When planning wood, selecting the right router bit is crucial for achieving the desired finish and quality in your woodworking project. The router bit you choose will depend on the specific purpose of your planing task, the type of material you are working with, and your desired cut depth, width and finish. Some key factors to consider are straight vs spiral bits, upcut vs downcut, and diameter. This comprehensive guide will walk you through the key types of router bits for planing wood and how to choose the best one for your needs. Whether you are smoothing rough lumber, flattening warped boards, cutting grooves or dados, or putting decorative edges on boards, having the right bit is essential for success.
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Router Bit Basics
Router bits come in two main styles – straight and spiral. Straight bits have cutting edges arranged in a helix along the length of the cylinder. Spiral bits have one continuous spiral cutting edge from top to bottom. Here are the key differences:
Straight Bits:
- Less expensive
- Good for general purpose planing, edging, and grooving
- Produce more tearout in grainy woods like oak or walnut
Spiral Bits:
- More expensive
- Produce very smooth, tearout-free cuts in all wood types
- Excel at planing duties across grains and figured wood
- Stay sharper longer than straight bits
In terms of diameter, 1⁄2 inch and 1⁄4 inch shank router bits are the most common. 1⁄4 inch shank bits can be used in both standard and trim routers, while 1⁄2 inch shank bits require more powerful standard routers. Smaller diameter bits 1⁄2 inch or less are good for edge planing or smaller grooving tasks, while larger diameter bits 1-3 inches work better for surface planing larger boards.
Planing vs Cutting
It’s helpful to distinguish between planing and cutting functions when choosing a router bit. Planing involves smoothing, flattening, or surface preparation. The goal is to remove material evenly across a surface without leaving grooves. Cutting involves removing material to create a specific profile shape or cut grooves, rabbets, or joints. For dedicated planing, straight or spiral upcut bits are recommended. For cutting edges or joints, straight or spiral downcut bits work better.
Upcut Bits
Upcut router bits pull chips upward out of the cut as they rotate. The lifting action provides a super smooth surface ideal for planing. Upcut bits are recommended for:
- Smoothing rough sawn lumber
- Flattening cupped or warped boards
- Preparing surfaces for finishing
Downcut Bits
Downcut router bits push chips downward into the cut as they rotate. This plunging action leaves clean edges ideal for cutting defined shapes. Downcut bits are recommended for:
- Cutting rabbets, dados, grooves
- Edge profiling
- Cutting hinge and joinery recesses
Bit Selection for Planing
If your primary goal is to smooth and flatten lumber, here are some router bit recommendations for planing wood:
Surfacing Lumber
For removing saw marks, smoothing rough sawn lumber, and preparing boards for finishing, a 1-1/2 to 3 inch diameter straight or spiral upcut bit is ideal. The large diameter allows you to hog off material aggressively to flatten uneven stock. Lower feed rates produce very fine finish planing.
Flattening Cupped/Warped Boards
A 1-1/2 to 2 inch diameter spiral upcut bit will make quick work of removing cups and twists from warped lumber. The spiral upcut willplane smoothly across changing grains with no tearout. Reduce passes for a final smooth surface.
Edge Jointing
1/2 to 1 inch diameter straight or spiral upcut bits allow precision planing of board edges to create tight seamless glue joints. Use a guide bearing for consistent edge planing depth along the length.
Smoothing Rough Edges
Use a 1/4 to 1/2 inch diameter spiral upcut bit to cleanly smooth saw marks and rough edges on boards. The narrow width provides excellent control for delicate edge planing tasks.
| Planing Task | Recommended Bit |
|---|---|
| Surfacing Lumber | 1-1/2″ to 3″ diameter straight or spiral upcut |
| Flattening Boards | 1-1/2″ to 2″ diameter spiral upcut |
| Edge Jointing | 1/2″ to 1″ diameter straight or spiral upcut |
| Smoothing Rough Edges | 1/4″ to 1/2″ diameter spiral upcut |
Bit Selection for Cutting
When the goal is to cut defined profiles or joinery, downcut bits provide superior chip clearing and edge finish:
Edge Molding
Use a 1/2 to 1 inch diameter straight or spiral downcut bit to cleanly shape decorative edges for boards. Bits with guide bearings excel at maintaining a consistent edge profile depth.
Cutting Dados and Grooves
1/4 to 1/2 inch diameter straight downcut bits are ideal for cleanly cutting narrow dado and groove joinery cuts for shelves, panels, and splines. Use multiple passes for wider grooves.
Rabbet Joints
Cut smooth, chip-free rabbets with a 1/2 inch diameter straight or spiral downcut bit and rabbeting guide bearing. Adjust bit height for precise rabbet depth control.
Hinge/Hardware Slots
1/2 inch straight downcut bits with guide bearings are excellent for recessing hinge and hardware mortises with clean edges and depth control.
| Cutting Task | Recommended Bit |
|---|---|
| Edge Molding | 1/2″ to 1″ diameter straight or spiral downcut |
| Grooves and Dados | 1/4″ to 1/2″ diameter straight downcut |
| Rabbet Joints | 1/2″ diameter straight or spiral downcut with bearing |
| Hinge/Hardware Slots | 1/2″ straight downcut with bearing |
Bit Speeds, Feeds, and Passes
Along with choosing the right router bit type and size for planing and cutting, proper adjustments of bit speeds, feed rates, and number of passes will ensure high quality results:
Bit Speeds: Refer to router or bit manufacturer specs for ideal RPM. Faster speeds require slower feeds. Too slow risks burning.
Feed Rates: For planing, 30-50 inches per minute is ideal. For cutting, slower 20-30 inches suits detailed work. Too fast risks chip out.
Passes: For planing, make light passes of 1/64″ or less. For cutting, take shallow 1/32″ depth passes for clean chips and minimum force.
Don’t overload the bit – several light passes achieves better results than one deep pass. Let bits spin back up to speed between passes. Go slow and progressive. Proper router speed control and feed rate technique is key for success with any bit.
Summary
The type of router bit you choose for planing wood depends on your specific project needs and desired results:
– Use large 1-1/2″ to 3″ diameter upcut bits for aggressive surfacing, flattening, and edge jointing.
– Opt for smaller 1/4″ to 1/2″ diameter upcut bits for fine smoothing and finish planing tasks.
– Choose downcut bits from 1/4″ to 1-1/2″ for edge shaping, rabbets, dados, grooves, hinge slots, and joinery cuts.
– Spiral router bits excel for smooth, tear-out free planing on figured and changing grain woods.
– Straight bits are more economical for general purpose stock prep and woodcutting tasks.
Adjust feed rates, speeds, and passes appropriately for clean results. Following these router bit selection guidelines will have you planing boards, flattening surfaces, and cutting joints with ease. The right bit makes all the difference!