• Vacuum: What is it?
 

• How is vacuum measured?
 

• How does vacuum work for the woodworker?
 

• What kind of vacuum pumps are available?

 
• Advantages Air-Powered or Electric Vacuum Pumps
• Air-Powered
• Electric

 
• Pump Capacities and how they are defined:
• Vacuum Level
• Vacuum Flow
• Time to evacuate

 
• Automatic Vacuum Systems for Veneering:

 
• Manual Veneering Systems:

 
• Bags and Bag Material:

 
• Frame Presses:

 
• Vacuum Bag Connectors:

 
• Other Considerations:
• Filters:
• Vacuum Tanks:
• Accessory Tools:
• Glue Considerations:
• Veneer Tape
• Cost Justification:

 
• Vacuum Clamping
• What is Vacuum Clamping?
• Vacuum clamping considerations:
• Air-Powered vs. Electric Vacuum Pumps for Vacuum Clamping:

 
• Factors to consider in selecting a vacuum system:

 
• What kind of Glue should I use in a VAKuum Press?

 
• How Long does it take for the Glue to Dry?

 
• What is the color of VAK-Bond 2000 once it dries?

 
• Differences in Glues

 
• Typical Glue Problems

Your elevation from sea level affects the amount of vacuum that can be achieved. A rule of thumb is to subtract 1"Hg for each 1000' above sea level. Thus if a pump normally reaches 27"Hg at sea level, then in Denver (5000' above sea level) it will only get 22 - 23"Hg.

Air-Powered:

• High Reliability -  No moving parts, nothing to wear out, break, or overheat and shut off.
• Lower Cost -  Compared to an equivalent capacity electric pump and air-powered vacuum system can be 15 to 40% lower in cost. No maintenance or replacement costs for the pump.
• Upgradable -  Add increased performance or function without losing original investment.

• Convenience -  Can plug it in anywhere, no compressor required.
• Capacity -  Can have more capacity if you only have a small compressor.

  Vacuum Level: (“Hg) is thought of as the force or work that vacuum can do. The higher the vacuum level, the more force that is applied. If we have 1 sq.ft. (144 sq.in.) board under 20"Hg, we have 1440 lbs. of force holding the board in place (144 X 20 X .5).

  Vacuum Flow: is the volume of vacuum air (measured in cubic feet per minute [CFM]) pulled in by the pump at a given vacuum level. Therefore, vacuum flow changes (decreases) as vacuum level increases. It is an inverse relationship. A pump will have its highest flow at 0"Hg and no vacuum flow at its highest vacuum level, i.e., it can’t pull in any more air. Be aware that vacuum flow at 0”Hg can be misleading (no work is done at 0"Hg). When dealing with porous materials, higher vacuum flow capability will mean higher vacuum levels which translates into more holding force.

  Time to evacuate can be important in some applications. As mentioned above, time to evacuate a given volume of air varies at different vacuum levels. This concept is true for all types of pumps, whether air-powered or electric. For example, a 1/3 H.P. electric pump may evacuate 5 cubic feet per minute (CFM) at 0 “Hg, however, at 20"Hg it will only pull 1.5 CFM. Another manufacturers 1/3 H.P. pump may pull 5CFM at 0"Hg and at 20"Hg pull 1.2 CFM. Thus, the second pump will be slower.

Time to evacuate is important when you must get to a given vacuum level in a specific period of time. General industries use this information to calculate the speed of a particular operation in the assembly line. Generally, most woodworking applications are not affected by a slight time difference. Whether it takes 65 seconds or 75 seconds to evacuate a vacuum bag is not critical.

