What drill speed for a diamond core drill

[Steve]

Hi.

I've hired a drill (Metabo BDE 1100) and 127mm diamond core drill.

The drill has 2 speed settings. The handbook says the fast setting gives

0-1200rpm and the slow setting gives 0-640rpm. Does anyone know the best speed for cutting through concrete and breeze blocks?

The plan is to drill my holes tomorrow a.m. and return the kit in the afternoon. So any replies before then welcome. (I know not to use hammer action before anyone tells me! - the drill doesn't have it anyway.)

Cheers

[R]

Use the slower speed and if the unit has a variable speed trigger slowly is good, and withdraw frequently to allow the spoil to clear the core. If drilling through a wall drill until the pilot *just* protrudes through the other side and then finish off from the other side (Space and access permitting) to produce a more clean finish at the break out point. DON'T DON'T DON'T cool or lubricate with *anything* the core.

[Steve]

Thanks R. I'll go slow.

[The Medway Handyman]

Nice & slow - and hang on to the bugger ;-)

[John Rumm]

One thing I would note, is that in some materials the core will drill much faster than the pilot - so keeping the pilot in there will often slow you down. I either drill right through with a 10mm SDS bit first so the pilot bit only needs follow a hole rather than cut it, or take the pilot bit out once the core has cut into the wall and can keep itself on centre.

[Andrew Gabriel]

IME with a Tungsten Carbide one, it depends on the material being drilled. With near-engineering bricks, I ended up on top gear top speed, as there's so little bite. With softer commons, you can't do that and need low gear.

Be prepared for the core to jam and try spinning the drill. Hold it very firmly so that it can't spin, and then its inbuilt clutch will slip and protect you from harm. Keep your face and anything else well clear (a friend ended up in A&E having stiches in his chin after a core drill spun and whacked him on the chin).

Watch the drill temperature -- it doesn't look like that Metabo has thermal protection (my Metabo does, but it's a different model). If you aren't running the drill near full speed, the air cooling may not be enough and it might overheat. If you suspect it is overheating, disconnect the core drill (which may itself be hot enough to burn you) and then run the drill at top speed with no load until it cools. Never just leave it switched off to cool on its own; that's what often kills a hot drill.

[PeterK]

The speed should be in the range 900 - 1300 rpm and where in that range is down to experience. The size of the core would put the speed down towards

900 and the hardness of the material is also relevant - "harder = slower". If you get excessive vibration try reducing pressure until you are happy that the core is cutting at its "own speed" .

Peter K

[Steve]

Thanks for the advice everyone.. I now how 2 round holes in my wall.