Bits&Bits 1/4″ Short-Flute Compression Router Bit

A 1/4″ collet. Every bit in this range has a 1/4″ shank, including the 1/8″ and 5mm cutting-diameter bits, so it fits a router with a 1/4″ collet. Cutting diameter is a separate spec: most of the bits cut 1/4″, the long-reach compression bit cuts 1/8″, and the 5mm up-cut bit cuts 5mm.

It depends on the bit. Bits&Bits states that its spiral and compression bits can be used in a CNC, a handheld router or a router table, and that the compression bits are designed for CNC work at high feed rates. The three 1/4″ flush-trim bits (up-cut, down-cut and compression) are the exception: Bits&Bits specifies them for light, controlled trimming in a trim or compact router after rough-cutting close to the finished shape, and does not recommend them for heavy stock removal, larger high-torque routers or router-table use.

It depends on which face of the cut needs to stay clean and where you want the chips to go.

• Up-cut bits move chips up and out of the cut; the low-helix version uses a shallow spiral to help reduce upward pull on the workpiece, and the single-flute O-flute version is made for plastics, acrylic, aluminum, foam and solid-surface material where chip clearance matters.
• Down-cut bits push chips into the cut and help leave a clean upper edge, so they suit grooves, pockets and profile cuts in plywood or laminated material where the top surface matters; plan chip removal when routing deep pockets.
• Compression bits combine an up-cut tip with down-cut upper flutes to help control tear-out on both faces of wood, plywood and double-sided laminated panels, provided the cut runs deeper than the spiral change.

It varies by bit, so check the workpiece materials listed on each product. The spiral, compression and flush-trim bits are rated for wood, plywood and laminated material (each listing shows which), and the compression bits are the ones also called out for double-sided laminated panels and melamine. The 1/4″ low-helix up-cut bit is rated for plastics, acrylic, foam, wood and plywood, and the O-flute up-cut bit is the only one rated for aluminum and solid surface, alongside plastics, acrylic and foam. Set feeds and speeds for the specific material; a setting for acrylic is not a universal setting for aluminum or other materials.

Slightly deeper than the bit’s up-cut section, so the down-cut flutes are cutting the top face of the workpiece. Bits&Bits’ rule of thumb is that the up-cut section is typically equal to the bit’s cutting diameter, but go by the figure on the product page where one is given. On the 1/4″ spiral compression bit (425-CM250) the spiral change is at 0.22″; on the short-flute compression bit (425-CM250SF) the up-cut section is only 0.12″, which lets the down-cut flutes engage closer to the bottom of the cut for mortise-style cuts and thinner double-sided laminated material. At the correct depth you should not see tear-out or chip-out on either edge; if you do, the first pass is not getting past the up-cut flutes.

AstraHP is Bits&Bits’ proprietary high-performance coating, and every bit in this range has it over a solid-carbide body. Bits&Bits says the coating allows higher speed and feed rates, extends tool life, and increases lubricity in abrasive material.

Bits&Bits does. Every router bit we carry is a Bits&Bits solid-carbide bit, a third-party brand we stock alongside our own accessories; they are not made by ToolCurve. Because they are not ToolCurve-made, they do not count toward the $75 free-shipping threshold.