How to Choose Linear Rails and Blocks for a CNC Build
Please note: this guide was written with the help of AI and may contain mistakes or outdated information. It is general information only. Always do your own research (DYOR): check product specifications with the manufacturer, and use a qualified professional for any electrical, security or gate installation.
Linear rails and blocks (also called linear guides or bearings) carry the moving parts of a CNC machine and keep them running straight. Choosing the right size and type is one of the most important parts of a build.
How a linear guide works
A guide has two parts: a hardened steel rail bolted to the frame, and a block (carriage) that rides on it on recirculating steel balls. The block bolts to your moving part. Because the balls roll, movement is smooth and the guide handles load from several directions.
1. Pick the rail size
Rail sizes are named by their width in millimetres, for example 15, 20, 25, 30 and 35. Bigger rails carry heavier loads and resist twisting better. Small machines and 3D printers often use a small size, while routers and mills move up in size with the weight of the gantry and the cutting forces.
2. Choose the series
- HG series: a high-load, rigid series that is a popular choice for CNC machines.
- EG series: a lower-profile series for compact designs where height is limited.
- Miniature guides: small rails for light-duty or compact axes.
3. Standard or long block
Long blocks are longer and carry more load, and they resist tipping better, but they use more of your travel. Choose a standard block for general use and a long block where loads or moments are high.
4. Flanged or square block
Flanged blocks have a wide flange that bolts from above or below, which makes mounting easier. Square (narrow) blocks are more compact and mount from the top only. Pick the one that fits your carriage design.
5. Plan the layout
- Use at least two rails per axis, with two blocks per rail for a stable carriage.
- Rails must be mounted on a flat, rigid surface. Any twist in the frame goes straight into the machine.
- Keep rails parallel. Use a reference edge and check with a dial indicator if you can.
6. Match it to your drive
Rails guide the movement, but something still has to drive it. Compare ball screws and rack and pinion. A rigid frame matters too: see T-slot vs V-slot profile.
Shop the range
Browse all linear guides or go straight to linear blocks. Send your machine size and loads to info@diygeek.co.za, and we will help you pick before you order.
AI-assisted content. Please do your own research (DYOR) before you buy or install.