Remove Seized on chuck ??

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vtsteam:
As to causes, I was half joking about wringing, but maybe?

http://en.wikipedia.org/wiki/Wringing_%28gauge_blocks%29#Wringing

The other thing I was thinking of was an unnoticed cracked thread working loose and jamming across in a way that the more pressure applied the greater the jamming force.

In tractor restoration work one thing sometimes written about is trying to turn in the tightening direction first to break loose a really bad lock.

stirling lad:
sitting quietly reading this with interest and finally V T said what i'd been thinking...tightening first has always worked for me but then ive never had a problem this size before.. I would'nt imagine it could get any tighter so i'd give it a go,,1 whack to tighten followed by a bigger one to loosen,,but use the hand turning shaft in the back end of the spindle..to brace against....
as for causes,?? no idea,, but if theres a tight vacuum in there would a very small hole towards the shoulder or even the thread help break the seal??

...Mike..

Manxmodder:
Steve, the wringing theory is worthy of considering but I honestly don't believe that there is anywhere near sufficient cling to resist the type of force Mick has been using to try and remove the threaded chuck plate.
All the twisting force and shock that Mick has applied would have easily broken the attraction/bond of any wringing that may be potentially caused by oil on the 2 faces.
The easiest way to separate 2 wrung surfaces is to apply sideways shearing force to slide them apart which is exactly what Mick is doing by trying to unthread the chuck plate.

I do wonder if the soft iron thread inside the backplate has torn or galled a bit when it was screwed on,or if the thread in the backplate has run up against the shoulder of the spindle register and caused the lead thread to deform slightly.

The spindle nose/thread and backplates on my Harrison are the same as Mick's and to remove a chuck I use a 2 foot long piece of 1" square box section gripped across the jaws and with the lathe in a low speed gear for resistance normally only requires a good thump with the palm of my hand to break free.

There have been occasions after some heavy turning has tightened things more than normal the I have had to resort to using the copper mallet to strike the end of the piece of box section and a couple of very firm blows have been required to get things moving.

I wouldn't bother with air driven impact guns because the mass of the chuck or even the backplate is such that the relatively small inertia force from the gun is absorbed by the mass.

Mick, by all means try some heat and a couple of thumps with the mallet again,but beware of transferring too much heat into the head bearings.

This may very well be a situation where some very careful machining work is the only viable option to remove the backplate.

Another option I would seriously consider is splitting the backplate thread along its length.This would require at least one groove or slit be cut in the backplate parallel to the spindle and down as near to the crest of the spindle thread as possible,then a wedge or chisel used to open the slit and produce a break along the cut line axis.

Mick, beware that because neither the spindle or backplate are hardened if the thread has galled then just unscrewing it forcibly could tear and do a lot of damage to the spindle thread,that's why splitting it may be the best option. If you need any comparative measurements from my spindle for reference just ask......OZ.
Edit to add: your cutting the register boss with a parting tool idea also has merit,but just make sure no cast iron swarf or dust enters the small clearance gap between the chrome bearing cover and the spindle.

stirling lad:

Off topic for a second, but ..
Mick your lathe restoration is looking magnificent..I love it... :drool: I really feel for you, getting a monster snag like this especially at this stage when your so close to completion... :bang:

best of luck...

...Mike..

RussellT:
I'm not sure I can offer any useful advice but I can offer sympathy.

If the chuck wasn't fully screwed home and the lathe started it might have seated with a jerk which can get things fairly tight.

It seems to me that the main difficulty is applying enough force without damaging the rest of the lathe - in that case pulling the spindle out might be the best option - you could make suitable clamps to hold it without damage.

The other option is to sacrifice the back plate - which will cover your beautiful restoration with loads of nasty cast iron dust.

Good luck.

Russell

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