Where time to evacuate can be important is where large curved pieces are being made. A large curved form could have anywhere from 10 to 20 cubic feet of air to evacuate and a 1/3HP pump could take a half minute to evacuate 1 cubic foot to 20"Hg (where the bag is tight and applying pressure). Thus, for 20 cu.ft., it would take 10 minutes to get the bag to 20"Hg (.5 min X 20 cu.ft.) If we look at the total time involved; it may take 10 minutes to assemble the piece and get it in the bag, then another 10 minutes to get the whole bag to an acceptable vacuum level with a 5CFM pump. A total of 20 minutes may be too long, as the glue could set before sufficient pressure is applied. A better solution is a faster pump of 10CFM, which would cut the time to evacuate in half. Other tools such as a glue spreader would help reduce assembly time thereby decreasing total time to get the work piece under pressure.

If you develop a leak in the bag, the pump will cycle on and off at a constant rate consistent with the size of the leak. Constant cycling on and off is detrimental to an electric vacuum pump. When any motor starts, it draws higher amperage than when it’s running. This causes more heat buildup and the motor will shut off or worse burn out. Most vacuum pump motor have a built in thermal overload that will shut the motor off when it overheats. It could take 15 to 30 minutes for it to cool off and restart. This would mean the job is lost.

Air-powered pumps do not have a heat problem; they actually run cool because of the air running through them. In some cases the exhaust air ends up cooling the other electrical components used in the automatic controller. Dirty or unfiltered compressed air can sometimes cause problems with air-powered systems. Rust or dirt can prevent an air solenoid from closing, thus the air-powered pump would continue to operate until the air line is removed (this is better than having it break and be out of commission). Normally, cleaning a solenoid is a 5-minute process. A filter on the air line will prevent this problem.

An automatic system is strongly recommended if you fall into one of the following:

• Do veneering on a regular basis - even 3 or 4 pressing per month.
• Want the convenience of turning it on and walking away without being concerned about having to check it every 15 to 30 minutes.
• Loss of one job will equal the additional cost of an automatic system. If you lose one job, what is the cost of your labor and materials. Generally, the additional cost of an automatic system is only $250 - $300 more than a manual system.

If you must start with a manual system, remember that some manual systems are upgradeable to the automatic system without losing your original investment.

Polyurethane is an industrial grade material and is much tougher than vinyl. Poly will stretch better, return to its original shape better, not cut as easily nor develop pinholes as readily as vinyl. Poly is usually available in .020, .030 and .040" thickness. Poly is a better choice for those doing curved work, as it holds up better than vinyl, when stretched. The thicker the bag, the more abuse it will take. Thickness can be a disadvantage when doing some curved work. It may bridge across in some areas instead of flowing or stretching into the curve. If this happens you will not get pressure where it bridged and the job will have to be reworked or scraped.

Vinyl bags are available in .020" and .030" thickness and are usually purchased when funds are limited or it will have limited use. For example, pressing 10 flat panels a month with a .020" vinyl bag should last a year or two if normal care is taken. Some vinyl bags are made with two different types of material. The top is clear and the bottom opaque. If the bag is made with clear material, top and bottom, then the bag can be turned over if it has the removable type connector described below. These two features, clear top and bottom and re-locatable vacuum connector, mean more life from the bag. What happens is the top of the bag gets cut and patched as well as stretched. The stretching causes pinholes to develop and thus the bag leaks and it’s not practical to patch the pinholes. With a clear bag and re-locatable connector, the connector is removed and the hole patched. Then the bag is turned over with the bottom now on top. The top side is basically unused. The bottom will self seal against the bottom of the baseboard (usually 3/4" melamine coated particleboard which the work piece sits on) or platen because it doesn’t have the grooves in it like the top of the platen. This simple feature allows you to get almost twice the life out of your bag.

The bag can also be used without a baseboard. For example, those doing curved staircases or arches. In these cases, the form is outside the bag. A long narrow bag is used where the laminates are glued, put in the bag, formed around the arch and vacuum pulled on the bag. The vacuum now holds the arch in its shape and the bag can be removed from the form. In this particular situation, the form can be used again without waiting for the glue to dry. One vacuum system can handle several bags at the same time, all with one form.

