Reconditioning a Relmac lathe

[irving2008]

I think I know whats happened... the bullgear is keyed onto the spindle but to get the shaft out you have to turn it so that the mark on the spindle lines up with a mark on the headstock casting, that puts the key at the 3-o-clock position looking into the headstock allowing it to move through the bearing (you can see it out of focus on the left in 1st pic). If you don't line it up and try bashing it out with the bullwheel at the 'normal' position (i.e. the locking pin at 12-o-clock) the key tries to cut through the bearing - hence the partial slot at the 6-o-clock position in the 2nd pic. Sometime in the past someone has tried to remove the spindle and gave up, smashing the bearing in the process... this also probably explains why the back end of the spindle is burred over and wont admit a 3/4" bar (fortunately the thread for the changewheel retainer doesnt run right to the end).

Here are the spindle journals...

Front


Rear

[irving2008]

I think these need regrinding (I would if this was a car crankshaft, but maybe a lathe is different), at least the front one does, its well pitted.

Here's a view of the broken up bearing , note the small pieces of my carefully tapped oiler hole :(, the bearing material went right up through the headstock casting. Does this suggest they might have been poured in situ??



and a view of the headstock with front bearing removed. Is that an oil well in the bottom? If so I dont see how it works as theres no hole in the bearing and it wasn't full of oil. Also I notice the bearing is offset in the headstock - there's considerably more metal to the right where the pinch bolt is than to the left. I have no idea how to specify this or replace it...



Finally, the rear bearing. Its intact, but do I need to replace this? Its a bit scored but otherwise doesn't look too bad.



The last pic shows clearly how offset these bearings are... would these have been manufactured/bored in place? How would I go about specifying or making new ones? have I bitten off more than I can chew? All answers gratefully received...

[irving2008]

Wel I've decided to pour new bearings and have read up all about it in various places and I am now collecting what I'll need. I have some white metal bearing alloy coming, as well as a ladle and some fire-cement. Watch this space :)

I've rigged up a temporary arrangement to polish the spindle as a precursor to pouring the new bearings



After a few minutes with 80, 120, 150 and 360 grade abrasives it looks like this for the front journal



compared to


Clearly some way to go but improving...

my concern is whether I can take too much off this way? Currently the spindle is 31.62mm - 31.72mm dia (about 4 thou variation) and there are some noticable hills and valleys on the front jounal through wear. Where the bullwheel sits, just inboard of the front bearing is where is measures 31.72mm as this would have had the least wear (nothing turning at that point). Nominally its a 1.25" - 31.75mm - shaft. The rear journal and where the backgeared pulley runs are about 31.68mm. If i don't even it all out this means that the front bearing must be able to open up to 31.72mm+ from 31.62mm to allow the spindle out. My theory is that if I don't shim the front bearing and lock it down when I pour it then 0.15mm - 0.2mm shims will give suitable clearance on the bearing and they will open up to maybe 0.5mm overall which will give clearance to remove the spindle in the future.

Should I just aim to get the worst of the scoring out (that pitting is quite deep), or should I aim for a mirror finish?

Is wet n dry the right way to go, or should I be using something more esoteric like an abrasive paste (in which case with what and how do I apply it?)