ER20 Floating Collet Chuck/Reamer holder files.

[Ken226]

I just spent a couple hours converting my floating ER20 collet chuck / reamer holder models from Inventor, over to Alibre Design and recreating the dimensioned drawings. If any of you guys are interested, I uploaded the drawings in PDF, hopefully you can download them strait from this post.

I made one last year, and have used it about a dozen times to ream rifle chambers and holes. It works quite well. When the outer collar is loosened a turn, it frees the chuck portion to operate as a 2 axis floating reamer holder. It allows for about .04" of radial float, and about one degree of axial float. When the outer collar is tightened, it pulls everything to center and locks it for rigid drilling/tapping. When i made mine, instead of making the mt3 body, i used an old Chinese live center, and machined the threaded portion and holes for the pins and ball.







I'm sure i missed a few dimensions and deviated plenty from the GD&T handbook, and maybe even made a few mistakes . Feel free to correct them and change anything else you like to meet your own needs.




Here is a partial transparency and an exploded model, so you can see how it works.

 

[keeena]

Thanks for sharing! What is the purpose of the 1/4" ball bearing? And does cinching up the collar center the whole assembly (if it does, I can't tell how).

[edit] - strike the 2nd part of that question; I assume it centers via the taper mating between the chuck body and collar. And I'm also thinking the ball bearing may help assist in the centering. But I'm sure I'll be schooled in a moment...

 

[Ken226]

Thanks for sharing! What is the purpose of the 1/4" ball bearing? And does cinching up the collar center the whole assembly (if it does, I can't tell how).

[edit] - strike the 2nd part of that question; I assume it centers via the taper mating between the chuck body and collar. And I'm also thinking the ball bearing may help assist in the centering. But I'm sure I'll be schooled in a moment...

You are correct on the the chuck/collar mating tapers providing the locking and centering feature.


The ball has a completely different function.
It sits in a hemispherical socket in the front face of the mt3 body, ( cut by plunging a ball mill), and protrudes slightly from it's front face (around .05") if I remember correctly. The drive plates rear face rests against the protruding ball, which allows for the angular free floating ability.


In short, sliding contact between the rear face of the chuck/front face of the drive plate allows for radial float.

The interaction between the ball and the rear face of the drive plate allows for axial float.

The chuck/collar tapers provide locked vs floating use.



Which is why at a minimum, the ball, drive plate and drive pins should be hardened. If not, the ball will peen a divot into the center of the drive plate, which will cause the tool to lose its radial floating ability, as the peened divot will ride the ball, rather than sliding.

 

[Steve-F]

Saved, Thanks!