DIY Internal Concrete Vibrator

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DISCLAIMER

The device outlined in this tutorial runs at very high rpm and is dangerous to use. It has been neither engineered nor designed, and is completely a Rube Goldberg contraption. My advice is to skip this page and go buy a professionally made internal concrete vibrator. It's the best way to maximize your safety.

However, if you like building stuff and are willing to assume the risk associated with using homemade tools, click on the following link and you'll get some instruction on how to build an inexpensive device that will allow you to consolidate small batches of stiff concrete with relative ease. I made mine for $25, but depending on what you have laying around the shop in the way of odds & ends and what your budget allows for equipment purchases, expect to spend anywhere from $30 to over $100.

OK, I understand the risk

This vibrator is little more than a die grinder which drives an off-centered weight. It uses off-the-shelf router bearings to bracket the off-centered weight inside a short piece of metal pipe (I used electrical conduit). To provide the necessary flexibility in the center of the device, it employs a short piece of wire cable soldered into the ends of two 1/4" rods (one solid, one threaded). The image to the right shows the nearly completed vibrator. In it one can see a homemade, silicone impregnated cloth sleeve the making of which is discussed in another tutorial.

List of Required Items

1. Die Grinder:

   Whether pneumatic or electric, one is after the variable speed and the high-end RPM capability this type of tool offers. Prices range quite a bit. Low-end units start around $20, so if you want or need to keep the budget small, it's doable.

2. 1/4-inch Rod (threaded & non-threaded) :

   You can pick this stuff at a the local hardware store (big-box or small-box). You'll only need about 1 foot of each. Strictly speaking, you can get by with only the threaded, but I had some of each laying around so that is what I used. You could also get by with solid rod too, but then you would need a 1/4" die in order to create the threads needed for the nuts used to lock everything in place.

   Finally, you don't have to use 1/4" all-thread for the off-centered weight. Any size will do as long as you select the appropriate bearings and sleeve (see items 3 and 4) for the size you choose.

3. Router Bearings (two) :

   these come in lots of different combinations of outer diameter (OD) and inner diameter (ID). For this project I used an OD of 5/8" and an ID of 1/4".

4. Metal Sleeve :

   Once you've assembled the off-centered weight on the threaded rod, it needs to be housed inside a metal cylinder. I was trying to keep the O.D. as small as possible, so I used a piece of electrical conduit from my scrap pile. A thicker wall would be safer, so if your application doesn't really need a small O.D., you might try using a piece of galvanized pipe.

   I put a plug of "5-minute" epoxy in the open end of the sleeve. To help guard against it loosening over time, drill a series of holes around the perimeter of the sleeve for the epoxy to fill.

5. 1/8th-inch Steel Cable :

   You'll need about 1 to 1½ inches. Drill a hole into each end of the rods big enough for the cable to slip into relatively well, then fire up your torch and solder the cable into each rod.

   Resist the temptation to use more than an inch or two of cable. This device will run at several thousand rpm and anything other than the off-centered weight which is "out-of-round" could have a tendency to undermine its operation.

6. Flexible Sleeve :

   In order to maintain flexibility of the off-centered weight, it is recommended that one make a water-tight, flexible sleeve using the technique outlined in the page which shows how to make a silicone-impregnated cloth tube. There might be other alternatives, but this is one approach that seems to work quite well.

7. Short Length of Pipe :

   I used a 3-inch long 1/4" pipe nipple for the off-centered weight. Just grind away about half of it, leaving it intact at each end. There is nothing sacrosanct about this. You just need a hunk of something you can sandwich between the nuts and bearings that is sufficiently heavy and off-center so that it will set up a nice vibration when you give the die grinder plenty of "throttle".