Monday, August 27, 2007

Part 3: Lowe's Tool Case Wristwatch Conversion

The next problem was how to make the slots in the horizontal and vertical dividers so they could be latticed into a grid. A slot half-way up from the bottom on one and half-way down from the top on another where it intersects will allow them to form a lattice. The Plexiglas is 1/8th inch thick, therefore the slots should be just slightly wider than that (so they don't bind during assembly).

Also needed to decide which should have the upper slots and which should have the lower ones. Sounds trivial, but it can affect structural strength. The two overwhelmingly common orientations for the tool case are resting on its bottom or resting on its back (when closed). When resting on its bottom, little if any force would be exerted on the dividers. Not so when resting on its back. The weight of the watch in each pocket is resting on a horizontal divider. Since the watches will be at the tops of the pockets, their weight will be more on the top half of the horizontal dividers. Very little force from the weight of the watches will ever be exerted on the vertical dividers in normal use. Therefore, the strongest latticing would have the slots in the upper half on the vertical dividers and on the bottom half of the horizontal dividers. Forces tending to flex the upper portion of a horizontal divider at the back of a pocket will push it against the slots on the two vertical ones on each side attempting to compress them against the back of the case, and the dividers are much less likely to break, especially if the case is dropped several inches from its handle during transport.

Plexiglas, like most rigid plastics and other brittle materials can crack at sharp corners, the crack migrating from the corner outward. This is why the corners are almost always radiused slightly as it tends to inhibit cracking. The slots are only going to be just over 1/8th inch wide, but they'll be just over 1-3/8 inches long. Easy to cut each side of the slot, but not so easy to cut across it at the end, and the corners there should be radius. The solution? Kill two birds with one stone. Drill a hole 5/32 inch in diameter, just a tad wider than the slot needs to be, centered on where the slot needs to end. This provides a radius around the entire end, and eliminates the need to cut across the end. After the holes are drilled, straight cuts using the band saw down each side of the slot to the hole will create the slots needed. Significant time was spent scribing the Plexiglas for the hole centers, and the slot sides before doing any drilling or cutting. Making the hole and the slots just a hair wider than the need to be allows for a little slop in drilling and cutting, and ensure no stress is placed on the sides of a slot when assembled, something that can also precipitate a crack forming eventually at the end of the slot. Whatever slop or looseness there is will be hidden and tightened up by complete assembly along with the padding and upholstering; provided it isn't too sloppy.

Now for the drilling and on to the drill press. If you have a variable speed drill press, its RPM should always be set up for the drill diameter and the material being drilled. Here's the table under the sheave and belt cover on mine. Had to move the belt to another set of sheaves - it was set at a much too low RPM for a small drill diameter and plastics. Extremely important for safety! Ensure a machine with a huge motor on it is UNPLUGGED before doing things like this. The belt in a sheave can take the end of a finger off in the blink of an eye, and not even slow down.

Next was setting the depth of the drill. Notice the wood table on the drill press. Actually, it's 3/4 inch thick and there's a cast iron table under that. Reason for the wood? If the table is accidentally drilled into, the wood can be replaced much more easily for much fewer $$$ than a cast iron one. Even so, drill presses have a stop to prevent that (if it's used properly). A piece of scrap 1x6 will serve as the "backstop" underneath the Plexiglas strips and the drill depth is set to no more than half its thickness.

Now we can start drilling the holes and the score lines can be seen.
There were many holes to drill, but it was finally finished.
Back to the band saw to start cutting the sides of the slots. First slot was done, a lot more to go! The jury rigged fence used to cut all the strips of Plexiglas the same width is now gone. Additional care is needed now to not break any of them.

Just to make certain everything is working as planned, I cut the smaller right side dividers first, and assembled them on the band saw table. Yep, they fit together just as planned.

But would they fit inside the case as planned? Another Happy Day!
And how does my biggest watch look? Is there enough space around it, or were the dimensions botched? Looks like there's just enough; didn't want the watches rattling around either. Looks like I got it right. On to cuttting all the remaining slots in the rest of the dividers.

Finally done! Here is the lattice of dividers, assembled now inside the case, along with my largest watch (Tissot Seastar 1000) in one of the pockets. Doesn't have to look pretty, just has to fit together and be strong enough. The padding and upholstering with Ultra-Suede will cover it completely.
And a close-up of the spacing around the Tissot. Looks like just enough space around all four sides for the padding and upholstering, and the watch will be slightly snug into the padding to keep it from rattling around during transport.
The next task was cutting foam padding and gluing it onto the dividers.

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