READERS’ LETTERS

WINNING LETTER

Hi, PM team. I really enjoyed the article on the hammer drill versus rotary hammer comparison. I have found many seasoned handymen are completely ignorant of the rotary hammer’s existence and purpose. The article was very informative and accurate, except for one vital flaw. The author advised the readers to drill a pilot hole with a rotary hammer and then drill with a larger bit from both sides to prevent breakout.

Having drilled hundreds of rotary hammer holes in the hardest concrete, I have experienced pilot holes to be the perfect recipe for endless frustration. There are two major reasons for this: 1. The rotary hammer has immense forward impact that will effectively jam the sides of the drill bit into the hole, and the clutch of the rotary hammer will prevent the bit from twisting free. The natural reaction is then to shake the bit up and down, trying to free it. This then results in bending thinner bits and breaking thicker bits at the ‘neck’ of the bit where it enters the drill. 2. The drill bit will wear much faster on the edges since only the edges make contact with the concrete. This creates a drill bit that has a smaller head than shaft, instead of the other way around. This places a lot of extra strain on the drill as the shaft of the bit forces itself through a smaller diameter hole. Rotary hammers are, after all, designed for maximum forward impact and not for turning force. My advice would be to use one size bit and ease off the speed and forward force once you come close to the end of the hole. The exit hole breakout will be markedly smaller. It will need some practice, but then so do all practical tasks!

Jakobus, that’s really great advice; thanks for sharing it. Here’s hoping other readers with as much experience as you also get hold of us to share their expertise in their relevant fields.

For taking the time to write in, you’ve won yourself a Sjöbergs Nordic Plus Workbench, sponsored by BPM Toolcraft. They’ll be shipping it to you soon. I hope it aids you with some of your upcoming projects. – Mark, Editor