I am an electrical engineer, but I have a Mech. E. question.
I am helping a friend with a project that involves drilling holes in concrete. I am aware of the bits on the market (carbide, diamond ; percussion, non-percussion), but I am not sure what would be optimal given the paramters of the application.
If you know your concrete drilling and drill bits, can you please send me an email? I will send you the details, tell you what we are currently doing, and you can tell me if we are crazy or not.
No fair!! Keep a discussion of anything "mechanical" on line here! (Something a bit unusual for us to see!! )
Tell us "the paramters of the application" (did you mean parameters??) and see who answers. Lots of times, the replies to the replies are where the real good stuff comes out.
We need to drill multiple holes in "high-grade" concrete. These are
24 inches deep, blind, 3/8-in diameter.
The rotational speed is 100-200 RPM. (The drill already exists... I have not seen it, but it is a custom job.)
The hole will contain an accelerometer, packed in with an epoxy and filler. The electronics package attached thereto communicates via a wireless interface to a central point. (I designed all the antennas.)
The rub is that while we are drilling hole N, holes number N-1, N-2 and N-3, etc. already have their accelerometers in them. We want the drilling to make as little vibration as possible. We don't care how long it takes (within reason, but many hours is OK), but we don't want to interfere with the other sensors.
We have pressurized air that we can pump down the tool, but no other coolant.
The bit can be a custom design, it does not have to be available off the shelf.
The Question: What type of bit do we use???
Give examples, show your work, neatness counts, this is a take-home exam. Use only #2 pencils. Begin.
I do a lot of concrete drilling and cutting. I don't know if one is ever an expert. I know a lot of tricks, solutions, workarounds, and OmyGods. I would be happy to answer you here.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG
At work we sell carbide-tipped concrete drill bits that have a neutral rake angle. They are capable of drilling concrete (and hardened steel, granite, safes, etc.) without the use of the hammer action.
They are the GRT series of bits made by Relton
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3/8" wouldn't cost much, but you may have trouble getting the length you want (they do specials on request).
That's pretty skinny for so deep a hole. How about something a little more reasonable, like 1" or 1 1/2" and liner it down? Cast some concrete around a well greased rod to get your precision hole size. Would be easier to get a precision location that way, too. It's unlikely a hole will be straight if you try to bore one that deep and
3/8" dia., particularly if there's rebar in there. Any drill I've ever used in concrete is some variation on a hammer drill and that's going to shake up the surroundings pretty well. If it's all sand mix and no flint, you could probably do without the hammer action, but if you've got coarse aggregate and/or flint in the mix, you're going to have to hammer if using conventional drilling. I vaguely remember something about using water jets for cutting concrete, don't know where or when I saw it, though, and it might have been for doing slots like expansion joints and not holes. How about staging the accelerometer installation so all the holes and liners(if used) are done before installing the instruments?
I'm not an expert, but I've done precisely this installing geophones in reinforced concrete. We used a custom design waterjet. Messy, but glass smooth walls and vibration frequencies above the 'phones response. We were working outside on a vertical surface, so it was a pretty simple matter to channel the waste away. The compressor and pump were a long way away and spring isolated from the ground. We did several 100 holes in a dozen locations.
For your problem, m> Nick, you are more of an expert than I!
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