With 2007 sales of e260m and employees numbering 3,700 worldwide, the Leitz Group is a major manufacturer of precision tooling.
Founded in 1876 by Albert Leitz at its present location in the state of Baden-Württemberg, today the company has 34 sales and nine production companies, as well as a global network of around 200 service stations.
Its product range comprises the full assortment of machine-powered precision tools for machining solid wood, wood products and plastics.
The company says it devotes considerable resources to fundamental technological research and that it regards itself as a partner to its customers in developing safe and efficient operations.
Consultancy services as well as sales are thus part of the offering, covering areas such as tool management, software competence and storage. Training courses are also offered to customers’ staff.
After the initial sale, maintenance of the tools in efficient working order, and reprocessing of them at specialist centres worldwide, is another part of the package, with collection and delivery of the tools being handled by Leitz, says the company.
While the company supplies a wide range of tools for the cutting and shaping of wood based panels in general, an area of particular recent relevance is that of lightweight honeycomb-cored panels.
With their thin panel facings and paper-based cores, these panels offer particular challenges when machining the edges, to accept edge-banding for example.
“The industrial production of these lightweight panels requires special production tools,” confirms Dipl-Ing Richard Patsch, manager of research and development at Leitz. “They are very different in their machining characteristics, so in many cases demand specially-adapted tools.”
Of course the main characteristic of honeycomb-cored panels is that they have large cavities in the middle and this means that standard panel sizing saw blades do not tend to give a good cutting result.
Thus Leitz has developed thin-kerf panel sizing saw blades for this application. Leitz also recommends the use of tools with reduced cutting pressure to avoid collapse of the honeycomb.
“The ideal tool for a smooth cut edge is a circular saw blade with aggressive tooth geometry,” says Mr Patsch. This avoids material tear-out and delamination of
the board.
“The steep cutting edge results in a smooth rise in the cutting power – an essential prerequisite for the best cutting results,” he adds.
It is also important that the cutting pressure is always positioned against the outer layer in boards with an open honeycomb structure, says Mr Patsch, adding that it is important to use a scoring saw blade.
“When Leitz developed the new thin-kerf panel sizing saw blades with this cutting geometry, the cutting width was reduced by a third and with it the cutting forces. A range of saw blades with diameters of 250 to 450mm and appropriate scoring saw blades are available,” he says.
When first using thin-kerf saw blades for this application it is important to check the width of the machine riving knife. The standard riving knife may be too wide and may need to be changed, cautions Mr Patsch.
Edgebanding of these honeycomb panels is another specialised area.
In principle, there are two choices when edgebanding honeycomb panels, Leitz has found.
The choice depends on the structure of the surface panels and the honeycomb.
If the former are thicker than 8mm, the edgeband can be applied directly to the honeycomb panel, being glued to the edge of the surface panel. This requires sufficient gluing surface on the narrow edges of the surface panels and high edge rigidity. This process is preferred with work pieces with profiled edges or when high loads are to be accommodated, such as for table tops. Processing in this case is with conventional hoggers, jointing cutters or shank tools with cutting geometry optimised to reduce the cutting forces, according to Leitz.
The majority of the available light construction furniture boards, however, have thin facings such as 4mm HDF. Edgebanding requires the forming of rebates in the edges of the surface panels and applying an edging strip. Strips of MDF, particleboard or hard fibreboards are suitable for the edging strip.
Profiling tools, specially designed to suit the different materials, machine grooves in the face of the edging strip. These grooves must match exactly the profile in the surface panels. The cutting forces that arise from the milling tool must not cause delamination of the honeycomb core or the surface panel. The cut quality to the honeycomb is not critical, but the honeycomb chips must not constrain the application of the edging strip, says the company, adding that either tooling sets of stacked saw blades, or of tools with a staggered cut, are suitable for this operation.
Before gluing the edging strip, the faces of the surface panels are trimmed, either by hoggers or jointing cutters. If the excess to be trimmed is large, then jointing is preferable because of the high cutting forces on the thin panels. Using hoggers can cause the board to vibrate.
“In principle the two machining procedures are different in the power requirement,” says Mr Patsch. “The cutting power requirement for jointing rises linearly with rising board thickness, whereas it declines with hogging. That means that hogging needs less power than jointing to machine board thicknesses. The Leitz ‘DT-hogging program’ offers a suitable range of hoggers for this application.”
Finishing the edge banded edges on lightweight honeycomb panels is carried out with conventional tools and standard machine set-ups. However, to ensure a smooth-radius hogging without vibration, it is important to reduce the pressure from the surface rollers.