Vacuum clamping is an application that can be used in the shop every day. If
you have a vacuum pump, more than likely it can be used for vacuum clamping.
Vacuum can apply up to 1800 lbs./sq.ft. of pressure and has several advantages over
mechanical clamps: does not mar the surface, does not get in the way of cutting
tools (improves safety), fast set-up, even and uniform pressure unlike a mechanical
clamp that provides a point source of force. When used in template routing, the
templates can be lighter in weight and reproduces more accurate pieces.
There are many vacuum clamping jigs that can be made or purchased and all will improve the
productivity or safety in the shop. Picture 1 shows examples of basic vacuum jigs;
straight edge (SE), right angle clamp (RTA), base plate (BP), template, and toggle
clamp jig (TG). The (SS) is a solid surface jig that is used to butt glue two
pieces. It's two simple jigs sucked to each side and pulled together with spring
clamps. These are just the tip of the iceberg of what can be made or purchased.
For example, some have made 60 clamps to hold hexagons together while assembling. The
SE has the advantage of being able to place it anywhere on the work piece and does not
have to be at the edge in order to mechanically clamp it in place. The BP can be placed
on any flat surface (preferably nonporous) bench, floor or wall to hold a piece of stock
or door, etc. The BP can also be used together with the SE (Picture 8). The BP is under
the stock and holds it 3/4" above the table top, making routing or cutting a simple task.
Making a curved form for bent laminations (see Technique #2) is fast and accurate. Make
one rib, then turn it into a quick jig and reproduce as many as you need. They will all
be the same as in Picture 2.
Making a vacuum clamping jig. In general, jigs should be made from flat, nonporous
material and should be 3/4" thick when the vacuum connector comes in from the side. If
the jig is going to be used over and over, like a SE, then it should be made from
plastic that is nonporous, flat and dimensionally stable. Using plywood, hardwood or
MDF may work for a one time or quick jig, however, they are porous or will not stay
flat or both. Plastic 3/4" thick is available in 1' x 4' slabs and can be machined like
Cut the jig to size, then drill two intersecting holes as in drawing A. Attach a quick
disconnect to the side hole and apply vacuum tape to define the vacuum area on one or both
sides of the jig. If you use air line quick disconnects, your jig will have to be 1 to
1 1/2" thick to provide sufficient clearance. Also check to make sure they hold
vacuum, some need internal pressure to give a seal. For a quick jig, a dowel with a
diameter that's just larger than the I.D. of your vacuum line, can be used. Drill a hole
down the center of the dowel and glue it in the side hole then slip the vacuum hose over
the dowel (drawing B).
The vacuum gasket tape is important as it must be made from closed cell
foam, the right density, thickness and width for the job. Normally, weather seal gasket
material does not work because it is not closed cell and has too light of a density. If
the foam density is too light, then it will have a high compression set and not spring
back to its original height after a dozen or so uses. If it's too dense, then it may not
give enough when the stock has a slight curve, thus you will not get a seal. If it's too
high, then you can get a rocking motion when template routing because it does not compress
and become rigid enough when under vacuum.
Testing your vacuum jig for leakage is simple. Hook it up to the pump and block
the vacuum hole(s) with your fingers. Read the vacuum gauge on your pump. If your pump
normally gets 27"Hg and you read 20"Hg on the gauge, your jig has leaks. If it's made from
plastic, this means you have a leak somewhere in the connections, assuming your pump
is working correctly.
If you made a quick jig from wood, you should not expect to get maximum vacuum. When used
with a work piece, always check your gauge for the vacuum level and calculate the force
to make sure you have enough holding force.
Calculating the vacuum force. It's important to know the force being
applied with vacuum and it is easily calculated. You need to know the surface area under
vacuum which is defined by the vacuum tape used to make the jig and the vacuum
level ("Hg = inches of mercury) as read on the gauge when the piece is under vacuum. Just
divide the vacuum gauge reading by 2 and multiply this by the area of your jig. For
example, a vacuum straight edge 30" long and 3 1/4" wide would have about 90 sq.in. of
vacuum area. If the gauge reads 20"Hg, then the vacuum generates 20÷2 x 90 = 900
lbs. of holding force.
One jig can be designed to hold several sizes. Look at the SE and BP in picture 5. They
both have "gates". The lines going across the SE are vacuum tape where the top one is closed
and bottom one open. Thus, it could be used for 3 different lengths. In this case a gate
is made by removing only 1/2" of the paper that covers the adhesive on the bottom of the
tape. This is butted against one side and stuck in place. A small piece of tape is placed
where it will hold the gate open. This same piece keeps the tape in place when it's closed
as in the top gate.
