Router cutters - types, applications and care
There are two basic ways to guide a router:
- Using a fence or template to guide the body of the router:
- Using a self guiding router cutter.
- Plain cutters:
- Self guiding cutters.
Plain cutters consist of a plain shank attached to the cutter.
Self guiding cutters either have a solid guide or a bearing race attached 'under' the cutting edge.
The solid guide type is cheaper to purchase but the rotation of the solid guide against the workpiece can cause heat marks where it bears against the surface of the wood.
Bear guides (where a bearing is mounted under the actual cutter) tend to give a better finish as there is no rotational friction against the wood surface.
Router cutter material.
High Speed Steel (HSS)
Made from high speed steel, these are ideal for cutting and finishing soft timber (i.e. not hard woods or man-made board), however they are susceptible to damage due to overheating when heavily used. They can be re-sharpened by honing on a wet stone, but this is a delicate job if the cutter is shaped and can affect the balance of it.
Tungsten Carbide Tipped (TCT)
The actual cutting edges are made from tungsten which are brazed onto a ground steel blank. These are ideal for all timber and man-made board. The cutting edges will last far longer than HSS cutters, however TCT cutters are harder to sharpen; they really need a fine diamond or ceramic stone.
Solid Tungsten Carbide (STC)
STC cutters tend to be small diameter cutters which would be difficult to braze on carbide cutting tips. As the cutting edges are the same as TCT cutters, the comments above also apply to STC routing cutters.
Replaceable blade cutters
There cutters use a steel body to which replaceable tungsten cutting edges are fixed (normally screwed), they are useally cutters of large diameter as replacing cutting edges on small diameter cutters tends not to be economical.
Always insert at least three quarters of the shank of a router cutter into the router collet and ensure the collet is fully tightened. Failure to do this may cause the cutter to be subjected to excess flexing due to the side pressure of the workpiece, this can lead to a poor finish and even the cutter coming out of the collet, this can lead to damage to the workpiece (definitely), damage to the cutter (probably) and damage to the router or operator (possibly).
Before (and after) using a cutter check its condition:
- Make sure the cutting edges are sharp, if necessary re-sharpen or discard;
- On HSS cutters, check for signs of overheat - this can be indicated by the cutting edges turning blue;
- Make sure the shank is not scored, radial scoring indicates that the cutter has been used with the collet not fully tightened. Damaged shanks can cause the cutter to run 'out of true';
- Make sure the cutter is clean, remove all trace of glue, resin, sawdust etc.