If you have some bolts that need tightening or loosening you basically have two choices.. you can use a large socket wrench or breaker bar to remove them manually or you can use an Impact Wrench to reduce the labor needed to complete the task.
Now there are times and I have seen it in many shops where a bolt that needs to be tightened is inappropriately tightened with an impact wrench. I have seen people crack brand new out of the box mag wheels because they didn’t have the wheel aligned right and cranked down a bolt way too tight. There are also times when specifications require you to take out your torque wrench and get an exact measurement on the tightness of a bolt and you can’t rely on an impact wrench even if you use it every day and think you know how tight it can make a bolt. Just a little bit of oil can throw you off.
Other than that there are great uses for impact wrenches. You might be an auto mechanic or you might be in construction. Whatever your job is they can speed up the time needed to complete a job immensely over hand tools.
Also another thing about impact wrenches is because they hammer the bolt on they can often be used in situations where you might normally need to brace the part you are wrenching on. This is true for things like changing blades on a lawn mower or tractor. Instead of fighting the blade you simply impact off the nut in a couple seconds.
Lets look at the types of impact wrenches
There are three basic types of impact wrenches.
Pneumatic that requires compressed air to run. These guns are the strongest and are best used in a shop where you have access to high volume high pressure compressed air. If you are using a 1/2″ or larger impact wrench you will want a 5 horse power or larger compressor.. larger is definitely needed to get everything out of these tools.
Electric Impact Wrenches require availability of electricity so again best used in a shop but they don’t require compressed air. Electric wrenches are normally slightly weaker than pneumatic wrenches but since they don’t require a compressor they can be used for everything but the largest jobs. If you are working mainly on large trucks then you need pneumatic if you are working on assembling parts other than automotive an electric impact wrench will normally have you covered.
Battery Powered Impact Wrenches… a lot of people are using these tools in a variety of work sites. You might see them in professional garages that have access to compressed air because the workers don’t like pulling around air lines but they are the weakest of the bunch. The best setting for battery powered impact wrenches is when you are mobile. If you are someone who installs garage doors, sill plates, decks or any other situation on a job site where you need a lot of bolts wrenched down pretty tight in a short period of time then they can be really helpful.
How to rate the actual strength of your impact wrench
Ok so you are thinking about buying an impact wrench. You already know the setting it will be used in. Maybe you are in auto repair, working an a steel shop or out on the road or at a work site assembling things without easy access to electricity or compressed air.
The first thing you want to do is find out what the torque rating of the work you will be doing is.
Lets say you are assembling garage doors and the specs say 25 foot pounds which is not very tight but you are working with light steel and sheet metal.
So, you know you want to find a battery operated impact wrench that has at the minimum that rating. I would suggest that you don’t stop at the minimum because this will put a lot of stress on the tool. You should use a tool that has between 20 and 30 percent higher rating than you need. This will reduce stress on the tool and might get you out of trouble when you need a bit more from your tool.
If you are working in a shop then you have to look at the capabilities of your compressor. You might find that although your compressor is rated to supply 7 cubic feet per minute cfm at 90 PSI it can only do it for a short period of time.
Impact wrenches require a lot of air. Not as much as paint sprayers but pretty much more than what you might consider a light duty commercial or retail compressor used in someone’s home garage. If you do this work a lot I seriously suggest you look into a 7hp or better compressor with a very large vertical tank. Maybe a 60 gallon tank might do well for a small shop and be able to run most of your tools continuously. And again larger is better.
Final Note
When you are choosing an impact wrench you have to understand what it is best used for. Personally even with lithium batteries I would not invest in a battery operated impact wrench if I was doing automotive or general shop production. But they are the best choice for people out on the road or on a work site.
Electric is a compromise. It doesn’t require investment in a compressor and can do general work pretty well but you might find they are not strong enough for production work on heavy work.
Pneumatic Wrenches are the best for heavy use but they aren’t great for job sites. If you are in a heavy construction industry then you are likely to have tow behind compressors and much higher rated tools than the average contractor but for everyone else this choice requires a shop / place of business and a good compressor.
Costs for all of these tools are all over the place however for general rule of thumb the electric models are the least in overall investment because they don’t require expensive compressors or backup batteries.
After that you are going in two directions and personally I like Air because they still provide the best performance for the buck but if you are on the road get a good lithium tool that has a high voltage rated battery.