Floating ER20 mt3 collet chuck / reamer holder.

[Ken226]

I've been planning to build a floating reamer holder forever. I'd have just bought one, if I'd ever seen one with the features I want.

I wanted one that has both radial and axial float and uses ER style collets rather than just a 7/16" reamer socket.

I took inspiration on features for my design from the Hemingway reamer holder kit, and a design I saw on grabcad.

I liked the Hemingway kits ball and drive pin design. Also, the grabcad design has an outer lock ring, that when tightened, pulls everything to center and locks it up rigid for drilling.

I incorporated all of those features, plus I machined the front to take ER20 collets and a collet nut.

I've got all of the parts made, except the outer locking taper cap/ring. Just waiting for a peice of 12L14 steel for that ring, and a 1/2" ball bearing from eBay.

I cut up and cannibalized an old chinese live center for the mt3 arbor.

Here are the parts so far. When it's done, it will allow .06" total radial float and 5.28° total axial float. I haven't decided yet if I should mill wrench flats on the collet chuck body, In case the mt3 shank doesn't have enough grip to allow for torquing the collet nut.

 

[brino]

Great idea, and beautiful build!

Thanks for sharing this.

-brino

 

[Ken226]

I finished the last part this morning. It seems to work! The knurling could have been better.

Since the post office lost my chunk of 12L14, I resorted to using a scrap piece of 304 stainless. Nice surface finish, but knurled like crap.

 

[jwmelvin]

I liked the Hemingway kits ball and drive pin design. Also, the grabcad design has an outer lock ring, that when tightened, pulls everything to center and locks it up rigid for drilling.

I incorporated all of those features, plus I machined the front to take ER20 collets and a collet nut.

I think when I saw this before it made me curious but your recent post on collets made me go back and look. Can you show more detail of the floating interface? I can see how tightening the tapered collar would pull the collet centered and fixed (no float). With the collar loose, what bears on the slotted plate? I guess it’s a spherical surface, to allow the tilt freedom?

Also, is tilting freedom desirable in reaming?

 

[woodchucker]

While your knurls didn't come out great, I like the finer knurls better than the ones that are coarse and sharp. They always seem to hurt after a few grips.. finer is finer in the morning.

 

[Ken226]

Sure.

The hardened ball sits a few hundredths proud. The slotted drive plate is hardened tool steel as well



The tilting (axial) freedom allows the pilot of chamber reamers (piloted form cutter) to follow the bore, should it have some curve, and diverge from center as you ream deeper.

Now that I've chambered some barrels with it, it's my go-to. It's alot better than the commercial version I paid a hundred bucks for.

 

[jwmelvin]

The hardened ball sits a few hundredths proud. The slotted drive plate is hardened tool steel as well.

Thank you, I appreciate the description and picture. Nice tool.