Lathe Chuck Attachment Methods.

I've been reading Curtis Rutter's thread about removing a chuck and realised (again) that I don't understand why something has been done in a particular way.

Curtis has a lathe with a threaded spindle, which appears to be quite a common arrangement. The trouble is I don't understand why threads are used given the long list of disadvantages this method accrues:

• The lathe can't be reversed
• Over time a well used thread will wear. Presumably this increases run-out
• Any shock load, such as taking interrupted cuts, will tend to over-tighten the chuck.
• Threads damaged by rough use tend to wedge.
• Swarf in the thread could jam the chuck as will any corrosion.
• Some oils exposed to air and warmth harden over time, with a risk that the chuck will eventually stick.
• Some people (like me) get their 'righty-tighty, lefty loosy' wrong, or like to tighten everything as hard as they can.
• It's not unlikely that a combination of these problems could happen.
• Finally, when releasing a stuck chuck, it's apparently very easy to damage the lathe.

One alternative is to fit the spindle with a spigot to which chucks etc are bolted. This method has disadvantages too, but, unless I'm missing something, they seem pretty mild in comparison with using a thread.

So why are threaded spindles used? What's the strong advantage I've missed?

Ta,

Dave

.

Economy of manufacture.

MichaelG.

It is repeatable and very accurate.

The positioning is done by the plain concave corner.

Thread wear is not important

Edited By Niels Abildgaard on 18/04/2017 14:25:21

SillyOldDuffer:

By way of comment on some of your bullet points:

• The lathe certainly can be reversed; eg, I regularly do so on the Myford to wind a tap or die off the work. I agree that care is needed
• Normally there will be a register behind the thread which is what provides the truth; the thread doesn't need to be a very good fit
• Shock load, etc - agreed

To Michael Gilligan's suggestion of economy I would add the factor of tradition.

An advantage of the threaded mandrel is the ease of changing chucks.

I'll raise you a fiver that Camlock is quicker, especially if you're going to clean the mating surfaces first. Removing the threaded chuck on my dividing head is a right royal PITA.

Andrew

Andrew Johnston:

I have no experience of Camlock which, however, I associate with larger, more expensive, modern lathes. For many, I think the real comparison will be with the flanged spigot which I understand is used by some modern popular machines (again, I have no experience of these).

Thanks for your article in MEW 254.

My experience is of 2 lathes with "bolted flanges" and my Super 7 with threaded mandrel. The first two really were a PITA! I've never had the S7 chuck stick on, it's quite easy to remove, and easy to change over to a collet system when I want to.

I have three lathes, all of which have differing methods of chuck attachment.

Sieg C3, bolted....80/100mm chuck

Chester 9 x 20, screwed nose....100/125mm chuck

SPG 2129 (Warco 290 lookalike)  has a D1-4 Camlock.....160mm chuck

Off all three, the Sieg is worst to change, quickest is the Camlock....the Chester, needs an Allen key to undo the grub screw on the chuck backplate, then needs the spindle holding steady whilst undoing the thread

Edited By John Rudd on 18/04/2017 15:57:47

UThe lathe can't be reversed. As posted, it can. It is not needed as a normal procedure, other than cutting 'other'threads'.

Over time a well used thread will wear. The back plate should wear, over a very long time. Worn threads are no real problem.

Presumably this increases run-out Wong assumption. It does not.

Any shock load, such as taking interrupted cuts, will tend to over-tighten the chuck

. True, but not normally a problem. They do not tighten on the threads, per se, only the register which is a flat face.

Threads damaged by rough use tend to wedge. Again, the threads are only there to screw on the chuck. The register is the important part.

Swarf in the thread could jam the chuck as will any corrosion. Swarf anywhere between mating surfaces will create a problem. Get used to it! No different than any other fixing method. It is only swarf on the registers that will cause damage.

Some oils exposed to air and warmth harden over time, with a risk that the chuck will eventually stick. An operator problem? Mineral oils recommended have been around for millions of years and have not oxidised. They are hydrocarbons which only react withoxygen at high temperature (ie they burn!). Simple enough to use the correct oil, I think.

Some people (like me) get their 'righty-tighty, lefty loosy' wrong, or like to tighten everything as hard as they can. There is no real answer to human disorders!

It's not unlikely that a combination of these problems could happen. It is unlikely if one simply follows the rules!

Finally, when releasing a stuck chuck, it's apparently very easy to damage the lathe. Once again, sometimes you can't teach some to do it properly. It is also easy to drop the chuck on the ways.

Often the chuck is only stuck after the lathe has been subjected to poor storage conditions. Not really the lathe's fault.

Other possible causes are fitting the chuck while at a considerably different temperature to the spindle. On a similar comparison, would you suggest that any morse taper fitting is unsuitable for use?

Yes, economics does play a part. Most of these lathes were manufactured when screw-on chucks were perfectly adequate for purpose, yet were economical. They also worked. Alternative fixing methods were considerably more expensive, not just a little bit.

Advantages are that they are far quicker to change than bolted chucks which may wear the spigot over time. They also work just as well. No problem of getting the chuck off a spigot, like some have experienced. Loose spigots are useless for minimising run out.

