Friday, May 02, 2008

Bolt Hole Cleaning

One crucial step of sport bolting is thorough cleaning of the hole before placing the bolt. This is particularly important when using glue-in bolts but is often overlooked as a step in placement of cone style, 5p rawl and fixe bolts. Dust and loose rock particles left over from the drilling process can only weaken the bolt placement. Removal of only the loosest [dust] particles by forcing air down the hole results only in a partially cleaned hole.

An effective method of cleaning a bolt hole requires a brush slightly larger than the hole to be inserted and removed with a spinning motion। Several repetitions of this while blowing the hole out in between will clean a very large majority of loose material from the hole.

Glue-in bolt considerations:
When cleaning holes for glue-in type bolts, it is best to use a bulb - type blower or canned air. Lung - generated air will introduce moisture to the hole, decreasing the amount of fine dust that is cleaned from the hole and also leaving behind moisture which can reduce the bonding power of the resin. Also , when using a wire brush, do so in moderation. Excessive cleaning with a wire brush can smooth over very small irregularities caused by the drilling process that are crucial for the glue to perform at its peak abilities. If possible, test your brush on a small piece of stone from the area you're bolting and of the same stone. Softer stone (such as sandstone) won't hold up near as well to wire brushes; in this case, nylon or other plastic may be a better choice.
Finding a brush to clean bolt holes may be a chore so I have provided the following how-to for a homemade cleaning brush. Total material cost is under $5 and labor involved is roughly an hour. Requires access to a torch, power drill with 5/32" bit and welder. Materials list is:

7" 1/4 cold roll steel ($3.00)
1 4.10 shotgun bore cleaning brush (Wal-mart; $1.98)*
A couple feet of some leash line of your preference.
*Note: the 4.10 shotgun size is perfect for 3/8" holes. Some measuring will have to be done at the gun section of wally world to figure out the optimum size for a 1/2" hole. I will update and post back here when i get around to figuring this out.

Use a center punch to mark the center point of one end of the 1/4" steel rod. Drill out about a 1/2" depth into the end of the rod being careful to go in as straight as possible. Access to a drill press would be very beneficial for this step. I eyeballed mine with good results. Cut off the rod at the desired length to make a t-handle. I made mine capable of a 5" depth with the brush attached.

Cut and weld the t-handle onto the top of the main body. If you are feeling creative, leave enough to form a loop on one end of the handle as in my example for the leash line. Otherwise, a leash can simply be attached to the main shaft. Remove the threaded knob from the brush and insert it into the end of your brush holder. Several taps will ensure a good seat. I actually tapped mine in with a hammer to the point of the coils of the brush buckling up slightly.

You should have something to this effect (click on image for larger view).

Several variations of this basic design may be accomplished with some creative thinking। This design is particularly useful because the brush tips may be easily changed out 'in the field'. To change the tips, simply grab the exposed portion of brush with a set of needle nosed vise grips and pull with a twisting motion. Keeping a supply of brushes on hand won't break the bank either at $2 each.

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