Core drilling questions
phildcr...@yahoo.com
I have a question about core drill bits: How long do they last? I've
got literally thousands of holes, 7/8" diameter, 3 1/2" deep to drill
into concrete and epoxy all-thread rods for a job, and none of the
factory reps seem to want to give me a straight answer on how many
holes I can get from one bit. The Hilti guy wouldn't even get pegged
down between 50 and 500. I can assume I'll hit the occasional rebar,
but the plans outline the bolts not being in line with the rebar. And
we all know that if it's in the plans that way, that's exactly how it
was built, right? I know I'll need a bunch of bits (right now I'm
figuring 200 holes per bit), but at a hundred bucks apiece, I want to
estimate enough of them into the job that I won't take a huge hit
buying bits.
I don't want to use a roto-hammer as most of these bolts are 4" away
from the edge of the concrete pedestal, and I'm worried both about
precision (not having the drill straight or having it wander) and
breaking off the edges of the concrete pedestals that I'll be drilling
on. Also, if I hit rebar with the roto-hammer, I'm in a bad way,
because these bolts can't be moved.
Third, how long does it take? How many minutes to core drill a hole,
remove the core, clean out the hole, insert some epoxy and set an
anchor bolt to grade? If my per-hole estimate is wrong by one minute,
that equals about 9 days of production. I realize it's just a guess,
but I want it to be an educated one, and frankly, I'm not very
educated on the production aspects of 7/8" core drilling. Currently,
the average of people I've surveyed is about 10 minutes.
If any of you have any thoughts or guidance on this issue, I'd
appreciate your wisdom and opinions.
Thanks,
Phil
phildcr...@yahoo.com
Bobk207
Phil-
You're on the right track ...asking all these questions in advance.
That's the good news.
The bad news as you mentioned is being off by a a minute per hole
makes a huge difference.
Hilti rotary hammer are awesome tools you can drill fast & straight.
But not through rebar.
Hilti core drilling setups are awesome as well.
Having drilling 100's of holes personally, I would suggest a two prong
approach
Use the rotary hammer, its faster, cleaner...no water mess. If you
hit rebar stop & finish with the coring system.
Is the coring system a Hilti vacuum base? If so make sure you have
the room & appropriate surafce finish for it to suck down.
Setup, placement & suck down is much slower for core drill than point
& shoot with the hammer drill.
Rotary hammer will give at least 100 holes 3.5" deep IF you don't
abuse the bits. Same with core drills, hitting rebar will reduce life
by 50% absolute worst case.
Don't lean on the hammer drill, a Hilti hammer drill works fine on its
own weight.
I drilled 52 holes 1.125" diameter by 12" deep...used 2 Hiilti hammer
bits, hit partial rebar in 5 holes & cored them no sweat.
If your Hilti hammer is variable speed you can easily accurately place
holes. Since your holes are only 3.5" deep I doubt you'll hit much
rebar unless they placed really close to the surface. I'm figuring
its at least 2" deep.
I suggest you do some process development prior to bid submittal. It
will be worth the effort
How many men in the drill, prep & place team?
What chemical anchor are you using?
Who supplies the material? If you supply the material can the hole be
13/16" (allowable by chem mfr & dwg specs?)
mechanical dispenser or pneumatic?
Anchors precut?
Anchor setting tolerance? hole pattern x-y tolerance? protrusion
tolerance?
I suggest you "productionize" the process; efficiency is the name of
the game, your crew skill level & motivation are key factors. Simple
aids to production will greatly improve efficiency, work flow
organization is key as well.
As you can probably tell, I've done this sort of thing before but
every situation / job site is a little different and for 1000's of
holes, minutes make a huge difference, even 10 seconds per hole
matter. I design & specify these sorts of processes.
Your average time estimate is 10 minutes, what was the range in times?
