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Vacuum Holddown Systems:

Vacuum systems can range from simple, homebuilt setups using Shopvac-style vacuums to Commercial units that can cost as much as a ShopBot. Here's where you can find out about creating and using your own vacuum system.

The first thing someone has to do (if they can) is to try and identify the kind of material, and work they plan to be doing with their machine.People working with large, sheet goods will find that they need to go with larger, "vacuum zones", or areas that can be masked off to handle pieces which might have some irregularity in their surface due to the nature of the material and size. Because of the surface area that needs to be held down, more air flow is important in these situations. This is because in a shop environment certain variables such as excessive dust, and chips on the table, warped products, or even a porous product can produce "leaks"in the system. This means that while the pump is trying to create a closed "chamber" the leak will prevent the proper buildup of vacuum and the part is then susceptible to movement, either from the cutting motion of the bit, or the possibility that it will become more "flexible"as the piece is cut into smaller sections.

So while a smaller piston type of pump might produce a higher rating of vacuum (measured in inches of mercury, with 26+" being about the maximum most small pumps will produce)the smaller unit will only move between 1-5 Cubic Feet per Minute (CFM) of air flow. The larger rotary pumps, or regenerative blowers will produce less vacuum pull (typically 10-14" of mercury) but their flow can sometimes be measured in hundreds of cubic feet per minute (CFM). This helps to maintain a constant flow of vacuum, and overcome any leaks in the system. In the photos below you can see the most common types of vacuum setups currently used by Shopbotters; the left photo shows a Fein vacuum set up to hold material on a 4'by 4'table.

The second picture shows how a table has been broken down into vacuum "zones" and each zone is controlled by PVC valves and piping.

The third photo shows one of the larger regenerative blower units, (this one made by the Siemens company) that can produce a medium vacuum with a very large flow of air.

The 4th photo shows a large vane-type vacuum pump, which can produce approximately 22-27 inches of mercury vacuum. This example is manufactured by the Becker company.

Vacuum generators

Vacuum tables, plenums and spoilboards

Jigs, pucks, and gasketing

BillP, Harold weber
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