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Turn Your Rotary Table into a Super Spacer with a handy #3MT Chuck Arbor
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May 4, 2013
12:18 PM
Uncle Russ
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Way back when when I first got into metalworking one of my early projects was to create a lathe chuck arbor that fit both my lathe spindle and my rotary table. This basically allowed me to turn my rotary table into a Super Spacer. For those of you who haven't heard of a Super Spacer, it's basically a rotary table with a 3-Jaw chuck attached. There are also simply "spacers", which lack a hand wheel.

You see, when the nice folks at Grizzly shipped my first mill, I suddenly had the quandary of choosing the tooling (which ended up costing more than the mill) before I could even use the thing.  Not having the money for both a rotary table and a Super Spacer I chose the rotary table thinking I could get more use from it.

If you think about it, quite a bit of the time a part you wish to mill just came out of the lathe in the first place.  So, why disturb it if you don't have to?  I made an adapter to do just that.  Remove chuck from lathe with part still held tightly and pop it into the rotary table for the little spin down easy street.  Here's how:

My rotary table is a 12" Yamasa.  It will mount both horizontally and vertically and includes the changeover disks, cranks and parts to easily turn it into a dividing head.  All in all, a pretty nice unit, pretty heavy anyway.  I kind of wish it had a set of spacer plates, but oh well.

The table is equipped with a #3 morse taper in the center.  Off to the 2nd hand tool store I go and there they have a big old box full of trash.  Well not really, but close.  Seems the only requirements to be include in this receptacle is to be big and ugly.  Drills, reamers, large old burrs and the like live there.  Tooling of the #3 Morse taper variety is considered small and there were few to be found, so I had to get creative.  A drill that was not bad looking but slightly bent in the flute area was chosen as the only important part to me was the #3 taper section itself. Price on this fine, experienced, work-tested tooling is pretty fair at .50 cents a pound.

Back at the shop I heated the drill to a nice dull red and stuck it in a bucket of sand.  next morning I put the bit in an abrasive chop saw to do some chopping.  Squaring off the bent fluted section best I could, I whacked off the taper.  Turned out my annealing efforts were just wasted time as the morse section proved to be rather soft to begin with.  I chucked it into the #3 taper in my lathe spindle and trued it up.  Then I dug through the junk and found a little piece of 2.25" round stock.  I drilled a .250" hole ½" deep centered in the end.  Then drilled a matching hole in the #3 morse piece.  I do this as a little prep work to hold things in place while welding.

I put the small end of the morse in the vice, put a .250" pin just shy of 1" long into the hole and place the 2.25" long piece on top of that.  Clamp lightly, turn over so to be easy to weld all around and preheat to a nice, nice warm but no color.  I prefer stick over wire for the welding as in my very limited welding experience that I get better penetration.  Not that I really need it on this job but I practice to win!  Tack at least three to four times to anchor the pieces so they do no spread apart.  Weld at least 3 passes all the way around.  One to hold it together, two more so there is some fillet material to be cut off so it looks good when done.

3MT_chuck_arbor_for_rotary_table_3

After a total slow cool, machine to size.  In my case 1 7/8" x 8 tpi.  Neat part about threading this piece is there was no shoulder or groove to stop the cut in.  Just trip right off the end.  I cut the threads to a stiff fit in the chuck back plate, then took off another .001" and proceeded to chase the threads forward and reverse not touching the dials for at least a half dozen times.  Anything that screws onto the lathe now screws onto the rotary table.  Oh yeah, by chasing those threads with plenty of oil while doing it, these items truly spin into place.  Accurately.

3MT_chuck_arbor_for_rotary_table

As a last note I drilled and tapped a ¼" x 20 hole in the tail to help hold the taper in place.  A 1/8" x 1" flat with a 1/4" button head cap screw secures  the taper if needed.

Had I to do it again I would have used a 3/8" x 16.  And of course if the taper is stuck, a sharp rap from the back side pops it out in a heartbeat.  A smart rap on the backside fixes many things many times in many ways.  Parents of young children these days should follow my advice.  This advice can be expanded to include adult liberal children by moving the striking point up to the head and increasing the hammer size appropriately.

Lately I have been reading several articles from guys who solved this mounting dilemma with rotary tables.  A few of them pretty well thought out, planned and executed but I think mine is faster and easier and does not leave any telltale tracks from use.

Have fun.  It is what it is all about!

Be there.  Be square.  And make the SWARF fly!

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