Removing a stuck chuck.

I have never had the need for a copper washer or regular loosening and retightening or any of that palaver. Never Seize compound on the thread does the trick. And keep the thread on the spindle and in the chucks clean. And don't slam the chuck home when putting it on. Just tighten by hand and let the cutting forces do the rest. My chucks come off with the bump of a hand every time, using a spindle locking spanner I made.

FWIW here are some pics of my Myford ML7 spindle lock spanner, cut from a piece of 6mm aluminium plate. Can't remember if I drilled and tapped the bull wheel and threaded the pin I added to it, or if it is a light press fit and a drop of Loctite.

No that's not a crack from the hole in the bullwheel, it's scriber marks from laying out for drilling. Gave me a heart attack when I first saw it!

Nice job there, Hopper

… and it demonstrates an important point;

The forces needed to remove the chuck are not particularly high; but a bull-wheel tooth will snap like a carrot.

Oh for a modestly-priced Finite Element package !!

[ a simple thought-experiment should suffice, but isn’t as much fun ]

MichaelG.

Thanks MG. Not much force on a well lubricated chuck thread. Usually I can smack the chuck key firmly but not very hard at all with the heel of my open hand and it easily comes loose. Never Seize is the secret, I have found.

Stuck chucks are a different story. I reckon 150 foot pounds would not be uncommon in a real stuck case. Enough to snap a good sized Grade 5 bolt let alone a bull gear tooth made from cast iron.

Interesting thread ( non engineering term).

I was taught/ told never to oil the chuck thread as it promoted sticking.and attracted dirt and debris. Moreover I always remove a chuck after use and put a nose protector on the headstock.

I have never in the last 30 years had a chuck stick on my Boxford.

This seems to be contrary to most of the tips offered previously ,but in my experiment with n=1 it seems to work.

Paul

Yes old dino oil possibly went gummy and stuck chucks in the long term. Maybe synthetic engine oil would work better? It certainly does on ways.

But I have never had a stuck chuck using Never Seez or similar on the threads. It lives up to its name. As an ex-steam fitter I swear by the stuff.

Personally, have never lubricated thread or register.

BUT, every time that a chuck is off, the thread and register are cleaned with a toothbrusj, as is the thread of the chuck that is going to be fitted.

The chuck is only run on by hand.

Even after heavy cuts, a shock or two (NOT via the chuck key! ) will loosen the chuck, even a 8" 4 jaw!

Howard

Apart from lack of cleanliness a properly fitted chuck should never stick. There should be a clearance fit on the parallel portion of the nose with the registration taking place by the flat mating surfaces and concetricity being controlled by the screw thread. Hard to see what sticks. Tightness yes but seizure no.

regards Martin

Edited By Martin Kyte on 17/01/2023 15:33:55

I admit I had always understood that concentricity comes from the plain, parallel register and the spindle shoulder and that the thread should not be a close fit.

There has to be some clearance or the chuck will not go on. However the screwthread by definition must be surfaces in intimate contact. Therefor the defining surfaces are the flanks of the thread. You must keep them clean.

regards Martin

The Myford ML7 manual might be at odds with this as it states on page 31 - " Register bores are held to very close limits. When backplates or threaded body chucks are supplied as separate units after the machine has left these works the register bore may need very light scraping or polishing with fine emery cloth. Do not screw equipment onto the spindle nose without ensuring that the spindle register diameter is lightly smeared with fine oil."

I too was always under the impression that accurate alignment came from the parallel spindle register and face and not from the thread.

John

There is some varying opinions on the collar vs thread thing. ISTR some years ago John Stevenson, I think, did an experiment of some sort on a Boxford with a screwed on chuck with no collar and it ran just fine. Indeed, older lathes such as the very early Myfords and their ilk ran no collar and seemed to do ok. On the other hand, there had to be a reason the collar became ubiquitous in later years, one would think.

I take the point about hard contact between the flanks of the thread but making this feature the dominant source of accuracy puts a severe burden on the user who makes his own backplate or other component to fit the spindle.

Presumably, the respective flank angles would have to match closely. Also, in practice it is easy for a minute fragment of swarf to lodge in the thread which, on or in the register, would more readily be detected and removed.

When I make a chuck back plate I aim for a good fit on the register and an easy fit on the thread. I am more likely to plain turn a short parallel register than a thread that fits with any pretence of precision.As they say “your mileage may vary”

Mike

There's other reasons chuck back plates are most often made from cast iron other than that metals vibration absorption quality's. Decent cast iron has good friction reducing property's as well, even on steel spindle threads and it's locating face. It's also well known in engineering design that locating parts with threads is considered very poor practice due to the required clearances to allow the parts to thread together. Even more so on threaded parts that are removed and replaced fairly often. So those non optional clearances will not provide the concentricity the spindles parallel portion and spindle register does for the chucks axial and radial alignment. So yes that spindle parallel portion and the spindle face are both highly critical location surfaces. Even though cast iron does have that built in good bearing surface, chucks get stuck both because of the male / female threads slightly stretching under tension and the friction of the back plates locating face against the spindle. Without that elastic deformation bolts and nuts couldn't hold any two parts together for long.The tighter the chuck gets the more the threads stretch and the higher the friction.

However there's a very old machinist trick used with threaded spindles that seems to be little known today. Cut yourself a doughnut shaped washer from light cardboard. An old shoe box, cereal box etc. Multi layer corrugated type cardboard will NOT work, it has to be a single layer type. That thin cardboard is remarkably consistent for thickness simply because the rolls used to press it during it's production run are set with a high degree of precision. You want that card board doughnuts ID cut just slightly larger than the parallel section on your spindle and slightly smaller than the back plates OD for it's recess. In use that cardboard very slightly compresses between the back plate and spindle as the threads tighten up preventing the metal to metal friction and those stuck chucks. If it were me I'd also soak that card board washer in some light oil for a few seconds before using it to prevent the paper from picking up any air bore humidity and causing rust.

Interesting that a doughnut is also recommended for preventing a chuck from coming off in reverse.