Category: Machine Shop

Having flycut the acrylic panels to the proper width, I had to cut them to the proper length, too. This picture shows the lashup I used to hold them down during the operation…

The brown bar sticking out to the left is one of the bookshelf struts that held the toolmaker’s vises down during the flycutting; it’s now secured to the Sherline table with a T-nut. A vise clamped to the bar serves as an end stop for the panels.

A pair of brass tubes around studs serve as locating pins. To get the things lined up:

• Loosely clamp a panel down atop a spacing plate
• Push it back against the loose tubes: crudely parallel to X axis
• Snug the clamps
• Align the panel to the X axis using the laser
• Push the tubes against the panel
• Tighten their nuts

Crude, but good enough for this purpose.

Then a bit of manual CNC to shave off the end. Half-inch mill, 1500 rpm, 150 mm/min, more-or-less 0.5 mm cuts. The panels don’t have to be any exact length, as long as the clock circuit boards fit inside, but the ends must be perpendicular and smooth for good gluing.

The exact part will come when I rabbet the side panels…

The side panel setup was much simpler: same brass posts, same spacer, no need for the long bar hanging off to the left.

The Totally Featureless Clock will have a black acrylic case with a Graylite Lexan faceplate. The top & bottom panels are 11.75 inches long, which is much too large for the Sherline’s 9-inch maximum X travel.

Fortunately, in this case I can cheat.

This setup cut the panels to the proper width. A pair of parallel blocks, made from some mysterious glass-like material and ground very nicely flat, support the panel just over the body of the four toolmaker’s vises lined up along the tooling plate. I drilled the brown bookshelf rails to match the tooling plate and secured them with 10-32 studs.

The front rail secures the vise bodies to the tooling plate; they’re aligned parallel to the X axis by the simple expedient of laying a parallel along the back edge and matching that to the tooling plate. No real precision is in order here; the flycut is across the whole top edge.

The rear rail holds the movable vise jaws down; they tend to rise up just slightly when tightened, but the difference amounts to barely enough to release pressure on the parallel blocks. Not enough to matter, as it turned out.

The general notion is to flycut about 2/3 of the length of the panel, then slide it far enough to cut the remainder. Flip it over and flycut the other side the same way.

About 1000 rpm and 150 mm /min, cutting 0.5 mm or so on each pass.

This worked surprisingly well. I expected to find a bow in the middle due to an uneven bandsaw cut on the initial downward side, but it was all good; evidently the blocks were wide enough to average things out.

The joint where the two cuts meet turns out to be visible, but barely detectable with a fingernail: entirely suitable for this application. I’ll hit the sides with  sandpaper on a sheet of plate glass before bonding them  to the faceplate.

Flycutting the end panels was much simpler: one pass clears their entire length. I moved the clamping rails to simplify the whole process; turned out that clamping the movable jaw didn’t really gain very much at all while complexicating the slide-the-stock process beyond belief.

Overall, the width varies by about two mils along the length of the long panels and they’re perfectly straight as measured against a surface plate. Definitely close enough!