PCD Router Cutters

Introduction

Recent years have seen the adoption of Polycrystalline Diamond (PCD) routers, characterised by their free cutting ability and long life, for many applications especially in the wood work and plastics industries. PCD is now the first choice for machining materials such as MDF, laminated chipboards and many of the glass filled epoxy resins. Hamilton Lichfield manufacture a complete range of these tools the great majority of which are to customers' specific requirements. The following notes offer a guide to the choice of tools available and to our standard products.

Advantages of PCD

There now exists many video and written case histories to demonstrate the considerable advantages that may be expected from PCD when used on the correct application. These may be briefly stated as follows:-

1. Exceptionally long production runs between tool relaps when compared to other tool types. This leads to enhanced cost effective production with reduced machine down time and consequent savings in tool stock holding.

2. Tighter tolerances may be held throughout the extended life cycle of the tools giving more consistent finished components.

3. Usually higher component finishes are obtainable than with conventional tooling.

Tool Construction

PCD has significant advantages over tungsten carbide, but may initially appear to be a relatively expensive material to use as a tool blank. Usually the resulting high initial tool costs are more than amply repaid in service, however several different approaches can be adopted to reduce tool costs in cases where price is pre-emminent, such as for short runs of a given component.

There are other manufacturing considerations which may also effect the type and price of the router purchased. These are listed as follows:-

a) Does the router need to plunge through the work piece before routing, as it would if commencing the cut from the centre of the board? Or will it be used for profiling only?

b) Does the router require a straight edge cut or is a formed profile needed, for example; Edge Moulding Cutters?

c) Is the material to be routed laminated? In this case the router may require 1 or 2 shear angles depending upon whether the material is laminated on only one or on both sides. The purpose of the shear angle is to provide positive pressure on the laminated edge, during cutting, to prevent it from lifting.

The following notes describe some of the methods of fabrication employed and the range of standard tools:-

1. Segmental Routers

The essence of the segmental router is the use of either rectangular or half round PCD pieces to build up the cutting length in an inexpensive manner. Figures 1 & 2 schematically illustrate the construction of these segmental routers, it is important that the tips on each side of the tool overlap to give an effective continuous cutting length. Figure 2 shows the plunge tip positioned so that it crosses the centreline of the tool to provide a drilling facility.

Figure 1

Standard Segmental PCD Router
(without Plunge facility)

Figure 2

Standard Segmental PCD Router
(with Plunge facility)

It may readily be seen that providing the tool diameter is large enough the segmental principle may be utilised to produce tools of any required depth of cut. Table 1 gives the tool codes and dimensions of our standard range of these routers.

Table 1

Standard Segmental Routers

Cutting	Tool	I-----------------------Length of cut---------------------------I
Diameter	Code	15MM	20MM	25MM	30MM	35MM	40MM	STD Holder
1/2" or 12mm	SR1-	SR1-15	SR1-20	SR1-25	SR1-30			1/2" DIA x 50mm
1/2" or 12mm	SR2-	SR2-15	SR2-20	SR2-25	SR2-30			12mm DIA x 50mm
5/8" or 16mm	SR3-	SR3-15	SR3-20	SR3-25	SR3-30	SR3-35		5/8" DIA x 70mm
5/8" or 16mm	SR4-	SR4-15	SR4-20	SR4-25	SR4-30	SR4-35		16mm DIA x 70mm
3/4" or 20mm	SR5-		SR5-20	SR5-25	SR5-30	SR5-35	SR5-40	3/4" DIA x 85mm
3/4" or 20mm	SR6-		SR6-20	SR6-25	SR6-30	SR6-35	SR6-40	20mm DIA x 85mm
1" or 25mm	SR7-		SR7-20	SR7-25	SR7-30	SR7-35	SR7-40	1" DIA x 100mm
1" or 25mm	SR8-		SR8-20	SR8-25	SR8-30	SR8-35	SR8-40	25mm DIA x 100mm

Note: - If plunge cut is also required modify code by adding P eg: SR1/P-20

Advantages of Segmental Routers

* Inexpensive for the length of cut obtainable.

* Flexible - segments may be pulled out to maintain diameter when relapped.

* Top and bottom segments may be positioned to give shear cuts.

* Individual segments may be replaced if badly damaged.

Disadvantages of Segmental Routers

* A small witness mark may be seen on certain materials where teeth overlap, sometimes this is unacceptable.

2. Non-Segmental Routers

To overcome the potential problems with marks being left in the material, a range of tools are produced from full PCD strips. This approach is more expensive, particularly for the longer cutting lengths, as the PCD strips have to be cut from the centre of a large disc. However, now that 70mm diameter discs are available there is little practical restriction on the size of the tools that can be manufactured in this manner.

