Drummond Pre-B runout

[AlexBrown_1]

Hi, I've got a Drummond PreB which I've been put off using recently as I've been struggling with runout. So I removed the spindle and bearings, cleaned everything and tightened the bearings up (solid bearings).
I'm measuring around 20 thou runout on the spindle thread which seems enormous, where do I go from here? I would like to use this lathe as its a well-made piece of history but realistically is it past it?

Cheers all

 

[Kram]

Have a photo of spindle? Should ideally be a register/shoulder for it to locate on.

 

[AlexBrown_1]

 

[AlexBrown_1]

 

[tigdlo]

I'm measuring around 20 thou runout on the spindle thread which seems enormous, where do I go from here?

You could measure the runout at other points of the spindle to see if it is bent, also measure the register and face were the chuck back plate fits.

If you are measuring the dead centre it could be that running out, mark the high point pn the spindle and dead centre and try it in a few different positions to see if the runnout relates to the spindle position or centre position.

 

[Jelly_Sheffield]

I would like to use this lathe as its a well-made piece of history but realistically is it past it?

It really depends how much effort you're willing to put into it, what other equipment you have, and what you can get friends to do (or pay a small firm to do)... How much is too much, is ultimately your call to make.

Assuming that @tigdlo's suggestions don't result in a less alarming number, then there's several options, at various levels of difficulty depending on what's causing the run-out.


First off, as long as it's only run-out and not play in the bearings...

If you mount a brand new chuck backing plate, pre-drilled for fixturing bolts, then turn it in-situ, it (and any chuck you mount on it) will run true as long as it remains mounted, even if the spindle does not... The same goes for a dead center mounted in the spindle taper.

That could potentially allow you to make replacement parts to correct the underlying problem, using the lathe


Going one step further,with this approach, you could make a semi-permanent modification by tapping a piece of steel ¾" BSW and attaching it to the nose with red locktite, then turning that down to any of:

- the 1" BSW spindle nose common to many wood lathes,

- the 1⅛" BSW spindle nose used by Myford (probably the best choice),

- the 1½"×8tpi Whitform standard used on Boxford lathes.


Going further to try to fix the underlying problems...

If the bearings are worn (likely if it's been run with them loose, unlubricated or both), you could get a new set turned. If you can get a chuck running true then you could make new bearings on the lathe itself.

Better yet, new bearings could be fitted and bored in situ. As it's entirely feasible to turn the whole headstock on a faceplate of a large lathe, or line-bore it on the carriage of a medium lathe.

Alternatively the bearing seats could be bored out with a suitable lip to accept new taper-roller bearings... This would be easier to do either by line-boring on a lathe or using a nice rigid milling machine.



Similarly if the spindle is deformed or worn you you could either...

Turn a new one between centers (turning a soft dead center true in the nose before starting), then install it to drill and bore the spindle taper. (You would need to use a hand drill to put the centre-pips the ends first, and allow extra material for the runout inherent to that)



Or If the spindle isn't worn, and is not deformed apart from the runout, and the bearings are good (or have been replaced)...

You could re-work the actual spindle nose in situ, it's unhardened which makes it much easier, but it's still quite a challenging operation as you'd need to:

- take a skim cut down the outside of the thread to bring it true,

- then pick up the thread and re-cut it to a consistent depth (of 0.128" minus the depth of your skim cut)*.

- face the rear and front faces to run true

- re-bore the taper slightly oversize (not a massive deal, but will alter how deeply things seat into it).

*The ¾×8tpi Whitform, and later ¾" BSW threads used on these (check which you have) are both quite deep thread, so you could lose 20 thou of thread off the top without messing with the pitch diameter, or having too little surface area for it to hold well... It's not ideal to weaken it, but it's the most conservative option in a lot of ways.

If picking up the thread is impractical due to how much you need to remove, then you could either:

- build it up with braze metal and recut a ¾" BSW thread (I wouldn't recommend recutting the ¾"×8tpi Whitform thread if that's original as it's totally nonstandard and was depreciated even by Drummond),

Or

- turn the threads down, and cut a common thread that suits the size (⅝" BSW or M16 would both work well), and then re-make chuck back plates to suit.


So yeah... Loads of scope to sort it, but some potentially quite drastic choices.