The extension surfaces on the Sears sewing table in the Basement Sewing Room unfold from the top, leaving the hinges exposed:
Alas, quilts snag on the squared-off ends of the hinges, a situation that is not to be tolerated…
This protective cap isn’t as small as we’d like, but it must be that thick to cover the hinge, that long to cover the squared-off ends, and that wide for symmetry:
Two neodymium magnets fit in the holes and secure the cover to the all-steel “bronzed” hinges:
We’re not sure how well that will work in the long term, but early returns seem promising.
It could be slightly narrower left-to-right and maybe fewer vertices should be oriented differently.
The OpenSCAD source code as a GitHub gist:
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| // Vacuum Tube LED Lights | |
| // Ed Nisley KE4ZNU January 2016 | |
| //- Extrusion parameters must match reality! | |
| ThreadThick = 0.20; | |
| ThreadWidth = 0.40; | |
| HoleWindage = 0.2; | |
| Protrusion = 0.1; // make holes end cleanly | |
| inch = 25.4; | |
| function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit); | |
| //---------------------- | |
| // Dimensions | |
| Hinge = [7.0,52.0,6.0]; | |
| TopThick = 3*ThreadThick; | |
| PlateThick = Hinge[2] + TopThick; | |
| NumSides = 8*4; | |
| //---------------------- | |
| // Useful routines | |
| module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes | |
| Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2); | |
| FixDia = Dia / cos(180/Sides); | |
| cylinder(r=(FixDia + HoleWindage)/2,h=Height,$fn=Sides); | |
| } | |
| //---------------------- | |
| // Build it | |
| difference() { | |
| hull() | |
| for (a=[0:7]) | |
| rotate(a*360/8) | |
| translate([Hinge[1]/2,0,0]) | |
| scale([1.5,1.5,1]) | |
| sphere(r=PlateThick,$fn=NumSides); | |
| hull() | |
| for (k=[-1,1]) | |
| translate([0,Hinge[1]/2,k*(Hinge[2] - Hinge[0]/2)]) | |
| rotate([90,0,0]) rotate(180/8) | |
| PolyCyl(Hinge[0],Hinge[1],8); | |
| for (i=[-1,1]) | |
| translate([i*Hinge[1]/2,0,-Protrusion]) | |
| PolyCyl(4.8,2.5 + Protrusion,8); | |
| translate([0,0,-PlateThick]) | |
| cube(2*[Hinge[1],Hinge[1],PlateThick],center=true); | |
| } | |
The Smell of Molten Projects in the Morning 
Alternative #1) Is it possible to flip the hinge, countersink the holes, and re-install?
Alternative #2) Replace with Butler hinges.
http://www.ebay.com/itm/like/180900885522
Alas, the Butler hinges don’t fold “the right way”, either. The hinge must rotate 180° from open to closed as the table extension stows atop the base, so the hinge axis must sit above the table surface to make that work.
We just got a new-to-us table with much larger extensions that fold 90° downward along the sides: the hinge axis sits under the extension, inset on the bottom surface. The extensions have awkward legs (actually, planks) on their ends that fold 90° downward to the floor from more hinges on the bottom.
I could put the hinges on the bottom of these extensions, but only after extensive router work and delicate carpentry on the table base. If the plastic caps aren’t too awful, they’ll be Good Enough.
maybe fewer vertices should be oriented differently
I’m having trouble figuring out what you mean here.
The overall shape comes from a hull around eight spheres, whacked in half across their common equator, because I figured a straight ramp from table to top would produce a too-acute bottom edge. However, I assumed fabric would slide up-and-over the ball at each vertex more readily than up a flat side, so the overall shape puts vertexes in all the directions Mary moves the fabric.
If I’m right about the desirability of pointiness, then only four vertexes (at north / south / east / west) may work better than that shapely octagon. Conversely, if I’m wrong, they’d be aligned with the hinge axis at the NE / NW / SE / SW corners. If all else fails, we’ll try a rounded hockey puck.
The hinge surface sits slightly recessed into the table. Drat!
Nothing like a field test to show why hell hath no fury like that of my unjustified assumptions…
I think the hinge you want is called a “sewing machine hinge”, the butler hinges are for folding wings on a table top that fold down, whereas the sewing machine hinge is designed to fold up.
I am using them on a folding chair woodworking project (a chair that folds into a step ladder), I got mine from Rockler:
http://www.rockler.com/twin-pin-sewing-machine-hinges-select-option
This hinge has 2 barrels, so it can fold 180 flush and when open is flush with the surface of the table top.
Daniel is right, you have to mortise the top to fit the mechanism, which takes a few moments with a sharp chisel.
Exactly those!
I wonder why Sears didn’t use real Sewing Table Hinges, instead of the Butler Tray Hinges? Cost, most likely.
The existing hinges are 2×3.5 inches overall, with four screws on each plate; I poked around a bit and didn’t find anything larger than 1-3/16×2-3/4 with three holes. They require filler that wouldn’t go well in this application, even if I reinforced the holes and got it glass-smooth on the top. [grin]
For future reference: http://buildingdesks.blogspot.com/2011/12/sewing-machine-table-hinge-upgrade.html
If all else fails, I have a Sherline metalworking project!
Thanks for the pointer…