TIPS ON VENERING
Whether you're a hobbyist, small custom shop or a mass production facility, there are three steps that must be performed to take veneer from the raw form to finished component.
1 - JOINTING
2 - SPLICING
3 - PRESSING
JOINTING (back to top)
The goal is to prepare the joint lines straight, parallel and square. Two parallel cuts are made in the bundle with the grain. The joints must be parallel so that when the veneer is laid up you do not have the fanning effect. They must be straight in order to avoid gaps in the layup. The edges must be square so that the joint line will be as nearly invisible as possible. There must also be as clean a cut as possible with minimal tearout.
Effects of poorly jointed veneer
Unparallel Joints
Joints that are not straight create gap problems. If joint line is bowed in just one millimeter, the result is a two millimeter gap when two sheets are laid up. If the joint is bowed out one millimeter, the result is a two millimeter gap at either end.
Fanning
If one end of the 8 foot bundle is 5 inches wide and the other end is 5 1/8th inch, you will have a gain of one inch over eight pieces. If the table is a 16 piece, balanced match, the two inch gain will easily be recognized.
Unsquare veneer edges
Jointing with dull tooling or jointing the veneer improperly can leave a rounded edge on the leaf being cut. When two leaves are placed together, this forms a groove. This is either filled with putty or worse yet, glue and the poor joint shows up at the finishing end.
Jointing Methods
Hand Tools
Everyday hand tools like utility knives, surgical scalpels and Exacto knives can produce fine joints when volume is not critical. If you're producing custom jewelery boxes or doing low volume / high quality veneering, this is more than adequate.
Veneer Saw
A veneer saw is the entry level machine for low to medium volume veneering, less than 14,000sq ft per day. The bundle is placed under a pneumatic pressure beam. The veneer is aligned to the rear register and to the selected depth and the pressure beam is lowered. A six inch circular saw and a 3.5 inch milling head are drawn along the bundle at the same time. The circular blade leaves about 5 millimeters of veneer exposed outside the pressure beam. The milling head is about 15 inches behind the circular blade. The milling head then takes off an additional 2 to 3 millimeters. The result is a straight joint with a 90 degree edge and no tearout of the same quality as a guillotine.
Advantages
It can also be used for cutting light metals, plexiglas, plastics, dimensional lumber and core stock. This flexibility makes it the ideal machine due to it's additional cutting capabilities. You can properly joint veneer and have an extra saw in the shop.
Disadvantages
You can not re-cut spliced panels to create pie and other fancy face rework. The accumulated kerf loss shows up when you reassemble the veneer. Consider a grade A face with nice cathedral (flame). If you want to make a multi section pie table, the kerf loss of about 1/4 inch will be lost along the cut. This skews the resulting sketch face as far as the grain match is concerned. The minimum veneer width is 3/4 inch
Guillotine
Guillotines are the ideal machine for jointing. They are easier to justify at daily volumes of about 14,000sq ft of veneer per day. Shops doing less veneer but higher quality work like sketch face, parquetry, a lot of inlay, file and border work and re-sizing should consider a guillotine over a veneer saw. Bundles are placed under a hydraulic pressure beam. A light line indicates the cutting point. Once the operator has the veneer correctly positioned, the pressure beam is activated and the veneer is held tight at 100 bar pressure. After the pressure beam is lowered, the operator can again inspect the cut point and then activate the knife beam. You can cut a single sheet of veneer or a three inch stack per cycle.
Advantages
One machine with a proficient operator can joint up to about 50,000 sq ft per day. You can also re-size panels for fancy face / sketch face work. You can strip cut down to about 1/4 inch. This is beneficial for making your own inlay pieces and filed and border work. For production facilities, computers can be added for repetitive cut sequences. This eliminates the potential for operator error.
Disadvantages
None
SPLICING (back to top)
The goal here is to assemble your layup for further processing. All joints must be tight and secure so that there is no movement during handling and processing.
Veneer Tape
There are two base weights in veneer tape, 34 gram and 40 gram. The 34 being lighter and made of cellulose. The 40 gram is brown kraft paper and heavier. Both styles are acid free and use vegetable adhesive. Widths for each tape run from about 3/8th inches to 2.5 inches. The tape can be plain with no holes, or have 2,3,4,5 or 6 holes across the width.
FAQ's
Why would I want 34 gram instead of 40 gram or vice versus?
This depends on how much handling will the face get between the layup table and the press. If it gets a lot of handling then the heavier bond is needed in order to hold it together. The second thing to consider is the species. Burls and species like anigre will need more secure bonds due to the nature of the wood. It will want to flex and may have a lot of tension in it. Therefore you need heavier tape.
Why would I want holes in the tape?
This also plays on the nature of the veneer and the handling. Additionally, some craftsmen like the three hole tape because you can see the splice line through the larger holes in the center of the tape. This allows visual inspection of the joint quality while taping. Also, the more holes you have, the less tape you have to remove after press. This is highly desirable for those of us who do not have the big (and expensive) five head veneer sanders.