I would prefer a cam lock or L100 type, but the spin on chuck works just as well at a price which was affordable when new. Not many run around in a Rolls Roce or Bentley. There are usually adequate alternatives, without spending a fortune.

What arrangement do you have on your lathe(s)? Of the choice between bolted spigot and screw on, it is a easy choice for me. Screw on every time (I have had/used both types).

Edit: Sorry about the paragraph, or rather lack of.  Out of my control.  Forum has its drawbacks when trying to post!

Edited By not done it yet on 18/04/2017 16:05:14

I made my own smaller version of a camlock fitting on the stepperhead lathe, which as stated in previous posts is accurate and quick to remove/replace. Plus the benifit of being able to run in reverse safely releases opportunities in machining operations not available with screwed chucks.

Alan

John Rudd:

I would say your stable pretty much covers the field with the exception of the (I think) obsolescent long taper spindle nose L0, etc.

My Willson slantbed has this feature and, apart from the extra weight of the much heavier chucks, the need to clean the taper and lock ring and tighten the latter with a large C spanner makes for much longer changeover times.

Due to a previous stuck chuck on my Super 7 which cost me a new mandrel spindle,a chuck back plate, plus all the back gear cogs, I now never fit a chuck without a washer behind it. Yes I know I lose some of the accuracy, but not much, and this is preferable to having another expensive disaster.

Simply put, screw on chucks are simple and convenient. I'm forever changing chucks and moving them around the lathe and dividing head on the milling machine - 3jaw SC, 4 jaw SC, 4 jaw independent, er25 collet and Myford collet. Never had a chuck come loose or seize on in 35 odd years. Mind you, the only time I ever reverse the lathe under power is when screw cutting metric threads. But, this is all on a 3 1/2 " lathe. Any bigger and I would probably have a different view - there's a lot of energy stored in an 8" chuck rotating at 1000rpm

Rod

cost me a new mandrel spindle,a chuck back plate, plus all the back gear cogs,

Ahh, a back gear locker-upperer? Even if not, the cheaper solution would have been to carefully turn away the back plate before resorting to wholesale replacements? Tell us more about how this disaster came about. Normal use or what?

You can turn in reverse with a threaded on chuck, its just the cut has to be less than what it takes to undo.

I do not know for sure how the damage occurred as it was in this condition when I purchased it, for a bargain price. I assume by looking at the way a lot of teeth where missing on the back gears, that the previous owner must of taken a club hammer to it ,and then lost his temper. I still have the mandrel with its back plate attached in my toolbox.

As it is probable damaged beyond use now I have tried every way I can think of to remove the chuck plate from the spindle , but alas it still defeats me. I can only think it must have lock tight on the threads ,although heating it to cherry red still did not shift it. Could be it has been welded on, who knows.

Mike

The main reason for a screwed thread is that if you use any other method to make a spindle you either have to turn away a huge amount of surplus material, weld on a flange OR use a custom casting - all much more expensive. All the advantages of a screw fitting are really with the lathe maker, not the lathe user. It is very much the 'old fashioned' way of doing things, it works perfectly well - if well made - but it can go wrong by jamming or coming free in reverse.

A bolt on flange is the second cheapest way of doing the job, it won't jam or come off in reverse and it is cheap for the user as some chucks won't need a back plate and those that do the cost is no more than with a screwed nose. Iif you have a small gap between flange and headstock it can be inconvenient (the roller bearing mod for mini lathes paradoxically reduces overhang and increases the the gap to make fitting nuts much easier - unmodified mini-lathes benefit from making a nut-holding do-dah).

Camlock is an excellent engineering solution and where time is of the essence rather than cost i.e. industry is the only sensible option. You get the freedom from problems plus rapid change.

But don't bash Myfords for using a screwed thread, aside from being normal practice at the time, the original Myford ML7 was a successful attempt to make a model engineering machine to a price - there were better lathes at a higher prices and simpler/inferior ones at lower prices - a flanged spindle would have added too much to the price of a hand built lathe. For mini lathes, planned as mass-production machines from the start, economy of scale made a custom steel casting a practical solution.

The Myfords hit a 'sweet spot' of cost versus capability in the late 40s and 50s just as lots of people were getting into model engineering, just as mini-lathes hit a somewhat different but equally sweet spot fifty years later.

Neil

Thanks, I hope you found the OMAHL article interesting/useful/not_a_complete_waste_of_paper. Delete as necessary.

It's a shame my name was spelt incorrectly though. At least my name was correct on the front cover; I'd have been a bit miffed otherwise.

Andrew

If you machine a small groove in the cylindrical section of the spindle register you can add grub screws to backplates which will prevent the chuck from unscrewing if stopped sharply or run in reverse.

This is the standard nose on my 1950s Super 7 with the groove I added, I did loads of turning and threading in reverse and never had a chuck so much as slacken slightly.

The problems cited for screw on chucks are user behaviour related, I never encountered any of them in over 20 years of using this old lathe

Perhaps MEW-255 could contain a corrected version to cut out and stick over it?