse sand paper to get the final smooth curvature. . It does not take long at all and, for me, is preferable to investing time in making a jig.
I would not call my techniques "etch-a-sketch" ... it is even more primitive than that because I don't have any well-developed coordination skills for turning the hand wheels on the lathe in a synchronized way.
Sometimes I have to calculate an angular setting for the cross feed and that is just a little challenging if you have no recollection of your high school trigonometry but once you review the concept of tangent and arc-tangent it becomes quite straightforward.
One word of caution though .... do not rely on the angular calibration marks engraved on the cross feed cuz they're rather coarse.
It is much better to buy and use a "Pro-Angle Digital Protractor" - Part No. 1702 from General Tools & Instruments. . This helpful tool allows you to set the angle to an accuracy of better than 0.1 degree. . I use it all the time after I've calculated desired angles for a "new" shape that I want to create.
Note, however, that after a little experience you get to know the appropriate cross-feed settings for your common pen shapes.
Many of the shapes you want to create are very similar. . For most pens it's just a matter of fine tuning what you've done before.
Keep a notebook with a record of what you have done so that you can refer to your previous experiences.
The "etch-a-sketch" term is just a term and does not necessarily imply any sophisticated skills. . You can do most things with a file and/or sandpaper without even touching the angled cross-feed adjustments if you want to keep things very simple. . But learning to use the cross-feed settings and wheels can be helfpul.
If you do alter the angled setting of your cross-feed, make sure you reset to the zero setting when you're finished your task.
Otherwise, you could forget to do it later and then screw up an important cut on the next pen. . Any angled settings that you make are almost always very small and you might not notice such a small angle when you start your next pen.
Another word of caution if you are using a file ... don't let the file contact your bushings (if you are still using bushings) and don't let the vile file contact your dead or live centers if you are "turning between centers" (a highly recommended method).
That is very cool. I think I want one.
