Hi I have often used 5mm and 6mm non-SDS drill bits for rawl plug holes. I am thinking of buying a set of SDS drill bits and have noticed that sets usually include a 5.5mm bit. What is the reason for this size?
David
I think 5.5mm is the 'official' size for red rawlplugs, probably originally from 7/32"
In many materials, SDS bits end up with a wider hole than the same size non-SDS bit. With SDS, I will almost always use a smaller bit than I would have with a plain hammer drill. If the hole is too tight, I will then widen it with the next bit size up, but not operating in hammer mode. This gives a cleaner and stronger hole for supporting rawl plugs.
Flexibility? As 5mm and 6mm are the probably most popular sizes an intermediate size offers the possibility of using a 6mm plug with a thinner but longer screw which would be too long for a standard 5mm plug. So it offers more purchase on the actual plug. Also if the walls are a bit on the ropey side I've often found it can be a help to use bits which are a bit undersize in any case. The eventual size of the holes is another matter.
michael adams
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It's my drill of choice when drilling holes in most materials for red rawlplugs. I only use 6mm if drilling into something very hard - concrete or engineering bricks. I get a much firmer fixing that way.
That's what the brown rawl plugs are for;-)
On 28 Oct 2014, Andy Burns grunted:
My yellow plugs say "5/5.5 mm" and I do tend to use both, depending on substrate generally.
I have to hand some "Woodworkers" brand that say 5.5 mm and some Rawl brand that say 6 mm.
In article , Andrew Gabriel writes
I always use a pilot hole, more so for old school hammer drilling than SDS as the former will more likely take longer and so has a greater chance to wander.
It's mainly (soft) sandstone here so it makes sense to drill a pilot and then give it a single run down with the right size bit.
Despite my favourite plugs 'requiring' a 7mm bit, I don't own one but know just how much wiggle to apply to turn a 6 into a 7.
I have some 4mm and 4.5mm SDS bits which I find *very* useful for yellow plugs to get a nice tight fit. It's very rarely I find that I actually need to run a 5mm into the hole to get a yellow plug in.
In softer substrates an SDS bit will tend to make a slightly larger hole. I always use a 5.5 drill bit for a red rawlplug. In harder maretials a hammer is needed to insert the plug (4.. screw) Malcolm
Yes, I find the 'recommended' drill sizes for plugs are nearly always too generous. I'm happiest when I just have to tap the plug in gently with a hammer (or something else when I've not got a hammer!).
I often use the back of the drill.
There is a unique problem to SDS bits. When the front of the bit goes blunt (esp the small sized), it still drills fine with the SDS drill (though and ordinary pistol drill wouldn't make any hole with it.)
But as the side of the drill also wear, you get undersized holes, sometimes greatly undersized. This can be a problem you can't resolve by sharpening. So you end up using the worn drills for the "next size down".
+1 :-)
It's the 'old' Number 10.
I find that with 5.5 in harder materials, plastic plugs often buckle when you try to hammer them in. That's when I use 6mm instead.
I wanted a 7mm bit the other day, and the newly-opened hardware shop in town didn't have one. Their supplier listed .....5.0, 5.5, 6.0,
8.0, ...... Needless to say, I went to the builder's merchant over the road, and bought what I needed.
You use SDS bits in an 'ordinary pistol drill'?
All the masonry bits I've seen have a much wider tip than shank.
Or simply buy a new one? SDS drills tend to have a very long life.
but when you meet a reinforcing rod in a concrete beam, they don't like it.
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