Vacuum Table for CNC Router

(Video of build at bottom)

Anyone who has ever dealt with a CNC Router before will know
that one of the biggest challenges, time factors AND annoyances is workholding.

Workholding (for the non-techies) is how we stop the thing that we are wanting to cut from moving around when a very heavy and powerful cutting head drives into it very quickly.

When it comes to workholding, I have tried it all: Top clamping, Side clamping, T-slots, Screws, Masking tape + superglue, the list goes on! and although some of those methods do work for many scenarios, they all have their limits. For example, you can imagine what happens when you run the cutter full pelt into a screw or clamp…

So, you might ask, how do they do it in industry?

Well the answer is… drum roll please… a Vacuum Table! These are very commonly used in a production environment, so why would we not be using them in our workshop?

The vacuum table has some massive advantages over other methods:

• Ideal for sheet material
• The work is held down incredibly securely.
• There is nothing in the way of your cutter.
• There are no consumables.
• Best yet, you don’t need an industry standard vacuum pump, a shop vac will be plenty sufficient for wood, and if you have a much smaller table, a standard vacuum cleaner may even do!

Limitations:

• Like all workholding methods, everything has it’s limits, and for a vacuum table, its the size of work. The more surface area you cover of your vacuum table, the higher the vacuum, so cutting small parts doesn’t work so well (for this I would personally suggest the tape and glue method)
• BUT, there is a method for cutting smaller parts using a vacuum table - by cutting a recess into a larger board which is then held by the vacuum.
• If there is a significant amount of force pulling the workpiece upwards, air will find a place to rush in and it will lose suction, therefore downward fluted cutters are advised (but not completely necessary)

How does it work?

• It consists of a chamber which is under a negative pressure. One side of the chamber has lots of small holes which allows for air to flow into it and pull down the part. The other end has a vacuum pump (vacuum cleaner in our case)

Worst case, if you don’t like it, just attach a blower onto it instead, and you’ve got yourself an air hocky table!

• 3x pieces of MDF, cut to the size of your machine (My machine is 1200 x 600 so I managed to use a single 4'x8' sheet (other materials would also work well, some plastics for example)
• A cnc router for drilling all the holes and cutting the parts
• CAD software - I use Autodesk Fusion 360 which is definately the best CAD tool you can get for free. It not only allows you to produce industry standard CAD models, but will also allow you to produce GCode to run your CNC and manufcature your part.
• A vacuum adaptor. I made one on a lathe from a block of PVC but if you dont have a lathe, you could definately cut one from the left over mdf (if you want to buy one, do a search for 'shop vac inlet flange' or something similar)
• A vacuum cleaner / vacuum pump

• Metal wood inserts (I used M6)

Chamber

We need a chamber.

On vacuum table v0.1 I tried to be clever. I used just 2 pieces of mdf and cut channels into one of the pieces to keep it simple. The issue with this was that the side closest to the vacuum worked well but the other side had hardly any suction at all. The small channels also clogged up with dust quickly.

The chamber acts to dampen the flow of air and the suction throughout the table becomes much more uniform because of it. I had limited working height so the thickness of my chamber is 1x mdf sheet (18mm) but if you have space, make it deeper. It's worth noting however, that even with a chamber it will still have a stronger suction through the holes nearer the vacuum inlet.

Holes

Many manufacturers of vacuum tables make a 'grided table', where you place a seal around your work piece within the grooves. These are a much more complicated design and all sealing is subject to a good outer seal.

The beauty of this 'hole matrix' design is that the seal is created throughout the entire face of the material, and it's really simple to make! If you have a workpiece that is smaller that the table, you can easily seal off the unused holes off with some scrap board or tape.

The hole diamater and spacing is a tricky subject and is purely up to you. Many industrial tables have very large holes which have less chance of blockage, the issue with this is that the there is less force applied per hole, so if say one hole not completely sealed, you will be losing a lot of suction very quickly - these holes are really only designed for an industrial vacuum pump. I have also found that a clogged hole quickly unclogs once a vacuum cleaner is applied directly to it so it's never become an issue for me!

