Drilling holes with SDS drill

[RickH]

I need to drill 16mm diam holes in a reinforced concrete slab.
14 holes each 150mm deep.

The holes will be used to resin in anchor studs, and then right angle straps are being bolted to slab ... the vertical portion of strap will then be secured to vertical studs of timber frame walls.
http://tinyurl.com/87wnxa


The main thing is here is that the holes in the 10mm thick galv straps are pre-made and fixed, so I can't allow the holes I drill to wander off line.

I have an SDS drill and a new 16mm bit.

When I have drilled SDS holes before they tend to wander about until a cm or so into the material.

Any tips on doing this ....
some options I have thought of are :

#1 use a non SDS pilot hole, before using SDS drill ... although I read on DIY forum that SDS bits should not be used with a pilot hole, due to way they work.

#2 bolt straps to vertical studs first and drill through the clearance holes - risk here is damage to the galv finish, and this is an external job so need the protection.

 

[swbjackson]

I've never had a problem with pilot drilling with SDS drill bits. Doesn't necesarily mean that the main bit won't slip if it hits a bit of flint. Surely if you're using resin you've got a bit of leeway anyway.

 

[xerxes]

I'd be inclined to drill a pilot hole first: but why with a non-SDS drill bit? That sounds like hard work.

I can't see any reason for the suggestion that SDS drill bits won't enlarge a piloted hole.

Wandering is usually the result of trying to drill non-uniform material; the more uniform the concrete, the less tendency to wander.

If you hit any rebar, you will of course need to change to a HSS bit to drill through that.

If the holes in the straps give clearance for a 16mm bit, I don't see a problem about using them as a template. If you're concerned about the galvanising, you could use a spare one as an expendable template, or (if you don't fancy fixing and unfixing it each time) you could touch up any damage with a product like Galvafroid.

 

[Bilioustrumpstaine]

The wandering off line usually happens in the first few seconds of drilling. Pilot holes are fine and will provide you with a good starting point. I often start masonry holes off with an HSS drill bit (a cheapie) especially when the positioning is critical.

You could make a template out of timber.

Get someone to assist you when drilling just to ensure that you are drilling dead square, it is easy to go off at an angle when looking down at the drill, get somone to look at the angle you are going into the wall at by standing to one side, get them to hold a square near to your drilling area if necessary.

You could start by drilling all holes 6mm to check alignment and then adjust as required.

Take your time and all will be fine.

 

[XtraRaptor]

I have always found Resin Anchors to take an age to cure in cold weather, so I would be tempted to use Through Bolts like these


http://www.rawlplug.co.uk/index.php?option=com_content&task=view&id=10&Itemid=25


Never had problems with them, also you may find you can drill smaller holes.


Nick.

 

[Symptoms]

Rick - jig it up by using a square of thick ply (with the hole positions accurately bored through it), position the ply, stand on the ply, SDS into the concrete. Accurate every time 'cos it won't slip 'cos of your weight standing on it. Move the jig to the next position, and so on.

 

[^woody^]

If you start the drill without hammer, then the bit wont wander.

Depending on your preference, you can either start it slow with the bit on the slab pressing moderatly, or start it fast with the bit off the slab and lightly touch the slab.

If there is a stone on the surface of the slab where the hole must start, then chip this off first

When it's in 10mm or so, then turn the hammer on

 

[RickH]

I have always found Resin Anchors to take an age to cure in cold weather, so I would be tempted to use Through Bolts like these


http://www.rawlplug.co.uk/index.php?option=com_content&task=view&id=10&Itemid=25


Never had problems with them, also you may find you can drill smaller holes.


Nick.

I had thru anchors initially for base plates used on phase1 of this job. ... but although rated for pull out force |I needed, as they were torqued-up they would pull themselves out of the hole before reaching correct torque setting.
Even had manufacturer come to site with test jig ... they found holes correct diameter, but for some reason the expanding sleeves were slipping on concrete .. almost as if it was too smooth.
We ( at manufacturer's cost) swapped all thru anchors for resin fixed studs.

This 2nd phase ... not even going to waste time trying anchors - hence going straight for studs.