Another use of vacuum bags without a baseboard is for free forming curved laminates. In the above example we used a form to get the shape of our arch. In free forming, it’s just that. The laminates are glued, put in the bag and then bent into any shape before vacuum is applied. Once vacuum is applied, the shape is maintained because the laminates are being pressed together by 1800 lbs/sq.ft. of pressure, thus they can’t slide or move. The general rule of thumb is “if you can bend it into a shape, the bag will hold it”.

In general, a vacuum bag offers more flexibility in what types of geometry or shapes that can be pressed in the bag verses a frame press. If you are doing a variety of work, flat, curved, etc., then a vacuum system with a bag is the best way to start.

  Filters: They are essential with electric pumps. Some vacuum pump manufacturers build their pumps with an internal filter. However, an external filter is also strongly recommended. Most vacuum pumps used in the woodworking industry are rotary vane types and the clearance between the vanes and the sidewalls is only .0002". Therefore, the incoming vacuum air must be filtered. If small particles enter the vacuum chamber, they could cause the vanes to stick or break.

It’s good practice to flush the pump chamber with fresh air for 1 - 2 minutes at the end of the day. Glue vapors can build up along the wall and cause the vanes to stick. The next time the pump is turned on it may not spin causing the motor to over heat and shut off, or worse, snap the vanes. Most manufactures will recommend periodic flushing of the vacuum chamber with a liquid to clean the insides.

Air-powered vacuum pumps do not normally need filtration like electric units. Dust drawn into the vacuum line will normally pass through the unit. A buildup inside the pump can occur if the airline contains oil from the compressor. Two piece pumps made for the woodworking industry can be disassembled, flushed out and reassembled in a few minutes. If a few strands of course steel wool are put in the vacuum line, they will trap large chips and allow the dust to blow through. If you decide to filter a vacuum system always use a filter with a clear bowl. It allows you the see the screen and clean it before it gets clogged.

If you use a filter on the vacuum line, it is normally placed between the bag and the vacuum gauge. If the filter gets clogged, it will cause a false reading of the vacuum level in the bag. The vacuum gauge and vacuum sensor are on the other side of the filter. Thus, you can have in essence, two vacuum systems caused by a clogged filter. One will be from the filter to the bag, the other from the filter to the pump, which includes the vacuum gauge and sensor. When the pump cycles on, it evacuates the line up to the clogged filter and the sensor then turns the pump off. The gauge is reading high vacuum, however, on the other side of the filter, in the bag, nothing happened. Thus, be aware that a dirty or clogged filter can cause a problem and must be kept clean.

A tank is also used where a fast vacuum draw down is needed. For example, consider the case where you have a small vacuum pump and later purchase a large frame press. Because a frame press has a large surface area to seal (a 4' X 10' frame press has 28' to seal verses a bag with 4' to seal), using a vacuum tank could make a difference on getting the initial seal. The tank gives a large initial vacuum flow, which pulls the frame down to the table and provides the perimeter seal needed by the small pump.

For a small shop doing panels, a hand veneer taper is a good investment. They are designed to wet the paper tape, pull the two pieces of veneer together and roll the tape over the seam. Anyone doing hand taping of veneers for panels should consider this tool.

A urea glue is normally recommended for laminating and veneering. Urea glues cure by a chemical reaction as compared to white or yellow glue, which cures by the water migrating away from the joint. A urea glue gives a very rigid glue joint, thus minimal or no spring back on curved work. Because it is so hard, it sands easily without gumming the sandpaper. Another advantage is its ability to never soften under heat. If your finished piece is placed next to a sunny window or in a trailer in 120 degrees, it won’t soften or delaminate. It also affords a type II waterproof bond and is available in powder or liquid form. The powders will keep for 12 months, the liquids for 3 to 6 months depending on the temperature.

