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Discussion Starter · #1 ·
Yesterday I was drilling some 32MM(1 1/4") holes with my buldog extreme and I started wondering which was better-

To Hold the drill with just enough pressure to "Float"(for lack of a better term) on the hammer effect about say half way down the "Float" depth

Or to bottom everything out max pressure kind of thing?


Sorry I hope I explained the question well enough.(Yes I know this bit is larger than what the drill is rated for but the same would apply to a 1" bit)

Cheers Jim
 

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With holes that size your better of with a core bit as it will bind a lot less. If you do have to use a normal tungsten bit then the best way is to let up on the pressure otherwise the bit can bind up pretty quick and jam it's self in there. It's good idea to let the drill do the work and not force it in hard at all.
 

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Discussion Starter · #3 ·
Thanks
Thats the answer I was looking for. As seldom as I do holes that big I cant justify a core bit and bigger hammer drill. Not that I would not want one. I was binding up on the first hole but I suspect it was becuase I was boaring out from 5/8" On subsiquent holes I did not use a starter hole.
Any tricks to reducing the chunk blown out the back of wall when you punch thru. I usualy patch it back up but would rather have small enough hole I can cover it with either large fender washer or in the case of larger holes a reducer washer that is usually used to resize holes in electrical panels.

What I am doing is punching a hole in the wall and lineing it with a length of PVC pipe then using two bulkhead fittings on stainless fenderwashers and short lenght of tube to pass 5000PSI air thru a wall. Sometimes the customer (like yesterday) want the tube to go thru the wall without any fittings so in the interest of future maintence I need to make the PVC pipe large enough to fit the nuts thru the PVC Pipe so I dont have to cut a tube to remove it. (Sometimes they want to remove pipe to hydro it instead of hydro in place)

Cheers Jim
 

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If you want a nice hole without the parging upon exit then a core rig is the best solution.

With your little bosch I'd use medium pressure, with a bit that big your really not getting the impact energy you need from an sds plus hammer. The heavier the bit the more ummph you need, SDS Max combi hammers are a little better suited.

I'm surprised the pilot hole didn't help that was going to be my suggestion, I found that it speeds things up and reduced the "exit wound".

My only sound advice is to keep your face away from the drill for when you hit bar...unless you want to loose some teeth.
 

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Discussion Starter · #5 · (Edited)
With the Pilot hole I think I had less "parging"(learned a new term today, thanks) But the bit wanted to bind up easier. I think what was happening is the hole was getting deeper at two points and the bit would bounce in and out and then bind.

Got lucky and did not hit any rebar but there was expanded metal mesh about 1.5" in. I was not sure if it was a lathe to support plastering(but this was concrete on both sides of it) or some kind of RF shielding the military had put in the building when it was built. Mesh slowed me down and I pulled out to see if I was hitting rebar but ended up punching thru it.
 

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With the Pilot hole I think I had less "parging"(learned a new term today, thanks)
No you didn't I don't know why I said parging, parging is a thin layer of concrete spead on a surface, it cracks like a crust and makes a mess when you hit it with your hammerdrill. What I meant to say was spalling, I don't know if its a technical term, its just what we always called it when you drill a hole or fire in a pin and bust a pile of chunks off.

I think what was happening is the hole was getting deeper at two points and the bit would bounce in and out and then bind.
Hmmm, to be honest I've never used an SDSplus for a hole that size...I guess there is a reason most combi's hit harder and spin slower.
 

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Discussion Starter · #7 ·
No worries
I am familiar with spalling but did not realise it applied to punching a hole out the back of the wall.
So I still learned a new word today as I have seen parging and now I know what to call it.

Yea I know its on the edge of what its built for but like I said I dont do it enough to justify anything larger. I borrowed my buddies spline drive when I had 25 holes to drill to run tube all over an EOD compound. No problem with spalling there as the holes exited into 3" of exterior insulation. My next bigger $ tool purchase will probably be a drill press. I just have to decide which one.

Thanks for the schoolin'.
 

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Discussion Starter · #9 ·
maninthesea, check your PMs.
I dont seem to have PMS. Maybe I went thru MAN-A-PAUSE when I hit 40

If you meen private message then that would explain the popups that my computer keeps telling me it does not seem to like. I dont see a PM button.
 

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Since you tried pilot holes I assume your using a cruciform bit not a core bit right?

If its necessary to make a clean exit, run a pilot then drill from both sides if possible.
 

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Another good way to stop the back blowing out as the drill exits is to measure the death of the wall and set your drill up so that you stop just short of face of the wall then turn of your hammer and carry on drilling. It takes a little while to do that last inch but it cuts down blow out a lot.

The other good thing about a core bits is you dont have your drill on hammer so you always leave a clean exit hole.
 

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No way you need a core bit for drilling 1 1/4 inch holes. A hilti cruciform bit will go 2 1/2 inch no probloem and drill with sds max drill. The core bits dont match the cruciform ease in my opinion.
 
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