Tuesday, July 9, 2013

Double Curved Handwheels

There is something lacking in many modern mechanical components. The plain utilitarian aspect is partly driven by cost considerations and manufacturing optimization practices. Why do we fall in love with old machinery and equipment? Many old machines are visually pleasing as if the designers really cared that the visual impact of the machine was an attribute worth investing in. Sadly most of the demise of art in machinery is cost and profit driven. We can all appreciate nice looking machines but are voting is generally dictated by our checkbooks.

I was talking to an engineer friend of mine on this very subject and he had a pretty good line of reasoning worth sharing. Before the invention of automatic machine tools many machine parts were cast in steel or iron. All of these parts had to have foundry patterns made for them at some point. There is a  big fundamental difference in the manufacture of something like a machine hand wheel that is cast and one that is machined. The hand wheel is just a simple example of the potential for adding some pleasing aesthetics to an otherwise mundane part.

When a part is cast the pattenmaker makes the pattern one time. This one time effort yields thousands of parts with all the features and embellishments the patternmaker puts in. The fundamental effort to produce the part is the same for all the parts cast from that pattern. Whatever the extra cost for the time the patternmaker spent to make the part beautiful is spread over the cost of the thousands of parts that follow.

The modernization of some of these manufacturing processes has eliminated most of this decorative aesthetic in machine parts. Modern generally means spartan, or clean crisp simplified lines. Is it better? I like the modern style when its well executed with thought behind it throughout the article or machine.

But what I wanted to talk about in this article is something that old time machinery buffs all over can agree on. Who doesn't like a nice old time cast iron hand wheel or pulley? In particular one with double curved spokes. There is something cool about the curved arms and legs of a simple article like a wheel that give it life at a basic level.
A simple valve handle with double curved spokes. It looks poised to turn all by itself. All the operator has to do is give it a little nudge.
 These pulleys were at a recent flea market for $400 each when I passed them in the morning. When I walked by a couple of hours later they were both gone. Somebody made something cool out of them.
And we finally come to the actual subject of the article. This is a handwheel for a fine arts etching press. The hand wheel is the signature part of a high end etching press. The large wheel diameter gives the operator fine control of the printing process with low human power input. Most presses have some kind of gear reduction to further reduce the force on the operator. A few presses have hand wheels in the five foot diameter range.
About six years ago I built a small etching press for my wife to print small etching plates with. It was really a stop gap for building her a larger press. Well the time has come to get moving on the big project for real. I have laid the groundwork for building the press in my home shop. A few items like the lathe were selected on their ability to produce the needed parts for the machine. A crane and forklift were added for good measure and spine health. I figured I might as well start with some of the more complicated bits of the machine. The hand wheel and drive system are first on the list.

I wrote a blog article and posted a YouTube video of the heart of the system. The press I'm currently working on will be larger than the French American Tool press in the picture above with a much more interesting handwheel. The current design projections put the final weight around 3500 lbs to put the project in perspective.
Here is the layout of the handwheel in Solidworks. My goal was to try to duplicate the graceful tapering curves like we see in old cast iron handwheels. I set the Solidworks sketch up and drove some of the proportions with equations to allow me to create handwheels of almost any diameter by changing one number. The layout is interesting in how the arc tangencies are created. If folks are interested I will do a separate article describing how to do it. Post a comment if this is something you would like to see.
Here is the Solidworks model of the handwheel sub assembly and Wabble drive for the press. You can see the motif of the press is the curved spokes. The arms of the Wabble output follow the same layout.
Here is the beginnings of the handwheel for the Ox tool etching press from the layout above. Looks kinda dinky right?
For those of you that have been following the steady rest built on YouTube you can get a sense of scale now. The handwheel is four feet in diameter and and inch and a half thick. The spokes are five eighths thick. When I had the handwheel sections burned out by Nowell Steel in Antioch. I threw in the steady rest profile while they were cutting inch and a half plate. I need the steady rest to machine the large solid rolls for the press. The steady rest that came with the lathe can only handle seven point eight inches in diameter so I had to build a larger one.
I was worried about the open C shape moving around when they oxy fuel burned the profile so I had it cut larger to allow me to machine the profile accurately. I don't want the rim to run out much so it will have to be carefully put together. Here I am preparing the blank for machining. I weld it to a backing bar that is then clamped in the vise allowing me full access around the profile with a tool.
Even in steel not much weld is required. You just have to get it in the right place and not cut it away!
Here is one segment after profiling. I used a one inch diameter high speed cobalt fine pitch roughing end mill made by YG tools that I cant say enough good things about. Two passes three quarters deep and approximately a quarter inch on the periphery. Three hundred fifty rpm at six inches per minute feedrate. One tool removed maybe forty pounds of material and is still fresh as a daisy.
Here is the finish left by the end mill. I have cut off the backing bar and smoothed the welds. Eventually the rim will be rounded off so it feels better in the hand. These joints will be weld prepped and then blended for an invisible seam.
In this shot you see the wood sample I gave the "customer" for approval of grip size and rounding. I have some serious grinding in my not too distant future.
All five segments sitting together on the weld table. It measures right on the forty eight inches. There will be notches cut at the rim joints to insert the spokes to make a rabbet joint. Next will be an assembly fixture to make sure the segments are aligned in as good a circle as they can be for welding.

