When you go to core drill your first hole in concrete there is bound to be some tension if this is something that you haven't done before. Vacuum base's, core drill bits, core drill rig, hole diameter VS. drill speed. These are all questions you may have.
First Lets talk some about the vacuum base and what it is used for. In a perfect world the vacuum base attached to the core drill rig would suck the core drill down tight every where you needed to core drill a concrete hole. But it don't and won't in every situation. If the concrete is smooth and revetively flat the vacuum base will suck down to the concrete surface and hold the drill perfectly still and rigid while you drill the hole. But often this is not the case. Some simple and usually easy items to find to fix this problem may be mud. Mud can be used to pack around the bottom of the core drill base where the rubber gasket could be losing vacuum. This trick works good where line breaks are in the concrete.
Otherwise you may be in an area trying to core drill where the vacuum base just won't work.
If this is the case you can remove the vacuum base altogether and use a 4 to 5 inch concrete wedge anchor to hold the core drill rig in place while you core drill. Tools for this task would be a hammer drill, hammer, wedge anchor and socket set or crescent wrench to tighten the anchor down. If you are planning to remove the anchor after you have drilled a grinder may be needed too. This method works great where you can not get vacuum to the concrete.
But wait. What if you can't get vacuum and can for some reason use a wedge anchor to fasten the core drill down? Well...
Stand on it. This is probably breaking the #1 rule that is posted on each core drill when sold new and definably in the core drilling manual. But at time it is the only thing that will really work. Of course when even breaking the rules there are some basic's you should pay attention to. Especially if you are core drilling on a balcony or dangerous place.
1) Always stand to the left of the drill. it turns right and if it gets hung up for some reason the it will always spin to the right.
2) Position the drop cord tight to the left so that if the core drill does spin the power will disconnect itself and stopping the drill. (For this reason don't use locking electrical plugs. If you own the core drill change this out first thing.)
3) If in a high place where it could fall and hit somebody then tie it off with a safety rope to a solid object.
More information about the core drilling can be found at Charlotte Core Drill