The drying time is affected by several factors such as the type of glue, surface area being glued, wood being glued, and shop temperature. Yellow glue drying time will range from 20 minutes to 3 hours. White glues, which typically give more open time, will take from 1 to 4 hours to dry. The urea formaldehyde glues normally are 4 -6 hours and must sit overnight before being machined. The higher the temperature the faster it dries. Some shops use a household electric blanket over the bag and it can reduce drying time significantly, especially cold shops in the winter.

Many laminations of hardwood will take longer to dry compared to the same number of bending plywood laminations. The reason being that bending ply is more porous than the hardwoods as most water based glues dry by the water wicking away through the substrate. Hardwoods don’t wick away the water very quickly. If using an epoxy or other type of glue that hardens by a chemical reaction, then the substrate material is normally not important with regards to drying time.

When gluing large panel’s (4x8), consider leaving it in the bag a little longer than normal. What some have experienced is the center of the panel not drying as fast as the outer part. This has shown up especially where the veneer is taped down the center of the panel.

Comments like “I didn’t know how to get clamps on the piece (odd shaped curved piece), so I made a vacuum clamp and it worked!” “I made four right angle vacuum jigs to hold a cabinet together while I assemble it. For a typical kitchen job, it cuts my assembly time down by 2 hours". “I’ve been doing vacuum pressing for two years and decided to try template routing with a vacuum template. I had 50 pieces to make and not only was it fast, but all my pieces came out the same". “I had a quick routing job to do, by holding the piece with a vacuum jig; I can finish the job before I could get set up with mechanical clamps. Also, with the vacuum jig, I don’t accidentally dent or mar the work piece and then have to rework it".

Advantages of vacuum clamping over mechanical clamping:

• Doesn’t mar the work piece - The vacuum tape (special foam tape that gives an air tight seal between the vacuum jig and the workpiece) protects the workpiece.
• Fast - Vacuum is instant on\instant off. Template rout around a piece in one pass, with mechanical clamps you need to remove the clamps and re-clamp the work piece. No need to use double sided tape or screw the template to the work piece, no cleanup or filling holes required.
• Accurate - Because you do not have to remove and reset the clamps, you get a true reproduction every time. This is extremely important when make several mating parts, as all will be interchangeable, all will fit together.
• Low Cost - Make your own basic or unique vacuum jigs to handle day to day operations or special projects.
• Strong - Up to 1800 lbs/sq.ft. of force, much more force than can be applied with typical mechanical clamps.
• Even and Uniform Pressure - Mechanical clamps provide a point source for the force to hold. A typical mechanical clamp provides 200 - 300 pounds of force at the point of contact. If you are holding a 6" square piece of 3/4" pine with a mechanical clamp, it averages about 8.5 lbs/sq.in. Where a vacuum clamp would typically give 10 - 12 lbs./sq. of even and uniform holding force.
• Safe -  No obstruction to interfere with the cutting tool. In some cases a cutting tool would come close to a mechanical clamp and present a danger to the operator and equipment if the tool hit the mechanical clamp.
• Versatile - Can attach a vacuum clamp on any flat surface, horizontal or vertical. For example, to hold a straight edge to a 4 X 8 sheet, the mechanical clamps must be at the edges in order to grip the sheet and straight edge. With a vacuum straight edge, it can be placed anywhere on the sheet and when vacuum is applied it will pull straight down. The vacuum jig does not have to be near the edge.
• Can rout the complete edge of a piece-  because the vacuum jig holds the work piece off the bench top unlike a routing mat.
• Jigs are lighter in weight - Some two man shaper operations can be reduced to one man because of reduced weight.

Disadvantages of a vacuum clamp.

• Work piece needs to be relatively flat - some cupping is acceptable as the gasket tape not only provides a seal but also permits some unevenness.
• Less force on small pieces - A mechanical clamp can apply more total force on a small piece.
• Very porous material can result in low holding force - cracks and knots present leakage and a large vacuum pump maybe needed to overcome this leakage and give an acceptable holding force.