Eyeballing the center hub material for the handwheel at one of my favorite scrap yards Bataeff Salvage in Santa Rosa.

Thanks for looking.

26 comments:

  1. Hi Tom,

    I've been wondering what your "secret project" spousal comission would be. Very cool, this is going to be great to observe!

    I have a couple comments to add about the pattern making trade as it applies to machinery and design. My personal background is pattern making and my hobby is furniture making. As I understand it, these two spheres overlap in some important ways. Back in the heat of the industrial revolution, the natural candidates for pattern making were the highly-skilled joiners and cabinet makers. These folkes were trained in elements of not only technical know-how but design, specifically the Classical Order. This sensibility had great overlap with the design asthetics of early machinery. The American Precision Museum has some nice old machines illustrating this.

    http://www.americanprecision.org/2011-12-09-21-27-05

    As the pattern making trade came into its own, so to speak, the old furniture and architectural sensibilities became obsolete. The Classical Order no longer served a purpose in industry. The function/cost equation trumped any percieved "antiquated" design decisions. the ironic thing is that the Modernists of the 20th century quoted industry and machines as their resoning for disregarding the centuries-old Classical Order in their buildings and arts.

    So, all of the above said, we Post-Moderns love to drool over the asthetics of old machines and say things like "She has soul." and "Look at the lines on her!"

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    Replies
    1. Hi James,

      Thanks for the excellent reply. It actually fills in some of the connections I was trying to articulate in a much clearer way. There seems to be some differences between the organic trades (wood) and many of the metal working trades. Metal casting and patternmaking appears to be an area where they came together with pleasing results. I fear that that modern culture is so cost conscious that they will never be willing to pay for "higher art". There is always a small sector willing to ignore a higher entry cost to possess the more pleasing and finely crafted items. Sadly there is not enough of this work to satisfy and support all the craftspeople that love to do it.

      Kind regards,

      Tom Lipton

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  2. Tom,

    This looks like it's going to be a fantastic project.

    I have been a solidworks user for a few years now and enjoy seeing how other people create part/sketch relations, so I am officially casting my vote for some clues on how you modeled this handwheel.

    Justin

    P.S. Between your book, blog, and videos you've released huge amounts of useful and interesting information. A big thanks from a huge fan down in Texas!

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    1. This comment has been removed by a blog administrator.

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  3. Hi Justin,

    Thanks for the vote and comment. One of the tricks I use was learned from an engineer friend that was a SW beta tester when it first came out in 95/97? I create a base sketch that stays at the top of the tree. Subsequent sketches use converted geometry from the base sketch for their elements. Its a subtle but powerful technique. It allows easy top level changes without the hassle of conflict resolution. Try it on your next part.

    Best,

    Tom Lipton

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  4. Always Fascinating to read you Blog!! Full of information... Amazed at how much I learn each time!! :-) CHEERS!!!
    CTM -- http://ctmprojectsblog.wordpress.com
    :-)

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  5. Hi Charles,

    Thanks for the comment and words of encouragement. I took a look at your blog and you have a project there that is something I have been thinking about. Where my shop is I don't have natural gas for heating water or any other use. What I do have is a natural alley between two tall buildings that channels the wind right in front of the shop. I have been thinking about a wind powered water heater booster. The wind runs in two directions depending on what time of the year so a vertical axis wind turbine would be a natural. I will definitely be reading more on your blog.

