New chuck doesn't fit new spindle

[zoltan]

I'm fitting a new spindle to my mini lathe so I can upgrade to a 4" chuck without an adapter plate. However, the register on the spindle is 72.02mm while the register on the new chuck is only 71.9mm. I can see the spindle register being a little oversized to allow it to be turned down once installed. However, I have a hard time believing the chuck is supposed to be 0.1mm undersized.

Did I just get a defective chuck? Can someone help me figure out what's going on?

 

[Nick Hulme]

This is a classic example of the answer being best supplied by the supplier of the parts, OTOH by posting on a forum first you might get a nice long thread full of speculation ;-)

- Nick

 

[zoltan]

I usually like to educate myself a little bit before calling the manufacturer.

This is also the first time trying to fit a new chuck. For all I know the chucks are always undersized to allow the machinist to do the final fitting.

 

[bazmak]

Chucks should not need to be machined,any fitting should be done by
trueing up the the spindle register.I have just measured a couple of my
chucks and they both read 71.95 and are a good fit on the spindle register
What you have seems correct.A fine skim on the spindle nose to ensure
dead true and you are good to go

 

[petertha]

Be careful there. I have a D1-4 spindle & several chucks that mate the tapered section as intended. But the faceplate (which coincidentally came with the lathe) did not fit the tapered nose nicely. It was machined, but a smidge undersized so it was not running true. I could tell something was fishy because the D1-4 pins were not pulling it in equally or properly. I verified this by blueing. I ended up making an epoxy putty partial mold from a known 'good' taper & used that to kind of lap the faceplate taper section into fitting. All is good now.

But I guess what I'm saying is: you need to verify if you have a spindle issue or a chuck issue. I would have thought the spindle would not only be dimensionally correct, but also be hardened & ground. So re-machining does not sound pleasant to me. Maybe check this with a file on somewhere obscure first. If you verify its off spec by Machineries Handbook type dimensions, I'd return it.

 

[Blogwitch]

I fully agree with Baz on this one.

You say you are fitting a new chuck, does the old chuck have the same problem?
If it does, then it is definitely the spindle plate that needs touching up so that it is running true to the rest of the machine.


John

 

[petertha]

Maybe we should clarify terminology first because you mention 3 components: spindle & plate & chuck.

In this sketch 1=lathe spindle 2=adapter plate 3=chuck. Sometimes 2&3 are married as one integrated or direct mount chuck. Another option is an adapter plate that resides in between. Maybe you are saying the plate/chuck diameters are not matching (red lines). If so, that's called a semi-finished plate. The intent is you mount plate to spindle in lathe, turn boss OD to fit chuck rear recess & it should be very concentric. A fully machined back plate means they did this already to some established spec (which can vary by chuck brand)

If its a standalone chuck where rear taper is already machined & mounting on lathe nose/spindle results in (green lines) mismatch, then a) chuck mount dimensions are wrong or b) lathe spindle dimensions are wrong. You said you are 'fitting a new spindle' so to I inferred (b).

Are we getting closer or maybe I made it more confusing?

 

[bazmak]

I have now measured 4 chucks and they all measure 71.95
Which I would say is correct.You say yours measured 71.9
Check again but even its correct its not bad.The spindle register should be dead size ie 72mm +0-1 but ideally it has a slight taper so the chuck can draw up to a dead fit.Your spindle should not be oversize even by 1 thou".The problem
will be if you skim the spindle to fit 1 chuck well, will it also fit other chucks
If I had your problem then I would emery down the spindle to dead size
and emery down the chuck to a good fit .Fine emery will take off 1 thou without problems.1 thou clearance between chuck and spindle can be used to help true up the runout

 

[petertha]

...Your spindle should not be oversize even by 1 thou".The problem will be if you skim the spindle to fit 1 chuck well, will it also fit other chucks...

This is exactly why I'm wondering why you recommend altering the lathe nose spindle? If the new & unknown chuck happens to be out of tolerance & he alters the spindle to match... Great, now the next 5 proper 'on spec' lathe accessories purchased in the future no longer fit & you are somewhat pooched. Which could mean replacing the the lathe spindle & starting over again. Am I missing something?

Not sure what make of lathe or chuck we are talking, but here is a typical middle road chuck catalog page showing recommended spindle tolerances. Not saying every lathe delivers on these specs but I always assumed more effort was put into grinding a spindle.

 

[Charles Lamont]

chucks should not need to be machined,any fitting should be done by
trueing up the the spindle register.i have just measured a couple of my
chucks and they both read 71.95 and are a good fit on the spindle register
what you have seems correct.a fine skim on the spindle nose to ensure
dead true and you are good to go

Absolutely no!

 

[Nick Hulme]

For all I know the chucks are always undersized to allow the machinist to do the final fitting.

Lathe spindle noses should be manufactured to a standard specification, as should chucks for use with them. Such specifications ensure that spindles and chucks should always be supplied to tolerance, this means they should fit together without fettling regardless of the source.

 

[Jasonb]

What are you measuring these two items with? If a calliper do the internal jaws read exactly zero when you close the calliper and zero the external jaws. There is usually a slight difference between the two.

As has been said check other chucks and the old spindle for fit rather than measuring them to establish which is at fault or it could even be both.

J

 

[petertha]

What are you measuring these two items with? If a caliper....
J

I don't see that the OP has posted his spindle type, but just using the common ones as an example..
http://www.tools-n-gizmos.com/specs/Lathe_Spindle_Mount.html

The various spindle profiles specify OD and length (with many zeroes in tolerance specs) & taper angles (to degree-minutes-seconds resolution). So I find it hard to believe anyone can measure across some used chucks & declare the spindle needs to be redressed on that basis. If you are truly seeing a dimensional discrepancy with calipers and assuming they are measuring the correct comparable dimension between chuck & spindle, there is something fundamentally wrong. But I think you have to start with a 'given' like a good known chuck that validates the spindle. Sounds like right now you have 2 unknowns.

 

[Jasonb]

Peter, its a Mini lathe nothing as fancy as a taper.

Think of the flange on the end of the spindle like the short spigot on a backplate, the chuck mounts directly to that using the shallow 72mm recess for location.

J

 

[bazmak]

If the spindle nose is oversize then you have only 2 CHOICES
Send it back or try to ease it down to size.For a home model
engineer with a cheap chinese lathe.My view is the second option

 

[zoltan]

UPDATE: I spoke with the manufacturer, and they confirmed the chuck was out of spec and told me to send it back. I purchased another chuck (4 jaw this time) and it measured 71.97mm, and it fits on the spindle beautifully.

 

[mcostello]

Measure twice, post once,call the supplier, then maybe cut something expensive.:thumbup: