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    lion mclionhead • 2 days ago • 0 comments

    Cord locks have been a key part of sandals, lion clothing & truck attachments but are too big & don't grip enough. 

    The problem with spring loaded cord locks is they don't provide enough grip.  They might as well not have a spring for the amount of grip.  It's normally not necessary to release the spring.

    Disappointment with spring loaded cord locks got lions thinking more about a permanent system.  Previous ideas centered on passing string through a TPU cylinder that was welded closed.  It would provide enough compression to keep the string in place while still allowing it to move with enough force.

    With a permanent system, it wouldn't be possible to take the string out & reinsert it.  For temporary applications, there could be a larger device.  The smallest device would be for clothing & sandals, so it could possibly be permanent.  The temporary design could be a larger thing which permanently attached to 1 end of the string & created temporary friction in the other end of the string.

    The 1st attempt was this thing with 3 identical panels.  The 3 panels slide next to each other to grip the string.  They're held in place with rivets.  This was 8x16x18mm, a bit too big.

    Cord locks began with the humble bread clip.  The bread clip was actually invented in the 1950's.  They're not optimized to keep string from sliding.  They're optimized to keep bags closed.  They're not secure enough.

    There are variations on the clothes pin which are too big.

    Confirmed a helical bread clip doesn't retain the string.

    There was the idea of a pair of bread clips which rotated to lock the string in.  Then, they're welded together.

    2 bread clips welded in opposing directions worked well.  

    It's not removable so it needs to be PETG to withstand drying.  The piece has to be big enough for the layers to adhere.  Printing at 20mm/s 260C is also necessary for PETG to adhere.  Found radius increments of .25mm to be required to get the right tension.  They need to be tight enough to stay on but loose enough to not shred the string.  It's a real pain to dial this in so it might be easier to print an assortment.

    Clothing drawstrings came in at a 2.25-2.75mm radius.

    A removable design was based on the string's own tension keeping the bread clips in place.  This requires more manual dexterity than chinese cord locks.  There seems to be a limit to how tight nylon string can get, with a finite amount of manual dexterity.  Making the cylinders longer might increase the grip.

    The idea of twisting something to loosen & tighten it appeals.