What is the most popular tape?
Without question the best sellers are
34 gram, 3/4 inch wide, with two or three holes
40 gram, 3/4 inch wide, with two or three holes
I removed the veneer tape and I can see where the veneer tape was. Why is this?
99% of the time the problem is caused by one of the following four issues
1. Species like cherry, walnut and beech oxidize when exposed to ultra violet light. When working with these species be sure to turn them upside down or cover them with canvas to block the light.
2. Over saturation of the veneer tape with water. Excess water is drawn into the veneer and affects the grain leaving a different characteristic where the tape was.
3. Hard water in parts of the country leaves mineral deposits in the grain. Try using distilled water.
4. A combination of the above.
Zig Zag Splicing
Zig Zag splicers splice the veneer on the back of the face. Jointed veneer is run through the splicer along an alignment guide. Hot melt glue thread is applied to the back side of the face. Immediately after the thread is applied, it is compressed flat by compression rollers. The glue thread is buried in the glue line, against the core, so there is no removal process.
Feed speeds vary from 20 to 147 feet per minute depending on the model. Throat sizes range from 27 inches to 48 inches. A 27 inch throat can easily make a 55 inch by 10 foot panel. All you need to do is save the center splice for last.
Haug zig zag's run on standard heat. There is no hot air required for operation. Warm-up time is 3 to 5 minutes. The machine is powered by 220v, single phase. The zig zag pattern width is adjustable. The veneer thickness range is 1/10th to 1/42nd inches. Optional accessories include a veneer tape applicator, footage counter and casters.
Advantages
Labor savings, time and finishing / rework. A 4ft x 8ft panel of six inch components could be spliced and in about five minutes. After it is pressed, it goes right to finish sanding. Compared to a tape layup of perhaps 30 to 45 minutes, to press, and about an hour to remove the tape, then to finish sanding. That extra 90 minutes of time can add up quickly. Tape also generates the potential problem of adhesive showing up at the finishing end. If so, the panel is either thrown away or stripped and reworked. This is particularly frustrating when you are working on a wall or cabinet of all sequenced matched panels.
Disadvantages
On thicknesses of 1/42nd and thinner the glue thread can telegraph onto the face. The glue thread has a very fine fiberglass thread which serves as reinforcement along the zig zag glue line. This is a physical constraint with no means around it. Curved work is also very limited as the joint is an open joint. The veneer will spread (open) if wrapped for columns or other similar type components.
Furniertechnik LZM
Urea or PVA glue is applied to the veneer prior to splicing. The veneer sheets are run under 39-inch dual heated zone. The sheets are transported via stainless steel chains. The chains are both pressurized and heated. While under the chains, the glue is cured. This method of splicing provides the highest quality, fully glued joints for a virtually invisible splice line. This is the best splicing machine for any type face you're making, curved, flat and multidimensional.
The chains, via air pressure, compensate for buckled and wavy veneers. The stainless steel chains leave no blue stain on red oak. The dual zone heaters allow you to splice PVA glues easier.
For example
When splicing with PVA's on a single zone, the adhesive is not fully cured and subject to open or spreading after outfeed. They must be handled tenderly to avoid putting stress on the splice line and having it open.
With dual zone, you can run the first zone at about 210 degrees F and the latter zone with no heat. The PVA is then activated in the first zone and it is allowed to cure, while still under pressure and no heat, in the second zone. At exit, you have a solid bond.
The Furniertechnik LZM is the leader in state of the art solid glue line splicing. The veneer thickness range is 1/10th inch to 1/64th. Feed speeds range from 32 fpm to 131fpm. All bearings are sealed and self-lubricating, reducing maintenance issues and eliminating fluid drip. Operating temperature is up to 446ºF. The throat depth is 37, 47 and 55 inches.
PRESSING (back to top)
Methods to bond the face to the core.
Vacuum Pressing
Vacuum pressing allows you to press flat panel, radius and other relatively complex forms. This expands your creativity and allows you to offer product quite a bit different than your competitors. The components of a system are a vacuum pump and a bag.
Pumps come in two sizes, 5cfm and 10cfm machines. The 5cfm pump is 1/3hp and can only extract from one bag at a time. The 10cfm pump is 3/4hp and can draw from three bags with the aid of a manifold.
Vacuum bags are made of either 30 mil vinyl or 30 mil polyurethane. Vinyl bags are ok for a one time use, but for long term durability, go with the polyurethane. For example, I can poke holes in the vinyl bag with a Bic pen with relative ease. I can not poke holes in the poly bag no matter how hard I force the pen. Sizes range from 4' x 4' on up to 5' x 12'. We can have the bags open on the short side or the long side, which ever you prefer. Loading 12 foot bags from the short side can be quite difficult.
