Stuck chuck

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Simon Collier 1 on 21/06/2016 00:49:15:

It's off! …

I checked the spindle thread once the chuck was off. My 8G Whitworth thread gauge was a perfect fit, although it is 55 degrees. The spindle thread is specified as 1-1/2 x 8 USS (obsolete but usual US 60 degrees, I think). I am, therefore quite confused about this.

But shortly thereafter:

Found a UN thread gauge; it fits better than Whitworth, so definitely 60 degrees on spindle nose.

Simon,

This may sound patronising, but it not meant that way:

There is a lesson here for all of us …

Your Whitworth thread gauge was not a 'perfect fit' it just 'fits where it touches'

Although [as recently discussed elsewhere] we can sometimes get away with poorly matched threads; in some situations, the Devil really is in the detail.

MichaelG.

.

P.S. … Delighted to hear that it's off, safely !!

Edited By Michael Gilligan on 21/06/2016 07:58:35

[Simon CollierParticipant @simoncollier74340]

Yes Michael, and I later held a torch behind the two gauges and it was then obvious that the Whitworth gauge was not touching all along the flanks of the threads.

Paul, mine has one piece 4 speed v belt pulleys. One possible point to lock the spindle is what might be a tommy bar hole on the left end of the spindle.

[J HancockParticipant @jhancock95746]

Have serious think before you do that, using that collar nut !

It will either ' do it ( the collar nut ) up' too tight or 'come undone' when you least need it to happen.

[Peter KroghParticipant @peterkrogh76576]

That collar with the hole is the end clearance adjustment for the spindle!! Don't use it to wrench on.

Pete

[Ian S CParticipant @iansc]

If the chuck is Whitworth 55*, there is room to take it out to 60*, either with a tap(unlikely at that size), or care full work single point in a lathe, it's only a small skim . Ian S C

[Brian WoodParticipant @brianwood45127]

Hello Simon,

The collar looks to be an adjustment to set up spindle end play on a thrust bearing, it seems to be threaded at the base and would not a good thing to use as Mr Hancock has advised.

In the absence of anything better, I would be tempted to make a clamp to squeeze the Vee belt so that it grips most of the way round the largest diameter spindle pulley groove and then block that in some way from turning as you lever at the chuck. The grip would I'm sure be sufficient.

If you have some suitable material to take an impression, it might also be useful to make an impression of the chuck mounting thread and then compare that with your gauges. I scrounged a pack from my dentist, the material has a shelf life and is just chucked away when past it's use-by date. It is a two part silicone material, mixed and kneaded together in equal proportions, setting time is within minutes and it peals away from the object with ease. The impression is sharp and will harden more on exposure to air.

Like the others, I am relieved to hear you have separated the chuck and spindle.

Regards Brian

[not done it yetParticipant @notdoneityet]

Now we know the reason, there is a known fix. However, that thread is

not an important part of the chuck alignment with the spindle. It only serves as a means of pulling the chuck onto reference surfaces or for pulling it away from those locating surfaces.

 

 

 

That means the thread fit is not the location item and the slight difference of the thread angles may be made worse as the chuck seats on its location surfaces (especially if one of those locating surfaces has any very slight imperfection(roughness)), if that thread is already tight. Slacking off the thread fit, therefore, does not need to be as precise as one might initially think.

 

 

My lathe has a zero tolerance diametral fit at the back of the spindle nose, where the additional item is located onto a radial face. There is another close-fitting diameter at the spindle nose, but with a thou difference between spindle and fitting. Many consider that the front fitting provides nothing towards the chuck alignment whatsoever.

 

 

 

Edited to say sorry for the lack of paragraphs.  I put them in, but on posting they disappear.  Same as the incorrect forced line change, which was not in my draft and only appears when posting (so I cannot correct these shortcomings).

 

 

 

 

 

 

 

 

 

 

 

Edited By not done it yet on 21/06/2016 10:51:35

[Simon CollierParticipant @simoncollier74340]

I can now see from my photo that that is a nut so, as advised, I won't be touching it. Anyway I anticipate no further trouble as I have applied copper-based anti seize to the nose threads. This stuff works wonders. Recently I made a steam brake valve for a loco, and on first use, after about 8 minutes, it seized solid. On getting home I had to use a staggering amount of force to drive the spindle (3/8" 316) from the bronze (LG2) body. I polished it up and re assembled. Next steam up, it happened again, exactly the same. Third time, I applied the anti seize, and it has worked smoothly and freely since.

I find Brian's post particularly interesting, as today, walking the dogs, I was thinking about just that: taking some sort of cast of the inside threads, but I didn't think of dentists' teeth impression goo. It will remain a thought experiment however, as I trust that the previous owner knew what he was doing with chuck selection. He was a skilled machinist and mechanic and was fastidious with his tools. I fitted three chucks and the driving plate to the lathe today, and all screwed on and off easily and with the same feel, and the driving plate at least is original equipment.

Thanks again everyone. Your responses to my problem show this forum at its best.

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