End play problem with (SDS+) drill (edited) when using a long 450mm drill bit

[Deleted member 174758]

They may leave the factory perfectly straight, but a 1m long x 16mm will soon bend in use. Which is why you start deep holes with a short pilot drill.

Which takes us back to where I started in this discussion...

I've found that cheap bits tend to bend a lot more in service, especially when you give them to idiots who think the way to use an SDS drill is to put their back into it and push... (for those unaware - you only need to guide and apply light pressure - the drill does the rest)

I have to say that it's a bit of a trade off. Once did a job where I had to drill 120+ 16mm holes through 150 to 200mm of reinforced concrete then through about 2mm of corrugated steel deck on the underside (to take bolts which held in place otherwise unsupported timber-framed pygymy walls in a call centre). The bits I used were 4-flute Hiltis and i got about 50 to 55 holes out of the first two bits, but they were still straight at the end if drilling, albeit completely blunt. It took me about 12 hours to do the lot including bolting up (after which the SM banned me from drilling on the job because it had been so noisy!). The office, who had ordered the bits for me, nearly had a fit when they got the bill - nearly £60 a pop! (and that was 7 or 8 years back). I had started out the day before with Bosch and DW 2-flute bits, but they simply couldn't handle the rebar or the the corrugated deck all that well. It took 3 to 4 times as long to drill each hole with them and they went blunt after 5 or 6 holes. It convinced me to buy multi-flute (3 or 4 flutes) over 2-flute drills in future, at least for reinforced concrete. These days Bosch, DW, Heller and Milwaukee all do multi-flutes from about 7mm diameter upwards, although they can take a bit of finding

 

[blup]

Are you saying that Hilti 4 flute sds bits drill through rebar? They have tungsten carbide tips or similar?

Blup

 

[johnny2007]

My opinion:
Sds drills are not tools of precision.
Just drill the damn hole.

 

[Mike13]

When you drill a hole the precession always means the hole has one more lobe than the drill used to make it.
A two lobe drill gives a slightly triangular hole etc, so the multi-lobe bits will always give a better hole. for most things you drill the error does not matter at all. If you are drilling near an edge for instance it might matter.

 

[JohnD]

.

 

[opps]

Are you saying that Hilti 4 flute sds bits drill through rebar? They have tungsten carbide tips or similar?

Blup

4 flutes will go through the bars in concrete lintels, whereas regular bits will end up with broken tips. I once broke a Dewalt bit putting up a curtain track. Ended up buying the 4 flute Makita set and it went through without issue.

You can get SDS bits for thick rebars but they are expensive

Bosch SDS Plus Steel Rebar Cutter Drill Bit | Rebar Drill Bits

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They are carbide but the hammer action should be turned off.

 

[blup]

That's interesting, I've been looking at the makita nemesis 4 flute bits which seem to have a good reputation. @JobAndKnock was talking specifically about Hilti sds bits (sds max?) going through rebar, I imagine the carbide tips are of the highest quality and form a single piece welded onto the end of the drill.

Blup

 

[opps]

That's interesting, I've been looking at the makita nemesis 4 flute bits which seem to have a good reputation. @JobAndKnock was talking specifically about Hilti sds bits (sds max?) going through rebar, I imagine the carbide tips are of the highest quality and form a single piece welded onto the end of the drill.

Blup

I have two sets of the Nemesis bits (SDS+) and have been very happy with them. I have never tried the Hilti ones though.

The tips are indeed one piece, see

 

[Deleted member 174758]

You can sometimes pick-up Hilti SDS bits on eBay. They are good, but I'm not certain they are worth the money at Hilti official prices

Looking at my Heller Tri-Jet 3-flute bits, they are also a one piece tip. All the 3- and 4-flute bits I've tried to date drill faster than 2-flute bits.

 

[cdbe]

I've got some Hilti bits, I was slightly disappointed with them when drilling Accrington's - despite not forcing them they were prone to overheating - I'd pull it out and there'd be no tip left - just a melted stump - maybe they're better suited to concrete.

 

[Deleted member 174758]

I'd talk to the Hilti rep about whether or not those were designed for concrete alone (I know some of the SDS Max bits are materials specific).

Last time I did Noris I used a 2-flute Bosch Professional bit, and I did have to keep pulling the bit out to clear it. Maybe the material density affects the useability of the multi flute bits? The one in the sevond photo certainly doesn't look anything like the last Hilti 2-flutes I had, or the 4-flutes I mentioned earlier