Air Requirements for Fabrication

By Kevin M. Padden

So you’ve made – or will make – the plunge to fabricate stone with an honest-to-goodness fabrication shop. While there’s plenty of attention given to the latest and greatest in machinery, one of the least-talked-about factors in overall planning for your fabrication needs is compressed air; specifically, the amount that you’ll need now and in the future.
I’m sure everybody usually starts out the same way in this business – you get an electric grinder, an electric polisher, a rail saw or a plain old Skil saw. Your basic starter set-up works OK for a while, until your customers need more production from you, and you have those “good kind” of growing pains.
Then the questions come, such as, “How in the world am I going to fabricate one or two kitchens a day with my small shop?” The answer is simple, and yet complex; you will need to grow your ability to provide increased production prior to increased demand.
As you grow your infrastructure, there will be costs you’ll need to work into you budget, so you don’t “have enough money only for the cart, but not the horse.” One of those I’ve experienced, in expanding a granite fabrication shop, is with compressed-air systems.
In the summer of 2000, I inherited a not-so-basic starter set-up of a granite-fabrication shop. The operation, which had been running for six months, was producing two to three kitchens a week. The fabricating equipment consisted of an automatic bridge saw, a stationary line edge machine, a surface-polishing machine, a bunch of electric grinders and polishers, a flocculation tower for the water recycling system, a water curtain for dust control, and two reciprocating air compressors – all crammed into 1,800 ft² of work space.
Early on, one of the two air compressors began to wear out, even though it was less than a year old. The valves broke down, the filters clogged, and not enough air was being drawn into the compressor. It also overheated, due to the compressor not having sufficient time to cool down because it was running too much.
At the time, I rationalized that one of the compressors was just a lemon, and – since we had a backup –we had nothing to worry about. Wrong. Here’s where I got an education in Air Systems 101, in that not all air compressors are created equal.
There are two primary types of air compressors: reciprocating and screw. The system that I had inherited – two separate reciprocating compressors – was designed to supply a limited amount of air for a small number of machines.
Most reciprocating compressors have one, two or three cylinders, with most coming in the two-cylinder configuration. (It looks kind of like a Harley-Davidson V-twin engine mounted on a storage tank.) A reciprocating compressor is designed (and the key word here is designed) to “compress and rest;” it will compress a given amount of air and keep the compressed air in a storage tank.
When the storage tank is relieved of most of the compressed air, a sensor switch turns the compressor back on, and the tank fills back up. This cycle repeats itself over and over again.
The important thing here is that the compressor needs to rest. If it doesn’t have enough cool-down time between cycles, heat builds up in the compressor cylinders and heads – which equates to wear – and eventually the unit breaks down. In the case of my inherited situation, the continual running of one compressor and the fact that both compressor units sat in a corner full of dust with no air flow contributed to the partial failure of the air system.
So how could this scenario have been prevented? With proper research and planning, you won’t experience what I did.
The first thing you’ll need to do is inventory the tools and machines needing compressed air. Generally, most bridge saws, edge machines, CNC machines and surface polishers will need a moderate amount of compressed air to function,
This leads to step two: knowing the difference between PSI & CFM.
PSI, or pounds per square inch, is the pressure of the air as delivered to the tool or machine. Most of the equipment in our industry runs on a level of 100 to 125 PSI. That’s the easy one.
CFM, or cubic feet per minute, is the volume of air needed to run a tool or machine. The CFM level will vary widely with the equipment or tools that you operate.
Here are a couple of tips that have helped me:
First, map out all of the machines and tools that will require compressed air on a simple spreadsheet. It’s a, by the way, can also be used for water and power requirements for your planning of your new shop or current shop expansion.
Next, look at the potential for you to be using air polishers and grinders in the future in lieu of electric models. What are you spending per month to repair or replace the electric tools that your shop currently uses? Do you have the friendly folks at OSHA breathing down your neck because of injuries or (heaven forbid) electrical shocks in your shop? Are air tools in your shop’s future?
If so, you’ll need to allocate additional air volume (CFM) for that future need. (Note that most hand-held air tools gulp compressed air like a high-performance race car sucks gas.) You’ll need to look at the total number of air polishers and/or grinders, and add every individual tool’s CFM total.
Let’s say you’re going to duplicate my example and add three air polishers; one manual saw, one automatic saw, one stationary edge polisher, one line edge polisher and three air polishers equals 95 cfm. This is way more than your average reciprocating compressor can produce, so you’re looking at a serious investment in a heavy-duty air system.
This brings us to the other type of air-compressor system – the screw or continuous-feed air compressor. These are designed to run all of the time, produce ample air volume on demand for most of your equipment to all run at the same time, and solve all problems (short of eliminating world hunger). The one catch is that the screw-type compressor is much-more-expensive to implement than the conventional reciprocating type that you can pick up at any Home Depot or Lowe’s.
For example, you’ll spend $2,500 dollars for a respectable reciprocating compressor that puts out 50 cfm; for a screw type, you’ll spend five to six times more for a unit delivering 100 to 125 cfm. My new system, installed in January 2002, cost $13,000 for a 125-cfm screw-type compressor, dryer, filters, electrical wiring & installation.
The additional cost is a moot point if you just don’t have the funds to get into a screw-type compressor. But, if growth and increased production capability is in your business plan (as it should be), a screw type compressor system should be your plan for the future.
If you can set aside $1000 per month for one year, you’ll have enough to pay cash for a really good screw ty,pe compressor. If you’re doing three jobs per week, that’s 150 jobs annually (in a 50-week work year); $80 to $100 per job, built into your bids, can cover the cost of a new compressor and system.
Now for those hidden costs; so far, I’ve talked about compressors and their ability to deliver compressed air to a tool or a machine, but the setup I installed last year included more than the compressor unit. Most people overlook the accessories needed for a compressor to run at its optimum level as long as possible .
Dryers are designed to remove the moisture that accumulates in air as it is compressed, and avoid ruining an expensive piece of air-powered machinery. Oil and water filters work in conjunction with the dryer to remove excess oil, dirt and any moisture that gets past the dryer.
Storage tanks provide a reserve of compressed air, regardless of the type of compressor you use. Storage can also be achieved by creating a closed “loop” for your air lines in your shop, where the air supply line acts as the storage tank.
A back-up compressor is a “really-nice-to-have-and-glad-you-had-it-when-you-needed-it” item that will save your butt when your main system goes down, or undergoes maintenance. Don’t forget the electrical requirements that a back-up compressor – or your first-line unit, for that matter – will have, so get an electrician out to the shop to show you just how much power you can tap.
Once you’ve decided on the system, install your compressor or compressors in a shaded, cool location, away from excess dust. (Yeah, right, in a stone shop where there’s dust everywhere.) OK, work with me on this … try an area with as little dust as possible. Remember to also protect the area from forklifts or any vehicular traffic that could damage the tanks or equipment.
Next month, I’ll write about designing air lines (no, not Southwest or United) for delivering the air to your shop, and the machines and tools that require it.
Until then, Happy Fabricating!
Kevin M. Padden is vice president and general manager, Arizona, of IMC Inc. in Phoenix. He’ll present more information on this subject during the “Air, Water & Power Requirements for Your Fabrication Shop” seminar at Coverings 2003 in Orlando, Fla., on March 27.

This article first appeared in the February 2003 print edition of Stone Business. ©2003 Western Business Media Inc.