Picture 4 is a small vacuum table used for assembly and has a 6-jig
manifold. This allows several jigs to be used at the same time. It has a
vacuum plate on the side for holding doors or stock on edge. It allows the
user to set the work at the best height for him and makes cutting hinge
slots or filing or planing a door easy and
quick. This same set-up allows for one person to easily put large pieces together
Types of vacuum pumps. Both electric and air-powered (venturi) pumps
work with vacuum jigs. The air-powered are more suited because they run cool and do not
have any moving parts to wear out. The Q.V.P. VAK Pump is guaranteed for life. Pumps are
measured by vacuum level ("Hg) which relates to the force generated and vacuum flow which
is how much vacuum air it can pull in. Higher vacuum flow is important when working with
porous material like MDF, particle board, etc.
Electric pumps should be used with a pneumatic foot pedal. This allows the pump to run
continuously and make and break vacuum to the jig with the pedal. If you start and stop
the motor every time you use the jig, this can cause an excessive amount of heat and the
thermal overload protection, built into the pump, will shut the pump off and prevent the
pump from burning itself out.
The foot pedal has two major advantages verses using a hand valve. It leaves your hands
free to hold the work piece or cutting tool. For example, when using the side plate to
hold a heavy piece, as in the pictures on the back page, both hands will be needed to
lift and set it properly in place. The foot pedal is then stepped on to create vacuum. It
is also faster and less fatiguing when template routing many pieces in a day. Some users
claim 20% more productivity from this feature.
The above vacuum clamping jig holds a piece of stock on end to drill a hole perpendicular
to its length. The jig is bolted to the drill table and the stock is pushed into
the jig which keeps it centered and perpendicular to the drill. (Pictures 5
Applications: There are many uses for vacuum clamping, it's a
matter of need and creativity. One user had a job to rout and sand 1500 plaques. The
first time it took him 17 days to complete the job using mechanical clamping methods. He
received a repeat order and did it in 3 1/2 days with a simple vacuum clamping set-up.
Using vacuum to set glass in doors and windows is a unique application. We have made
special units for this application because they require low vacuum level with high vacuum
flow. The normal way to set panes for one mid size shop was to apply the glaze, set the
pane in place, then push the pane down with one hand and staple the frame in place. This
was slow and dangerous as the pane would break on occasion. The solution was a vacuum
table covered with gasket material where any size window could be assembled. When all the
panes were in place, a low vacuum (2 to 3"Hg) was pulled. This pulled the panes down and
the operator could use two hands to set and staple the frames in place without the need to
press on the panes.
Another variation on this was assembling large panes in entry doors. Here the door had a
rubber gasket placed in the opening, a large pane (up to 2" x 6") was set in and vacuum
pulled. Here spacing was critical. They controlled the vacuum to center the pane to
within .005 to .010" and then fix it in place with molding. Because vacuum provides even
and uniform pressure, it could be used to easily, accurately and quickly position the
glass. They went from assembling 5 doors in 4 hours to 14 in 4 hours.
A large shop used two men to put a bull nose on 3 and 4 diameter table tops using a
template held in place with mechanical clamps. They went to a vacuum template that was
much lighter and now the job is handled by one man.
Right angle clamps can be the biggest time saver when assembling cabinets. By using 3 or
4 RTA's, you can set the sides in place, now it is very easy to go back and set the
mechanical clamps in place while the glue dries. This is especially true when assembling
large cabinets. Again one man can do it efficiently and quickly. One user noted that he
saved on average 2 hours in the assembly time of a set of cabinets by using the right
Using the table top as a reference point for cutting biscuit slots for both pieces
will give exact alignment. The toggle clamp holds one piece securely to the table. The
RTA acts as a single sided vise and holds the other piece upright and at a 90-degree
angle to the table top.
Sometimes a vacuum clamp is so simple, it doesn't seem possible. The key is to think
and understand how it works and it can be a tool that you will use every day in the
shop. You're limited only by your creativity and imagination.
Do you have a Technique (either clamping or vacuum Pressing related) that you would like
to share? E-mail us the information and we may use it in future Techniques. If you
would like to see a Technique on a particular application, let us know, if enough request
a subject of general interest we will do it.
Vacuum Straight Edge, no mechanical clamps to interfere with router. Fast accurate
placement. A base plate is under the plywood piece holding it 3/4" above the table top.
Template rout in one pass, with no mechanical clamps to interfere, fast, accurate and safe.
One person can assemble two large pieces without help. Hold one piece to the side of the
table with vacuum. Align the top edge even with the table top. Note the foot pedal to
start/stop the vacuum. This leaves both hands free to handle the heavy work piece.
Slide the other piece over the edge and screw together. Vacuum clamping makes the job
easier, faster and it's simple to do. See inside for more.