The Ultimate CNC Clamping Guide

Clamping a workpiece correctly is maybe one of the most important steps in the whole CNC machining workflow.  

Indeed, your clamping system will directly affect the vibrations produced during the cut. These vibrations are significantly related to the quality of the cuts, the longevity of the tool and the noise generated by your machine.

However, clamping systems are various and making a good choice isn't an easy task. The following article will compare 8 different types of clamping systems and classify them in terms of safety, cost, ergonomy, adaptability and compatibility with different working areas.

Be aware that the following examples focus on kit frame-CNC machines, we are not dealing with industrial machines.

A video version of the guide is also available:

Attaching a workpiece on your spoilerboard with wood screws doesn’t really need any explanation, but it’s worth to compare it with other systems.

It is one of the most basic ways to clamp a workpiece, but it’s also one of the fastest to set up, while being very cheap and ergonomic. You don’t need anything except a wood board, a driller and some screws.

The two main advantages are that this fixing system is strong and secure and that it allows you to set the fixing point wherever you want.

Of course, it also has a main drawback: it will quickly damage your spoilerboard surface. You will have to regularly change it or flip it.

Another issue with this system is that, due to the fact that screws are on the top of your workpiece, you cannot fully surface it.

To summarize, screws are not the perfect way to clamp a part if you work daily on your CNC router, but we definitely recommend working with this system if you begin with CNC machines. You will have time to think about improving your clamping system once have made all the classical mistakes and your CNC skills improved.

Pros

• really cheap and easy to set up
• provides a strong and secure clamping
• adapted to (almost) any workpiece height  

Cons

•   damages the board quickly
• can't be used for surfacing operations

If you're working with wood, a composite nailer might be the perfect solution for you. 

It is one of the fastest ways to clamp a workpiece. With just a nail gun and a compressor, you can secure your parts in seconds and free them as fast after the job is done. 

Its main advantage is that composite nails will prevent from damaging your bit if you made an error in the G-code. 

We're one of the sole reseller of this solution in EU, and you can find our Raptor/Omer nailer here.

Pros

• really fast
• provides a strong and secure clamping
• no risk of damaging your mills
• allow to mill the entire surface 

Cons

• can't be used with every material
• there's an initial investment needed

Using double-sided tape is one of the easiest ways to clamp a part. It’s pretty straightforward: cover the bottom of your stock with tape and stick it to the working surface.

The first thing to know about this system is that it will only work with high-quality tape. If not, the part will easily detach itself because of the cutting forces, which can quickly become dangerous and generate projections. We recommend using this system with a full enclosure around your CNC to avoid any security issues.

This system can nonetheless prove itself very useful in a lot of different situations:

• When working with sheets of metal or very thin wooden sheets that cannot be easily clamped with another system.
• When you don’t want to leave tabs on your work for a perfect finishing. You need to be sure that the sticking surface of your part will be big enough for it to stay in place once cut from your stock.

In any case, the type of end mill you’re using will be very important. Indeed, upcut end mills will have the tendency to lift your part and detach it from the double tape, while downcut end mills will push the workpiece onto the board.

Pros

•   really cheap and easy to set up
•   very useful for sheets or parts without tabs

Cons

•   not very secure - can be dangerous
•   doesn't work with every type of job

At first, toggle clamps may seem like the perfect fixture for your CNC machine. They can indeed very quickly clamp or release a part, but they also show limitations in the daily use of a CNC router.

Toggle clamps are perfect if you always clamp stocks of the same thickness: very quick and very easy to use. However, as soon as you have to adapt the rubber part to another height, it will become complicated and you will loose the benefits of these clamps. Besides, they clamp the workpiece on the top surface, which doesn’t allow surfacing operations.

We would only recommend the use of toggle clamps for special jobs, such as production batches of identical parts for instance. They can also be very convenient to attach a spoilerboard to the machine frame, providing a very quick way to change the latter when it gets too damaged.

Pros

• the quickest clamp/release system
• can clamp different workpiece thicknesses (with adjustment)

Cons

• not ergonomic if the workpiece thickness changes too often
• suitable almost only with T-slot frames
• doesn't allow surfacing operations

Step blocks are one of the most common clamping systems used by CNC users since this solution is strong, easy to clamp or release, and ergonomic.

You can easily order kits online, containing step blocks of different sizes to fit most configurations with your workpieces. Note that you will need a T-slot working area or a threaded insert grid to use them.

If you're not planning on cutting very hard material, you can also mill these clamps yourself, to the size and thickness you wish, in many materials, such as plywood, aluminium or hard plastic. We’ve made a tutorial series on how to mill a simple plywood double screw clamp.

The only real inconvenience of step blocks is that you can't surface entirely the part you are working on, as the clamps are over it. You’ll also need to be careful when generating your G-Code in order to avoid any collision between the clamps and your spindle.

Pros

• easy to clamp and release the workpiece
• can clamp (almost) any thickness
• robust and secure system
• can be milled to fit your needs

Cons

• suitable only with T-slot or threaded inserts
• doesn't allow surfacing operations

Eccentric clamps are a very interesting clamping system for CNC machines. They use lateral forces on your stock in order to clamp it to your working area, providing a very secure clamping system without the need of putting anything onto your stock, and therefore allowing you to surface it completely.

Like the step blocks, you can find kits online or mill these clamps yourself in many different materials.

Their main disadvantage is that they require T-slots or a threaded insert grid to be used. You’ll also need a bunch of them to be sure your part is secured.

Pros

• easy to clamp and release the workpiece
• can clamp any thickness
• can be milled to fit your needs

Cons

• suitable only with T-slot or threaded inserts
• not the most reliable over time

Vacuum pads are an extremely versatile way to camp a part on your CNC. 

This system simply consists of several movable pads, which can be moved and attached to your working area. They are connected to a vacuum pump that will suck your workpiece, keeping it firmly clamped.

One of the main advantages of this system is its speed: in no time, you’ve moved your pads to your new setup and you can clamp your workpiece by pressing one button.

However, this comes with some disadvantages. You’ll need a vacuum pump, which makes it the a more expensive clamping system than the other solutions we’ve described in this article. Besides, if you need to go through your stock, you need to place your pads so you won’t mill through them, or have a perfectly flat working area, which can be a bit technical.

Pros

• fastest clamping system
• can clamp any thickness
• robust and secure system

Cons

• expensive

At last, you can also go for a full vacuum table, which is the easiest solution if you have a large format CNC milling, and you're in a production mode where loading/unloading your material impacts your profitability. 

One of the main advantages of this system is its speed: in no time, you can clamp your workpiece by pressing one button.

However, this comes with some disadvantages. You’ll need a vacuum pump, which makes it the most expensive clamping system we’ve described in this article.

Pros

• fastest clamping system
• can clamp any thickness and any size
• the most robust and secure system

Cons

• expensive