Rotary Percussive Vacuum Drill Bit
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Overview:
Concrete drilling is not like conventional drilling as concrete is a hard but brittle material. Drilling in concrete can be done using hammering also known as percussive drilling. But recent literature shows rotary percussive as a faster and more efficient way to drill in concrete. We are drilling into concrete to repair the delamination (horizontal cracks in the concrete). Due to the percussive action while drilling into delamination and the brittleness of concrete (becomes powder); the openings into these cracks get clogged and repair material cannot be delivered.
The purpose of this drill bit is to drill clean holes (clean cracks) in concrete. Also another purpose for the design on this drill bit is to sample the concrete powder at different depths to analyze it.
We started noticing that while drilling into cracks the holes are clogged at times. The hole drilled on the right side is a clogged hole. This was verified by pumping excess glue which came out from all holes except the clogged one.
1/4" drill bit with carbide 4 cutter tip and a hollow 316 Stainless Steel shank and HSS SDS head. It has 1 hole 1/8" for suction.
Suction part has two holes normal to the surface and sealed by shaft seals.
Few successful drills before failure Very little suction
Multiple problems: 1. Stress concentration at the hole for suction 2. Un concentricity 3. Non streamlined flutes at the tip 4. Shaft seals not smooth 5. Not great suction 6. Brittle material
Shows the failure due to stress concentration
Improvements/Changes: 1. Larger diameter (1/2") 2. Non brittle material (carbon steel)
Improvements: 1. 2 streamlined holes for higher and easier flow 2. Larger Diameter (3/4") than the shank to prevent stress concentration 3. Brazing instead of welding for avoiding distortion (Ni-Ag)
Jig to maintain concentricity while brazing
Removing the connected portion for all round access while brazing
Use of sealed bearings instead of shaft seals
Shank of drill bit milled and ground in streamlined flutes for easier flow
Testing the optimum drilling speed.
The Drill failed at the bearings during the tests. A stronger loctite was used to solve the problem and the problem never occurred.
Shows a clean hole is drilled and the crack is not clogged.
Shows that the crack has particles and is not clean.