Support

We all need support, and so does our MDF! The chamber would be quite weak and likely to bow if there is nothing supporting between the top and bottom sheet.

Mounting Screws

You are also going to need a way of securing this to your cnc router. MDF can warp so it is advisable to have mounting locations in the middle of the vacuum table aswell as the outside.

We need an array of holes, this will take a VERY long time to drill.

I drilled 1.5mm diameter holes at a spacing of 15mm, this turned out to be 2960 holes and took about 4 hours of drilling, be warned! Feel free to test out your own dimensions and let me know how it goes!

Tip: Drill from the back of the sheet, when you drill through a material, it leaves a bur on the other side. So drilling from the back ensures we have a clean hole inside of the chamber, the top face will be cleaned up anyway once we do a facing cut.

For the frame around the outside, I cut this from one piece of MDF to make sealing easy but you could definitely use 4 individual sides glued together.

I cut 10x ribs from a 9mm sheet of MDF. These run down the length of the vacuum table. They have holes cut throughout to aid with enlarging the chamber and distributing air flow.

To support the mounting screws in the middle of the vacuum table and prevent damage to the MDF, I cut a PVC tube the same height as the ribs. I made 7 of these.

I cut slots for the ribs to sit within, and I also cut bores for the PVC spacers to sit within.

This helped with locating everything when glueing together and adds stability. We also need to drill mounting holes.

Finally we also need an outlet hole for the vacuum cleaner. I chose to do this on the bottom as it kept it out of the way, but you may prefer to do it on the surface, do this the same bore diameter as your vacuum hose.

Glue together the base, frame, ribs and spacers with PVA.

Apply the glue to both mating surfaces to ensure a good seal between everything, just don't use so much that it goes everywhere!

Leave for a few hours, once the glue has dried, do a skim cut over the top of the ribs, spacers, and frame to make it as flat as possilble. Go slowly and with the largest cutter you have. Secure the assembly to your machine using the mounting holes.

Apply glue to the top of ribs, spacers and frame. Be careful to not allow glue into any of the small holes!

Place the top piece onto the assembly. Once it's aligned well, add some weight onto the top to help the glue adhere. I used some old sheets of mdf stacked on top of each other.

Leave to try for a few hours.

I made the vacuum inlet using some old PVC and a lathe. I then drilled some mounting holes.

If you dont have access to a lathe, you could cut a ring out of mdf the same size as your vacuum nozzle and bond that to the vacuum table.

Alternatively you can purchase similar flanged inlet ports.

Apply glue to both the inlet and the vacuum table and bond together. It's also advisable to use screws to bolt the inlet down. Drill holes first to avoid splitting the MDF.

Coat edges with PVA. Apply 2-3 thick coats all over.

Tip: This step is important! MDF may look dense but it is actually porous. By coating the surfaces you are preventing any vacuum from leaking through the edges!

Drill holes into your cnc router at the mounting hole locations. I used some M6 metal inserts for wood and placed these inside my router bed.

Secure the vacuum table down and do a skim cut on the top face to true the surface.

Now you are ready to test it! Apply a vacuum to the inlet and place a sheet of wood onto your new Vacuum Table.

Hopefully if all went well, you'll never have to use other clamping methods again!

So you've just built this amazing addition to your CNC and you want to start cutting things asap but then you think "If I cut through my work piece I'm going to cut a gouge into my brand new vacuum table! What do I do!?"... Fear not! There are a couple of things you can use as a spoilboard laid on top! I use a porous rubber matting found here. It works really well but I would suggest sealing the edges with something like tape or glue. In industry it is very common to use a sheet of MDF which has had both sides skimmed ~0.5mm. Because MDF if porous, vacuum can pull strait through - The issue with this is that it is really dependant on your vacuum pump! I found that my vacuum cleaner could not produce enough of a vacuum through an MDF spoilboard and so I have found the rubber mating above to be better suited for my workshop :) If you come up with any other ideas, let me know in the comments!