Battery Drills

In this part of our battery drills review series, we have a look the inside of a professional cordless drill. This part of our cordless drill review series starts here.

When you try to compare professional battery drills, three areas are of key interest:

  • Mechanical Gear
  • Serviceability of Motor
  • Ergonomics of Housing/Handle

Mechanical Gear on Battery Drills

What is a mechanical gear? - Similar to an old fashioned gearbox on a car, a mechanical gear switches the speed by interlocking different sizes of gear wheels. Most cordless drills do come with a 2 step gear box. Depending on the voltage of the battery drill first gears usually run around 400 RPM (no load speed) while second gear is set to approx. 1500 to 1700 RPM ( on 18 volt units).

Battery Drill with 4-Step Mechanical Gear
Perfect power selection with this 4-step mechanical gear settings on a Protool battery drill.

But if the battery drill does already come with a variable speed switch - why do you need any mechanical gear ?

The answer to this often asked question is pretty simple. Any variable speed regulator, such as electronic switches, do loose power while changing speed. In fact a variable speed switch reduces or raises the voltage through the motor as it changes the motors speed and its power. This enables the cordless drill motor to operate at variable power providing appropriate torque. A simple example to demonstrate this:

  • Assuming you had an 18V - battery drill without any gear. At full speed it would run at 2000 RPM. Now you use the variable speed switch and get it to turn e.g. 500 RPM. The motor would need to run at 1/4 of its power to get you the lower speed. Obviously you would have only 25% of the torque ( simplified example since the switch itself "consumes" energy ).
  • Now assuming you would have the same 18 V battery drill, but with a 2-step mechanical gear. Setting it to first gear - the max speed would be 500 RPM. If you run your drill now at this speed, the battery drill motor would run at full load giving you maximum power and torque .

Serviceability of Motor and Carbon Brushes

When it comes to the durability of any power tool, some simple areas of serviceability need to be examined. Before you decide which brand offers the best battery drills for your needs, you definitely want to have a look at how easy it will be to get spare parts in case you need them. Simple things like replacement batteries, a new switch or carbon brushes may make a big difference.

Makita Battery Drill Motor Maintenance Carbon Brush Change on one of the best cordless drills
With a simple screwdriver an end-cap is removed to get full access to the carbon brush.. Within seconds the brush can be changed, making any expensive repair shop visits obsolete.

In motor maintenance is where you can find an exceptional difference between a professional battery drill and a battery drill for the do-it-yourselfer. The DIY enthusiast should ask how easy it will be to change the carbon brushes when required. It is here that your low cost - cheap battery drill models - can fail and force you to replace the entire motor. This is the difficulty with a fully encapsulated motor that is found on most low-end drills. There isn't the opportunity to replace parts other than the entire motor.

The store is the opportunity to hold a professional cordless drill in your hand time where you can check the ease with which you can replace worn parts. Most professional battery drills such as Bosch or Makita even allow you to change carbon brushes quickly without opening the entire power tool. At a few cents of cost you get your drill back working again within minutes. That's what I am looking for on the best rated cordless drill.

Ergonomics of Battery Power Tools

The final area to look at as far as housing of a battery drill is concerned is its overall ergonomics and handling. Anything which makes you "like the tool" when you take it in your hand. Unfortunately ergonomics and handling makes this the one item that makes it rather difficult to buy your first cordless drill. Battery drill manufacturers constantly change and improve the ergonomics and design, sometimes with major implications regarding how you work with and hold the drill.

A very good example is Makita's recent change on the holding angle of its larger cordless drills. The picture left shows how Makita changed the angle of the handle (drill to the right is my years-old "dirty" cordless drill).

Additionally its good to see how Makita expanded the "rubber" coating (usually called softgrip ) over to the front part of the handle.

This just shows how important even minor changes can be to the look and feel of any tool. Therefore the best way to judge cordless drill reviews and test if you like any battery drill is to simply take it in your hand and and drive a few screws into a piece of wood.

Since we covered key parts of battery drills motor, gear, serviceability and ergonomics, lets have a detailed analysis of cordless drill batteries and what type of battery you need to look for when you buy your next drill.
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