Drilling a Straight Hole (Overhead, Into Concrete)

I'm using a Hilti drill to drill holes into concrete ceilings. Drilling overhead with a heavy drill and big bit is making it difficult to keep the hole straight. The Hilti is more than up to the job ... the problem is when you're applying upward force, the natural tendency is to pull the drill toward you or away from you, which makes for a slanted or "crooked" hole. Any tips on how to keep the drill straight so as to achieve the straightest possible hole?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Kinda depends. On how straight it HAS to be, and how much time you have to drill X many holes in a day, how many of these holes are you going to drill and how frequently, and how much equipment you have on hand.
If I (underlined I) had to drill some holes for my own use, I'd get a piece of 4 x 4 and drill a hole in that. Then I'd drill a starter hole in the concrete, slide the 4 x 4 on the bit, put the 4 x 4 flat on the ceiling, and drill a reasonably straight hole.
If it had to be EXACT, I'd put the 4 x 4 on a couple of screw jacks.
If I HAD to drill a bunch of holes every day, I'd make a drill holder (I'm a welder), and could do that cheaply. One could easily be mounted to the top of a screw jack and moved in a couple of minutes.
If I were a craftsman and had to do this a lot all the time, I'd have a welder make me a drill guide, and do consistent accurate work.
It really all depends on how accurate you have to be, and how often you have to drill the holes.
The 4 x 4 idea would be the hobbyist approach, easy, cheap, and reasonably accurate for a few holes. Plus, you could keep it on a shelf for future use.
From there, if it has to be accurate, and it's going to make you money, DO IT RIGHT THE FIRST TIME.
Steve
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Good ideas all, and maybe I'm just dense (well, I'm obviously not well educated about this type of thing at least), but I'm not seeing how a screw jack would help me hold the drill guide up against the ceiling. Would there be another way to hold the 4x4 against the ceiling? I'm up on a six foot scaffolding set with very little room to work ... I love the 4x4 idea and think it would work for us .... but I'm stumped by how to hold it in place.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

to
drill
piece
and
(I'm a

top
have
reasonably
DO
Transmission stand, pipe stand, etc... Something with a screw adjustment on the top for quick installation/removal. Any type of stand that would be adjustable for height that would wedge it up on the ceiling.
Or, have a welder make you a jig that could have a spring action that would compress as you're drilling.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@yahoo.com wrote:

Go to a thrift store and find an old three footed walking cane. The tripod base would make a very light stable platform on which to mount your drill guide. A piece of 3/16 aluminum plate with 2 or 3 steel guide rods for a cobbled together drill holder mounted to the feet should slide straight. If clearance around conduit and such would make it a problem for the rubber footed tripod, simple 3" spikes on the flat plate would suffice for legs. We had a sheet metal shop here in town who's owner would give me all sorts of scrap pieces of different metals from the scrap bin, I really mourned the closing of that shop. I have a portable drill guide like this one that I use:
http://www.garrettwade.com/jump.jsp?itemType=PRODUCT&itemID 5318
I don't think it would fair well with a hammer drill unless the chuck was changed out to a hammer drill chuck. It could give you a good idea on how to build your own heavy duty guide.
TDD
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Stick-on level vials are a good idea and might work well enough.
Depending on the drill and you, it might be possible to hold the drill on your shoulder, and provide upwards force with your knees. Should be much easier to keep straight with a little guidance from a helper. Might need padding on your shoulder or against your ears ;-)
Given "hilti" and "big bit" suggests that a guide (such as a chunk of 4x4) might not be accurate enough.
To hold a guide such as this against the ceiling without timewasting fuss (eg: drilling other holes), what you need is 2 jackposts of some sort. Not the "real thing", but things more like telescoping cargo bars. These are essentially just a spring-loaded shower curtain rod with a locking mechanism.
If you got a long drill bit extension, it'd be a lot easier to keep straight.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@yahoo.com wrote:

Try hanging one or two 'plumb bobs' near the drill, stick them to the concrete with bubble gum and use the string as guides ;)
Free men own guns - www(dot)geocities(dot)com/CapitolHill/5357/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.