Wobbling Drill Bits-Human or Tool Error?
corleone
| Posted in Tools for Home Building on
I have a good quality Bosch hammer drill and good quality hammer bits, but I have noticed a wobble when the longer bits are used. I tried other long bits in other drills that I own and also noticed a very slight wobble.
This is particularly troublesome when installing mechanical anchors in masonry (especially soft brick) where the size of the pilot hole is critical to the success of the anchor.
Is the drill faulty? The bit? Am I setting the bit incorrectly in the chuck? Any suggestions?
Replies
I'm not familiar with the Bosch but some types of hammer drill use a cam to give the hammer action which does tend to make the chuck move.
Have you tried starting a hole with the drilling action before switching to hammer?
IanDG
Check the chuck for burrs, common if a bit spins, or crud, masonry dust, on the chuck jaws. They can cause the bit to ride unevenly and wobble. Open the chuck all the way and look closely using a strong light. Clean as needed. A three-square file or stone will remove any galling of burrs.
Look at the inside of the jaws and the operation of the jaws. A burr on the jaw slides can cause one jaw to delay causing the bit to be off center. Rare but I have seen it. In extreme cases the jaw will be easily observed as 'lazy'. A bit slower.
Check the bits also. If it spins the galling or burr can cause the bit to sit crooked. pretty common with hammer drill as the vibration tends to loosen the chuck. File or stone can redress it.
It could also be a defective chuck or mismanufactured chuck mounting thread. Either could be slightly canted. Check the chuck by mounting the drill in a vice and a piece of known straight rod stock in the chuck. Run the drill slowly and observe. Better still would be to use a dial gauge to check runout.
The othr thing that comes to mind is that your forcing the bits. Those thin masonry bits can bend when forced if they are hot. The pressure on a hammer drill only need be strongd enough to keep the bit cutting. Pushing too hard can actually slow cutting and dull or destroy bits.
Edited to add last block.
Edited 2/14/2005 12:30 am ET by 4LORN1
Another thing to test: Roll the bits slowly on a good flat surface, and watch the ends to see if they're bent.
-- J.S.
Good point.Another situation I have seen, mostly, if not exclusively, on generic, no-name, bits is the carbide insert brazed in either canted to one side or off center. In some situations we were buying these bits by the dozen and while most were pretty good their quality control missed a few. What do you expect for a couple of bucks a piece. Mostly all that was needed to avoid the defective ones was a quick visual inspection. We caught one with the insert brazed in upside down. Foisted that one off on the new guy. Trick was to palm the defective one while substituting a good one. Just before showing him 'how its done' and that there is nothing wrong with the equipment. 'A poor workman blames his tools.' Once again age, cynicism and trickery overcomes youth, optimism and energy. Kicker is by the time he figures it out he will take it out on yet another new guy. So it goes. The beauty of the balance of nature always chokes me up.