Posted: Mon Sep 08, 2008 4:15 am
Let's try analyzing it a different way. First of all, locate the assembly that's to blame, then find the part of the assembly. You're dealing with three distinct assemblies -- bit, chuck, and quill. (The bit isn't technically an assembly, but it is a distinct item from the other two.)
1. Test the bit. This is simply done by mounting several other bits in the chuck and measuring their run-out (wobble) in the manner described by Dusty earlier. If the other bits run relatively true, or if some run true and other don't, then the problem is the bit. If most of them describe circles of approximately the same size, the problem is either the quill or the chuck.
2. Test the quill. The quill is the next easiest to check. A two-bearing quill should have no more runout than +/- .001" at the drive shaft end. Remove the bit and chuck and extend the quill until the drive shaft almost touches the table. Mount a lathe faceplate or sanding disc on the PTO opposite the quill -- this will let you turn the drive shaft without touching the quill. If you have a dial indicator, place the tip against the very end of the drive shaft and slowly rotate the shaft, watching the dial indicator. If you don't have an indicator, place a metal block, the base of an engineer's square, or something metal with flat surfaces and a little weight to it. Rotate the shaft several times and watch to see if the shaft pushes the metal block sideways and a tiny gap appears and disappears as you continue to rotate the shaft. This would indicate that the problem is the quill; possibly a bent shaft. If no gap appears or the gap is so tiny it can barely be seen, go on to the chuck.
3. Test the chuck. Mount a hardened 1/2"-diameter pin in the chuck, or a 1/2" straight router bit if you don't have a machine pin. You need something that you can trust is dead straight. Extend the quill so the pin or bit protrudes through the table insert. Perform exactly the same test as you did for the quill, with the dial indicator or metal block against the part of the pin/bit just below the chuck. Rotate the shaft and watch for indications of runout. If the needle on the dial indicator moves more than 2-3 thousandths, or if the pin moves the block sideways far enough for a noticeable gap to appear, and you are sure the problem is neither the drill bit or the quill, then it's got to be the chuck.
With all good wishes,
1. Test the bit. This is simply done by mounting several other bits in the chuck and measuring their run-out (wobble) in the manner described by Dusty earlier. If the other bits run relatively true, or if some run true and other don't, then the problem is the bit. If most of them describe circles of approximately the same size, the problem is either the quill or the chuck.
2. Test the quill. The quill is the next easiest to check. A two-bearing quill should have no more runout than +/- .001" at the drive shaft end. Remove the bit and chuck and extend the quill until the drive shaft almost touches the table. Mount a lathe faceplate or sanding disc on the PTO opposite the quill -- this will let you turn the drive shaft without touching the quill. If you have a dial indicator, place the tip against the very end of the drive shaft and slowly rotate the shaft, watching the dial indicator. If you don't have an indicator, place a metal block, the base of an engineer's square, or something metal with flat surfaces and a little weight to it. Rotate the shaft several times and watch to see if the shaft pushes the metal block sideways and a tiny gap appears and disappears as you continue to rotate the shaft. This would indicate that the problem is the quill; possibly a bent shaft. If no gap appears or the gap is so tiny it can barely be seen, go on to the chuck.
3. Test the chuck. Mount a hardened 1/2"-diameter pin in the chuck, or a 1/2" straight router bit if you don't have a machine pin. You need something that you can trust is dead straight. Extend the quill so the pin or bit protrudes through the table insert. Perform exactly the same test as you did for the quill, with the dial indicator or metal block against the part of the pin/bit just below the chuck. Rotate the shaft and watch for indications of runout. If the needle on the dial indicator moves more than 2-3 thousandths, or if the pin moves the block sideways far enough for a noticeable gap to appear, and you are sure the problem is neither the drill bit or the quill, then it's got to be the chuck.
With all good wishes,
