Dead-Length Collets

 "Why do I need Dead-Length Collets or Step Chucks?"

"All draw-in collets have a diameter-to-length ratio when doing secondary operations. When using collets with a 10° head angle, the ratio is 1:3. For every .001" change on the chucking diameter, the part will either pull back .003" or stick out .003" from the setup part. This can mean a total length variation of .009" when the chucking diameter varies .003". If the print calls for a length tolerance less than .002", a standard collet cannot be used. This is where the Dead-Length collet or step chuck fits in. If the stock diameter varies .003", the finished part lengths will not vary more than a few ten thousands (.0002" to .0005")."
 "Is there a time when I would use a Dead-Length Spider-Stop Step Chuck for small diameter work?"

"Yes. Occasionally a customer finds that the standard 5C Dead-Length Collet does not allow them to hold their parts to the print's concentricity requirements. A Dead-Length Collet does not run as concentric as a hardened and ground collet even though it may be bored in place. This is because of the allowances between the moving parts. A Dead-Length Spider Step Chuck is identical to a standard collet, there is only one moving part - the step chuck. This attribute will allow closer concentricity between chucking and machined diameters than with a standard Dead-Length collet."
 "What is the difference between the Dead-Length Collet and Dead-Length Spider-Stop Step Chucks?"

"The Dead-Length Collet uses the face of the spindle as its locating surface for the inner collet. Because the spindle doesn't move when the draw bar pulls the collet back, the inner collet also doesn't move, resulting in length control. The Dead-Length Spider-Stop Step Chuck uses a spider stop that fits inside the slots of the step chuck and locates against the collet seat (angle) of the spindle. Because the collet seat doesn't move when the draw bar pulls back the step chuck, neither does the spider stop."

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