How to fixture material to the machine bed

MATERIAL HOLD DOWN: Vacuum hold down VS fixture

The Laguna CNC machine has several options for work holding.  The machine has a vacuum pump that draws a vacuum down thru the MDF surface in up to 6 zones.  There are also 2 hold-down rails running along the long axis of the machine bed.  Care should be taken when choosing hold-down methods.  Several factors affect the efficiency of the work holding:

• The integrity of the MDF surface has a large effect on vacuum hold-down power.  You should always clean the surface of the table and your workpiece before laying it on the table.  Dust and chips on either the MDF or the material can prevent a good vacuum hold down. 

• The type of material may negatively affect the vacuum.  Overly porous materials like untempered MDF or non-veneered particle board may not be able to be held down with the vacuum system.

• The size of the material may cause issues with vacuum effectiveness.  Materials that are sized to exactly cover up 1 or more zones will work best.  If the material is smaller than the size of an individual zone, or larger than 1 zone but smaller than 2 zones may cause too much vacuum power to be lost.  In either case, scrap materials may be used to block off more of the zone(s) in order to create a 'seal' so that the vacuum can form.  The 6 vacuum zones are roughly 32" x 24" each.  Trial and error may be needed to ensure effective hold-down.  

• Material conditions (flatness, brittleness, etc.) may have a large effect on vacuum hold-down.  If the material is cupped or bowed, the vacuum may not be powerful enough to overcome the distortion, and the material will not be held down.  A slight bow and cup may be able to be held down.  One technique to check this is to turn on the vacuum pump and then push down on the material to flatten and hold it to the table.  When released, if the material stays flat and cannot be moved around on the MDF surface, the vacuum *may* be strong enough to keep the material in place for the entirety of the cutting process.  

  • • • • NOTE: If warped material is successfully held with a vacuum, the warping tension can still cause issues or damage the machine. When designs have many through cuts, especially on a large and warped piece, there is a higher chance for the tension from the warped material to cause the tabs to fail (and the material to spring upwards/enter the end mill's travel path). Also, as the tension from the warped material is released from multiple through-cuts, the vacuum hold-down effectiveness may fail. 

        • Overly brittle materials and plastics may fracture or come apart during cutting, causing the vacuum to lose effectiveness. In these cases, traditional fixturing to a fixture board should be used. 

• Tool path design can affect the vacuum power.  Tool paths that remove significant amounts of material all the way down to the MDF surface may cause too much vacuum to be lost, and then the material will be moved by the tool as it cuts.  The amount of surface area that remains to cover the vacuum zone(s) will dictate effective hold down.  A strategy to mitigate these issues is to program the tool to cut down near to the bottom of your workpiece, but not thru it.  The remainder of the cutting may be accomplished with a jig saw or router, and then cleaned up with a sander or by hand.