Botula
Bollinger Ovalturning Lathe
- 82" swing, 24" sway
Dan Bollinger 
West Lafayette, Indiana, USA

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click for demo

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In 1979 I made a Holtzaphel style elliptical lathe chuck to screw onto the university's 12" HD Rockwell lathes. Machined from steel and brass, the chuck can offset 2.125" from the centerline for a maximum sway* of 4.25" Like most of these chucks, it was very noisy and had to be spun slowly. Each rotation responded twice with the customary "Slam-Bang!" I started turning a poplar bowl, but never finished it. Too scary! Later, I decided to go back to school and then onto a career in Industrial Design.  Now, 22 years later, I'm returning to ovalturning. (read more)

Here are the photos of the Big Green Machine in process.  I'll add more as time goes on. Click on the images for a larger view.

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One-quarter inch steel pedestal welded by my buddy Ken Vetter. Ken runs a family owned welding shop, Vetter Welding, in southern Indiana in the Louisville area. Give hime a call if you need something made! (12/9/02)

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Green enameled and bolted to the floor. Drive compenents being added.

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Low voltage controls connected to a Variable Frequency Drive. 'Jog' feature enabled, forward and reverse.

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Hitachi variable frequency drive below the 2HP TEFC motor.

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Double tapered roller main bearing with 1.5" bore. Cross rods (on top) are part of the vibration mitigation. More bracing and vibration absorbers are mounted inside the pedestal, which can be filled with sand if needed.

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Wiring completed

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Indexer and stationary sprocket for Goodyear Eagle Synchronous Belt

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Close up of indexer and sprocket.

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Left side with 1" x 8tpi threads for "ho-hum" plain, circular turning.

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Main cross-arm and its hub on left

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Carriage for secondary shaft slides on cross-arm to change amount of elliptical 'sway.'  Bearings are tapered roller bearings. (3/15/03)

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Secondary shaft installed with gearbelt sprocket attached. Threads are 1" x 8tpi. (7/6/03)

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Epoxy/fiberglass/hardwood veneer laminated clamshell guards. Ready for paint. (7/29/03)
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Clamshell guard installed. Top half opens up, note the over-center latch. Inserts close up the opening depending on the sway, protecting the turner.(8/22/03)
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18" diameter disc of 1/2" aluminum carries cogged belt idler shaft. Rotating the disc re-tightens the secondary belt when the carriage moves along the cross-arm. A counter weight will be added to balance this disc.

 

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Jackshaft assembly showing eccentric belt tensioning feature. (6/12/04)
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Here you can see both cogged belts, their pulleys and shafts, plus the main crossbar and the disc that carries the jackshaft (3/15/04)
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Closeup of jackshaft assembly with cogged belts. As you can see, I'm using the Goodyear Eagle PD herringbone cogged belts. They are quieter running than any other cogged belt. Plus, they are narrower reducing overhang. (3/15/04)
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Overall assembly of the epicyclic
mechanism. I rotated it under power for the first time on March 14th, 2004 and it works! Very smooth and quiet. (3/15/04)
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As the carriage moves along the crossarm, the disc can rotate tightening the second cogged belt. Counterweights have not been installed yet. (3/15/04)
Click here to watch 3MB video of lathe turning.

Click here to watch a 30MB video of the lathe turning.

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Spindle Lock with saftey interlock, pulley was rebalanced (6/25/04)
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Lead counterweight (left) balances idler shaft (right). (6/30/04)
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Sliding c'weight balances second shaft and workpiece. Tested it today, no noticable vibration at 800 rpm.   (7/20/04)
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I've been too busy to make much progress on the oval lathe since summer. I have managed to rig a temporary cutting frame using a router motor. Cove bits work well for roughing and ball burrs for fine cuts. Hand holding the router is difficult. I need to add some mechanical advantage to moving the router. What I don't want is an X-Y table, which will interfere with making curved cuts. (11/20/04)
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After a lot of testing using a handheld router and many types of cutters, I've come to the conclusion that the router needs more control than I can supply with two hands. So, I found these parts on eBay auctions to assemble a <shudder> X-Y router table. It will rest on a toolpost, so I can quickly change to a traditional toolrest when needed. The good news is that I've found a 1/2" carbide ball router bit with 4" shaft, which will make cutting easy.(3/10/05)
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Ken Vetter also welded up this floor mounted tool post will bolt to a grid of floor anchors allowing positioning every 3". The tool post top will accept a wood turning lathe 'banjo.' A traditional tool rest can be inserted, or the X-Y table mentioned to the left. (4/6/05)
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The last coat of green paint went on the final parts last week. Here is the tool post pedestal shown with a scavenged Rockwell/Delta HD banjo (with reversed lever) and tool rest. A custom tool post riser puts it on center. Once a dust cover is made to protect the oval turning mechanism the chips can fly! (4/25/05)
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Finally! After months of eBay auctions and locating small parts, the X-Y router table cutterhead is finished. It sits on the lathe banjo. Besides the two degrees of freedom in the cross slides, the router can pivot and has 1.5" of feed.
(9/15/05)
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The first bowl being cut! It is 4" wide, 12" long, 3" high in solar-dried cherry. The dust cover protects the mechanism from flying chips. This first bowl goes to my wife, Rebecca, who has had to live with my crazy project for three years.  Thanks, hon!
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The bowl's foot being cut. Much less wood fiber pull-out than I expected. I still need to figure out how to reverse the bowl to cut its top and interior.
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The first bowl from the lathe! Finally, after four years of designing and building, I'm turning ovals again. This bowl, designated #100, goes to my wife Rebecca for having to live with me during this 'project.' The bowl is solar-dried Indiana cherry, 4"w x 12"l x 3"h. (10/07/05)
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The floor mounted tool post did not work well, it require releveling each time is was moved. So, I put a 3/8" steel sheet under the lathe to act as a bed. It is anchored to the floor and leveled with grout. A grid of tapped holes allows the tool post to move easily without releveling. A rubber floor mat will surround the plate. (11/06/05)
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An adjustable faceplate for oval work. The workpiece can be screwed to the faceplate using screws using the holes in the movable brass blocks. Moving the blocks with the opposing set screws permits alignment on the lathe. This is critical when reversing the workpiece, or turning a lid for a box. A two-jaw chuck can be bolted to it, too. (11/21/05)
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Oval Milling Effect - Using a router cutter on an oval cutting mechanism introduces a condition where cuts are 'not true' (not parallel). The same cuts a simple lathe cutting a circle would produce 'true' (parallel) cuts. The effect is reduced as the oval approaches a circular shape and as the cutter diameter decreases. In the example pictured, the 1/2" (12mm) ball cutter produced a visible non-true error. At the thinnest portion the effect was 0.088" (2mm) less. 

Theoretically, cutting edges such as gouges or skew will not produce this effect since their 'radius' is infinitesimally small. However, in practice this is not the case. Handheld tools wiggle. The wiggle can be seen as causing the cutter to have an effective cutting  radius, which in turn introduces the same milling effect of non-true edges. This may not be visible, but would be measurable.
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After a one-year hiatus, I've returned to working on the lathe. I wanted to alter the X-Y router cutting table to make if faster and easier to use. This alteration adds a pivot so the angle between the X-Y axii can be changed. This will speed cutting considerably. (2/5/07)
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One of the slides had a crank that worked backards because it's slide was mounted upside-down. This spur gear arrangement reversed the screw direction, solving that mistake prone defect. (2/5/07)

   


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