Best way to "go oval"?

Kerry Burton

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SUBTITLE: Not elliptical orbits, but the 'orbiting' of things elliptical

Stu's new Escoulen eccentric chuck and the recent discussion about ferrous metals (cast iron vs steel) have somehow "spun" me off on a couple of converging tangents. :rolleyes: My brain took in "eccentric", chewed on it for a bit, and eventually spat out "elliptic"...

... which reminded me of a neat-o section in David Springett's 1994/95 book called [Adventures in Woodturning]. My copy has a price sticker of $24.95 on the back, but according to the link it is now available at the low, low price of anywhere from $61 to $390! :eek:

The last section of the book deals with Elliptical Turning. Mr. Springett dedicates an entire 16-page chapter (pp. 181-196) to the construction of an "oval chuck" and its mounting to a regular lathe:

OvalChuck.gif


The "Slide" spins in place, centered on a "boss" that's turned with a Morse taper and held tight to the spindle with threaded rod that passes through the headstock. The "runners" ride on the "cam", which can be offset by different amounts to vary the "oval-ness" of the cuts made in the spinning project (which is attached to the "faceplate").


The remaining 28 pages of the book are dedicated to several projects that can be made with such a chuck:

OvalProjects.jpg



Pretty cool stuff!

Before I get around to my questions, I need to note a couple things:
1) The "bed" of the lathe pictured in the book is a single round tube, as opposed to the parallel, flat ways on most of the lathes I've seen.

2) The "headstock housing" shown in the diagram above is just that ... a wooden box that is built up around the headstock (such that it "hugs" it firmly) and anchored to the lathe stand with clamps.​

HeadstockHousing1.jpg
HeadstockHousing2.jpg



Now for my questions:
A) On a "normal" lathe with flat ways, could the wooden headstock housing be replaced by a stiff piece of L-iron (or similar) ... firmly fastened between the ways, up against the headstock?

B) Would it be reasonable to replace the threaded rod & drilled boss arrangement with a threaded boss ... made with one of Lee Valley's [Lathe Spindle Taps]??

C) Do any of the oval chuck parts seem like they would be better executed in metal than in wood? (And would Travis or Randy be willing to machine them for a fee? :eek:)

D) Would I be better off just looking for a manufactured oval chuck setup? Does anyone make such a thing?
 
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Kerry, I read your story with a lot of interest.
In the first place it looks to me very complicated.
I understand the whole system, how it works as well.
Not any doubt about using wood (hardwood) for such a construction, my own build lathe is build up of hardwood, including my tailstock and tailstock barrel. So my experience with hardwood constructions are good.
In my opinion better than using sheet metal.
I think that it is possible to find a more simple solution, maybe they excist.
 
So my experience with hardwood constructions are good.
In my opinion better than using sheet metal.

Thanks for the feedback, Ad. :thumb:

Well, I was thinking of something more substantial than "sheet metal" ... something fairly hefty indeed. Perhaps 1/8" (3mm) steel or thicker? I figured that if hefty steel can be welded up at right angles (like Stu does all the time) and bolted or otherwise attached to the ways, I could get away without having to build a "headstock housing". That might be tricky if the spindle has little or no overhang away from the headstock. (The bracing material might interfere, and reduce the swing available for the chuck and/or projects.)

I agree with you that nice, dense hardwood should work well for the moving parts. Using metal for the slide and runners would almost require some kind of ball bearing construction, it seems to me.


I think that it is possible to find a more simple solution, maybe they excist.

We can always hope!

Have you ever seen an oval chuck in use? I remember watching an episode of The New Yankee Workshop where Norm visited the Old Schwamb Mill in Arlington, Massachussetts. The (water-wheel-powered?) shop specializes in assembling, turning, and gilding oval picture frames. (Hey - I just found a cool link! Check out "How the Lathes Work" [HERE])

In the show, the operator stood in front of a "whirling dervish" of a workpiece ... but the line along which they applied their turning tools was "quiet".

Anyway, I don't know if there is a much simpler arrangement for the moving parts. I was mostly hoping for a less involved (and stronger?) way to attach it all to the headstock.
 
Thanks for the link! Section 4 of that website contained a reference to an American named Dan Bollinger who has created a LARGE "oval lathe". A quick Google search turned up [THIS PAGE].

Check out the two videos about halfway down that page. Wild!
 
Kerry, thanks for pointing me on the websites, I understand how it's works.
Never saw such a demonstration, to be honest nearly possible here in the Netherlands, not so many wellknowned woodturners here, as in compare with the USA. Most of the woodturners here are anonymous.
Using hardwood would be my chooce, for the sliding construction I would use Shambam, is a linear bearing material, don't have to lubricate this stuff, so it can run dry. Used this material as linear bearing material in rotating tables in my profession many times. Maybe I come in the future to that point to develop such a unit by myself, would love it to brake my brains on that subject.
Do you have serious plans in buying or building this?
With what you came up it seems to me to complicated.
 
Using hardwood would be my chooce, for the sliding construction I would use Shambam, is a linear bearing material, don't have to lubricate this stuff, so it can run dry.

Hmmm ... Shambam? Is that wood known by any other name? It sounds like good stuff ... something like the way Roy Underhill (of "The Woodwright's Shop") describes dogwood. If I remember right, he says they once used it for machine parts, and that it just got smoother and better with wear.


