WELLLLL... things did NOT go exactly to plan, the best laid plans of mice and men - and all that crap. My very first plan was to remove the gear from the end of the axle shaft, shorten that end, cut new flats on the axle to match the gear, and cut new threads to match the screw that holds, the gear on. The only problem with that plan was that I could not get the screw to break free, I even tried heating the screw to try get whatever thread locker they had used to break free. The only thing I managed to do was to round out the hex socket in the screw. The next plan WAS that I would cut the steel axles in two, turn a stub about 10mm long on the cut ends to a 3mm OD, cut a piece of 5mm OD x 3mm ID brass tube to use as a splice, then Loctite everything back together. Easee-Peezee, right?
Things did not go well from the beginning, then went downhill rapidly after that.
Problem 1 - How do I hold these little turds to cut them? My first thought was to use my metric ER16 collets. Something like this IS after-all why I bought them, and the collet chucks for the Unimat and the Sherline. So I blissfully cut the axles apart with a hacksaw, figuring that I could easily clean up the ragged ends with the lathe. Heck I could even chamfer the ends, 'cause chamfers are what separate us from the savages - right?
Problem 2 - I knew that the collet chuck for my Unimat registered on the shoulder on the spindle nose, I ASSUMED that the collet chuck for the Sherline did something similar. Imagine my surprise when I opened the box to find that the collet chuck for the Sherline registered in the spindle taper, AND uses a 1/4" bolt as a drawbar to hold it in the spindle. OK, that means that if I need to work on a longer part I'll need to work on the end hanging out in the breeze, and not work next to the chuck where there's less flex. That procedure actually worked fine on the ends that were threaded for the wheel attachment.
Problem 3 - The other two pieces of the original axles still have the gears FIRMLY attached to them, and I need to work on the OTHER end. NO Problemo, I'll just slide the gear into the spindle bore, the bore on the Sherline is HUGE compared to the Unimat. AAWWW CRAP, there's already a drawbar there. The gear fits inside the collet chuck, maybe there will be enough room to put the part in from the back - THEN tighten the collet down? Nope, there may be a mm or two of clearance there, but there's just not ENOUGH extra mm's. OK, lets swap out to the 3 jaw. Then the gear can just slide into the spindle bore.
Problem 4 - I got out the 3 jaw, cleaned everything up, and installed it. It has been sitting in a box for years - remember? I opened up the jaws, slid that part in, and... IT DON'T FIT!!!! WHADDAYAMEAN, it don't fit? That bore is huge, it's 10mm, and the gear is only... 10.6mm. OH Crap!
Problem 5 - I can't work on the area of the shaft I want to - at least not where I want to work on it. But, I've got a lot of the brass tubing, I can make the splice as long as I want. I can pull the part out until it bottoms out on the back of the 3 jaw, I want to eliminate that cross drilled hole if possible. Pulling the part to the back of the 3 jaw puts the existing cross drilled hole inside the sleeve, but not by much. But, it IS inside the sleeve, so MAYBE it'll be OK?
Problem 6 - I needed to turn a 3mm OD stub on the cut end of the axle - Easee-Peezee. I figured I'd take off 1.1mm then sneak up on it - no problem. So, I made several passes taking a few tenths of a mm at a time and didn't stop to measure until I hit 1.1mm of movement. WTF, whaddayamean 2.82mm OD?? I only took off 1.1mm. But I took it off of each side now didn't I. I was much more careful on the second axle. That gap is way more gap than any of the Loctite that I have is good for, but I can always use JB Weld. So that's what I did, This is what the axles looked like at this point.
Problem 7 - I needed to shorten the brass sleeve to length. Since the gear's OD is larger than the spindle bore I had a LOT of stick-out, about 25-30mm's worth. It did not end well.

It snapped off right at the cross-drilled hole location. I think the axle would have been strong enough for the loads it will see, if only I would have just put the splice in a spot that's not close to an existing cross-drilled hole. I also found out that I need to make any axle shaft modifications starting on the outboard end, rather than the inboard end like I did this time.
The good news is that because I ordered complete extra axles, instead of just the extra pinion that I needed to make a center drive axle, I've already got spare axle shafts to work with. The extra bearings are the same size as what I would need for the front wheels if I decide to make a powered front axle.
Don