Power Hand Tools: Air vs. Electric

  I’m sure you’ve been in the typical scenario: You started your fabrication operation with a couple of trusty electric 4” grinders, and maybe a bigger heavy-duty grinder for heavy stock removal and shaping. It’s the standard recipe for most of America’s stone fabrication companies.
  Whether you work out of your truck with a helper, have a full blown operation with a real shop building and all of the responsibilities that go along with it, or fall somewhere in-between, there comes a time when you start evaluating power options for your main set of hand tools.
  Let‘s clarify hand tools: I consider a standard stone shop tool to be something along the lines of a 4” angle-grinder or a heavy-duty 4” or 6” grinder. There are many high-quality manufacturers out there, and I’m sure you have preferred brands – I do too – but what I want to discuss here is the challenge that we face when it comes to squeezing the most productivity out of the tools that we buy.
  No matter where you line up on the air vs. electric argument, we all need to have electric-powered hand tools for jobsite installations. With that being said, the main focus of this discussion here is with tools in the shop – and, believe me, there’s a good solution for virtually every shop out there.
  Here are some questions you need to consider when mulling over air vs. electric:
  • How much money and time do you spend on new purchases of hand tools every year?
  • Are you buying new electric hand tools to add to your available tool inventory because of company growth?
  • Or, are you buying new electric hand tools in order to replace the ones that have been rebuilt one too many times  – i.e.; your electric hand tools are just wearing out?
  • Are you spending money rebuilding your electric tools more than once a year? Twice a year?
  • What kind of daily (yes, daily) preventative maintenance are you doing on your electric tools? Are you blowing each tool out with an air jet a couple of times a day?
  • What kind of CFM (cubic feet per minute) air volume is your current (or future) air compressor capable of producing on demand?
  • What kind of air compressor do you now (or will) have – reciprocating or rotary-screw type?
  • What kind of dollar volume are you willing to invest in order to have an efficient hand-tool collection in your shop?
  • What matters most to you:  price, quality or lack of down time?
  Here’s where I’d start sorting things out: If you have the same 4” grinders and polishers that you purchased over a year ago, you use all of them every day, and they are all still running well – you’re doing real good. Chances are you’ll be a candidate for a tool-replacement program in the very near future, and rest assured that there’s a tool salesman in your neck of the woods that’s going to become your friend in a big way.
  Speaking from personal experience, and from the opinions of the many friends I meet that are fabricators, it’s time to look at the overall cost of rebuilding a tool (more than once a year) and compare that cost with the upfront cost of an air tool. This, however, is not where the overall cost comparison ends.
  If you’re considering switching to air tools, the bigger factor in the equation is the air compressor you have in the shop, and its ability to produce cubic feet per minute (cfm) of compressed air. If you already have, or will be purchasing, a 25-horsepower or greater screw-type rotary compressor, you’ll likely be able to support a number of air-powered hand tools.
  The big red flag to watch for when traveling down the air-tool path is that the devices gulp your cfm. While most of your machines (line edge, stationary polishers, CNCs, etc) require 2cfm to 5cfm, hand-held air tools use anywhere from 15cfm to 25cfm each. That’s right… each hand-held air tool requires (let’s go conservative here) 18cfm.
  Multiply that load demand times four tools, all running at the same time, and you’re at  72cfm. That’s also the maximum rating for many lower-priced screw-type rotary compressors.
  Here’s an estimating gauge for cfm/horsepower ratio on a compressor: For a reciprocating air compressor, the ratio is 3½cfm for every unit of horsepower. This means that your typical 10 HP reciprocating air compressor yields approximately. 35cfm.
  I can already hear someone doing the math – “If I link up three reciprocating compressors, I’ll have the ability to compress 105cfm!” In a perfect world, that sounds great. However, we’re not in a perfect world, and (as simple as this solution seems) it won’t work.
  Reciprocating compressors are designed to turn on, run and compress enough air to fill the storage tank, shut off, and cool down. The cool-down phase is where most of us fry our first (and sometimes second) compressor.
  The metals used in the valves and cylinders in these reciprocating compressors aren’t able to withstand continuous operation at a sustained high temperature. When you start out with a couple of machines and add a couple of air hand tools, you max out your compressor’s ability to supply usable cfm, and, your compressor turns itself into a boat anchor.
  A rotary screw-type air compressor, on the other hand, yields approximately 4½cfm for every unit of horsepower. With a 25 HP model, you get up to 112cfm of sustained compressed air.
  Before designing your system around a compressor running at maximum delivery, here’s some friendly advice. To guarantee a long service life on your equipment, plan on running your compressor (on a daily basis) at 75 percent of delivery volume.
  It’s the same advice my good friend Dave gives about flying an airplane. He, and most of the private pilots like him, fly their aircraft at 75-percent power. This helps to conserve the engine life, and holds a percentage in reserve – in the event more power is needed.
  The price difference will be the biggest reality check for the fabricator ready to make the change from electric to air. I recently set up a new air system at a price tag of $12,000. It included a 25 HP screw-type compressor with a drier and assorted filters that improve the quality of the compressed air delivered.
  Next month, I’ll go into detail on some of the various air and electric hand tools available to us as fabricators.
  Until Next Month – Happy Fabricating!!!
  Footnote: I’d like to take this opportunity to thank all my fellow stone fabricators (or, as I jokingly refer to us all as, ‘stoners’) for all of the many encouraging comments I receive from many of you every month. My aim in this column is to share my experiences and opinions with you and give back to the industry as a whole from a perspective of “here’s what’s happened to me – learn from my successes and my mistakes.”
  To this end, I am most grateful to all of you who take the time to respond to my articles with your constructive criticism.  Please, keep it coming, as I’m always trying to do provide a better product. Additionally, please feel free to contact me or Stone Business if there’s something on your mind that you’d like to see as the subject of an article. We all have a love for this great industry.
  Kevin M. Padden operates KMPadden Consulting in Phoenix.

This article first appeared in the January 2004 print edition of Stone Business. ©2004 Western Business Media Inc.