Drilling in hard concrete possibly into rebar.

[Duramen]

I have to drill about 50 holes on the side of a concrete driveway to attach some garden fixtures with dyno-bolts. Initially started drilling with my green Bosch impact drill, and destroyed two masonry bits without even getting one hole to the desired depth :eek: . Did a search on this forum and learned that I needed a rotary hammer drill with sds bits. So now I have bought a rotary hammer drill with sds plus bits.

What I need to know before I start drilling again is, can the sds bits drill through rebar?

If not, I can change the position of the holes. Would I have to seal the half done hole on top of where the rebar runs to prevent corrosion ?

I have read on one internet site that if the drill bit gets caught between the rebar and concrete than there is possibility of kick-back. Could someone share their experience with this phenomena of kick-back. Is it just a small force to the hands or something more dangerous.?

Thanks

[Jack E]

Could someone share their experience with this phenomena of kick-back. Is it just a small force to the hands or something more dangerous.?

Kickback on a large or powerful drill can be bad, I am unsure but maybe some of the flash (expensive) ones have a clutch.
Think about the amount of torque the drill is using to turn the bit. If the bit stops, that torque has to go somewhere and that somewhere is whatever is holding the drill, ie: you

I have used a drill to crank start generators. If the genny isn't timed correctly it can try to start in the opposite direction to that which it is being cranked. If the drill bit does not disengage from the crank dog a kickback results. I have seen people end up on their butt a few times and have heard of people breaking bones.

The drill was called the "WIDOW MAKER"
Sounds cool and beats the hell out of hand cranking a genny but not much fun if it all goes wrong.

I would definately plug any holes that aren't going to be used. I would also drill small diameter holes first to make both the drilling and the plugging easier.

Cheers, Jack.

[Dan_574]

Duraman your not going to know where the reo is so just drill the holes where you want them and hope for the best, the reason you destroyed those two bits was probably because your drill was too fast, you'll find your rotary drill with the sds bits will turn alot slower. Just hold on to it with a firm grip and expect it to kick back, dont get complacent cause thats when you'll hurt yourself, if you hit reo just move across a bit and you should be right.

[arms]

if you hit a reo bar on the horizontal just drill a bit lower or higher whatever the case
the bit will drill concrete but wont drill steel,

[Lucas]

Duramen you didnt brake a drill in the hole did you?

another reason if its not reo bar could be that the rock in the concrete could be river pebble which makes it a b*tch to drill

all i can advise is if you hit reo start again next to it and use good quality drill bits

[numbat]

And if you you need to fill holes that you have drilled you can use Selleys Knead It - get the multi purpose one. I can attest that you can fill a hole in brick or concrete with KneadIt and drill a hole adjacent to it. Make sure that you let the KneadIt fully cure though.

I drilled the holes with a rotary hammer and SDS bits. You can get them for $99 from SuperCheapAuto - less if they are on special. The ones from SuperCheap also come with 3 SDS bits and some chisel bits. This has to be one of my best tool investments.

Good luck.

Cheers

[johnc]

Depends on the power of the drill, there is an old bosch 720W in the shed and the kickback from that can tear it out of your grip. Generally though unless the bit grabs hard and stops instantly the torque will not be sufficient to do any damage, it will usually kick in slow enough to release the trigger or give some indication somethings up. In what must be fifteen years I've only had the drill pull its self free once, as it did so it kicked the trigger lock on, wound the cord around its self in the process and unplugged itself from the wall, pretty smart drill that.

Just be carefull, don't hurry the job, its usually either driving to hard or twisting the drill in the hole that causes it to jam, most likely because its skidded off a bit of reo or hard aggregate.

JohnC.

[Pulpo]

It will not drill through reo.

Yes if it hits reo the drill bit will invariably stop turning and the drill will start.

My wrist has been injured from this on too many occasions.

I wear big welding gloves to help if the kick back occurs.

The problem is you need force when drilling, although a lot less with a rotary than a hammer and its this force that's the problem, for holding the drill tight can cause a painful kick back.

Experience will teach you to let go.

Think which way the drill will turn on kick back.

Make sure the spinning drill will not hit some object at the wrong time, ie a post near the hole being drill could be used to stop bad kick back.

I find that if the hand holding the trigger, is in a fore hand position so that when kick back occurs it pulls out of the front of the hand rather than forcing the wrist back in the back hand position.

Hope something make sense.

The Rotary has made your exercise a hell of a lot easier.

Good Luck

Pulpo

[Tankstand]

When I was still working at Mitsubishi, and we hit reo while trying to accurately drill holes for positioning / holding down machinery, we would then go down the hole with a HSS drill bit ( Re-sharpening often! )

[Lucas]

Duramen
how deep are you drilling down anyway ?

[Duramen]

Thanks for the advise. Drilled some of the holes today without any issues. The rotary hammer went through the concrete as if I was drilling in pine. It was more the hard aggregate in the concrete which caused the problem, not the rebar.

The rotary hammer does have a safety clutch so I think I am safe from kickbacks. Just from the experience I gained today I don’t think it is always possibly to hold the drill firmly with both hands, posts and walls come in the way of drilling, also the person drilling has to stand, crotch in an awkward position at times. So a safety clutch should be must have feature on all rotary hammers.



When I was drilling the holes with the Bosch impact drill (rated at 600W) I spend over 1 hour drilling 6 mm diameter holes in different places in the concrete to only 10 to 15mm in depth. I needed 40mm deep holes.
The frustration took better of me and I pushed the drill bit hard at highest speed, the friction/heat melted the brazing that holes the tungsten-carbide, hence the bit was out of shape.

Some of the advice such as drilling through rebar with HSS bit will become handy in future work when position of the hole is of importance.

Cheers
Duramen

[journeyman Mick]

If the position is critical then mark out and drill all holes. If you hit steel than you can drill through using a diamond coring bit (don't use hammer action). I've seen this done when balustrading was being fitted to concrete balconies on high rise. They hit the steel more often than they missed it. (There's a fair bit of steel in some of those high rise balcony edges)

Mick

[soundman]

duramen as you have just found out there is a world of difference between a hammer drill and even a cheap rotary hammer.

As for speed.
The number of blokes I have seen trying to drill masonry on high speed :confused: .
For many materials the RIGHT speed is important. Too slow or too fast & the progress & tool life suffer.
Masonry likes to be drilled slow.
I have too ordinary hammer drills, a old AEG & a much newer Black & decker industrial ( dewalt ). The B&D is a good drill & more powerfull but in masonry the AEG is all over it because the hammer action is slower.
Running a hammer drill fast just makes it skip on top of the agrigate & overheats the drill bit.
cheers

[Iain]

Rotary hammer drill will freewheel until pressure is applied, if someone has already stated that, sorry, I didn't see it.
This should minimise any nasties associated with kick back because as soon as you move back that little bit the drill is disengaged, even if it is running.

[John99]

Duramen, I was just interested in the type of drill you bought as I may need to get one soon, was it a cheapy $100 or so, the type that comes with the various drill bits?