Conduct endurance tests of 18-volt cordless reciprocating saws to determine work that can be anticipated at fire/rescue incidents.
Subject: Cordless Reciprocating Saws, Part 4
Topic: Endurance Testing of 18-Volt Cordless Reciprocating Saws
Objective: Conduct endurance tests of 18-volt cordless reciprocating saws to determine work that can be anticipated at fire/rescue incidents.
Task: Measure the capability of reciprocating saw batteries and saw blades to perform typical vehicle rescue tasks.
It seems no one really knows what the endurance capability of an 18-volt reciprocating saw is when used by firefighters. I therefore set out to determine just how many cuts can be made with an 18-volt saw and one battery.
To accomplish my mission, I designed a series of endurance tests to determine the work output of two different 18-volt batteries from DeWalt and one type from Milwaukee under various rescue situations. The endurance tests began in November 1998 and have progressed continually since then. Each test simulates a real-world situation or condition that firefighters may encounter with a reciprocating saw.
The No-Load Test
To determine the maximum run time of an 18-volt battery, I secured the trigger of an 18-volt Milwaukee and a DeWalt reciprocating saw in the "on" position. I then snapped on a fully charged 18-volt battery, letting the saw run unloaded. I recorded the running time of the saw until the 18-volt battery discharged and the saw action stopped. This elapsed time was my baseline run time. All other tests, in which the saw had to operate under a load and actually cut material, were compared to this maximum no-load run time.
Milwaukee’s 18-volt batteries powered its saw from 11 minutes, 50 seconds to over 15 minutes. Milwaukee’s average no-load run time was 13 minutes, 24 seconds. DeWalt’s original XR2 batteries powered its saw almost twice as long, a remarkable 23 minutes on average. In 1999, DeWalt introduced a 2.4-amp hour NiCad battery called the XR+. This battery, advertised as having 40% more power than its original XR2 battery, represents the maximum capacity available in NiCad battery technology today. In no-load tests with the new XR+ battery, the DeWalt saw increased its run time from 23 to 30 minutes.
The "Aged 60 Days" Battery Test
Both DeWalt and Milwaukee claim that their batteries experience a 5% loss of energy per day when not on a charger. To determine how battery deterioration could impact fire service users, I designed an "aged 60 days" battery test. Three Milwaukee batteries were fully charged, then left to sit alone on a shelf at normal room temperature for more than 60 days. After this aging period, I repeated the no-load test with these batteries. Whereas a fully charged Milwaukee battery ran in excess of 13 minutes, the two-month-old batteries averaged a little over eight minutes. This represents a loss of almost 40%, a significant loss of energy. This reinforces the recommendation that all cordless tool batteries be left on a charger at all times to maintain their fully ready state.
The 2x4 Lumber Test
The next series of tests was designed to evaluate the saws on a material that any fire department could readily have to cut through. Common 2x4 dimensional lumber was selected and placed in a workbench clamp. With the stopwatch running, inch-thick slices were cut off until the useful power of the battery diminished. A record was made of when each cut was completed as well as the total number of cuts and the total battery operating time.
For all wood-cutting tests, each saw used a Milwaukee AX 10-tpi (tooth per inch) wood-cutting blade. A new blade was used for each test. During the DeWalt tests, the blade came loose in their old-style key chuck system twice and the handle design hurt the operator’s gloved hand at the base of the thumb upon conclusion of the rugged tests. During the Milwaukee tests, saw vibration caused the battery to disconnect from the handle of the saw.