stop 3 jaw chuck from jamming ?

It has happened a couple of times now in 6 months.

3 jaw chuck got very very tight on the mandrel and I couldn't dismount it from the lathe. After using flycutter to cut a spur gear ( I made a hopeless mess of it but learned heaps)

Eventually I gave the chuck key a tap with a rubber hammer. And yes I know I shouldn't but it did the trick.

Any tricks I can try ? ie put a paper or rubber washer between the chuck and the register ?

Keep it clean and tidy with no swarf where it shouldnt be, extra bit of oil / grease / wax / other ?

............. and google found this for me http://www.practicalmachinist.com/vb...torial-165028/ so I wont use a hammer next time - as that chap says its interrupted cuts that really jam it tight.

.... does everybody accept that an interrupted cut can really tighten the chuck onto the lathe and simply deal with it when it happens.

Bill

Hi Bill,

Yes I know what you mean. I haven't done any fly cutting on my Myford for years now, but I like you, when I did, I experienced the chuck getting very tight on the spindle. I also used a rubber hammer on the chuck key to shock it loose. Its the interrupted cut that behaves like a little hammer pushing the chuck round ever so slightly and making it tighter and tighter. The heavier the cut the worse it gets.

I have this problem nowadays with slitting saws and the screw on the mandrel holding the blade getting so tight that you end up destroying the Allen key whilst trying to release it. So I have now ground a couple of flats on the retaining collar so I can get a spanner on it. Even so I sometimes have to put the mandrel in the vice and grip it to get enough leverage to loosen it. I'm forming the opinion that individual mandrels are needed for each saw blade.

One reason threaded chucks get stuck is when they are "slammed" up to the shoulder.
Now I just gently bring it up and it's not the problem it sometimes used to be.

Jordan

Quote:

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Originally Posted by steamingbill

It has happened a couple of times now in 6 months.

3 jaw chuck got very very tight on the mandrel and I couldn't dismount it from the lathe. After using flycutter to cut a spur gear ( I made a hopeless mess of it but learned heaps)


Bill

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You should be using a collet chuck when fly cutting gears IMHO - if the lathe has provison in the spindle.

That way the spindle taper takes the load and you won't get the "rattle gun" effect on the spindle thread.

Also you are not going to get slip/wear in the chuck jaws if the mandrel slips (and you may not see it happening).

Of course most small Chinese lathes don't have this problem as they use a fixed drive plate on the spindle.

Rob

Quote:

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Originally Posted by nearnexus

You should be using a collet chuck when fly cutting gears IMHO - if the lathe has provison in the spindle.

That way the spindle taper takes the load and you won't get the "rattle gun" effect on the spindle thread.

Also you are not going to get slip/wear in the chuck jaws if the mandrel slips (and you may not see it happening).

Of course most small Chinese lathes don't have this problem as they use a fixed drive plate on the spindle.

Rob

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Thanks Rob,

Any and all advice gratefully received - have been browsing your web page several times for the spur gear cutting tips.

Will investigate collet chucks.

A friend described his experience with his metal lathe and milling machine like this .....

"If you want to do this you need one of those and in order to fit one of those you need two of these and if you havent got an xyz to fit these onto you will have to make a pqj and to make a pqj you need one of the things that you are trying to make in the first place"

At which point to quote Terry Pratchett there is a danger of disappearing in a "puff of logic"


Regards

Bill

Quote:

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Originally Posted by steamingbill

.... does everybody accept that an interrupted cut can really tighten the chuck onto the lathe and simply deal with it when it happens.
Bill

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This is just one of many reasons, why newer lathe designs do not use threaded spindle nooses anymore. On the many older lathes still around you just have to live with the many shortcomings.

If your particular lathe has a Morse taper spindle bore, you could buy an inexpensive Chinese milling collet holder with collets in a set. ER25 and ER32 are two very common sizes easy available with an MT 2 or 3 shank. Make sure the one you buy has a shank for a drawbar to pull it into your lathe spindle. That way you can mount milling cutters and drills and fly cutters etc without using the threaded spindle mount at all. It is pretty well spent money: the day you buy a mill, you will already have a chuck and a set of toolholders, and if one day you decide to make a real feed-through collet chuck for the lathe, you will already have a set of collets.

Quote:

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Originally Posted by steamingbill

Thanks Rob,

Any and all advice gratefully received - have been browsing your web page several times for the spur gear cutting tips.

Will investigate collet chucks.

Bill

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I did a couple of intro videos recently on collet chucks which you may find interesting:

http://www.youtube.com/watch?v=JUNq4...1nJBgHdxPdvkjQ

http://www.youtube.com/watch?v=kH9Dr...1nJBgHdxPdvkjQ

Also after attempting to resize a spare CTC ER32 collet with my tool post grinder, I can confirm that these collets are made from almost unmachinable spring steel. Man, are those things hard.

Definitely nothing substandard about their quality.

Rob

Have sometimes had to free threaded chucks on older lathes, including a 3 ton brute from around 1900 which I still have. Usually resort to a suitable length of shaft or crowbar to place across the jaws with the lowest gear engaged, leave a little slack in the jaws and yank the bar down hard. You will not damage the gears, as it takes the same force to unscrew as it did for the lathe gears to screw it up in the first place. If it's totally stubborn you may enlist a helper to smack the bar with a block or soft hammer while you pull down on it. A piece of wood between belts and motor pulley is an efective brake if you have no other way to lock the drive train. Brute force wins any argument.
Combustor.

COMBUSTOR
i recently purchased a dglmh hercus ( geared head model) from a tafe college thats how they removed chucks, each machine had piece of 19mm square bar about half a meter long to remove chucks . how many chucks have one or more pinion split in half by too much sideways force using the key
JOHN

As an addendum to this thread. The Myford ML7 has a spindle lock built in.
You push the pin forward into a hole drilled in the belt pulley and it locks the spindle so that the chuck can be removed and refitted.
Though I must confess that I just stick it into back gear and pull on the chuck key to remove the chuck and when putting a chuck on I just push it tight with the chuck key. I always make sure that the threads, on both the spindle and chuck, are clean and well oiled before putting the chuck on.