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Mill away your problems

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Edgebanding is an art, and like art it needs to be perfect to impress.
We can see the smallest imperfections and once we see it, it cannot be ‘unseen.’ The smallest nick, gap or glue line gets amplified once we know what to look for. The same goes to a certain extent for feeling or hearing, but that is not as relevant for this subject.
For many years, woodworkers have tried to create an edge that is as clean as possible, but environmental conditions and processes in our shops make this very difficult. Some of us can ignore some imperfections, but most of us are pushed by our customers to produce a product that is as close to perfect as humanly possible.
So, what are the issues we have to deal with?
A common problem is the little step on the bottom edge of a board that is created by the scoring blade when cutting on a panel saw. Even on a perfectly-adjusted panel saw, the scoring blade is set a tiny bit wider than the main blade to avoid chipping with the main blade. This small offset will create a wider glue line on one side of the panel. 

If the boards are cut by a nesting router there is no scoring blade, but the nesting process produces another problem. The router bits used in the nesting process, because of their small diameter, pull instead of cut some of the fibres in the loose center of the panel core. These fibres stand out and prevent a perfect edge application and/or contaminate the glue application unit. You can easily tell the difference between boards cut on a saw or a router by sliding your fingertips over the cut edge.
Another issue is the swelling of particle board. Sometimes we cut panels for a job that is only due to be edgebanded the next day or even the day after. If our shop is in an area with high humidity, especially in the summer, the particle board edges soak it up like a sponge. This can lead to significant swelling of the outer board edges, which affects the tracing of the top and bottom trimming units. The result is a line where the trimming unit cuts into the top laminate layer. 
The most common flaw is tear-outs in the laminate at the edges. Whether these tear outs are due to dull tooling while cutting or are made later during handling, the result is the same – highly visible spots, which stand out like a tuxedo at the beach.
To fix these imperfections either before, during or after assembly requires a lot of time, manpower, lots of white-out and a steady hand.
The fastest and most efficient way would of course be to prevent the imperfections right from the beginning, but there is a close second. How easy would it be to simply mill away all these problems and their associated costs? This can be achieved by one of the most useful aggregates in the edgebanding process, which is the pre-milling aggregate, also called a jointing unit. The main component of the pre-milling aggregate is a set of milling heads, which are mounted precisely in line with the glue application unit and provide the reference line on the edgebander for all the processing aggregates. The shafts of the pre-milling motors are mounted perfectly vertical to provide a 100% straight-up edge so that the pressure zone puts even pressure on both the top and bottom edge. 
The adjustable infeed fence allows you to adjust the amount of material, which will be milled away. Most pre-milling aggregates can trim up to 3mm.
To avoid chipping at the front end or the tail end of the board, the two milling heads are designed to jump in and out pneumatically. The first milling head is rotating against the feed direction and is milling into the front edge of the board. The second milling head, which is rotating in the opposite direction, meaning in feed direction, will jump into the board after the front edge has passed, and the first milling head will retract from the board once an overlap has been established. 



The laminate layer is more abrasive and harder than the particle board core and will dull the cutters faster. The bottom side of the board is typically at a fixed height and will wear a fixed point on the milling tool. This part of the tool will wear out fastest. Therefore it is important that the milling heads can be vertically adjusted to utilize the whole cutting surface of the tools. To reduce the noise during operation the tooling manufacturers have created special low-noise designs and the aggregates are mounted under noise dampening hoods.
Another benefit of the pre-milling comes into play when all four sides of a board are edge banded. The end-trimming unit on edgebanders can never cut 100% square to the board, it always requires a small angle to keep the cutting edge of the blade away from the leading and trailing edge. This means that when I apply the 3rd and 4th edge to a board, I have an incrementally larger gap on the vertical edges. If I use a pre-milling aggregate this tiny angle will be removed together with the 1-2 mm clean-up allowance and my glue line on the vertical board edges is just as perfect as the one on top and bottom.
Pre-milling is one of the most helpful features and thanks to the latest developments, this technology is available (and affordable) even in the smallest machines. To quote someone who has owned and operated many edgebanders in his life: “I would accept a lot of compromises, before I would give up pre-milling.”

Christian Vollmers is the president of HOMAG Canada Inc. He can be reached at Christian.Vollmers@ homag-canada.ca or visit the website at www.homag-canada.ca

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