Laminating bags are also available. These bags are for creating arch top for windows and doors or for long stair stringers and even spiral staircases. The largest standard laminating bag is 20 inches by 21 feet long with custom sizes available.
Always, purchase the largest size bag you can right off the bat. There is nothing worse than buying a 4x8 bag and then being awarded a 4 x 10 panel project. The difference in price between the 4x8 and 4x10 is about $60.00. In this example you would have had to buy another bag at about 500.00 to do the job. Get the capacity right from the start.
If you intend on always doing flat panel jobs or small profile work, then a flip top system is worth investigating. Looking much like a screen door frame, the lid is hinged at the rear. A neoprene gasket serves as the seal around the platen. This is a very easy one person load and unload.
Hot Press
Presses come in nearly every size, shape, color, heating medium, and pressure that you can think of, in addition to a myriad of bell and whistles.
What you have to ask yourself is:
What is the largest size that I will need? To determine capacity
How often will I be using the press? To determine heating medium
What am I pressing? (veneers, laminates) To determine pressure
What adhesives will I be pressing with? To determine temperature
What cycle time do I need? Determines pressure and temperature
Do I have physical constraints? Overall footprint or weight constants
Considerations
If 95% of your needs are 4x8, then you have a few choices. Spend the extra money for the 5x10 or you can buy the 4x8 and step press or simply sub out anything larger.
If you're pressing a few hours a day then electrical heating makes the most sense from an energy usage perspective. If you're pressing full time then you would want to go with thermal oil or super heated water. These can be heated several ways depending on the costs of energy in your area. Oil and water systems can be fired either by electric or natural gas.
Hot pressing veneer requires a minimum of 30PSI, vacuum bags operate at 12 to 13psi maximum. This is needed due to the platen tolerance of +/- 2mm. The extra pressure "crushes" the veneer and really drives the adhesive into the grain for a great bond.
Urea and PVA's are pressed in the 190 to 210F range. If you plan on or expect to be pressing with dri glue film, you need a minimum of 280F, and higher pressures. Build in about 25% excess heat capacity so that when the press is turned on, it is not at 100% power. This costs fractions more initially than burning out platens from full time, full power operations.
Cycle time for most hot presses will be in the 3 to 5 minute range. Cycle time is dependent on the thickness of the veneer, adhesive, core dimension and temperature. Rule of thumb: Higher pressure and temperature reduce cycle time for simple face and back pressing. Creating you own 5 or 7 ply can increase cycle time to perhaps 6 or 7 minutes. The extra time is needed for heat to penetrate to the core.
Hydraulic Cylinders
How large are the cylinders?
This leads to the pressure that the cylinder is under and it's over all longevity. The larger the cylinder, the heavier it is made and longer life it will have. Generally, it is also indicative of over all system pressure.
How many cylinders does it have?
A 4 x 8 foot press should have at least six cylinders. A 5 x 10 press should have at least 8 cylinders. Yes there are presses on the market with four so just consider the following;
On a 4' x 8' press with four cylinders, on the long side, the cylinders are 33 inches on center. That is quite a distance when it comes to maintaining even pressures. If a panel spans cylinder to cylinder, the center of the panel may not have the same pressure as the part of the panel that is directly over the cylinder. If a panel is placed between cylinders, the platens could close and become damaged and bowed. A new 4x8 foot platen is about 7,000.00 not installed.
With six cylinders, the on center distance is 24 inches and more consistent pressure is maintained across the face of the layup.
Look at the framing construction. The heavier the construction, the long life cycle of the machine. As in any machine, light weight construction of a machine exerting 80 tons of pressure or higher, will affect the structure over time unless it is built heavy. Is it angle iron or I-beam construction? Is it 4 inch or 10 inch? How many I-beams are across the top and bottom of the main frame? Are the uprights made of four inch or ten inch angle iron or I-Beams
Highly Recommended Options
Rack and pinion gearing.
This ensures the platens close parallel to prevent damage. If it closes out of parallel due to pressure loss or incorrect loading, a limit switch is tripped and the platens open. This is on average an $800.00 insurance investment versus the need for a $7000.00 platen or worse yet two of them.
Anodized platens
The platens are gold anodized. The aluminum platens are by nature soft. The process hardens them. They are much less subject to damage from loading (sliding instead of placing layups) and from glue cleaning. Shops that do not use ACMOS have to scrape the glue off the platens. Usually using scrapers like putty knifes. ACMOS is to platens as Pam is to your frying pan. ACMOS prevents the glue from drying to the platens. At the end of the day you simply take an air hose and blow off the glue. This is much faster, saves time and is less invasive than scraping.
Article Copyright 1999 John Ersing, Veneer Systems Inc.
(back to top)
Veneer Processing
by John Ersing and John Van Brussel
Veneer Systems Inc.
www.veneersystems.com
Tel: 800-825-0840
Email: jvanbrus@veneersystems.com
