why spiral cutters ?
Straight fluted Tungsten Carbide tipped cutters are certainly the most popular type of cutter used by router users . Improvements in design , materials and manufacturing technology over the years has enabled these cutters to cut a multitude of abrasive manmade materials .
With certain applications , the impacting action of straight fluted cutters as the tool rotates can cause fibres to pick up and this results in feathering on veneers and softwoods . Also when feeding fast they can cause the chips to choke up in the cut grooves , limiting cutting efficiency and this reflects in the finish .
But , with the arrival of the spiral or helical shaped fluting which is machined from solid carbide rods or high speed steel , a number of advantages appeared , especially for the large operators with CNC equipment . But even those using hand routers are now choosing to benefit from the slicing “ scissor type action ” of helical fluting . This slicing action imparts an even load on the router and reduces vibration , as there is always a cutting edge in contact with the material .
by Jim Phillips
Jim Phillips gives an insight into the benefits of using spiral cutters .
The design of spiral tooling enables faster feed rates , up to 10 metres a minute depending on the cutting depth . The helical geometry of spirals vary to suit different applications of the industry . There are three basic types :
Up-cut spirals with right hand helix
This type of fluting lifts the chips in an upward direction away from the cutting area , thus preventing clogging . Although this is an advantage , some form of dust extraction is necessary .
Burning when plunge cutting is all but eliminated and drilling with the router set at a lower speed , becomes an attractive proposition .
On laminated boards there may be some surface feathering which a down-cut tool would prevent . The upwards action of the up-cut may cause the workpiece to rise and good clamping is recommended .
Down-cut spirals with left hand helix
With “ down-cuts ”, feed speed is a little restricted but feathering is virtually eliminated and the finish of cut is first rate . For this reason , such tooling is often chosen when machining boards faced with veneers , laminates or foils .
Combination up and down-cut spirals
When boards are faced on both sides , the combination spiral comes into its own . If the router is grooving or trimming veneer edgings , the finish is guaranteed to have a clean cut edge on both faces . In operation , the upper down-cut part of the spiral severs the grain on the top surface of the board and the lower up-cut severs the grain on the underside .
When deciding on the choice of cutter , the extra cost of using spiral cutters should be considered . First check to see whether your standard TC cutters have been regularly honed to bring them back near to the original edge . A tendency to feather edge can also be avoided by scoring a pre-cut line prior to routing the groove . IP
Up-cut spirals remove the waste , but leave a slightly ragged edge .
Down-cut spirals give a clean sharp edge but compact the waste in the mortise .
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