Vacuum
Bridge Clamp
Overview
The design of our Vacuum Bridge Clamp
- SPVACPB has evolved through several versions into to a solid,
very professional unit. This unit is used by factories exactly as it
comes from our warehouse. The thin rubber membrane is bolted in place
between two machined aluminum rings that form the body of the clamp.
The clamping area within the clamp frame is a full 8 1/4" X 3 1/4"
- big enough to accommodate any acoustic guitar bridge.
A 1/2" foam rubber gasket is glued
to the bottom surface of the frame to conform to the top and produce
an air tight seal for clamping. The flexible, yet firm, foam rubber
gasket can even form an air tight seal when a portion of the clamp is
placed over a pick guard or the top is very arched. And of course,
the foam bottom gasket does not mark or harm the top or finish.
The clamping fixture is designed to
pull vacuum in the area between the membrane and the guitar top surface
under the membrane. There is a vacuum outlet in the frame below
the rubber membrane and this air outlet hole is connected to a Pisco
quick connector on the outside of the fixture. The fixture is connected
to the vacuum pump by 1/4" hose attached to this connector.
In operation, air is pulled from under
the rubber membrane by the vacuum pump and the vacuum created sucks
the membrane down to the guitar top surface at a pressure of 14 pounds/square
inch - atmospheric pressure at sea level. That's 98 pounds of clamping
pressure on an average bridge - about 7 square inches of surface. That's
enough to glue it well.
The Vacuum Bridge Clamp - SPVACPB
works well with our Vacuum Pump - SPVP and will be demonstrated
here using this pump. There is no additional preparation of the Vacuum
Bridge Clamp as it comes to you. Our only preparation here is setting
up the vacuum pump and connecting it to the clamp with our vacuum hose.
These instructions are not intended
to demonstrate the complete bridge gluing process but rather to show
how this tool is used in the clamping portion of this process. All
other steps - preparation of the top and bridge surfaces, locating the
bridge accurately, pinning the bridge in place, glue clean up, etc.
- are the same as for gluing a bridge down with ordinary deep-throat
clamps. We are assuming that there is already bridge gluing experience
and the entire bridge gluing process should be familiar already.
This vacuum clamp can be used to re-glue
a bridge in a repair situation or to clamp down a new bridge during
construction. We are demonstrating here the use of this clamp in a
repair situation, re-gluing a bridge onto a Martin 00-21. The clamping
procedure is the same for attaching a bridge to a guitar in construction. |
The Clamp in Use
Vacuum Bridge Clamp in the foreground. The fixture has
been connected to the LMI Vacuum Pump by inserting the pump's hose
into the Pisco connector at the end of the bridge clamp fixture.
The hose is merely pushed into the connector - it locks in place.
The hose is released from the connector by pushing in the white ring
on the connector and pulling the hose free.
The vacuum pump and Vacuum Bridge Clamp are ready
for use. The guitar top and the bridge bottom are leveled and prepared
for gluing. The plastic bridge pins will be used to pin this bridge
in place during gluing. There are a variety of ways to pin the bridge
in its exact location, this is a simple one that can be used when
re-gluing a bridge that was originally in the correct location for
accurate intonation.
The bridge has been glued and placed into
position. The top of the bridge pins have been clipped off so they
won't protrude above the bridge during clamping.
The clipped bridge pins have been pushed into
the outside string holes and the bridge is now secure from movement
during clamping.
Tape has been placed over the bridge pin holes
to seal the vacuum during clamping. Without sealing these holes into
the guitar body the vacuum clamp will never create vacuum pressure.
This hole sealing process is not needed when a bridge is attached
to a new guitar.
With the bridge fitted, glued, and pinned in place
the clamping will begin. Carefully place the Vacuum Bridge Clamp
over the bridge as shown here with the bridge about in the middle
of the fixture.
Turn the vacuum pump "on". Gently press
down around edges of the clamping fixture - maybe using both hands
- to create a solid seal with the top all around the fixture. With
this repair we are clamping the bridge down with the pick guard attached
and the pick guard is under one corner of the fixture. The foam rubber
seal on the bottom of the fixture must be pressed down tight around
the pick guard before the clamp will create vacuum pressure and begin
pressing down on the bridge. The moment that a good seal to the top
is created the vacuum will begin and will suck the rubber membrane
down over the bridge as shown in the photo.
Glue Clean up - After about 10 to 15 minutes of vacuum pressure on the
bridge, turn the pump "off" and carefully remove the clamping
fixture from the guitar top. By this time the glue squeezed out along
the edge of the bridge is beginning to harden and this is the best
time to clean it away. This glue cleaning should be done quickly
with a damp cloth and soft probes - DO NOT use an abundance of water.
At this stage excess water can dilute the glue under the bridge.
With the visible glue removed, place the vacuum bridge clamp fixture
back on the top over the bridge and turn the vacuum pump "on".
Press the clamp frame down around the edges until vacuum pressure
is once again clamping the bridge to the top, as in the
photo.
Clamping Time - It is best at this stage to continue the vacuum clamping
pressure at least 45 to 60 minutes - longer if you like. Most water
soluble glues will have firmly tacked and set enough by this time
to allow clamp removal without harm to the joint. Of course, it is
best to let it cure more fully overnight before any other procedures
on the bridge or instrument.
The Vacuum Bridge Clamp is removed from the bridge and
locating pins are removed. The bridge is firmly glued to the top.
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