ARTiFacts

This new section called ARTiFacts was created to provide ART customers and anyone interested in the industry information and useful tips & tricks on how to get more out of your CNC Router or Plasma Cutter!

By David White, Director

Did you know that…

Vacuum does not exist? (applies to CNC routers)

Vacuum is used among other things to hold down material on CNC router
beds. The power that holds the material down is not actually vacuum but
the pressure in the atmosphere pressing down on the parts. Vacuum is
simply a lack of pressure. By pumping the air out from under the
material, the atmospheric pressure on top then becomes greater and
forces the material against the bed. The most pressure you can ever have
is one atmosphere (100 kPa or about 14.5 psi) but most vacuum pumps can
only achieve between 40 to 80% of this. Any air that leaks under the
material being cut will expand up to 500% (5 times) of the original
volume. This will reduce or completely cancel any ability for the vacuum
table to hold down the job.

To make sure your parts hold down follow these rules:

  • Always seal the edge of the sacrificial sheet (spoil board) with tape , glue or paint to stop leakage through the edge of the board.
  • Remove all dust from spoil board between jobs
  • Cover any unused portion of the bed with non-porous material such as plastic sheet or offcuts of material
  • Do not remove cut parts until all have been cut to avoid losing more vacuum
  • Keep the gasket seals under the spoil board in perfect condition – never allow any gaps or breaks.
  • Replace worn gasket material immediately
  • Cut the smallest parts first while the sheet is still stable. The larger parts will maintain enough vacuum to stay in place.

Cut order and start point must work together (applies to CNC routers and
plasma cutters)

If you position the start points (lead-ins) correctly and wisely choose
the cut order, it will assist in keeping parts from moving during
cutting. Failing to do this can lead to inaccurately cut parts. The best
way to hold parts still is to keep them connected to the remainder of
the sheet until the last moment. If you position the start point badly,
or choose the wrong cut order then it can result in a part being cut
while it is already separated from the sheet.

To keep parts in place better while cutting follow the following guidelines:

  • If cutting clockwise around parts such as climb milling on a router, or plasma cutting – position the lead-ins as close to the bottom right corner of the parts as possible.
  • If cutting anti-clockwise around shapes such as when doing conventional milling, position the start points at the top right of the
  • parts.
  • Climb milling (reverse milling) tends to push parts away from the cutter when it breaks through the end of the cut avoiding gouging
  • Select a cut order that works from left to right across the sheet

Following this method means that you will cut the scrap away from the part first while the part is still attached to the rest of the sheet. The final part of the cut will separate the component from the sheet.

Onion skins help your parts turn out better! (applies to CNC routers)

Using a method known as Onion Skinning will give you better quality
routed parts. This is where you will cut the entire shape out leaving
approximately half a millimeter offset outside of your required part,
but also only run the cutter at 90 percent of the depth of your
material. This will leave an “onion skin” of material in the bottom of
the cut. This helps to hold each component in place without losing any
vacuum through the cut lines. Then once this is complete, you can run
back around the parts at full depth using a compression cutter to clean
up the edges. Most routing software supports a “Cleanup Pass” for this
purpose.

Plasma cutters need a breath of fresh air (applies to CNC plasma
cutters)

The compressed air used for a CNC plasma cutter must be clean and dry.
If you have any contamination such as oil or water in the air lines it
will travel into the torch during cutting. When drops of moisture or oil
enter the plasma stream they expand violently into super-heated steam or
vapor. These small explosions cause damage to the consumables which
shortens the life of the electrode and nozzle. The contamination also
causes poor cut quality and excessive dross. Another possible issue is
contamination of internal sensors for air pressure inside the plasma
power supply. ART can supply refrigerated air dryers that solve this
issue completely.

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