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Thread: Sphere Turning Tutorial

  1. #1
    Join Date
    Feb 2008
    Location
    Grand Rapids, MI
    Posts
    383

    Sphere Turning Tutorial

    Well, just for fun I thought I would give a photo tutorial of sphere turning.

    Tools needed:
    1.) Roughing Gouge
    2.) Parting Tool
    3.) Skew or Bowl Gouge
    4.) Spindle Gouge
    5.) Narrow Scraper/Hollowing Tool
    6.) A Pencil/Colored Pencils
    7.) Padding/PSA Foam Pads/PSA Sandpaper
    8.) Sandpaper
    9.) Utility/Spot Light
    10.) Dividers

    Photo #1:
    First, rough out a cylinder between centers. The diameter of the cylinder will determine the diameter of the sphere. The larger the sphere (diameter), the easier it is to approach perfect roundness.

    Photo #2:
    Approximate the location of the center, and mark a line. This can be done with colored pencils to make it easier to keep track of the axis on which you are turning. Estimate the radius of the cylinder using dividers. Err on the generous side with this measurement, for the rough ball must not be shorter than the diameter marked in RED (that is, the width of the cylinder). Mark the two ends of the ball using the dividers and a pencil.

    Photo #3:
    Part off the material outside the lines.

    Photo #4:
    Now rough out the ball. This can be done with a spindle gouge, but in this photo I used a skew. Both work well, but a spindle gouge is always less nerve-racking. Be careful not to turn the rough ball too small, and use a radiused pattern if you have trouble seeing where the outside of the finished ball will be upon completion.
    Attached Thumbnails Attached Thumbnails Turn Cylinder.jpg   Mark Center and Width.jpg   Part to Width.jpg   Turn Rough Ball.jpg  

  2. #2
    Join Date
    Feb 2008
    Location
    Grand Rapids, MI
    Posts
    383

    Chuck Making and Mounting

    Making the Tailstock Cup Chuck (Not Pictured):
    Now comes a little time consuming setup, but necessary for accurate results. It's not shown, for I did all this yesterday at a demo. I chucked up a block of wood and trued the endgrain. Next, I mounted a forstner bit just SMALLER than the diameter of my live center in my Jacobs chuck, and drilled out the workpiece. Then, as if hollowing a box, I scraped the inside to exactly match the diameter of my live center.

    Following this, I created a jam chuck onto which I fitted this workpiece. Then I hollowed a cup, making sure I didn't hollow into the drilled out recess just made. I then sanded the cup, removed it from teh jam chuck, and pressed it onto the live center by advancing the tailstock quill.

    See Photo #1.

    Photo #2:
    Next, mount a block onto a faceplate or self-centering chuck. Hollow a cup slightly larger than the small tailstock cup chuck. Sand this smooth. Then, pad the two cups. The less give a pad has the better, and PSA backed sandpaper would probably be best. (Spray adhesive on regular sandpaper would probably work as well.) The pads shown are PSA foam rubber, and less then ideal. I found they were much to spongy for this application. The reason for this is that upon changing the axis, it is much more difficult to maintain roundness, and 'runout' when turning away the ghost image is too great.

    Photo #3:
    After sawing off the nubs left from roughing out the ball, mount the piece with the center line horizontal. It will not seat in the cup well at this point, and firm tailstock pressure is recommended. The sphere is now oriented in a faceplate position, and a bowl gouge works great for cutting these next steps. I used a skew for this tutorial, but it is much easier with a bowl gouge.

    Upon turning on the lathe, you will see a very distinct ghost image, showing how out of round the workpiece is. Using localized lighting is very helpful for these final steps. The object is to remove that ghost image, bringing the ball to roundness by not turning away the previously marked red line. Stopping regularly to monitor your progress is very helpful. Again, try not to turn away the red line.

    Photo #4:
    Here I have begun removing the ghost image, yet being careful not to remove the line. Use either a bowl gouge or skew. NOTE: When using a skew, be careful not to hog off material too quickly. It is very easy to knock the work off axis.
    Attached Thumbnails Attached Thumbnails Tailstock Friction Fit.jpg   Cup Chuck Setup.jpg   Turn Off Nubs.jpg   Ghost Image 1.jpg  
    Last edited by Matt Hutchinson; 03-15-2009 at 06:56 PM.

  3. #3
    Join Date
    Feb 2008
    Location
    Grand Rapids, MI
    Posts
    383

    Final Stages

    Photo #1:
    Upon removing the ghost image, mark the diameter with another pencil line. This one is marked in green, and widening the line is helpful in making sure the marking will show after the next axis change and material removal.

    Photo #2:
    Now remount the work, with both the Red and Green lines running horizontally. They may not both be able to achieve perfect parallelism to the axis, but find a happy median. The closer to horizontal they both are, the closer your sphere is to perfect roundness. But don't worry if they are off, this can be fixed by continuing to change the axis and turning away more material.

    Remove the ghost image, and leave the marked lines if possible. Though not shown, you can mark the new diameter again. Also, if there are large discrepencies in the surface, continue to rotate the axis, gently skimming off material each time.

    Photo #3:
    Once satisfied that it's a round as it's going to get, proceed with sanding. You will have to change the axis at least once with every grit, and the surface should even out quite well. I sanded this Mulberry ball up to 320. Even though this is much less round than the walnut sphere posted in the Lathe Projects forum, it still looks pretty nice.

    Hope this was clear, and please ask questions if a process needs further explanation. Thanks!

    Hutch
    Attached Thumbnails Attached Thumbnails Ghost Image 2.jpg   Ghost Image 3.jpg   Mulberry Sphere.jpg  

  4. #4
    Join Date
    Aug 2008
    Location
    Reno, Nv
    Posts
    3,632
    Cool! Thanks Hutch, you make it look easy
    Your Respiratory Therapist wears Combat boots

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