Your 10 minute number, at this point, without prior experience or some
process development, is pretty much a WAG (wild ass guess)
be careful, I'd hate to be very far off on the estimate per hole on
1000's of holes.
cheers
Bob
Bobk207
Phil-
All my rambling is all well & good for developing a really good number
but if you're not needing to have a really sharp pencil to win the job
job it wasn't all that useful.
Are we talking about a fixed price & you pocket any excess? :)
IMO based on experience, for multiple groups of multiple holes, your
10 minutes per hole is more than adequate. Use that plus 100 holes
per bit. Base the bid on all core bits but also use the rotary hammer
idea. It'll be faster.
If you have a decent crew & give them some sort of incentive (& work
flow guidance) to work faster I'm sure you can beat that number by a
BTW a 4" edge distance in decent concrete is plenty for a 7/8" hole.
I hammer drilled 1" holes in unreinforced concrete with only 2" edge
distance.
I whimped out on a 2" hole (x 10" deep) with 6" edge distance and used
the core drill.
cheers
Bob
phildcr...@yahoo.com
My comments are interspersed. Thanks for the insight.
Phil
> > Phil-
>
> > You're on the right track ...asking all these questions in advance.
> > That's the good news.
>
Thanks.
Snip
> > Having drilling 100's of holes personally, I would suggest a two prong
> > approach
>
> > Use the rotary hammer, its faster, cleaner...no water mess. If you
> > hit rebar stop & finish with the coring system.
>
> > Is the coring system a Hilti vacuum base? If so make sure you have
> > the room & appropriate surafce finish for it to suck down.
>
It is and I do.
Snip
> > Don't lean on the hammer drill, a Hilti hammer drill works fine on its
> > own weight.
Easier said than done with a crew of carpenters.
>
> > I drilled 52 holes 1.125" diameter by 12" deep...used 2 Hiilti hammer
> > bits, hit partial rebar in 5 holes & cored them no sweat.
>
> > If your Hilti hammer is variable speed you can easily accurately place
> > holes. Since your holes are only 3.5" deep I doubt you'll hit much
> > rebar unless they placed really close to the surface. I'm figuring
> > its at least 2" deep.
>
According to the plans, the rebar shouldn't be in the path of the bolt
holes anyway. And we all know that if it's shown that way on the
plans, that's how it was built, right?
> > How many men in the drill, prep & place team?
>
I was thinking two--one to do the actual drilling, one to tend the
hoses, cords, bits, etc. When the drill guy gets tired, they can
switch.
> > What chemical anchor are you using?
> > Who supplies the material? If you supply the material can the hole be
> > 13/16" (allowable by chem mfr & dwg specs?)
>
It specs a 7/8" hole. I'm sure the owner would give us a break on it,
though, if we needed 13/16". We're supplying the epoxy, also called
out in the plans.
> > mechanical dispenser or pneumatic?
> > Anchors precut?
> > Anchor setting tolerance? hole pattern x-y tolerance? protrusion
> > tolerance?
Electric dispenser, precut anchors, x-y pretty tight (within 1/8" and
protrusion probably 1/4".
>
> > I suggest you "productionize" the process; efficiency is the name of
> > the game, your crew skill level & motivation are key factors. Simple
> > aids to production will greatly improve efficiency, work flow
> > organization is key as well.
>
We've already discussed templates, layout procedures and order of
operations. Most of the anchors are in groups of 10 or 12, so we'll
make a 12-hole template or three, double nut the anchors onto the
template, drill the holes and set 12 bolts at a time. While the epoxy
is drying, we'll drill 36 more holes.
> > As you can probably tell, I've done this sort of thing before but
> > every situation / job site is a little different and for 1000's of
> > holes, minutes make a huge difference, even 10 seconds per hole
> > matter. I design & specify these sorts of processes.
>
> > Your average time estimate is 10 minutes, what was the range in times?
>
> > Your 10 minute number, at this point, without prior experience or some
> > process development, is pretty much a WAG (wild ass guess)
>
While none of the folks I've talked to have drilled holes at a level
like this, the consensus is 10 minutes to drill the hole, clean it
out, squirt some epoxy into the hole, and set the bolt.
