SPECIAL SERIES: INS & OUTS OF CORE DRILLING #2 CORE DRILL ANCHORING, VACUUM BASES & ACCURATE DRILLING
In the previous post in this special series, we reviewed concrete core drilling applications, project prep work, and concrete core drill categories and options. You can view that post here.
Once you’ve ordered everything you need for the worksite, you’ve had your cup of morning Joe or energy drink, met with your crew and you’re ready to start, the first concrete action is to anchor the drill.
“Measure twice, cut once,” I can still hear my junior high shop teacher saying. In the case of anchoring concrete core drills, it’s more like “measure twice, set anchor, bolt into place and adjust leveling screws.” Doesn’t quite roll off the tongue, and it takes several steps:
- Measure the length from the anchor-bolt slot in the drill base to the centerline of the drill spindle. Don’t forget to start in the center of the anchor slot/hole and finish at the spindle center.
- Put your “x” on the spot you want to core, then measure and mark the anchor hole using the measurement from step 1.
- Drill your anchor hole that you marked in step 2, drop a 1/2” anchor.
- Load your diamond-tipped concrete coring bit into your concrete core drill, and center it over your core mark; align anchor slot in coring equipment/drill base over the anchor, then partially thread a bolt into the anchor.
- Plumb the drill column to the hole location and stabilize the base by adjusting the (typically) four leveling screws.
- Tighten anchor bolt completely.
A HELPFUL HEADS UP - Even if running late, it could cost you to skip anchoring securely. If the base or column of the coring equipment moves at all during drilling, it will cause chattering, coring bit binding, and wearing your gear out faster, requiring more concrete coring bits for the job.
Special Precautions for Coring Walls:
Anchors and backing plates are needed to anchor to a wall. Backing plates used with anchors distribute the vertical forces that are added by anchoring the concrete drill equipment to the wall.
Also, do not use a vacuum base if coring through a wall, as it can result in injury or death.
About Vacuum bases for Coring Floors
If the core hole is 6 inches or less in diameter, a vacuum base is fine.
A vacuum base is NOT recommended for use on cracked or rough surfaces (it wouldn’t hold effectively).
Same thing when drilling deeper than the bit length or into a concrete slab with rebar bigger than #4 on 12” centers - a vacuum base is NOT recommended.
TIP: Keep down-feed pressure light when using a vacuum base on a tiled floor. Too much down-feed pressure can cause the tile to pop and the drill to wobble all loosey-goosey. A good quality concrete coring drill and bit should weather it if that happens, but no one wants to have to slow down or come back to repair tile. So if you use a vacuum base on a tiled floor, keep the down-feed pressure gentle and steady as she goes.
The vacuum pump is usually not designed to pump water, so it might be equipped with a protective water filter shut-off device. The rubber gasket that lines the bottom of the base is the seal for the shut-off system; it’s usually removable and should be taken off when the vacuum is not in use.
Accurate hole drilling
Starting off accurately will save headaches later on. To test out your accuracy, lower the concrete drill spindle down to about 2 inches above the surface. Turn on the water to the spindle and - when the water jets out of the tool - see if it hits the core mark you made on the surface (during the anchoring process).
It stinks to have to repair over-drilling or mis-drilling mistakes and re-drill; Start with a small hole use the shortest possible bit length. Never use a bit extension while starting a hole. Couple/seat the bit as closely to the motor as possible.
Spacer plates, used for the first time on the project, can’t be trusted to be pre-set.
Carriages that look the same might be machined differently and change the true of the bit, so check to see if the bit aligns with the center mark whenever changing core bits.
The biggest accuracy challenge is keeping the bit from wandering (aka “chattering”) when starting a hole.
SOLUTION: Hold a block of wood against the barrel of the concrete core bit while applying light down pressure to the feed.
You can add additional downforce on the bit using the down-feed control once the core bit has penetrated at least to the depth of a segment.Stay tuned for more in this special concrete core drilling series. In the meanwhile, please send any of your own tips, tales from the trenches, a profile of a project you did or blog topic suggestions to firstname.lastname@example.org. Please also indicate if you want your name and business included.