Fun with spheres

I've had this idea in my head for a couple weeks now.  Tonight I had to give it a try.  I started by turning a sphere.  The blank was cut slightly longer than the width (3 5/8" long, 3 1/4" wide) and mounted between centers.

The blank was turned to a cylinder and layout lines were made.  The important line is the one in the middle, the others were no measured, just drawn on as a guide.

The corners are knocked off back to the center line.  This is where the bulk of the material will be removed.  Almost no material will be removed at the center line as that is the largest diameter of the sphere.

Each side is then turned to a half sphere shape.  I prefer to do the left hand side first because it's my weak side and I can better match the curve on the right hand side.

A couple more cuts and the basic sphere shape has been formed.

The blank is then rotated 90 degrees and put between wooden drive centers.  If you look at this photo closely you can see the "shadow" of the nubs left by the drive center on the original axis and the rest of the wood to be removed to make this a perfect sphere.

The sphere is repeatedly repositioned on 3 axis (X, Y, and Z) so the entire surface can be trued.  Here you can see that the sphere is on the Z axis.  The X axis is noted by the single line on the top.  The Y axis is the double line on the near side.  The blank is turned on eash axis about 3 times, each time smaller and smaller cuts are taken.  If a cut is too deep the entire surface will have to be turned down to that new depth. 

Once turning is complete the entire surface is sanded with each grit. Once per axis per grit.

Next the sphere is moved off azis and a groove is turned.  The was repeated after rotating the sphere 90 degrees.

There are some flaws. Chipout on some of the edges where the wood was unsupported during the cut and a couple of areas where the soft wood was crushed by the wooden drive centers.

Off center sphere

Terry was pretty close in describing how I turned the piece from my last post.  The sphere was roughed between centers and I then used cup chucks on each end to fine tune it.  The nose of this live center cap was flattened and used to apply pressure from the tailstock to the cup center used to drive the piece from the headstock.

The cup center for the headstock is some scrap that was screwed to a faceplate.

There is a slight cup in the center, the size isn't really important, as long as the sphere makes contact around the rim before it bottoms out in the cup.

The cup was then moved off center by simply unscrewing all of the screws but one and then rotating the faceplate before driving them back in but in different positions.  This effectively moves the sphere off center so the V groove can be turned.

Lastly a jam chuck was turned so the piece could be hollowed through the opening created by the groove.  The fit has to be pretty good, like the cup center above the contact has to be around the outside before the piece bottoms out in the center.  Green wood was used because it's a little more flexible.







Below is a quick video I took showing the cup center on the faceplate in the off center position.  It's a very simple solution that I picked up from Christian Burchard.  The flat on the face of the live center cap was just wide enough to apply the pressure needed to drive the sphere.

Laser guided Pacman

I still need to make an actual jig to measure the bottom of bowls and hollow forms, in the meantime I used the laser from my hollowing system to temporarily locate the bottom of this hollow form.  When I get around to building the actual jig it will be carefully setup to measure exactly at center height.

The laser point was carefully aligned with the end of the cutting tip.  Where the laser falls on the outside of the piece should be where the inside bottom of the hollow form is.  Assuming that the cutter is bottomed out and is on the center line (I'm holding in place with one hand and taking the photo with the other) it looks like I have about 3/8" left in the bottom.  Just enough to finish it off and make a slight concave spot for it to sit on.

Next up was a sample for what I might want to do on a larger scale.  I saw a photo of a similar piece during Christian Burchard's spheres demo at the 2011 Desert Woodturning Roundup.

Turning a near perfect sphere is much harder than I initially thought.  I used Christian's technique and got pretty close but it's definitely not perfect but it was pretty close.

Can you guess how it was hollowed and how the groove was cut in the middle (or is it the other way around).  Also how was it held during these operation(s).  I'll reveal how I did it in a couple of days, after some guesses have been made.

Catch up II

Our club is submitting 1 piece to this summer's "Turning 25 - A Celebration" exhibit in Minneapolis-St. Paul.  This was one of my entries to our club's selection competition.  I'm happy to report that it was the selection and will be included in the exhibit and in the exhibition catalog.  It's titled "Relic I" and is made from a Desert Ironwood root salvaged from a lot being cleared for a new retail development.

After ruining the first hollow form I decided to give it another shot, slowing down just a bit so I don't ruin it.  I started off at exactly 4:05 PM

The finished piece (including a very quick sanding to 320) at 4:20 PM.

It was also cut in half to check the wall thickness.  It's  the one on the right and is quite a bit thicker in the bottom than I'd like and the opening is larger than I'd like but overall it's not bad.  The one on the left was my 10 minute attempt from earlier.

 Last night was a prototype for a new multi axis box.

 The inside is turned prior to the outside.  The outside is done on 2 parallel axis.  One Axis is turned as a large bead, the other is turned as a large cove.  The top and bottom are then turned using a jam chuck.

 There was a significant defect in the wood, making it perfect for a prototype.

Open view, showing the pinched oval cross section.

Catch up

 A bit of catch up and picture dump tonight.  This is going to be a long entry with limited notes.

This blank is Chinese Elm from my neighbor's tree.  It died last fall and had to come down last week.  This is the top part of the trunk, it split into 4 branches at this point.

 Alternate view.

I only took it as far as shaping the outside.  It's been coated with Anchorseal and set aside for the time being.

Alternate view.  The shape will be refined as work progresses.

Ahead of my Tucson demo I decided to do a little practice turning.

A simple spindle turned on 2 parallel axis.  This gives a pinched oval shape to the piece.

Next was another parallel 2 axis piece.  All 3 sections have a circular cross section, only the center section is offset.

Saturday was my demo for the Southern Arizona Woodturners Association in Tucson.  This was my first visit to this club and I did my multi axis demo.  Over the course of 2 1/2 hours I did 6 multi axis projects.  2 parallel axis spindles to warm up, a Mark St. Leger style multi axis final jig, a 3 sided lidded box with a twist, and finally a pair of multi axis pendants.

While there we stopped into the local Woodcraft, my only purchase was a Woodriver brand Stebcenter.  I've been playing with it for the last couple of day and I really like it so far and at $20 it's a bargain.

Sunday morning started with a small Olive hollow form. Approx. 3 1/4" X 2 1/2".

Top view.

Profile view.

That got me thinking, how fast could I turn a similar piece, start to finish.  I started at exactly  2:00

 At 2:10 I heard a somewhat familiar noise and stopped the lathe to find that I had cut through the sidewall near the bottom as I was shaping the outside.  I needed about 2 more minutes to finish shaping the outside and give it a quick sanding.

 Finished off the bottom but not yet sanded, no point sanding it at this time.

I wanted to check how I did inside, a little rough but pretty consistent down to the point where the inside gets bigger than the outside.  I could have gone a little deeper in the middle but a little more meat in the bottom isn't a bad thing as it helps keep it upright.

More tomorrow.