Problem with L0 spindle – help wanted!

[egaParticipant @ega]

My Willson lathe has the once-common American L0 long taper spindle. Faceplates and chucks are drawn on to the taper by a large nut whose pull is reacted by a backplate working against a shoulder behind the large end of the taper. Turning the nut the other way causes the backplate to contact the headstock thereby releasing the taper and allowing the faceplate, etc to be removed.

Yesterday, when removing a faceplate I noticed that the nut was unusually stiff to move once the taper was released. Removing the screws retaining the nut left the backplate, which is normally free to rotate, now too stiff to turn by hand (in normal operation the nut/backplate is loosened and tightened with a large C spanner but rotated by hand between the two).

Has any L0 user had this problem, please? And if so can you suggest a solution?

At the time I speculated that the current hot weather might be the cause but the overnight drop in temperature has not caused the problem to go away. I am thinking of holding the backplate stationary with the spanner whilst rotating the spindle slowly under power (and at the same time applying oil) to see whether this will free things up. The daunting alternative would seem to be to strip out the spindle and bore out the backplate.

 

 

[Martin Johnson 1Participant @martinjohnson1]

Hi from a fellow L0 or maybe L00 user.

I would be looking closely for swarf / debris around the nut-spindle area.  Try working a bit of thin oil or parafin kerosene or pentrating oil into the area.  Run under light power and try and clean the area.

HTH

Martin

[bernard towersParticipant @bernardtowers37738]

On my student the clearance is quite large so i cant imagine what would make it go tight unless the version you have has less clearance then as mentioned before it could be swarf.

[egaParticipant @ega]

Thanks to both; I will bear your comments in mind.

On the clearance point, looking more closely at the drawing in the Willson manual I see that the bore of the nut backplate is fitted with an O ring presumably intended to prevent oil escaping from the spindle bearing. A large clearance would, of course, defeat the purpose.

As with the backplate, so far as I can see the O ring can only be replaced by removing the spindle.

[egaParticipant @ega]

To my great relief I have now been able to free up this nut: separating the nut from its backplate made it easier to apply a generous dose of thin oil as suggested and I then ran the lathe at slow speed in reverse with the backplate held stationary. I did notice that the oil which dripped out was discoloured which lent some support to the swarf suggestion.

Although the manual does not call for this, I plan to apply oil here in future when changing chucks.

Apart from the thermal expansion speculation I wondered whether the cause of this problem was using a Colchester L0 faceplate rather than one expressly made for the Willson (this seems unlikely as L0 is a standard).

I remain puzzled by this episode which has made me conscious of how much I value this bit of vintage machinery!

[Chris CrewParticipant @chriscrew66644]

“Apart from the thermal expansion speculation I wondered whether the cause of this problem was using a Colchester L0 faceplate rather than one expressly made for the Willson (this seems unlikely as L0 is a standard).”

It should be a standard fit as the long taper, or L-series, should be manufactured to a particular specification. However, I recently purchased a new L0 backplate for my Colchester Student only to find that the ring would not screw on without requiring an apparent excessive amount of force which I declined to apply. The solution was to mount the backplate blank in the 3-jaw, pick up the 6-TPI thread and shave a couple of thou. off one of the thread flanks. I pulled the lathe round by hand so to alleviate any possibility of a ‘disaster’ under power. After this the ring screwed on easily enough by hand until in position for the final ‘nip’ with the C-spanner.

After relieving the thread I ‘blued’ the internal taper to check how much of it was in contact with the spindle nose and, as far as I could tell, there was about 90% contact between the internal and external surfaces which I think is satisfactory. I skimmed the face of the new backplate then removed and replaced it a couple of times checking with a DTI and found that it was within 0.0005″ each time. I haven’t checked if this is similar to the contact area of the tapers of my Burnerd chucks or Colchester faceplate simply because it has never occurred to me to do this before.  The backplate was manufactured in India, BTW.

[egaParticipant @ega]

Chris Crew:

I bought a perfectly satisfactory backplate some time ago from Gloster Tooling. I can’t say where it was made, however.

This Old Tony on YouTube describes machining one from a steel billet on his Colchester. I don’t remember how he tested the thread for fit – probably wired it.

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