"Iím using a small diameter split drill bushing and I canít seem to get the drill parallel to the centerline of the spindle. Why?"
Check to make sure that you are not locking the second set screw on the bushing. The holes for small diameter drills do not extend the full length of the bushing. The back end of the bushing usually has a large internal chamfer or a counter bore under the second lock screw. When you tighten this screw, the bushing may distort, shifting the drillís position. The solution is to use the front locking screw only. Or, you may find that you are using a bushing that is too short if the first set screw is locking on the back of the bushing, causing it to collapse instead of gripping the shank of the tool.
"I am trying to drill a very accurate hole using a DA-style collet system without any success. Any suggestions?"
Extremely accurate drilling requires a very good holder and collet. For extremely accurate drilling, the collet bore should be the same size as theshank of the drill. If you have a choice of holders, it is best to use the ER collet holder over the DA (double-angle) collet holder. The ER is considered a single-angle collet because the major closing angle is long and shallow. This results in better concentricity than the double-angle system. For larger shanks (vertical machining) the TG collet system is better than the ER system because it has an even shallower closing angle.
"Iíve tried rigid tapping using standard ER collets in my non-floating holders and Iím breaking taps. Why is this happening?"
Taps may be breaking because your machine tool may not be designed for rigid tapping, you did not buy that option, or there is a small error between the spindle reversal and slide reversal. These are machine tool problems that you can work around without disassembling the machine. Use a floating tap collet such as the ERQC or the ERTC. These collets fit in the standard rigid holder and will float longitudinally. (If you want to continue to use your current ER collets, floating tap holders are available.)
"The TIR of the drill being held in my ER collet is excessive. What TIR can I expect from a standard ER collet?"
If you are using a ball bearing cap on your ER holder, change it to a one-piece cap. The ball bearing cap allows you to use more torque when gripping solid floating tap collets, but when used for drilling, the TIR is not as accurate as the one-piece cap. Hardinge ER collets are made to the DIN 6499 specification. Refer to the chart shown. When checking the collet and holder, use a certified gauge plug. First, indicate the seat of the holder, then assemble collet and gauge plug and indicate the plug at the "L" dimension. Make corrections for holder seat runout (the most accurate check is to use a coordinate measuring system Ė most indicators do not give a true reading when rotating 360į from the lathe spindle). If this checks out within specifications, check the gauge pin at the actual drill length, which may be longer than the "L" dimension. If the TIR at this point is too great, you will have to acquire a higher precision collet such as the ERNC. If you were using a metric bushing to hold a fractional drill, a more reasonable solution would be to acquire an inch series collet for the exact shank of your drill.
"I am using an ER Collet in a high-speed spindle and am getting vibration that I donít get with my other holders. Whatís wrong?"Youíre probably using a standard one-piece cap. Acquire a one-piece cap that has a ring to hold the collet instead of the standard cap that has an eccentric slot. The eccentricity of the groove will cause an out-of-balancecondition at high rpm. If this does not eliminate the vibration, the complete assembly will have to be precision balanced in relation to the RPM you are running.