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What Is A CNC Router Spoilboard, Why It's Important

CNC Rouoter Spoilboard

by Garrett Fromme

If you’re brand new to CNC routers, then you’ve probably heard the term spoilboard, or waste board. Well, you’ve heard the term because it is an important aspect to CNC routers, and making sure your CNC router projects come out awesome.  
What Is A Spoilboard

The spoilboard is the surface your project is clamped to. It is usually made of a meterial called MDF, or other soft material.

What is a spoilboard for CNC rouoters

The spoil board is the surface beneath your CNC router project

When you are cutting a project, you sometimes want to cut it out. That means the router bit must cut through the project, and cut slightly into the underlying surface. The spoilboard is is that surface.

What is a spoilboard for CNC rouoters

Sometimes, we accidentally cut quite deeply into the spoilboard. You want to ensure your router bits will not be damaged when you do this. That’s why the spoilboard is made of soft material.

In fact, that is exactly why it is called a spoilboard, or waste board. Because we cut into it often enough, that it eventually gets ‘spoiled’, and needs to be replaced.

There is another thing you must consider when it comes to the spoilboard on your CNC router.

The top surface needs to be parallel to the motion of the router. If not, your projects will not carve right.

They will be cut too deep on one part of the project, and too shallow on the another.

A worse scenario is, if the spoilboard is warped relative to your router motion. In this case, when you clamp your project to a warped spoilboard, the project piece will be warped while it is being carved.

When the carve is complete, and clamps released, the project will spring back, and the entire project will be deformed.

Yes, even a slight warp will cause problems to your project. They are often undetectable until you start to do your finish work. Unfortunately, many new CNC router owners find this out the hard way.

How To Flatten A Warped, Or Non-parallel Spoilboard

When your CNC router is first set up, it’s standard procedure to make sure the spoilboard is properly flattened before you start carving projects. That way, you can prevent these issues from the get-go.

And spoilboard surfacing (or flattening) is the standard procedure to do this.

We need to write a program, or use a utility program, to write a surfacing routine. Some CNC router control programs, like gSender, will do this for you.

It may sound intimidating to ‘write’ your own program to do this, but it is actually quite easy, provided you have design softyware to design your CNC router projects. There are videos on the IDC Woodcraft YouTube channel that cover this.

Some CNC router control programs, like gSender, will even write the surfacing routine for you.

But, the one thing you must have to accomplish spoilboard flattening is a surfacing bit. It’s also called a spoilboard router bit, or flattening bit, or spoilboard cutter. The proper term is ‘surfacing bit‘.

What Is A Surfacing Bit

The surfacing bit is a wide flat cutter designed specifically for this purpose. 

When we are surfacing our spoilboard, we are only removing a thin layer of material from the top. The nature of the bit design allows for rapid cutting while leaving behind a smooth surface.

There is another benefit to a surfacing bit. You can flatten warped boards that otherwise would be no good for project work. And you can also resurface a botched project, so you can use it again.

The spoilboard surfacing bit is not used often in CNC router project work, but it WILL BE the first CNC router bit you will use. 

CNC Router Spoilboard Surfacing Bit

That’s why they call the spoilboard surfacing bit “the necessary bit“.

If you are unsure where to get a surfacing bit, or which one to use, you can get one from the IDC Woodcraft store by clicking here.

To know how to set up feeds and speed for this bit, click here to download a FREE feeds & speeds table. 

In any case, please be sure to surface your spoilboard BEFORE you make any projects. You’ll save yourself an unfortunate surprise.

Comments are welcome on this article. If you have other uses for surfacing bits, please make suggestions. Thank you!

Happy CNC’ing


Garrett Fromme - IDC Woodcraft

Are you ready learn & grow on your CNC journey. If you have any qustions or want to learn more about something, please don’t hesitate to reach out! I’m here to support you!

Learn more Garrett Fromme. Have Questions? Contact Me.

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