core drill guide bits

[Tim Watts]

On Thu, 10 Jun 2010 20:19:10 +0000, Tim Watts wibbled:

Or stuck it a high stress part of the wall like right under a lintel bearing.

[John Rumm]

Depends on how it slows - gearbox slowing being better than electronic in this case. I would try it at the top speed. (helps if you have an accelerating trigger to get it up to speed a little less violently)

Yup that is the desired result!

[John Rumm]

400 is easy enoough to find.

The smallest long SDS bit I found was 8mm. Most places go down to about

10mmm

[Fred]

I was hoping for something slightly smaller still (for use in the cramped conditions under the stairs)

[Fred]

I don't know how the Titan works but it is a (relatively) cheap 6kg lump that Screwfix (I presume) import, so I doubt it uses an expensive or complicated method. It certainly doesn't have a fancy trigger; it's either on or off. I had it set to slow because I thought big holes required slow speeds.

Daft question: why don't sds drills have a reverse like "ordinary" drills do? TIA

[Fred]

Thanks. Is there a rule of thumb: keep x cm away from lintels or space holes three diameters apart?

[John Rumm]

Unless its a mechanical feeling slider, or knob of some sort (and then only offereing two or at most three speeds) you can be fairly sure its electronic. That means at slow speed the motor is turning slowly and is less able to get rid of heat (fan performance increases non linearly with speed). So I would tend to go full speed or close to it (which will be 900 - 1100 rpm probably)

Mine does... ;-)

[John Rumm]

The only thing I can suggest is get a 12mm 160 or 200mm SDS bit to make the initial hole, and then a conventional masonry 22mm short bit to open it up without hammer action in a normal chuck.

[Fred]

Thanks. Is 1100rpm ok for big cores such as 107mm? I always thought big holes needed a slow speed? In a way it's a design flaw that the fan doesn't go fast enough to cool at low speeds.

[Fred]

It is strange that there aren't any 200mm long, 22mm wide sds bits. It is just breeze block to go through though, so an "old fashioned" masonry bit would probably be more than enough to do the job. Thanks very much for the idea.

[John Rumm]

Yup, I would think so. 11k rpm is slow in drill terms (i.e. similar to a conventional drill in low gear)

To be fair its not often you use a hand held drill with a high continuous load at low speed.

[John Rumm]

Must admit until you mentioned it, I had not noticed really! I suppose I have not yet needed to drill a shallow hole in a confined space. (on the occasion I needed to drill through a brick wall with a joist 8" away, I normally switch to a long bit and drill at a shallow angle instead (by overdrilling the size required you can still create a smaller straight through hole).

Maybe - depends on what your breeze blocks are - the phrase seems to be used for everything from quite low density blocks to very solid high density concrete ones.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Fred saying something like:

I've had a 25mm, 200mm long SDS bit for years, so look around.

[tony sayer]

In article , Grimly Curmudgeon scribeth thus

Seems that you need a decent hardware outlet. I've seen some a matter of feet long in Mackays in Cambridge!...

[Dave Osborne]

x 250 if that's any use.

[Fred]

Yes, thanks and a sensible price too. BTW who are heller, is it a good brand. I think I have seen the name before in the tool station catalogue (but not those bits at those sizes).

[Fred]

[...]

Thanks. Until this thread I hadn't appreciated that an sds drill was much slower than a conventional drill, thanks for pointing that out. So to sum up: you do need a low speed for a large core but the top speed on an sds still counts as slow, so it's safe to do so. Thanks again.

[John Rumm]

Oops typo - make that 1k rp, is slow (11k would be 'kin fast!)

Yup, a conventional drill will often be 2000 - 3000 rpm at full speed.

[Fred]

On Fri, 18 Jun 2010 21:37:30 +0100, John Rumm wrote: [about sds drills]

[...]

Ah, so that might answer my earlier question about why people buy conventional drills: they are faster. Whilst looking through the cpc catalogue for something else, I did spot a blue bosch conventional drill that mentioned having a two speed gearbox and clutch for cores but on closer inspection was only for cores up to 68mm but rated 1100W IIRC. What a shame it wouldn't do 107mm cores, I might have treated myself otherwise ;)

Thanks for all your help on this subject, I have learnt a lot.

[John Rumm]

Well my 720W Makita in theory only does cores to that size or possibly a little smaller. However it has drilled many 107mm cores in its time. So I expect the Bosch would do as well or better as long as the clutch is not set to disengage at too lower a torque.