Without the correct tooling Nested Based Manufacture can pose some problems when routing. The following article outlines which tools to use and when to use them.

There are so many different types of tools available on the market today. Some are suitable for NBM and some are not. Knowing the difference will mean either sucess or failure in the NBM world.There are Brazed tools, diamond bits, single flute, double flute, triple flute, up shear, down shear compression shear etc., etc. We at PROCAM have after hundreds of hours of study concluded that solid tungsten carbide spiral router bits are best suited to NBM.

   


High speed steel router bits have been available for many years and although they did a good job of shearing the fibres in softwood routing the edge could not stand up to the high speeds and feeds of the modern day machines. Over the past few years huge advances have been made in the process of Micro Grained Carbide. Modern CNC tool and cutter grinders mean that a perfect tool geometry can be achieved time after time, resulting in higher cutting speeds and longer tool life. The part of this process which will have the greatest impact on the NBM process is that the cost of this tooling has dramaticaly reduced over the past few years.

Solid tungsten carbide routers will not bend when under the harshest cutting conditions resulting in a cleaner and more accurate cut. Tungsten carbide being much harder than high speed steel, allows significantly longer tool life when cutting even the most agressive materials.

Spiral bits are at their best at high feed rates, so if the application calls for a lot of straight line or large radius routing, spirals excel. But keep in mind: higher feed rates require more hold-down force of the work piece! The efficiency of a spiral is much better at the higher feed rates when compared to conventional straight router bits.

The great advantage of using Spiral Compression Cutters is that they prevent laminate chipping because they push the edge of the laminate towards the core material where it has support. The other advantage is that the cut being both up and down spiral eliminates the lifting action normaly ascociated with spiral flute cutters.

Solid tungsten carbide router cutters are available in roughing and finishing design. It is generally recommended to do a roughing cut prior to the finishing on solid hardwood. The roughing tool's cutting edges feature "chip-breakers". This design allows removal of large amounts of material (high hogging volume), but produces a surface, which is as smooth as a conventional cutter.

The finishing tool is designed to give optimum quality of cut.

The disadvantage of a roughing / finishing manufacturing process is that an additional tool change is required. This disadvantage however is compensated for by higher possible feed rates, longer tool life and better quality of the end product.

There are three basic spiral designs - up cut and down cut and compression (up and down spiral combined in one cutter)

Up cuts shear up, pulling the chips up, this supports the dust collection action. Up cut tools are used when you need good chip removal, and/or when the finished or laminated surface is on the underside. Also an up shear router bit is usually the best choice when grooving, because they won't pack the chips in the groove. Up cuts, by their action, also apply a lifting effect to the work piece, so unless you have a good hold down on the table they cannot be used effectively.

Down cuts are working just the opposite way. They spiral down, pushing the material downwards. They are most effective when the finished surface required is facing up during machining.

Down cuts will also work at higher feed rates because they are enhancing the hold-down force working with the vacuum hold-down, not against it like the up cuts. For this reason they are generally recommended for small parts or hand tools where hold-down may not be as good. The other disadvantage is that the dust removal becomes more difficult because the chips are being forced downwards and away from the dust extractor. With the Procam high velocity dust extraction system because the system was designed with nested base manufacture in mind dust collection is not a problem.

Compression spirals are a more complex tool in that they have down cut flutes on the top and down cut flutes on the bottom. These are used with a large number of nesting manufactures and are primarily for applications where there is a laminated surface top and bottom, and both must have an excellent finish.

Spiral routers can be used in hardwoods, particleboard, MDF, laminates, other composites, plastics, fibreglass, and even aluminium. Once again, because of the variety in materials and machinery, a number of variations in the basic up cut/down cut designs are available.

The following is meant as a general guideline that should help you narrow your choices.

• Double Flute (2 wing): good finish at high feed rates is the prime factor where two - flute bits are used.
• Triple Flute (3 wing): used where an extra fine finish at highest feed rate is required, or in materials that are more difficult to cut. Also three-flute bits can be used when the horsepower is a little low for single or even double flute tools. The disadvantage of a 3 flute cuter is that the clearance pocket between the flutes is much smaller than the 2-flute cutter and therefore clogging of chips may occur.
   
• PROCAM CNC can provide all of the spiral tooling needed for Nested Based Manufacture. See our on line tooling catalogue at www.Procamcnc.com.au or contact Procam CNC on +61 08 9302 2850
  
  When considering the spiral design options, cost and productivity as they relate to the job have to be factored in. Tool cost goes up with size, number of wings, the addition of the chip breaker grind and provision of alternating shear angles. But at an average cost of $1.50 per kitchen this should not even be a consideration. 

Servicing: re-sharpening of spiral router bits requires special grinding machines. Very few in-house service facilities in Australia have such machines available