> > be careful, I'd hate to be very far off on the estimate per hole on
> > 1000's of holes.
Obviously, while we'd like to be dead-on with our estimate, I'm mostly
just trying to get into the ballpark with the time estimate. We have
a schedule we have to meet, and I was wondering how many drilling rigs
I needed, etc. With our current manpower shortage, I want to have as
few guys on this as possible, and just have them work for the duration
of the job on this one item. A few man-days one way or the other
won't break the bank on this job (it's a big one), but closer to the
"true" value of the work is always better. That way, there's less
variability in our estimate, and the smaller contingency we need to
build in. With less risk, we can bid at a lower margin, and hopefully
get the job. But I'm sure you knew all that already, Bob. :)
>
> > cheers
> > Bob
>
> Phil-
>
> All my rambling is all well & good for developing a really good number
> but if you're not needing to have a really sharp pencil to win the job
> job it wasn't all that useful.
>
> Are we talking about a fixed price & you pocket any excess? :)
>
Yes. This is a lump sum job.
> IMO based on experience, for multiple groups of multiple holes, your
> 10 minutes per hole is more than adequate. Use that plus 100 holes
> per bit. Base the bid on all core bits but also use the rotary hammer
> idea. It'll be faster.
>
> If you have a decent crew & give them some sort of incentive (& work
> flow guidance) to work faster I'm sure you can beat that number by a
>
> BTW a 4" edge distance in decent concrete is plenty for a 7/8" hole.
> I hammer drilled 1" holes in unreinforced concrete with only 2" edge
> distance.
That's good to know. Also, I don't think I mentioned it, but this
concrete is no longer green. It's currently about a month old, so
it's pretty well set up. If we get the job, we won't get in there for
at least another month. So that's good.
>
> I whimped out on a 2" hole (x 10" deep) with 6" edge distance and used
> the core drill.
>
Sissy.
> cheers
> Bob
Thanks again, Bob, for the insight. I hadn't considered the 2-pronged
approach. If we can save a few bucks that way, that will be great.
I'll be sure and post an update if we get the job.
Take it easy,
Phil
Bobk207
Phil-
Good luck on getting the job.
Having an electric dispenser will be a big help. On those 52 each 1
1/6" holes by 12" deep we used a dual cartridge hand
dispenser....after about 5 holes we were dying!
I would suggest drilling & "rough" cleaning a large number of holes.
Have a good shop vac with lots of extra filters (washable ones).
Sweep up most of the debris with dust pan & brush.
A modified 2" (or 3") PVC elbow can be used as a vacuum hose nozzle.
Drill a hole thru the back side of the elbow to accept a 1/4" tube on
a modified blow gun.
Using this setup you can blow the holes & capture the debris (so the
crap doens't shoot up into everyone's face)
Sticking with a single process with save a LOT of time, switching
between tasks really eats up time.
SO drilling & rough cleaning is one process (one guy). Drilling is
really quick, clean & easy with a hammer drill. The most tiring
thing will be leaning over the drill. I tend to use the REALLY long
bits, so I can stand at a more comfortable height & controlling
drilling squareness is easier.
If you go with shorter drill bits, encourage the guy to get
comfortable, sit on a bucket or use knee pads
A guy with the vac can follow when the driller gets far enough ahead.
The cleaning process should be:
1) blow with vacuum hose debris catcher
2) brush with proper hole brush
3) blow without vacuum
4) final brush
the correct sequence is: blow brush blow brush
the last thing to go in the hole (before the epoxy) must be the brush.
if you blow last, it coats the hole with dust & weakens the epoxy bond
when the "hole cleaner" catches up with the driller, he can switch to
setting anchors.
Depending on whose product you're using & how big the hole diameter
is...the anchors can stand up by themselves.
Be careful on hole depth...too deep & you're screwed.....it makes
controlling anchor protrusion a bitch.
