A SECOND CHANCE FOR A BEST GUESS
To review a little, I'm working on the development of a workstand that holds sewing machines and rotates them easily for restoration and maintenance work. I am trying to find the ideal pivot location for the greatest number of machines.
All machines are a little different in the way they balance. Machines with motors have a little more weight above the bed. One sewing machine might be a little top heavy, another might favor the bottom. Some machines are just about right. The purpose of this effort is to provide the best balance, optimized for the greatest number of machines possible. In other words, maximizing the "just about right" pivot point among the varied and diverse machines.
I've made a different metal swing frame for another workstand that I am currently testing. The second swing frame has a variation in the hole positioning of the uprights.
The new frame and the original are shown below. The pivot shafts have been removed to offer a better view of the uprights. The new frame hasn't even been painted yet.
(Comparing Two Frames)
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The first machine to go into the new frame was our Miracle. It's one of our favorites and has a broken wire inside the pillar. The light doesn't work because of it. There are several signs that the short lamp cord got yanked by a previous owner, which broke the wire to the switch inside the pillar. The Miracle's wiring problem needs a separate post.
In the new frame I have tried two older White Rotarys, the model 43 and the model 11. I also tried a Singer 201. I'm just getting started. I have many more machines to try, but already have the sense that this modification will optimize balance for a wider variety of machines. I like it better.
The original swing frame pivot point is 3 inches above the sewing machine bed. The new frame offsets the holes for the pivot point down half an inch, to 2-1/2 inches above the bed.
WHAT WENT INTO MY FIRST GUESS
When I started this thread, the first prototype workstand was already complete. As a result, I had no pictures of the building of it. Building another one gives me the chance to post pictures of some of the steps in making it. And I'm posting some of the research that went into the development of the first workstand too, for completeness of documentation.
Before building the fist workstand, I didn't know very much about the measurements and mounting conventions of the many kinds of sewing machines. And what research I did showed no information on the center of gravity of sewing machines.
I wondered if it was a good idea. Any such workstand device would need to be versatile. If a separate baseboard was needed for every kind of sewing machine, the workstand idea wasn't practical. And, if center of gravity varied too widely, adjustment might become cumbersome. These concerns made me hesitant to actually build the first workstand without knowing more.
Having a rather extensive variety of sewing machines as a resource, I set about collecting measurements. In addition to center of gravity, weight and bed measurements for mounting, I gathered around forty other measurements and specifications, too.
My Setup For Measuring Center of Gravity
I thought to myself that if I could lay a machine down, either on its back or its face, onto a flat board, then the weight distribution of the machine would be transmitted into that board. A flat board can be easily teeter-tottered on two points to determine balance. Where it balances is the vertical center of gravity.
I made a board with inch markings up each side and a baseline to align the bed of the machine. Aligning the bed of the machine with the baseline on the board is crucial.
(Balance Board)
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The machine is propped up so that the bed is at a right angle to the balance board. Gentle padding protects the machine.
(Propped Up)
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The pointed blocks, front and back, allow balancing the board by trial and error by repositioning it on the points. It may look a bit precarious, but it really isn't. Not seen in the photo below are two blocks under each side of the board, which only allow a small amount of rocking back and forth. That prevents possible mishaps in the trial and error process of finding the balance point.
(Center Of Gravity)
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I did this for each unique kind of machine I could find. From old black machines to the newer plastic ones, the best overview of the machines I could get. For each machine I made a data sheet of information and measurements that I gathered.
(Data Sheet)
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I developed a system of defining measurements that is shown in the following two illustrations. Measurements from the data sheets was entered into a computer for study and comparison.
(Sewing Machine Measurements 1)
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(Sewing Machine Measurements 2)
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From the data collected I learned two important things.
1) The center of gravity among sewing machines varies up to one and a half inches, possibly more. Finding the ideal spot for the most machines might be tricky.
2) I saw definite patterns in the mounting of the machines. I realized that with as few as four or five baseboards, almost any machine commonly encountered could be accommodated.
Based on number 2 above, I decided it was worth it to go ahead and build the prototype workstand. And then try to figure out number 1.
Which brings us full circle to the top of this post, a second best guess in fine tuning the balance of the swing frame.
And for perspective, these balancing matters are minor. Even what I would call "out of balance" can usually be rotated with one finger. Just pushing a little harder.
More on the new workstand soon.
John