My Modifications‎ > ‎

4 Inch Chuck

This isn't technically a modification; it's more of an add-on.  However, once it was on I have not put the old 3" back on so I consider it a modification.  My fine Son was kind enough to get this for me for Fathers' Day this year.  It's a, 3-jaw 4" with the adapter plate with new studs and hardened mounting nuts.  It also comes with inside and outside jaws.  My Mini only had the inside jaws when I got it and limits stock sizes to less than an inch and change.

Out of the box it was heavily packed in preservative grease, so the first thing I did was clean it all Real Good.  The Jaws and the chuck were marked pretty well but you can see by the picture I had it laid out the way it came apart.

After cleaning I lubed up all the moving surfaces, installed the inside jaws and ran it in and out several times with the chuck key to make sure it worked smoothly.

Next was to mount it and check it for run out with the 1/4" ground rod.

As you can see I was able to get it down to .002, but only after considerable futzing.  Turns out the three studs actually like one position better than the other two and it took a while to figure this out.  I kept bumping it lightly with the nuts more or less finger tight with the test gauge on it, until I got the idea to check the other two positions.  Sure enough it started coming in tighter.  Little Machine Shop's web pages say it's good to .003 max, so I guess all the futzing paid off.  The other important thing was not to tighten the nuts too much...I always cross torque, but with three studs and nuts, it's necessary to tightening them up a little at a time, checking run-out, and tighten some more until you get there.

Overall, I am extremely happy with the chuck and adapter and all the things that can be done with it now.  I wish the adapter could be a little thinner as you lose about an inch or so in bed length.  Another nice thing is the ID of the chuck (.87) matches the ID of the spindle now, so you can almost put a piece of 7/8" bar through the spindle. 

I get a bit of vibration from this one at about 1,ooo rpm.  It may be the main spindle bearing (that has a harmonic at that rpm because of the extra mass) but a little above or below that rpm it smoothes out.  Mainly what I am happy with is being able to chuck up larger stock, inside or out, as the picture below shows.  (Obviously I wouldn't routinely chuck up a piece this long but it turned pretty smooth with out support from the tail stock).

This is a piece of 2" Brass tube I had in the bin...quite heavy too.

My next big modification will be the Extended Travel Cross Slide Kit from Little Machine Shop because the larger the stock the closer you get to running out of room with the tool post and cross slide.  Who knows, one day I may even get the 14" Bed Kit they sell. 8-)  I just love my Mini and what is possible with it!