It is easier to shorten a anchor that sticks out too far than deal
with a "shorty". Discuss QC with whoever will check or sign off on
mistakes. I'd m
Whose cutting or supplying the anchors? Are they off-the-shelf Hilti
threaded rod or just cut threaded rod?
Variable anchor lengths will be a problem to deal with.
cheers
Bob
Wayne Whitney
> the correct sequence is: blow brush blow brush
> the last thing to go in the hole (before the epoxy) must be the brush.
> if you blow last, it coats the hole with dust & weakens the epoxy bond
Interesting, Bob. Simpson's instructions for their SET epoxy say to
"blow brush blow". Do you think that they have it wrong?
<http://www.simpsonanchors.com/catalog/adhesives/adhesive_anchoring_install.html>
Cheers, Wayne
Bobk207
> On 2007-10-21, Bobk207 <rkaza...@gmail.com> wrote:
>
> > the correct sequence is: blow brush blow brush
> > the last thing to go in the hole (before the epoxy) must be the brush.
> > if you blow last, it coats the hole with dust & weakens the epoxy bond
>
> Interesting, Bob. Simpson's instructions for their SET epoxy say to
> "blow brush blow". Do you think that they have it wrong?
>
>
> Cheers, Wayne
My experience plus my interaction with home office Hilti
engineers ....they said brush, blow, brush
They explained that the "final brush" drops the drops the dust off
the hole wall.
I added the extra blow / vacuum on the front end but kept the Hilti
"finish with brush"
Again my experience based on drilling, cleaning, bonding & testing
anchors in concrete in the lab.
flour (dust) is used as a release agent when working with dough
paint doesn't stick to dust; I use a brush & a tack cloth when
prepping for paint
YMMV.....draw your own conclusions
counter argument / theory? :)
cheers
Bob
Wayne Whitney
> counter argument / theory? :)
Oh, I don't really have one, although one can imagine a counter
argument. Mostly I was surprised that Hilti and Simpson give opposite
instructions in this regard. I guess the obvious question is what is
the bonding mechanism of the epoxy to the concrete? But this is
academic.
Cheers, Wayne
Bobk207
Wayne-
>>>Oh, I don't really have one, although one can imagine a counter argument. <<<<
If you can imagine one....let's have it.
Dust inhibits adhesion.
cheers
Bob
Tim Mulvey
"Bobk207" <rkaz...@gmail.com> wrote in message
news:1193011694.3...@i38g2000prf.googlegroups.com...
Hilti says brush,blow for their epoxy systems. End it by brushing and the
hole won't be clean enough. You don't need to brush at all, only blow if you
use the HVA capsules.
Tim
Wayne Whitney
Absolutely, dust inhibits adhesion. But then the question is which
procedure, brushing or blowing, yields a dust pattern that has the
lower impact on adhesion. You mentioned brushing last to dislodge any
loose dust on the sides, where it will fall to the bottom.
Arguments in favor of blowing last could be (1) blowing will remove
any loose dust at the bottom and won't significantly redeposit it on
the sides or (2) brushing may yield fine dust that is suspended in the
air, and blowing is the only way to remove this fine dust.
Anyway, I don't really know anything about this. But Simpson
recommends blowing last, and I see someone else said that Hilti's
written instructions say the same thing. I assume the only way to
resolve the question would be to do tests. Or perhaps it is most
important to just use whatever procedure was used when the published
strength data was developed.
Cheers, Wayne
Bobk207
BTDT I'll stick with my current procedure, it works
I'd like to see a link to the Hilti linfo,.
I'm not going research or search for more info about something I
believe to be a settled issue.
>>But then the question is which procedure, brushing or blowing, yields a dust pattern that has the lower impact on adhesion.<<<
Brushing.........
that's why when painting, blowing or vacuuming is followed with a
"duster"...a foxtail, a rag or even better a tack cloth.
cheers
Bob
Wayne Whitney
> I'd like to see a link to the Hilti linfo,.
