Keepin' Totes from Breakin'
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Far too many valuable totes (handles) of antique & collectible woodworking (smoother, jack, fore, jointer, scraper, Jeff) planes get broken because of the seasonal expansion & contraction of the wood. The metal screw is tightened in the wintertime when the wood is dry, and then in the summertime, the wood expands as it picks up moisture from the humid air. The head of the tote screw therefore digs into the wood unless the conscientious owner releases the tension on the screw. At the approach of the cool, dry season, the wood shrinks again and the screw becomes loose. If the owner then uses the plane with the tote screw loose, there is a strong likelihood that the tote will be broken by the excessive bending stress in the always cross grained tote. The tote depends upon the tension in the attachment screw to support the bending load without placing the heel of the tote under tension. The arrangement functions much like prestressed concrete in a beam.
Here is an added feature that I am trying to see if I can protect the totes on my favorite planes.
The device is based on the elasticity of a conical spring, called a Belleville spring. Belleville springs see a lot of use in zero emissions flanges in the chemical industry. The springs are sized and shaped to generate the design clamping force required to prevent leakage when the spring is defelcted into the flat condition - with all of the conical shape squeezed out of it. Then, when the piping cools off and the gasket material contracts thermally, the Belleville springs pop back up to a conical shape with nearly no change in the axial clamping force restrained by the joint's bolts.
I am trying the same sort of approach with the tote's attachment screw.
Here is a Stanley
tote attachment screw withs its separate brass head, to which I have added
six Belleville springs and a flat washer. The sizes available in Belleville
springs are somewhat limited unless one orders a large lot of them all
at one time. I obtained these stainless steel Belleville springs in a metric
size which very nearly fits the Stanley screw exactly. I did have to reduce
the outside diameter of the screw's threads from 0.214 inch to 0.209 inch,
simply by filing while it was rotating in a lathe.
Here are four
of the Belleville springs, three with the wide part of the cone facing
up and one with the apex of the (truncated) cone facing up.
Here's the MSC
label; the Belleville spring size is 10 millimeters OD, 5.2 millimeters
ID, and 0.75 millimeters thick. This spring generates 80 pounds force when
deflected 0.008 inch. Neither I nor Amenex Associates, Inc. have any financial
connection to MSC. MSC is just a handy supplier for us.
I stacked the springs in two sets of three nested ones, with the apexes of the two sets of cones facing each other. That put the wide part of the upper set against the flat part of the underside of the head of the screw, and it put the wide part of the lower set against the flat side of a #10 stainless steel washer on the bottom. The curved OD edge of the stainess steel flat washer therefore bears less stressfully on the corner of the cylindrical hole in the top of the tote. With the cones of three springs nested into one another, the force to deflect the stack of springs is tripled to 240 pounds. Having two sets of the nests of three springs each facing each other, the total deflection under load is therefore 0.016 inch, twice the deflection of a single spring.
This is the
label on the box of #10 stainless steel washers. Their hole matches the
ID of the Belleville springs, and the OD of the flat washers fits the hole
in the top of the tote. These washers came from a local hardware store;
I found that nesting the Belleville springs in twos did not produce enough axial force - it was too easy to tighten the attachment screw until the springs bottomed out. With the springs in nested sets of three, the tightening torque is much higher and close to the maximum that I would dare to tighten an unsprung tote.
The upper image
is the unfastened tote with the attachment screw placed with the stack
of six Belleville springs and the one flat washer against the bottom of
the cylindrical hole in the tote. The lower image shows the screw tightened
to the fullest extent. The tote can now be expected to shrink over the
rest of the Fall season (it is now late September); we shall see if there
is sufficient deflection available to keep the tote tight as the wood dries
out and shrinks over the Winter season.
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