SDS Drill bits producing oversized holes for Rawl plugs

[dobson156]

Hi, I feel like I am missing something here. I need to drill some holes into concrete block (not Airlights) for a 10x55mm rawl plugs

I am using a "Boschhammer" drill with a brand new Reisser 10mm SDS bit but when I drill the hole it's oversized for the 10mm rawl plug and when I then add the screw it doesn't really feel reassuring. So I also tried an 8mm bit but that's far too tight.

I guess a 9mm would be the answer, but that doesn't seem an at all common size and is not stocked at any of the local builders merchants; whereas 10mm rawl plugs are reasonable common - so I am guess I am doing something wrong?

Perhaps it's my technique? Is there a technique to drilling into masonry? Should I be drilling pilot holes, should I try and drill in as fast as possible to minimise the chance of the bit scraping out a bigger hole?

Thanks in advance

 

[opps]

Which plugs are you using?

Have you tried removing the sds bit and put it in to the hole to see how tight it is?

If your blocks are aerated concrete, I would just use a regular cordless drill with no hammer action and basic masonry bit.

BTW you can get 9mm SDS bits

Bosch 9mm SDS Plus-3 Drill Bit For Masonry & Concrete 2608831023

Bosch 9mm SDS Plus-3 Drill Bit For Masonry & Concrete 2608831023 Features: BOSCH 2608831023 9mm x 160mm Series 3 SDS+ Drill Bit has a high durable tungsten carbide 2-cutter for a long lifetime & good wear resistance.Featuring a centering tip for a precise drilling start and improved guidance in...

tools4trade.co.uk

 

[ETAF]

is the drill bit running out, wobble ?
I had a similar issue , and once i removed the bit, cleaned and put back in chuck it ran true

 

[dobson156]

So a bit of an update. If I drill an 8mm hole with the SDS Drill, then enlarge it with a non-SDS 10mm masonry bit in my cordless hammer drill-driver then it seems "okay". So I might just do this. I think there is a chance my hand is just not really steady enough with that much power I am just make an oversized hole.

Which plugs are you using?

The ones that came with some bike hooks for storing push bikes vertically. Hence why I want them to be nice and tight and not flopping around.

If your blocks are aerated concrete

They're not. They're proper concrete blocks.

is the drill bit running out, wobble ?

Does seem to, but then again, I might not have the steadiest of hands.

BTW you can get 9mm SDS bits

Yeah, I know they exist, just I can't find any locally and I really wanted this job done this weekend. And the fact they're not common place makes me feel as though it's probably me doing something wrong.

 

[Deleted member 174758]

is the drill bit running out, wobble ?

Maybe. In something like 45 years I've owned 9 or 10 2kg or 3kg SDS drills (I still have 3) including two Bosch blue drills, as well as having had a number of hire shop SDS drills by Bosch, Makita, etc - and the only one with a wobble in the chuck was a Ryobi corded SDS drill. Even that wasn't so bad.

So assuming that it is a genuine Bosch SDS drill I'm more inclined to look at the drill bit first - OP roll it along a kitchen worktop under your hand or other flat surface to see if the top is "helicoptering" (i.e. you can see the end wobbling about). Then install the drill bit in the SDS, run the drill and observe if the drill bit tip is wobbling. Often the issue is down to a drill bit, not the drill. Finally drill a hole in a more solid material, such as a concrete flag or concrete and see if the plug is a good fit in that. If it is you might want to consider changing to a plug designed to be used in softer blockwork

There is another gotcha - using drills which are too long for the job. If you have a 450mm long 10mm SDS bit it ideally shouldn't be used to drill a 50mm deep hole, or even be depended on to drill a 350mm deep hole in one - far better, and more accurate, to use a short drill bit to start the hole, then swap to the longer drill bit, and remember that an SDS drill requires only guidance and gentle pressure most of the time in the majority of materials - pushing like a mad gorilla at the back end of the drill, especially if you are using a long thin drill bit, only causes the drill bit to bend - which enlarges the hole

 

[freddiemercurystwin]

Are the SDS bits cutting holes in just a second or so? Sometimes an SDS bit/drill is overkill depending on the strength/type of material you're drilling.

 

[foxhole]

Try with hammer action off.

 

[dobson156]

Thanks for all of the replies. I think it's a hybrid of a few things. The drill bit is true, but it is also fairly long so and I think the hammer action is just causing too much vibration for material.

Using my two drill strategy seemed to work and I got my job done.

Thanks for all the help.

 

[Justin Passing]

For a more accurate diameter hole, use a smaller drill first. They almost always make a slightly bigger hole otherwise. EG for a 6mm hole I automatically use a 5.5 drill bit. The harder the material the more it's true. EG concrete lintels are hard.
So drill a 7 or 8mm, then a 10mm will drill so easily it'll be sized right.

 

[Deleted member 174758]

If I were to drill two holes for every screw I put in it would take forever to complete a job. If the hole is oversize when SDS drilling it is normally either that the drill bit is bent or that the material is soft. Soft materials are easy to deal with - go down in size 0.5 or even 1mm. The harder the material, the truer the bits seem to run unless there happens to be rebar or lumps of granite in the way, which can always push you off line a bit. Percussion drills are a different kettle of fish because they drill a lot slower and get pushed off course a lot more easily.