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From: George Huxtable (no email)
Date: Tue Jul 15 2003 - 10:48:32 EDT
Doug Royer said-
Over the weekend I
> bought a piece of black plexiglass 7x7 in.square,3/8 in. thick for $12.00
> at Ridout Plastics(any plastics store should have it).Drilled and tapped
> the plexiglass in each corner for a 6-32 machine bolt 1.25 in. long.Got 2
> more liquid levels and useing Dow RTV 3145 bonded the levels to the
> plexiglass>
Bruce Stark replied-
Only difference is, I like to level with three screws, one in the middle of a
>side. Also like to be able to reverse the level to check its accuracy.
=====================
I suggest that the optimum layout is somewhere between Doug's and Bruce's.
Four adjusting screws, at the corners, as Doug suggests, would be a
disaster, in my view. The assembly would become a device for warping
plastic plates; the last thing that anyone wants!
Bruce is correct when he suggests three screws, but his proposed layout is
not optimum. Instead, I suggest it would be best to use just three of
Doug's four corner-holes, in an "L" configuration. The screw at the
meeting-place of the two arms of the L does not need to adjust. The other
two screws will tilt the plate quite independently, in two directions at
right-angles, and the spirit-level(s) should be aligned with those two
directions.
I agree with Bruce that the spirit-level(s) should NOT be glued-down, but
simply placed on the surface so that they can be reversed. However, the
levels must be very light, and the levelling screws and base very rigid, to
ensure that removing the levels does not alter the horizontality of the
plate. This would need testing.
As for the mechanics of it, I suggest that at each adjustment-point there
should be a spring pressing the plate down against an (ideally) knurled nut
working below the plate. A couple of domed spacers would help in allowing
the plate to tip slightly without binding. Similarly, the holes could be
made with a slight "hourglass" shape to allow a bit of tilt. This is easily
done; first you drill a straight hole and then with the drill right through
the hole, wiggle the drill-bit in a narrow cone so that its flutes enlarge
the hole near its ends but not in the middle. It's useful to put a bit of
stiffness into the movement of the nut, such as by running a wisp of fibre
between the threads, or using a "nyloc" nut.
The above are no more than suggestions as I haven't tried to make such a
device myself.
Perhaps someone will tell me just how sensitive such levels are. How much
tilt do you have to apply before it can be detected?
George Huxtable
================================================================
contact George Huxtable by email at , by phone at
01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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