Choosing a Vacuum Pump on a Budget

There are basically 2 measures of a vacuum pump, pressure and flow. May 15, 2012

Question
I'm looking into buying a new, lower end CNC router and I'm trying to save money on parts that can be upgraded later. The vacuum seems like the best place, but maybe I'm missing something.

Here in San Francisco we have a place called TechShop. It's a membership organization that works like a gym, but membership gets you access to machines most cannot afford. This is where I'm leaning how to use a ShopBot, which has a vacuum table powered by a Fein Turbo III. It seems to do the trick, so long as you cover up open spaces with some plastic sheets. So my question is - why spend 10X-20X as much on a pricier vacuum?

Forum Responses
(CNC Forum)
From contributor B:
In my opinion if you are a small shop that will be using the CNC on a limited basis to start then this sort of system will probably work for you. In addition to the Fein vacs there are some very powerful vac motors you can purchase that can be paired up to give even more hold down power. They typically cost about $100 to $150 each and four would fulfill most needs. If, however, your needs are more like running 100 panels a day right out of the gate then you would be better served to spend a significantly larger amount of money on a full blown regenerative blower system.

From contributor Y:
I run two Fein vacs on my table and they seem to do the job. There is less noise and heat to put up with.

From contributor J:
I've been looking through these forums trying to decide what I need and frequently see people complaining about their $7000 vacuums not being powerful enough while a shop vac was working for me.

i>From contributor G:
There are basically two measures of a vacuum pump, pressure, and flow. The pressure (measured in �hg�) is the potential of the pump to generate (negative) pressure. Flow is a measure of how much volume at a certain pressure is available. Spending more money on a pump generally gets you a "deeper" vacuum.

A Fein for example is an example of a "regenerative blower" and would top out at something around 99" of water according to their specifications. To convert from inches of water to inches of mercury (hg) divide by 13.59. So the pressure potential is about 7.28" hg or about 24% of a perfect vacuum. It is typical that the actual pressure is less than the potential maximum. So in practice a Fein is about approximately 18-20% of maximum pressure possible. Adding more hp will not change the max pressure. More hp does change the volume available.

What this all means is that different kind of pumps have different pressure potentials. The deeper the pressure, the smaller the size part you can cut without movement (or using "finesse" in toolpathing). If you want to find out more, I've written a "white paper" on the different kinds of vacuum pumps and another on how hp effects the flow rates of the different styles.

From contributor U:
All Types and Horsepowers are used by operators of "smaller CNC Routers". When using a "smaller system" make sure you adjust the sealant that is softer or less dense. Otherwise the sealant will fight the vacuum and your quality of holddown will be dramatically impaired.