Air-Powered Advantages:

• Reliability- No moving parts means nothing to break, wear out or over heat and shut off. Can be cycled on and off thousands of times without causing it to over heat or damage any parts.
• Lower cost- About 1/3 to half the cost of an equivalent electric pump.
• Upgradeable- Some venders can upgrade a smaller unit to larger capacity with losing your original investment.

Electric Pump Advantages:

• Convenience- Plug it in anywhere, does not need a compressor.

• Function: What is it to do? Vacuum veneering, vacuum clamping, both? Other applications like degassing a liquid (epoxy resin, etc.). Run multiple bags or frame presses?
• Physical Size: Will it take up floor space or can it be tucked away under a bench?
• Reliability: What is the life of the pump, the expected bag life? If the pump ingests sawdust or chips, will it break or just need cleaning?
• Maintenance: How much maintenance will it require, are parts readily available, cost of parts, can you service it yourself or must it be returned to the factory?
• Warranty: What is the warranty period for the pump, the bag seams? Some venders give a lifetime warranty on certain products. Warranty on component parts?
• Vendor Support: Does the vender have a hot line or 800 number for problems related to the equipment or how to use the equipment? Will they return calls after hours or on weekends? This is important, especially when an equipment problem occurs and you have little or no knowledge of the system and how it works.
• Convenience: How easy is it to use? Can it be moved around the shop?
• Upgradeable: Can its performance and functions be increased later? What are the costs? If it’s a manual system, can it be upgraded to a fully automatic system?
• Motive Force: Air-Powered or Electric Vacuum Pumps.
• Performance: How high a vacuum level (how much force) do you need? How fast of an evacuation time is needed to get the work piece under pressure?
• Cost and Selection: Is there a range of pumps, bags, frame presses, accessories, components parts, etc. to choose from.

  Remember, innovative uses of vacuum will give any shop an edge over their competition.

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First, will the squeeze out stick to the bag. Normally yellow, white or urea type glues will not. The polyurethane glue or epoxies will. Therefore the bag must be protected with a slip-sheet material (wax paper, etc.) that traps the glue. The second consideration is whether the glue needs air or moisture to cure. This is true of the polyurethane glues. They need moisture in a normal glue-up, the moisture comes from the surrounding atmosphere. What polyurethane glue manufactures recommend is to wet the substrate (not the veneer, it will wrinkle) before applying the poly glue, thus it has sufficient moisture to cure when in a vacuum bag.

• Type of Glue- generally, the more open time the glue allows, the longer the set time
• Temperature of the shop- the warmer the shop, the faster the set time
• Substrate Material- With typical water based glues, the water will be absorbed into MDF, particle board, etc., faster than a solid wood like oak, therefore, the drying time is shorter.

If a caul was not used on top of the veneer (bag directly on the veneer), this could be the cause of wrinkles. The caul is needed to flatten the veneer.

I have a complex shape and making a caul is a problem!
If you have a complex shape and stiff cauls can't be used, try flexible materials. Linoleum, bending plywood (wax the surface so glue doesn't stick to it), plastic laminate, etc. Be creative, as the use of a caul is very important. If you can't use a caul, roll the lumps and bumps out with a hard rubber roller.

My MDF veneered door cupped as soon as I took it out of the bag!
This is usually due to veneering only one side. The MDF still has moisture from the glue on the veneered side. You must veneer both sides for proper moisture balance. The back side does not have to be the same type of veneer as the front.

My curved jambs did not dry!
If you are making arches, curved staircases, etc., from solid hardwoods using yellow or white glues, it can take an extensive amount of time for the water to migrate away from the joint and vaporize in the vacuum bag. Six layers that have been glued on every surface involves lots of water and it doesn't get absorbed or move to the edges very fast. If every other layer can be bending ply, will absorb the water and dry faster. If not try the urea, poly or epoxies as they cure due to a chemical reaction not evaporation. Also try adding heat with an electric blanket.