By: Stephen Horne
Most router tables that handle sheet goods require vacuum pumps for product hold down. The router table manufacturers often supply vacuum pumps for their tables that range from 15 – 50 hp. It is common that the capacity of the vacuum pump is less than the flow required to maintain the vacuum. When the work piece slips, the assumption is that a pump that can achieve higher vacuum is needed to correct the problem. What is really needed is a vacuum pump with a higher flow capacity. This is especially true with spoiler board applications.
When the sheet is first placed on the table, all of the holes in the table are covered and the flow needed to hold the vacuum is low. At this point there is sufficient vacuum to hold down the work piece. [A 4’ X 8’ sheet is 32 sq. ft. A vacuum of 15” Hg gauge is the same as 1,094 pounds pushing down on every square foot of the surface (a total force of 34,560 pounds!) and this is plenty of hold down force.] As the work piece is cut away, more holes in the table are exposed, the pieces get smaller, and more flow is required to maintain the vacuum at the part. If the flow requirement exceeds the capacity of the pump, the vacuum degrades and the work piece can slip. This phenomenon occurs regardless of the vacuum capabilities of the pump. This is a flow issue – not a vacuum issue.
Oil flooded vacuum pumps can require a lot of maintenance and be unreliable due to carryover of particulates from the process. These particulates can make their way to the pump and cause damage or failure. In many cases, operating the pump at reduced vacuum levels can lead to excessive oil carryover, which requires additional components to remove from the exhaust.
If you have several router tables, the maintenance on all of the vacuum pumps can be very high. Where higher levels of vacuum are not required, a rotary blower can greatly simplify this process. When sized for higher capacities, the blowers can provide the needed vacuum for the table without the need for high capacity inline filters or exhaust demisters. The additional pump capacity allows for the needed vacuum to be maintained at the part. Since the blower does not have oil in the air chamber, they are far less sensitive to contamination. For blowers, the recommended scope of supply for router table vacuum includes:
- Rotary Lobe Blower Package (configured for vacuum service)
- AFV Vacuum Regulating Valve (to ensure minimum cooling air flow)
- Inline Vacuum Filter (to protect the blower package)
- Blower exhaust silencer (integral or external for further noise attenuation