KeithB
Resident Half Fast Machinist
There have been several recent threads about tapping devices for a lathe and a references to collets and collet chucks/extensions. I needed a better way to hold taps in my CNC lathe. I have a tooling setup for my lathe that can hold 1" diameter round tool holders accurately. I tried using a rigid collet holder to hold a tap but kept getting ragged threads. I decided to buy a floating tap holder from Shars.com. It allows me to use regular ER32 collets to hold taps. It holds taps firmly against torque but allows the tap head to float forward about 1/4" or backward about 3/16".
You see, on a CNC lathe the rotation of the spindle and the motion of the carriage are controlled independently by sensors and motors and computer circuitry, they are not geared together in some fixed ratio by a gear train such as that on most manual lathes. If the process of slowing, stopping, and reversing the spindle rotation at the same rate that the carriage is slowed, stopped, and reversed in the Z axis isn't perfectly coordinated then at best you will get torn and ragged threads and at worst you will spend all day replacing taps and expanding your vocabulary. A floating tap holder provides enough axial freedom (under a spring load, it's not sloppy) to make up for a little mis-coordination.
They make special collets that have a square profile on the back end of the interior hole and have a diameter appropriate for the tap size. It provides a positive drive and is necessary for larger taps and harder materials. For small taps (IMHE up to about 1/4-20 in steel or 1/2-13 in aluminum) I have found that friction is enough.
I use ER16 and ER 32 collets, the former covers diameters up to .375", the latter up to .75" There are also ER11, ER20, ER25, and ER40 sizes. One of the next toolholders I plan to buy is an R8 shank that uses ER32 collets, so I can use my collet set on my manual vertical mill. I needed to use a 7mm ball nose mill on a job last week and didn't have an R8 collet in that size.
Not at all useful on a manual lathe but I thought I'd show you my new tool.
Floating tap holder w/1" round shank.
Nicely marked on the nut.
You can see the keyway type slot that provides the "float"
An ER32 collet with a 1/2" bore. This was laying on my desk because the bore was damaged when we broke off a carbide endmill. You can see the damage on the left side of the mouth of the bore. I'll get after with a Cratex wheel and put it back in inventory as a spare.
You see, on a CNC lathe the rotation of the spindle and the motion of the carriage are controlled independently by sensors and motors and computer circuitry, they are not geared together in some fixed ratio by a gear train such as that on most manual lathes. If the process of slowing, stopping, and reversing the spindle rotation at the same rate that the carriage is slowed, stopped, and reversed in the Z axis isn't perfectly coordinated then at best you will get torn and ragged threads and at worst you will spend all day replacing taps and expanding your vocabulary. A floating tap holder provides enough axial freedom (under a spring load, it's not sloppy) to make up for a little mis-coordination.
They make special collets that have a square profile on the back end of the interior hole and have a diameter appropriate for the tap size. It provides a positive drive and is necessary for larger taps and harder materials. For small taps (IMHE up to about 1/4-20 in steel or 1/2-13 in aluminum) I have found that friction is enough.
I use ER16 and ER 32 collets, the former covers diameters up to .375", the latter up to .75" There are also ER11, ER20, ER25, and ER40 sizes. One of the next toolholders I plan to buy is an R8 shank that uses ER32 collets, so I can use my collet set on my manual vertical mill. I needed to use a 7mm ball nose mill on a job last week and didn't have an R8 collet in that size.
Not at all useful on a manual lathe but I thought I'd show you my new tool.
Floating tap holder w/1" round shank.
Nicely marked on the nut.
You can see the keyway type slot that provides the "float"
An ER32 collet with a 1/2" bore. This was laying on my desk because the bore was damaged when we broke off a carbide endmill. You can see the damage on the left side of the mouth of the bore. I'll get after with a Cratex wheel and put it back in inventory as a spare.
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