Figures 3 & 4 illustrate the non-segmental tools and Table 2 details the range of standard tooling.

Figure 3

Standard Non-Segmental PCD Router
(without Plunge facility)

Figure 4

Standard Non-Segmental PCD Router
(with Plunge facility)

Advantages of Non-Segmental Routers

* Produces finest component finishes without tool marks or other blemishes

* Tools better balanced, important on high spindle speed machines.

Disadvantages of Non-Segmental Routers

* More expensive to produce.

* PCD teeth more difficult or expensive to repair if badly damaged.

Table 2

Standard Non-Segmental Routers

Cutting	Tool	I--------------------------Length of cut------------------------------I
Diameter	Code	15MM	20MM	25MM	30MM	35MM	40MM	STD Holder
1/2" or 12mm	NSR1-	NSR1-15	NSR1-20	NSR1-25	NSR1-30			1/2" DIA x 50mm
1/2" or 12mm	NSR2-	NSR2-15	NSR2-20	NSR2-25	NSR2-30			12mm DIA x 50mm
5/8" or 16mm	NSR3-	NSR3-15	NSR3-20	NSR3-25	NSR3-30	NSR3-35		5/8" DIA x 70mm
5/8" or 16mm	NSR4-	NSR4-15	NSR4-20	NSR4-25	NSR4-30	NSR4-35		16mm DIA x 70mm
3/4" or 20mm	NSR5-		NSR5-20	NSR5-25	NSR5-30	NSR5-35	NSR5-40	3/4" DIA x 85mm
3/4" or 20mm	NSR6-		NSR6-20	NSR6-25	NSR6-30	NSR6-35	NSR6-40	20mm DIA x 85mm
1" or 25mm	NSR7-		NSR7-20	NSR7-25	NSR7-30	NSR7-35	NSR7-40	1" DIA x 100mm
1" or 25mm	NSR8-		NSR8-20	NSR8-25	NSR8-30	NSR8-35	NSR8-40	25mm DIA x 100mm

Note: - If plunge cut is also required modify code by adding P eg: NSR1/P-20

3. Thin Layer Routers

Tool blanks are produced, by a special technique, from deep layer discs of PCD such that a long length of PCD is obtained but with only a 1.5mm diamond depth (see Figure 5). This is not only a cheap way of obtaining a long section of PCD but has the advantage of being seated on an 8mm depth of tungsten carbide substrate which will be more easily fabricated.

Figure 5

End View of Thin Layer Router

Angular Cutting of PCD Disc to produce segments
for 'Thin Layer' Routers

This process is often employed for thin machine knives and cutter blocks but it is also useful for router production either on grounds of technical merit, small diameter shanks etc, of cost. Currently, these tools are only made to order, we are always happy to advise on the application of this product.

Advantages of Thin Layer Routers

* Inexpensive non-segmental routers with long cutting lengths.

* Mechanical fixing, as opposed to brazing, can be considered.

* May produce small diameter or complex tools which are not suited to other
fabrication methods.

* Suitable for short production runs.

Disadvantages of Thin Layer Routers

* Relap life limited by small depth of PCD.

* Tools may be written off if badly damaged.

4. Formed Routers

There are many applications that require a profiled router, particularly in the woodworking industry such as panel raising and Ovolo cutters, Fig 6 shows a typical example.

Figure 6

Hamilton Lichfield employ computer aided design in the manufacture of this type of tooling to ensure optimum utilisation of the PCD. In production a variety of techniques including CNC wire erosion, die sinking and lapping are used to ensure that perfect profiles with keen cutting edges are obtained. Where necessary Hamilton Lichfield routers are balanced after manufacture to ensure optimum performance on all modern high speed routing machinery, this is of particular importance with single flute routers.

All styles of formed router are available to order and we are equally happy to work from tool or component drawings, samples of existing tooling or from the required formed component.

NOTES FOR THE USE AND PROTECTION OF PCD ROUTERS

1. Polycrystalline diamond is very wear resistant but also BRITTLE; it may be chipped very easily particularly by metal objects, spanners etc. Always handle the tools carefully and keep in a protective box when not in use.
2. The tools are most vulnerable when being installed or removed from the machine. It is advisable to protect the cutting edges when carrying out these operations, a wooden block bored to suit the tool is a convenient method.
3. After setting the tool always carry out a short test cut to ensure that the correct depth of cut has been programmed.
4. When the tools are ready for relapping they may become blunt and even chip; tools should not be left running in this condition as more extensive damage may occur.
5. Bluing of the steel shank, due to the build up of excessive heat and also increasing cutting noise are often good indicators of the state of the tools that are ready for servicing. Please return for repair before excess use renders them scrap.