M33 DrillCenter

Whether you use a faceplate or a chuck, the actual center of turning will not be where you planned it. The wood may shrink or swell due to humidity, the wood may give way to the pressure of the chuck jaws differently based on distance to the core, etc. When you use square stock, the wood is held pointwise and it may yield differently under different corners of the jaws. When you use a faceplate the actual center may not be marked on the wood at all. When you use a tenon in a chuck you may loose any center mark when you remove the tenon. This tool helps you to make or restore the center and/or mark it, centered, aligned and deep enough to keep the reference after the tenon is removed, or to use a tenon/pin type live center.

There are two .stl model files. One is for the actual tool. It represents a male threaded part shaped like the M33 spindle pickup of a lathe.  The image shows a cross section to show the inside.

It is hollow and on both ends it has a recess for a small ball bearing.  I sized the model to accommodate ball bearings I had around, originally intended for use in inline skates. The industry designation is roller bearing bearing type 608. You may however, like me, be able to source those in a sports/skater store. The axle diameter is 8 mm. Bearing size 22x8x7 mm. These were the ones I used, but simpler/cheaper ones may do also. Maybe just scavenge from an old pair of skates. 

Alternatively make do with inserts you print yourself holding a washer suitable for your needs.

 You obviously need one print and 2 bearings (or equivalent) for every application.

The other print file is for a utensil during mounting.  It has no other function and thus is minimalized:

The yellow ridge fits on the outer ring of the ball bearing. 

I sized the drillcenter to fit the Nova 2 chuck with M33 direct thread. It may fit other M33 chucks also. I found fit on a Record Poser SC4 satisfactory, as in a Oneway Talon with M33 insert. Note the ‘forward’ bearing is in a small extension fitting the 1" diameter hole in the chuck body. This provides extra support. 

Faceplates in general have no such limitations and the guide should fit any M33 faceplate, but again make sure to check.  

Make sure you test the fit of the large printed part on your chuck before you proceed. make sure the operation of the chuck jaws is not impeded.

The recesses have a  ‘retaining’ ridge to secure the bearings. in place the small printed piece fits just in and presses the bearing past the ridge.  

Note mounting is not reversible. Check everything and use common sense!!
To mount the bearings you will need a piece of threaded rod M8, two nuts and two large size (22 mm o.d. ) washers, and at least one of the small printed pieces. .Arrange on the threaded rod a nut, a large washer, the small printed piece with the flat side towards the washer, one of the bearings, the large printed piece, the other bearing, another of the small printed pieces(optional), the other washer and the other nut. Check the shielded side of the bearing is outside. Then align and gently squeeze the bearings into the homes. If you used only one small piece you can simply unscrew and redo with the small piece on the other side. 

The diameter of the drill is driven by the hole in the bearing: 8 mm. A standard 8 mm drill has sufficient length. Drills of smaller diameter may be too short to drill deep enough. 

Best use a metal drill because you need to mill away any old center and the guiding ‘pin’ on the top of a wood-drill may send astray.  

The flat sides of the back flange serve to dismount the guide. I sized it to meet the spanner that came with my lathe to dismount the faceplate, but any suitable spanner will do.

PRINTING: I used Prusa PETG at default temperature settings, a 0.40 mm nozzle on Satin Coated sheet. Support on bed plate in aft bearing housing.  I added a few extra rounds of perimeter for robustness.