Wednesday, April 30, 2008

Hand Drill Efficiency

NOTICE: The purpose of this review is to provide insight into the abilities and efficiency of hand drills. This review is, in no way, intended to provide instruction on how to bolt stone for outdoor rock climbing. Sport bolting of outdoor climbing routes should only be done by a trained professional.

Sport bolting has enough ethical dogma surrounding it without me generating fuel for argument so my goal here is to stick to the facts. I know i will stray somewhat, but the point of this article is to give some insight into the practical efficiency of hand drills. The intent is to provide some empirical insight into what lengths of time should be anticipated for sport bolting with a hand drill vice a power drill.

It is imperative that you drill with a bit the size of the bolt you intend to use. Several schools of thought are around on the Internet stating that it is acceptable, for example, to use a 12mm drill to make a hole for a 1/2" bolt. As there is (at the time of this article) no empirical evidence to substantiate these claims, no one should be making these judgement calls on their own. Bolts left behind by your efforts will someday be employed for use by others with similar aspirations and their safety lies in the fruits of your judgement calls. Responsible bolting is among the last lines of defense of climbers aiming to maintain access to what climbing areas are left open to the public. This means (however, not limited to) camoflaged bolts, bolts only were neccessary, bolting when other climbers aren't present en masse, and bolting correctly. Weak bolts are worse than no bolt at all!!

A Petzl Rocpec is used in this article however there are many other models and styles to choose from. The Petzl Rocpec may be purchased for around $60 at most rock climbing outfitters such as GearExpress. The Rocpec is specifically designed to take the SDS style masonry bit in sizes of 3/8" to 1/2" standard and 10mm to 12mm metric. Drill bits (aka: "drills") may be purchased for between $9 and $18 online but i find that Lowes hardware has the best deal going at $7 for a 3/8".

The sample rock here is about a hundred pound specimen of either limestone or possibly dolostone giving it a Moh's hardness of about 3-4. This is about or slightly over than the mean hardness for most US climbing areas. The hole being drilled is to 2 1/2" depth at 3/8" diameter.

The hole is drilled in 60 second intervals to provide photos of the bit head and hole at each minute through the process and to best simulate breaks and overall project lapsed time. A 16oz ball pean hammer is used with a strike frequency of about 90 6" swings per minute. Very light to medium strikes are used to minimize distortion of the hole and damage to the drill.

A word on technique: Holding the drill and drill holder 90 degrees to the plane of the rock face is the single most important factor in the process. Attention must be focused on drilling a hole with sides not only as straight as possible but also perpendicular to the rock face.

Okay so on with the show:

After minute #1 :

Very light wear being shown on the tip of the drill. About 1/4" inch of hole already.

After minute #2:

Drill point rounds over slightly. Hole depth at about 3/8".

After minute #3:

No noticeable change in drill condition. Hole depth at approx 1/2".

After minute #4:

Not that the picture reflects it but expected rounding of drill tip and edges slightly worn. Hole depth approaching 3/4".

After minute #5:

Drill shows expected wear - still very light. Hole just over 3/4"; almost 7/8"

After minute #6:

Hole at 1 1/8" depth.

After minute #7:

Hole at 1 3/8".

After minute #8:

Hole at 1 3/4".

After minute #9:

Hole jumps to just under 2 1/2" in a minute of drilling. My only conclusion here is that a soft pocket in the rock was reached.

So total drilling time in this example amounts to nine minutes. Now, personally, i don't have the forearm stamina to maintain a 90 strike per minute hammering rhythm for a continuous nine minutes. Between blowing the hole out and photographing the progress, i would say the breaks were about 3 minutes long. Rounding this up to 30 and adding the actual drilling time brings us to roughly 40 minutes per hole.

The mean depth per minute of drilling comes out to just under 5/16" (possibly 9/32") or between 7.5 and 8.0mm. I haven't crunched the figures this far but standard deviation on this example would be rather high due to the large jump on the last minute.

In closing consider the following: My swings were against the drill holder set against a horizontal surface meaning that my strikes were in the most comfortable and ergonomically beneficial configuration possible. I plan to do an exact replica of this experiment against a vertical rock for comparison but i would venture to say that adding an additional 4-5 seconds per degree of vertical rise from a horizontal plane should be anticipated.


Té la mà Maria - Reus said...

very good blog, congratulations
regard from Catalonia Spain
thank you

Kyle Rogers said...

Thanks if you have to share the post about drill efficiency Brit clips