Take a bottle-screw, and have it push the spreader out or pull it in.  In order to prevent the rather drastic change in effective spreader length as the "V" angle changes, instead of having a fixed pivot for the spreader, allow the pivot to slide in or out as well, but at an angle to the action of the bottle-screw.  The angle needs to be about 30 degrees for when the pivot slides as well.  Previously, the angle needed to be about 45 degrees when the pivot remained fixed but the spreader arm slid along the pivot (see the first "Adjustable spreader" page.)

With the dimensions shown, the spreader "V" changes by about 15 degrees from full in to full out, but the effective spreader length hardly changes at all.  The shrouds attach at the forward end of the spreader.  (Yes, I'm working on a spreadsheet which will allow you to calculate the exact "effective" length changes, if you'd like that, along with an exact range of "V" angles from "in" to "out".  It, erm, does involve some pretty awkward geometry...)

I've milled a 3 mm thick aluminium plate with slots.  For one spreader, the two slots run at an angle of about 30 degrees to each other.  This is the top view.  The bottle-screw is in fact pinned to the spreader plate, after adjustment, by setting a screw through its hole into a threaded hole underneath it in the plate.

The bottle screw controls the spreader arms.  As the bottle screw is screwed in or out, it pulls the spreader arm in or pushes it out along the track of the horizontal slots.  The spreader arm is attached to the second, angled slot, and slides along this slot as it moves.

The net effect is that, as the spreader arms are pushed out by the bottle screw, their overall effective length remains roughly constant while they form a deeper "V".

2005-12-18

©2024 Lester Gilbert