Using Auger and Spade bits in battery vs 240v drills

**seanlark** · 25th July 2013, 12:41 PM

Some time back I enquired of a supplier if one could drill holes in farm fence posts with auger bits using a powerful battery drill. (till now I have used a 1500w Ozito demolition drill with my generator and large auger bits and it has done a splendid job in most instances - it did once burn out the brushes).

Below is his reply which I thought some readers would find of interest in regard to use of spade vs auger bits and battery vs powered drills etc. No doubt others will add their views and experiences!

The drill in that kit is the middle sized drill mate. It’s as powerful as the biggest hitachi, dewalt and makita drills, and then the bigger milwaukee drill is the most powerful on the market, and none of those drills including the high performance drill are designed to use with auger bits into hardwood posts. That’s beyond something you should be doing with a cordless drill. Auger bits pull themselves into the timber and if I was using an auger bit at any time then I would always get out my big bosch 240V drill and use that since it spins at about 2500 rpm versus the cordless at 1500 rpm.

If you going to drill holes like that with a cordless tool you use a spade bit not an auger bit. Keep in mind I was a carpenter for 20 years so I’ve use auger bits hundreds of times. I’d get away with a 10mm auger bit for dyna bolts through posts but cordless drills even struggle a bit with that at times especially if it’s old redgum.
As I said to you if you want to use big spade bits all the time then the high performance drill is the way to go, but it’s too big and heavy for anything smaller, hence the middle size drill is much more suited to all round work. Drilling holes through posts with auger bits is not what I’d call all round work, that heavy duty for a cordless drill.

Keep in mind cordless tools have a limit and hence why we still have power tools and you will never get past the drilling speed and power of a corded drill versus a battery drill and you will always notice this difference when using bigger bits like auger bits that load a drill right up. For an auger bit to drill with a cordless drill you can’t push on it at all virtually and i need to almost pull it backwards well it drills so it wont bog down or otherwise the auger just sucks itself into the timber and will always bog itself in. It’s got to be spinning fast enough to remove the chips and make the cut faster than it screws itself in and that’s not going to happen with a cordless drill when it’s loading up.

I hope that explains it. Change the bit to a non self feeding bit, and use a spade bit if your drilling posts with a cordless drill or even use a normal HSS drill bit and it will solve your problem also.

regards, Sean

**Ratbag** · 8th August 2013, 11:28 AM

Augers demand phenomenal amounts of torque. This is really only available from corded tools, and even then only a select few are capable of the prodigious torque required for larger holes.

The torque or "twisting force" required is the square of the diameter of the hole. In other words, if the diameter is doubled, then the force required is quadrupled. In practical terms, a "normal" high torque drill will drill up to about 25mm in hardwood. Say a 36v Bosch cordless or 600w+ corded drill in low gear only.

If the hole required is larger, say 1 1/4" - 1 1/2" (32-38mm), then you need a bigger tool. The absolute best high torque drill available currently is Metabo's BE75-16. It's torque output to watts input is unequalled (750w input, 75nm output) for its size, and is the only compact drill on the market that can drill large diameters in hardwood. You have to step up to some very seriously power hungry and expensive kit to exceed this little drill's performance.

The speed (single but electronically variable) is low enough by virtue of triple reduction gears. I've used it for extremely difficult jobs, such as 100mm holesawing in 3mm sheet steel, 38mm holesaws in girders, big augers and even mixing 20l buckets of mortar! It also has a traditional keyed chuck too, which is vital for proper tightening in high torque applications.

Bigger drills require much more power, too. I can run this little beauty from the 1000w inverter from the twin battery setup of my ute!

I hate spade bits. They have their place, but they can be very messy, flinging swarf everywhere, and their high speeds generate a lot of heat, which reduces the cutting edges' temper rapidly. It's really difficult to maintain an effective cutting edge, too. I try to touch them up with diamond round and flat files at about 15 degrees, but with limited success. As a sparkie, I'm using them all the time, but tend to regard them as a one job disposable item.

**chambezio** · 8th August 2013, 12:31 PM

I whole heartedly agree that for heavy drilling work you need a corded machine. I have 3 battery drils that I use all the time. They drill smallish holes or screw things together. For roofing screws or batten screws I use a corded Tek gun. I find it works really well for me. I know I have heard of blokes screwing a roof off using a De Walt. Well that's fine for them but I wouldn't. I have witnessed other trades doing monstrous drilling jobs with a battery drill and I always wonder how long they will keep going till they burnout.

**Robson Valley** · 8th August 2013, 03:26 PM

Amps from a battery is not like pouring wine out of a bottle.
There's a sliding scale and it's always down hill.
Plug that puppy in for never ending constant juice.

Given your application, can you afford a chainsaw engine with the auger bit attachment?
I've seen a fairly large childrens' playground frame done with that and an enormous number of bolts.

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