The Ultimate CNC Clamping Guide

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  2. 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.

1 - Wood Screws

2 - Composite Nails

3 - Double-sided Tape

4 - Toggle Clamps

5 - Step Blocks

6 - Excentric Clamps

7 - Vacuum Pads

8 - Vacuum Table 

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

1 - Wood Screws

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.

A workpiece attached with wood screws
A workpiece attached with wood screws
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

2 - Composite Nails

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

 
 
         A workpiece attached with composite Nails.                                           
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

3 - Double-sided Tape

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.

Using double-sided tape to clamp small parts
Using double-sided tape to clamp small parts

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 high strength double-sided tape, or this one. We also 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

4 - Toggle Clamps

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.

Picture featuring toggle clamps used on a CNC milling machine
A toggle clamping system
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

5 - Step Blocks

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.
CNC clamping - step blocks
On the left, a home-made step block, and on the right, a professionnal steel one
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 that you can find here.

The only real inconvenience of step blocks is that you can't surface 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

6 - Excentric Clamps

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.
Homemade excentric clamps used on a CNC milling machine
home-made MDF excentric clamps
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
  robust and secure system
  can be milled to fit your needs

Cons

  suitable only with T-slot or threaded inserts

7 - Vacuum Clamps

Vacuum pads are an extremely versatile way to camp a part on your CNC. Note that we’re talking about pads here. If you have access to a vacuum table, this doesn’t apply.

This system simply consists of several 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.
Vacuum pads placed on a threaded insert grid
Vacuum pads placed on a threaded insert grid
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

8 - Vacuum Table

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. 

Vacuum table
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
  robust and secure system

Cons

  very expensive
  can't clamp every material

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