Altering an Old Toy Wood Lathe

Way back in the day, I picked up an old, tiny wood lathe when I was picking up some other tools (the guy threw it into the lot).

Well, it's been sitting around for a few years, doing nothing (no bearings or prep on the bearings, fairly loose spindle, basically not really usable).  I finally decided to turn it into a pen-turning micro lathe.  I picked up a few bearings, measured, and started to work.

I used a boring head to bore out for the radial needle bearings, and the thrust bearings just fit in like expected.

I'm using a 4" router ER16 collet, and put the headstock onto the mill as my spindle, because an ER16 collet will hold the 7mm pen mandrel perfectly.

Yes, I don't have the pulley installed there.  It's marked and the set screw divot has been bored on the spindle, but I still need to drill it out length-wise (so I can easily shorten the pen mandrel without adding spacers), and thread the back end (left handed m12x1.0 - the whole spindle is metric, I might as well do metric).

The lengthwise-drilling was where the puckering came in.  I had to drill 4" on a stainless steel 1/2", ground and hardened rod shaft, with a drill bit diameter of 1/4".  [shudder].

So, I started drilling.  About 1.5" in, everything ground to a halt (no pun intended because of the next paragraph, seriously).

I knew I needed a better drill bit as well, and a longer one, too, (that meant special degree points, and it needed to be an "aircraft" length).  I went through this whole project of setting up a drill bit sharpener (which wasn't long enough to accommodate an "aircraft" drill bit needed to get the length of the spindle, so I had to modify the device with a longer rod so the shoulder could support it), then ground the drill bit with a 118 degree point instead of the 135 degree point it came with.

I then took everything in to the lathe and started drilling again, and got a little further before it ground to a halt again (seriously, no pun intended).  I re-ground the drill bit and drilled again.  I repeated grinding a few times with drilling until I had punched all the way through.

Now, it was next ready for threading on the end of the spindle so I could lock that spindle in place in the headstock.  Back to the lathe, I set up for a 32 pitch, left hand thread (I didn't want deep in the spindle with such thin walls) and cut the thread.

Time to figure out how big to drill the hole for the nut that will lock it in place, I pulled out the machinery handbook, and started doing math.  I needed wire diameters, micrometers, outside diameter of the spindle, and some mathy skills.  Then I just got sick of trying to think, and pulled up a thread wire measuring calculator in order to get the root diameter.

 

I put the stainless plate into the four jaw, and dialed it in.  I drilled to a 27/64's drill bit to open the hole to 0.421" (surprise! the hole was slightly smaller than I thought it would be, and that's just fine for this).

The interior threading was a treat.  If I had a 0.472-32" left-handed tap, it would have been a quick job.  However, my threads in the new spindle were flat at the root, meaning that the crowns of the threads on this needed to be flat, too.  It took a lot of cutting a thread, flattening the crowns, and then repeating until I got the fit I wanted.  Granted, this is slightly tight still, but it is good enough for me.

Now I can take this "nut" out of the chuck, and drill a cross hole (metric 4mm fits well on the socket head within the walls of this thing, so it's going to be perfect).  So, I need to drill a 3.5mm hole (0.138", or a #29) all the way through the nut, followed by a 4mm (0.1575" or a #21 with added slop), I have the clearance for the threading.  If I then use an end mill to put the socket head in deeply enough, I'll be ready to chuck the spindle in, add the nut and tighten it down, then turn the outside edge round and knurl it, then face the remaining side.  Well, at least that's the theory.

 I wish it was that easy in reality.  This stainless does a fantastic job of work hardening.  [grrrrr].  I drilled through it with the #29 (which is 0.136", not 0.138", and is a bit shy of the 3.5mm hole I need to tap with).  Then halfway through with the #21.  It was ugly, but it did it.  I went with a letter I drill bit (0.272"), and dulled that thing faster than Spaceman Spiff loses focus in school.  Went with a "J", not much further.  In frustration, I swore a little and grabbed a 7/32" end mill (0.218") and plunged it in.  That finally let me get to depth, but it leaves a gaping hole on the side.

 
Okay.  Now I just need to tap it (beyond swearing just thinking about it) followed by a slitting saw to open the nut up a little bit.  Then we can make it round on the outside, and flat on the sides.

I needed a break from the shaky gut wrenching that is tapping hardened stainless.  So I broke out the 3D printer (Creality CR-10s), created some nuts for this small lathe in ABS (using a PEI build plate/printer floor, a brim, and 255 degree nozzle with a 95 degree bed temperature), and printed them out.

These have a raised lip on the thread side that will slide between the bed rails on the lathe and not turn, allowing me to simply tighten the 1/4"-20 nut on the top side.  I did three, because I thought they'd be great for the tool post and tailstock, too.  So with the nuts out of the way, it's back to the tapping, sawing, and turning of the "nut".

I tapped while it was still in the lathe as much as I could (up until the hole clogged up with swarf), and then used a slitting saw to slice it apart.

I then filed the burrs off, took it in to the band saw, and cut some corners so that it was closer to round, and I chucked it up.

Now I have to face and turn, then I can reverse and face so that ALL surfaces are parallel or perpendicular to the spindle.

Now to make it really round.  This was less of an issue once I got the collet tight enough, and the cross screw tight enough to prevent it from slipping off, but I'm loving this.  I tried to leave as much on the outside as I could, and wasn't worried about the inside (where the clearance hole came through the side) as that would be covered by the bearing race.  So, the spindle is now ready to be assembled.

Next up, I need to create the motor mount and the tension mechanism.  That will make this at least "usable", though I won't like it until I have a proper tailstock assembly with a live center (e.g. a morse taper #0).

1. Create some sort of a motor mount and tension mechanism.
2. Use a 1/2" ground stainless rod and drill all the way through it for the tailstock (including drilling and reaming for a #0 morse taper on one end.
3. Install the spindle and handle into the tailstock.
4. Test it.
   

I have this nagging worry that the motor/tension assembly is going to be a pain (need to figure it out before the headstock is installed back to the bed).