    Regards,

    Tom Lipton

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  6. Tom,
    Great post as always. I will add another vote to see some of your Solidworks know how. I've just started using the program a few weeks ago. I've found some of the fundamentals hard to wrap my head around, as I come from an AutoCAD (for architectural drawings) background.

    I also just bought your book, can't wait to see it delivered today.

    Cheers,
    Kent

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  7. Hi Kent,

    Thanks for the vote. Like you I started with AutoCAD and migrated to SW. Still use the ACAD for certain kinds of layouts and geometry. You can never have too many tools in your box.

    Regards,

    Tom Lipton

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  8. I always thought the curves were there for necessity...
    http://www.model-engineer.co.uk/forums/postings.asp?th=54280
    http://www.homemodelenginemachinist.com/f23/curved-flywheel-spokes-3279/

    Robert

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  9. Hi Robert,

    You are correct, but it is not a hard rule. The curves help relieve some of the stress from the casting shrinkage. However there are many examples of straight spoked cast handwheels. In the picture above of the scrap yard you can see a few straight spoked examples in the background. My point in the article was that while addressing engineering problems like casting shrinkage these old time patternmakers made things look more pleasing to the eye while satisfying the basic functional needs of the design. In modern times this has been cast aside (pun intended) in favor of stark utilitarian, and boring lines and shapes. Why do we love the Italian designers? They still have the curve and flow in their design tool kits. Thanks for the comment and good links.

    Regards,

    Tom Lipton

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  10. Hi Casper,

    Thanks for the comment. Check out my YouTube channel to see the finished project.

    Cheers,

    Tom

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  11. That's a cool project. I've been looking for those old cast iron handwheels to replace all the too small aluminum and plastic handwheels on my machinery. My manual combo shear/brake/roll came with a long bar with a handle on the end for a crank. I really want a gear reduction and a big handwheel to operate it.

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    1. Hi Brian,

      Thanks for the comment. Modern handwheels sure lack the nice flowing visuals of the early cast handwheels. I am familiar with the blasted handle on those combo machines. Designed by satan.

      All the best,

      Tom

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  12. The reason for curved spokes in a hand wheel is so the spoke will shrink the same in length that the diameter of the rim will change. To calculate the change in diameter you have to calculate the circumference and multiply that by your shrink factor then recalculate to determine the cast diameter. Once you know the change in diameter you then know that the spokes must be long enough to shrink that same amount. since that length is longer than the radius you have a choice of an "S" for each spoke or an "S" formed by a pair of opposing spokes the reason the spokes are tapered is so they cool in a desired way when cast to avoid shrink tears. On small hand wheels, particularly in aluminum this is not as important.

    I stopped by to admire the etching press you made as that is my next project. Any advise?

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  13. Hi Unk,

    Go big or go home. You will only want to build one of them.

    Cheers,

    Tom

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  14. As an apprentice I had the good fortune to be involved in the scrapping of an old steam winding engine on a mine. The workmanship and finish on that old machinery brought joy to my soul. I believe that level of craftsmanship contributed to the sense of pride that the old-timers had in caring for their machinery.
    Sadly, it all ended up in the melting pots, sacrificed to the gods of progress.
    Regards,
    Russell Dold in Germiston, South Africa

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    Replies
    1. I probably would have hauled home a few hundred pounds of that engine. Thanks for the comment.

      Cheers,

      Tom

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  15. Another vote on your SW drawing details. I would love to learn!

    Thanks,
    -Justin

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    Replies
    1. Tom, I made an attempt to copy you sketch. Got an email address I can send it to and you can check my work? Loving your book. Just picked it up this week. It is hard to put down.

      Thanks,
      -Justin

      Delete
  16. Another vote on your SW drawing details. I would love to learn!

    Thanks,
    -Justin

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    Replies
    1. Hi Justin,

      I don't post my email address on the blog for obvious reasons. The bots are constantly scanning these for useful and personal information. If you follow my oxtoolco Youtube channel you know where my email address is.

      Best,

      Tom

      Delete
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