Do you have serious plans in buying or building this?

Did you have to ask the "hard question"? ;) If there's one thing I know about myself, it's that I like to learn things more than I like to do them. But once in a while I surprise myself ... so who knows?


With what you came up it seems to me to complicated.

Maybe if you had 16 pages of David Springett explaining how to do it... :D (Just kidding!)
 
Kerry, please forgive me but... I can see what it do but for the life of me I can't fathom How it do...

Does the piece sling around in an oval motion? What makes it turn in an even concentric circle? I'm stupified here. My Son-I Law is a machinist and I might be able to talk him into some manufacturing if I understood what is actually going on.
 
Bill,

"Sling" is a pretty good word for it. It's a really odd thing to watch!

Let's see if I can demystify this at all. :huh: Referring to the diagram in the first post:
* It's not obvious from the drawing, but the "Bearers" and "Runners" are attached to each other and move together as a unit.

* Suppose that the "Cam" is centered around the spindle (as shown in the drawing). The Bearer/Runner assembly would spin around along with the "Slide", but would not move in relation to it. Result: Regular, circular turnings.

* Now suppose that the Cam is offset horizontally by half an inch in relation to the spindle. The Slide will continue to spin in a centered manner. But because the Bearers ride against the Cam, they (and the Runners and the Faceplate) will be forced to move back and forth on the Slide as the whole thing spins.

With the design shown in the drawing, the offset is entirely in the horizontal direction. So, every time the Bearers are horizontal ... riding on the top and bottom of the Cam ... the Bearers & Runners & Faceplate & Project are effectively centered. But by the time the bearers are vertical, the whole thing is offset by the same half inch as the Cam. On the Project this will show up as an "extra" half inch in opposite directions, creating both elongated halves of the oval.​
Clear as mud?
 
Ad, here's some more info from Mr. Springett's book. (Now that I'm reading it instead of just looking at pictures and captions. :rolleyes:)

He suggests a "dense hardwood" for the Cam (he used lignum vitae) and for the Slide (he used "cooktown ironwood, which was once described as 'organic steel'").

He suggests a "medium hardwood" for the Runners and Bearers (he used oak), saying that "it is better for them to wear out first as they are more easily replaced." Later on he says,
"I chose oak for the runners and bearers because I knew that at one time oak was used as a bearing in water and windmills. The oak was first soaked in oil or fat which, when in use, was slowly released, lubricating the bearing. So if you soak the runners and bearers in oil and allow them to fully dry, it will help your runners and bearers to move more freely."​
You implied that using Shambam would make this step unnecessary, correct?

Speaking of the Cam, he says, "The circular face should show end grain so that the edge is of constant density, providing even wear." (This is probably not news to you, but it wouldn't have occurred to me.... :dunno:)

==============

At this point, I think I'm satisfied about questions C and D in my first post. But I'm still looking for feedback on questions A and B. I think it would be pretty cool to switch from regular- to oval-turning mode by just:
* Clamping a cam holder plate to the lathe bed and

* Spinning a threaded boss onto the spindle. (The rest of the assembly would usually be attached to the Slide, of course, but the Slide would be the only part permanently-mounted to the boss.)​
Does anyone see any obvious "gotchas"?
 
...Does anyone see any obvious "gotchas"?
Just the first few dozen catches as you get the hang of using it. :D

Sounds like an interesting project. I understand the basic concept of how it would work, but still haven't really wrapped my mind around it enough to foresee the potential problems. I suspect having the ability to dial down the speed of your lathe would be pretty important.
 
Kerry, you can compare that ironwood with shambam, only shambam is a technical bearing material, but it's expensive stuff.
But now serious, think on the inside mechanic of a Dutch windmill.
All woodwork, and well oak. They build this mills a couple of hundred years ago, and they still are running.
Wood is stronger than most people think, well you have to make the right choice which wood is the best for using.
Anyway, a nice discussion huh. :thumb:
 
Ok Kerry, I'm still a bit confused, Does the work piece move in and out as it rotates, staying in sequence and keeping the surface at a constant to the cutting tool? :huh:

What speed do you cut?

I am a visual type learner and would love to see a video if there is one out there...
 
Does the work piece move in and out as it rotates, staying in sequence and keeping the surface at a constant to the cutting tool? :huh:

Yep - you got it!


What speed do you cut?
Fairly slow ... max of 500 RPM for smallish stuff?


I am a visual type learner and would love to see a video if there is one out there...
If you're interested in what happens at the tool tip more than the actual mechanism, check out the short demo video at the top of [THIS PAGE]. (There's a longer video about halfway down the page.)
 
Elliptical Turning Video

David Spingett produced a video in 1995 and it shows and explains how to build and use the chuck.It explains why he choose oily wood's for the runners and slides.On first viewing the chuck in action it looks scary, and is pretty noisey, it is only running at 500rpm. When he starts to turn the wood he sets the tool rest so that the tools are cutting centre line,or as he puts it his"point of traquilty". He also advise's only running the chuck for 10 minutes to prevent overheating,during the project he also had to wax the slides and runner's on a regular basis. The video can be purchased at this web site http://www.thegmcgroup.com/item--Elliptical-Turning--GMV-TURNING-16.html. Hope this helps
 
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