Skip to content
WISHLIST
Router Bits Explained: Upcut vs Downcut vs Compression vs Straight
When you're working with a CNC router, the bit you choose makes a huge difference. With so many CNC router bit types available — Upcut, Downcut, Compression, and Straight router bits, it can get confusing fast. This guide breaks down what each bit does, when to use it, and how to tell them apart.
Spiral vs. Straight Router Bits: A Quick Overview
Spiral router bits, like Upcut, Downcut, and Compression bits, are designed with helical flutes that cut through material with a shearing (think slicing) action. This design offers several advantages over traditional straight router bits:
- Cleaner Cuts: The shearing action reduces tear-out, especially in materials like plywood and MDF.
- Efficient Chip Removal: Spiral flutes evacuate chips quickly and effectively, minimising heat buildup.
- Longer Tool Life: Typically made from solid carbide, spiral bits maintain their sharpness longer than their straight counterparts.
While straight bits are more affordable and easier to sharpen, they cut with a chopping motion, and may not provide the same level of finish, speed or efficiency as spiral router bits.
Understanding the Different Bit Types: Upcut vs Downcut vs Compression vs Straight
Please scroll to the side to view all the details.
| Straight | Upcut | Downcut | Compression | |
| Function | Cuts straight at 90° into the material without any spiral action. | Pulls chips upward, away from the cutting area. | Pushes chips downward into the material. | Combines upcut and downcut flutes; downcut at the tip and upcut above. |
| Best for | Basic routing tasks, edge trimming, and applications where cost is a concern. | Deep cuts, mortises, and slots where efficient chip evacuation is essential. | Shallow cuts, dados, and applications requiring a clean top surface. | Cutting laminated materials like plywood or melamine where both top and bottom surfaces need to be clean. Must be used in conjunction with effective chip extraction. |
| Pros | Cost-effective, easy to sharpen. | Excellent chip removal, ideal for deeper cuts. | Produces a smooth top finish, minimises top-edge splintering. | Clean cuts on both (top and bottom) surfaces in a single pass. |
| Cons | Less efficient chip removal. Can cause chip-out in board products. | Can cause tear-out and chipping on the top surface of the material. | Less effective at chip evacuation. Only suitable for shallow cuts. | Requires full-depth cuts to utilise both cutting actions effectively. |
How to Tell If It’s an Upcut, Downcut, or Compression Bit
Here's a simple trick:
- Hold the cutter vertically with the cutting portion of the cutter at the bottom.
- Look at the cutting edge:
-
- If it is spiralling upwards from the LH side of the cutter, up to the RH side, it's an upcut cutter.
-
If it is spiralling downward from the LH side down to the RH side, it's a downcut cutter
- If it switches direction halfway up, it's a compression cutter. These bits start with an upcut at the bottom and transition to a downcut from the top.
Watch our short video where Glen explains the differences between the 3 main types of spiral router bits:
Matching Cutter Types to Materials
When it comes to choosing the right CNC router bit for your material, certain cutter styles are more commonly used for specific applications:
- Upcut cutters are often the go-to for cutting solid timber, plastics, and aluminium, thanks to their excellent chip evacuation and clean bottom-edge finish, perfect for materials without a delicate top surface.
- Compression cutters shine in laminated boards like plywood, melamine, and MDF, where a clean finish on both the top and bottom surfaces is critical.
- Downcut and straight cut bits are often preferred for thinner materials such as ACM (aluminium composite material) and thin plastics. They provide better control, reduce lifting or movement of the workpiece, and minimise tear-out when chip extraction isn't critical.
Selecting the right CNC router bits for plywood, MDF, HPL, board products, and other materials can be challenging due to the many variations and exceptions involved. If you're unsure which bit is best for your specific machining needs, our team is here to help! Contact us today at 0800 488 647 or sales@tungstenandtool.co.nz.
Chip Removal & Surface Finish Results by Bit Type
Please scroll down to view all the details.
| Bit Type | Chip Removal | Best Surface Finish |
| Upcut | Excellent | Bottom surface |
| Downcut | Poor to fair | Top surface |
| Compression | Good with dust collection | Top & bottom |
| Straight | Poor to fair | Depends on material |
Find and select straight or spiral cutters quickly
It’s simple with our online tool finder! Just a few clicks, and you can search and select tools that perfectly match your specific application requirements and machining needs. Our online tool finder not only saves you time but also helps you avoid the frustration of endless tool research. So, why not give it a try today?
Choosing between Upcut, Downcut, Compression, and Straight router bits
Selecting the right router bits comes down to your material and finish needs. For most serious CNC users, spiral bits are worth the investment—they’re faster, cleaner, and more efficient. But for certain tasks like trimming plastic or cutting on a budget, straight router bits still have their place.
If you're in New Zealand, Australia, or the Pacific Islands, and need reliable, high-performance CNC bits, our team can help. We have a full range of industrial router bits, including carbide tipped (TCT) router bits that work across various materials and machines.
Need help choosing the best bit? Contact us today at 0800 488 647 or sales@tungstenandtool.co.nz for more information.
