LOCK MECHANISM (cont'd)
This post will complete the construction details for the sewing machine work stand. I never expected to be writing instructions for building one and each part took time to prepare. I hope the little-at-a-time nature of this has not frustrated or diminished peoples' interest. After this, I will turn this thread over to others for comments, questions or discussion of their own efforts. I could use some feedback.
Material and Tools
Plywood was used for the two discs. I used 1/2 inch plywood, although 3/8 inch plywood would work as well. The small blocks that hug the swing frame upright were cut from a piece of wood that was on hand. It was about 1 inch by 1/2 inch, but another size could be used. What's important is to keep the back side of the holes clear.
There are several ways to cut the discs. The larger disc is used for locking the swing frame (and sewing machine) in the desired position. The smaller disc is simply for symmetry of the frame. The smaller disc is so simple that I have not detailed it, as I have the larger lock disc.
(Disc Parts)
[ATTACH=CONFIG]525359[/ATTACH]
If you have access to hole saws, such as those I've pictured here, they can do a great job of cutting circles. The drawbacks are that they are very expensive in larger sizes and the larger sizes can "grab" the work as they turn. If you use one you want to rock the hole saw around ever so slightly to favor one spot on the bottom of the saw at a time. This prevents the grabbing from the entire bottom of the hole saw connecting with the work at the same time. The big benefit to this is that the hole saw has a pilot drill that leaves a hole that is perfectly centered.
Select a hole saw that is the correct size on the inside. Normally the plug inside the saw, when done, is thrown away. In this case, this is what you want to keep. Carefully work it out of the hole saw with a small screwdriver.
(Hole Saws)
[ATTACH=CONFIG]525360[/ATTACH]
As I was looking for a sample of the wood I used, I found the piece that I originally cut the discs from, still in the wood scrap bin. The smaller of the two holes was cut with one of the hole saws shown above. The larger circle was cut with a jigsaw, also shown here. I would recommend making a fairly dark circle on the plywood. I used a compass and a ball point pen. Cut a little outside the line, then sand or file down to the line. The outer edges of the discs have no special purpose or requirements, so you can smooth them as much or as little as you like. For the best result, fill and sand the edges before painting.
(Jigsaw)
[ATTACH=CONFIG]525361[/ATTACH]
A diagram of the disc as seen from both sides is shown below. Two small wood blocks keep the disc fixed, relative to the frame upright. Without them, the disc would turn freely and not be able to lock the frame in place. These small blocks may be attached with glue and small screws (not shown in illustration) from the opposite side of the plywood disc, through pre-drilled holes in the disc.
On the side opposite the blocks, which will receive the pins, beveling the holes slightly will help the pin to work more smoothly in each hole.
(Both Sides of Lock Disc)
[ATTACH=CONFIG]525362[/ATTACH]
Lock Pin Operation
A simple metal pin is used for locking the desired position as shown below. Sixteen holes are available for locking with the pin. Each hole should exactly match the hole in the vertical part of the base, allowing the pin to slip into any of them. A hole radius of exactly two inches allows the pin to slip through the holes in the frame upright, when exactly right-side-up or exactly upside-down. The picture below has the frame tipped slightly forward, to better show the pin.
(Lock Pin Closeup)
[ATTACH=CONFIG]525363[/ATTACH]
Hole Positioning
Getting the circles cut is the easy part. The tricky part is getting the holes in the right places. I will suggest a few ways that may be tried, depending on the tools and circumstances you have.
But first, if you haven't decided on it yet, you need to have the pin you want to use. You will drill all of the holes (except the center hole) to fit the pin you select. To get the right size drill bit, you can experiment by drilling a few slightly different sized holes through a scrap of wood to see how the pin fits. A 2 x 4 is thick enough to give a good idea.
Hand Drill - Disc Holes First
A hand drill may be used to drill the holes. I would suggest using the pattern that I posted recently, maybe attaching it to the wood disc with light glue so that it doesn't slip around. I would recommend using small pilot holes to get holes as exactly centered as possible. Then work upward in hole size, in two or three steps, using the previous hole as a pilot. Go slow, letting the drill bit find its own way.
When done, assemble the swing frame with the disc. Place the swing frame into its support base. Then drill into and through the vertical member of the base using one of the disc holes as a guide. If the holes are consistently located, the pin should work in any of them.
Hand Drill - Hole In Vertical First
Another approach is to drill the hole in the vertical member of the base first. This is the approach that I took.
With the drill bit going through the pre-drilled hole in the vertical member, drill each hole in the disc, one by one, rotating the disc and frame as you go. This method may give more accurate radial positioning. But it is a little trickier than it sounds to hold the frame in the correct rotational position, especially if you are working alone. The lock disc pattern that can be printed out (last post) may help to gauge the rotational angle.
A drawback to this method is the possibility of enlarging the hole through the vertical after using it to drill all sixteen holes. Try to not rock the drill off of being perpendicular if you do this.
Drill Press and Jig
A jig can be built which will allow for the most precise drilling of holes. I have made an illustration of how this will work. The disc is held by and rotated around the center hole, allowing more accurate drilling of each hole around the edge. Afterward, the vertical member can be drilled through one of the holes. I intend to use this method on any future discs.
(Drill Press and Jig)
[ATTACH=CONFIG]525366[/ATTACH]
With the lock disc finished, regardless of how you do it, the swing frame of the work stand will stay where you want it to.
There have been other support configurations described earlier in this thread. Most of them would allow the same method of holding the frame still, only changing the position of the hole in the support member. Hanging from 2 x 4 supports, for example, one would drill the hole above the disc, rather than below it. It is a versatile locking mechanism.
Lock Label
I am providing a label for the lock pin, intended to go on the outside surface of the left vertical member. It is positioned just below the lock pin and points to it. I printed it onto photo paper, which seems more like plastic and makes nice labels. The arrow should print out being 4 inches in length. Cut away everywhere that is white, leaving the arrow shape. Any mild glue that is good with plastics can be used.
The label on ours is partly just my own sense of humor and partly for the swatch of color that it adds. But you really don't want to forget the lock pin. In other words... it's optional.
(Lock Label)
[ATTACH=CONFIG]525367[/ATTACH]
Conclusion
I haven't mentioned anything about weight. The metal swing frame (white part) weighs six pounds. The prototype support base (gray part) weighs seven pounds. The miscellaneous hardware for the work stand (clips, clamps, wrenches, etc.) weighs well under a pound. Baseboards vary, but tend to be light due to the fact that most of the wood has been cut away.
Several of you have expressed an interest in having one of these. Over the last few weeks, I have made arrangements so that components of the work stand can be available to others, or even a whole system. If anyone is interested, please send me a private message.
I've enjoyed the process of making the materials for this thread. I hope that this idea can make working on sewing machines safer and easier for others.
John