Home Made Vacuum Table

A vacuum hold-down for you CNC router provides some useful capabilities when you are limited by the use of T-bolts and other bolt/screw-down clamps.  It provides the possibility of machining an entire surface, all around an edge as well as better hold-down for thin materials that might otherwise not lie flat or tend to pull up (unless you are using a down-cut router bit).

After some internet research I have come up with my own design that seems to perform quite well.  It uses a standard shopvac as the vacuum source and  a plenum made from 2 layers of MDF.  The third layer is optional, but performs the function of the spoil board so it can be resurfaced and, if necessary, easily replaced from time to time.

The vacuum table is made like this:


The bottom two layers of MDF are grooved in X and Y, The middle and top sheets are drilled through at each grid intersection.  The bottom two layers are glued together, while the top layer is screwed down using a neprene seal around the edge.  All extenal surfaces are sealed with  polyurethene sealer.

Materials:

  1. 3 sheets of 12 mm MDF, 600 x 900 mm (the largest size I can fit on my machine)
  2. 3 m of  3 mm*24 mm neporene self adhesive sealing tape
  3. About 1 sqm of 1.2 mm rubber sheet
  4. 20 or so, 25 mm countersunk wood screws.
  5. Polyhurethane sealer
  6. 1 shopvac with bent end and crevice tool.

The following photos shows the building process and some instructions:

Machining the grooves in Bottom and Middle layers


The gooves are 9.5 mm wide and 6 mm deep at about 24 mm intervals (in the top of bottom and bottom of the middle sections) cut in both X and Y directions.

Drilling the Holes in  Middle and Top Layers


The holes are dilled at each grid intersection point in the middle and top layers (to align, of course)

Finished bottom layer showing cleared section of plenum to aid air flow into shopvac nozzle.


Here is the bottom section showing an area cleared for the insertion of the shopvac crevice tool and to provide some distribution of air flow.

Bottom and middle layers ready for gluing


Here are both bottom and middle sections ready for gluing. 

Gluing the bottom and middle layers


Now the gluing.  After gluing all surfaces are given two coats of a flat polyuretene finish to seal the MDF (it can leak air through its pores)

Fitting the shopvac crevice tool into the plenum


The shopvac crevice tool goes into the opening in the plenum, and sealed with a silicone sealer.

Inserting the Neoprene Seal into the goove in the top surface of the middle layer


The neoprene sealing strip goes into the grove in the top of the middle layer

With the top layer screwed down, ready to go!


An extra hole in each corner for a T-bolt hold down onto my router table.

Connecting the crevice tool to the shopvac


Test Machining



Note that I have used the  sheets of thin rubber to cover those holes not  covered by the stock, and a length of masking take along one edge as the stock is not flat on the bottom face.

Operational Notes

The use of a shopvac to provide  a vacuum (negative) pressure is perhaps not a really robust solution as there must be some air flow for the shopvac to work (and stay operating and not overheating tool much).  On the other hand the greater the vacuum (negative) pressure the better the hold-down.  For this home-built model we need to consider a number of operating conditions.
  1. The top layer has a full pattern of holes.  Thus will not hold down anything unless it is completly covered by  flat bottomed stock.  I have chosen to use some thin rubber sheeting (cut to a range of sizes) to cover all those holes not covered by the stock being machined.  You might alternatively just tape over these holes (perhaps with masking tape) as required.  You could also consider having a different top section for each machining task, and drill only those holes in the top section that are sufficient for the stock.
  2. If the bottom of your stock is quite flat then it can sit directly on the top surface of the table and it should hold down.  If not, you might need to use a thin rubber strip under the edge of the stock (all round), or perhaps some masking tape (as shown above) where necessary.
  3. There will always be some air leakage (and this is necessary for the shopvac to survive), but it needs to be kept to a minimum.