11.19.2011

modular musings, part 2 (mechanicals)

The enemy is variation. Avoid dimensional softwood lumber for portable applications; continual changes in temperature and humidity wreak havoc with it. You may be well served to seal any wood to limit the effects of moisture (something like sanding sealer or shellac, perhaps); beware of acrylic coatings, the painted surfaces can stick to each other after being clamped together.

Goals are fast and repeatable setup, and optimal strength-to-weight ratio. Heading straight to "lightweight" can lead to fragile construction. It won't matter if it's light if the first time you clamp it to another module the endplates flex or rip right off, or you drop it and it turns into a pile of kindling.

Track expansion. Attach rails firmly above the interface (soldered to PCB tie plate or brass screws), and allow for rail gaps somehwere inside the MODULE confines.

PC board tie plates (Free-mo)
http://www.bnm-hobbies.com/store/index.php?main_page=product_info&cPath=20_21&products_id=19

Thought points:
- (Simon's) profile blocks to ensure consistent rail height at each joint.
- A single socket directly below the main line. Fit pin as needed to align to next section or module.
- Minimum number of tracks crossing any joint.
- Solid vertical member under the subroadbed itself to prevent sagging.
- Track must be 90°to both the horizontal and vertical planes at each INTERFACE.
(an INTERFACE differs from a SECTION JOINT, as a MODULE differs from a SECTION)
- Maple Leaf Mafia aluminium CNC frames

Avoid using porous material in the subroadbed, especially if you use the water soluble method of applying ballast or scenery near the track. Absorbed water tends to swell and distort the material. Using soap or alcohol to cut surface tension just makes it easier for the water to get in.

90° ends are critical everywhere. Setup & check your chop saw carefully. Verify the alignment with a proper try square and the cut-flip-match method of ensuring 90°. Cut matching sides and ends in pairs (at least). Mark what they are for. Clamp up and assemble frame pieces on a flat surface. Check 90° Horiz & Vert again. Get the frame dead square! Apply top and/or corner gussets. Route off edges of top with laminate trimmer bit (if it has a flat deck).

The primary mechanical goal is to ensure accurate track alignment across the joints. The secondary goal is an even fascia for the sake of appearance. Scenic continuity can be accomplished through application of loose material along the joint after assembly. Keep some spice tins or shaker bottles of each type of material handy in your toolbox for shows. Accuracy can be a problem if many people are making their own modules; everyone executes cutting and fitting tasks at their own skill level.

Low density self-adhesive foam weatherstrip can be used to take up the eventual (hopefully minimal) gapping at the joints. This stops loose scenic material placed on the joint for exhibition from falling through to the floor. Do not use thick or high density foam, you don't want to make the gap bigger (foam tape the perimiter of the end board to create even compression).

Pierre Oliver, master carpenter and owner of Elgin Car Shops, recommends cabinet grade plywood ripped to appropriate widths for all framing members. There are no voids or inclusions, and the multiple plies offer greater dimensional stability.

Creating the boards: Take the ripped plywood and make a frame. Add braces across the width. Stanley corner brackets or gussets should be applied to ensure squareness and add screw locations. Keep clamping & cable area at MODULE and SECTION joints clear.

Fastening the MODULES or SECTIONS together: Quik-Grip clamps. Try to clamp immediately below the track itself. C-clamps need more clearance for the lever arm. Loose bolts, washers & wing nuts - adds to part count and things that can go missing. T-nuts (or threaded inserts) and furniture bolts can strip out or seize at inopportune times.

quick-attach adjustable legs - single pipe with foot, interchangable, retained (bayonet, squeeze fit, spring pin)

http://home.online.no/~bjornrl/modulebuild.htm

Lee Valley dowel pins, leg feet:
http://www.leevalley.com/en/hardware/page.aspx?p=40145&cat=3,43586,43588,40145
http://www.leevalley.com/en/hardware/page.aspx?p=41865&cat=3,40993,41283

patternmakers pins, etc.:
http://www.stationroadbaseboards.co.uk/menu_fittings.htm

make an accurate drilling jig, use drill bushings, store safely:
http://carrlane.com/catalog/index.cfm/27025071F0B221118070C1C512D020609090C0015482013180B041D1E173C3B285351435E

More thought points:
- dropping the egg crate example
- French cleat vs ledger board
- protect root of cleat (cover/scraper?)
- legs/supports
- tool-less height adjustments
- height adjustment at the top of the leg
- pads to protect floors (gymnasiums, churches, etc.)
- crowd barriers
- concrete post bases + ABS 'tees' with rope on a spindle (Jim)

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