For the HIT RE 500 epoxy (to pick a random one, I'm not familiar with
their products), see page 15 of this file:
> I'm not going research or search for more info about something I
> believe to be a settled issue.
I'm not trying to dispute your statements, I was just surprised to see
at the discrepancy between your theory (which makes sense) and the
manufacturer's instructions. It leaves me a little confused.
Cheers, Wayne
DanG
on any one job. Most of my applications have been indoors so we
developed a brush and suck method. A plumber's wire brush, cut
off the handle, chuck it into a battery drill and rig whatever
tube on a good shop vac to go to the bottom of the hole has worked
well for us. As has been said, controlling the depth is critical
if you can't run wild. What on earth are you setting that only
needs a 1/4" exposure and 1/8" tolerance? I think the biggest
issue will be maintaining that type of tolerance. I don't think I
would even consider a core drill, it sounds like a heavy hammer
drill or rotary hammer job to me unless they are so close together
that they generate a fracture line. You might consider two bits
in two drills, a lead hole with a 1/4" bit in a light weight SDS
drill for accuracy followed by the 7/8 in a heavier drill.
Another concern is concrete depth if you are drilling 3 1/2" are
you approaching blowing out the bottom? Relton and others make
special rebar cutting bits that work in the same size hole you are
drilling: http://www.relton.com/
Please follow up with your results.
--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)
dgri...@7cox.net
<phildcr...@yahoo.com> wrote in message
news:1192677704.5...@i13g2000prf.googlegroups.com...
Bobk207
> "Bobk207" <rkaza...@gmail.com> wrote in message
That's not what the Hilti factory new adhesive development engineer
told me in 1997.
brush, blow, brush
has got to leave a more dust free surface than
brush, blow
maybe they did more testing but when I was doing testing for them it
was
brush, blow, brush
and that's what I've done (& still do) and the anchors test out just
fine.
cheers
Bob
Bobk207
> On 2007-10-23, Bobk207 <rkaza...@gmail.com> wrote:
>
> > I'd like to see a link to the Hilti linfo,.
>
> For the HIT RE 500 epoxy (to pick a random one, I'm not familiar with
> their products), see page 15 of this file:
>
>
> > I'm not going research or search for more info about something I
> > believe to be a settled issue.
>
> I'm not trying to dispute your statements, I was just surprised to see
> at the discrepancy between your theory (which makes sense) and the
> manufacturer's instructions. It leaves me a little confused.
>
> Cheers, Wayne
Wayne-
its not my theory, its what the Hilti development engineer taught me
in 1997
looks like they have chosen to omit the final brush set and now
suggest
brush, blow
oh well,
I will still
brush, blow, brush
until someone shows me data that the final brushing is detrimental to
anchor performance.
cheers
Bob
Tim Mulvey
I hear you Bob. There's usually more than one way to do something and still
end up with a quality product. But, when an architect or engineer specs a
certain product, we're obligated to follow the manufacturers instructions.
That way, provided things are done correctly, it's alot harder for problems
to come back and bite the installer. Sometimes, as in your case, things test
out just fine. However, I've also seen the other side. Mostly with metal
roofing, flashings, etc. where guys either took shortcuts or thought they
knew more than the manufacturers. It's no fun going back to repair or
replace someone elses shoddy work in order to get the warranty reinstated or
stop leaks. I just figure that after spending thousands or millions of
dollars on research and development of a product or a system, the least I
can do is install per their instructions. It can save me alot of pain down
the road.
Have a good one
Tim
Bobk207
Tim-
I am an engineer AND I have done 100's of installed & tested anchors
(pulled to failure) for various mfr's.
The procedure was brush, blow, brush
now it looks like they say in their instructions brush, blow (omitting
the final brush)
looks to me like a short cut...........I'm giving my Hilti contact a
call on Monday to get the straight story.
cheers
Bob