Can a lathe chuck be too big?

strantor

strantor

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When I was looking for a lathe, everything that I saw that came with 2 chucks, had a 3-jaw that was smaller than the 4-jaw. I still don't know why this is. Sometimes it would just look downright silly to me, seeing a decent sized lathe with a puny looking little chuck on it. Well I don't have a lot of experience, so that's all I have to go on: the way things "look." If there's a practical reason for having tiny 3 jaw chucks, I don't know it; all I know is that it looks silly, and seems limiting of what you could put in there. The Logan I bought only came with a 4-jaw. I bought a cheap chinese 3-jaw, and I bought the biggest thing that would fit on a 9" lathe - an 8" chuck. I got the back plate done today and put that big ol chuck up there, and it looks equally as silly as the tiny chucks. Now I'm wondering if I've shot myself in the foot. Is there any reason that having this giant chuck on my little lathe is going to give me problems? The only thing I can think of it the jaws not having a whole lot of room to open without smacking the ways, but I checked all the positions, and it seems like there is going to be at least one way to chuck up any size piece of material in there. I'm more worried about the weight of it I guess.

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Yes. That chuck is so large that you cannot open the jaws much at all or they will hit the ways. You'd be able to grasp larger stock with a smaller chuck. The large chuck is worthless if you can't get the jaws open. And,the big chuck reduces the length between centers. Bad all around.

I suggest getting a 6" chuck. You can,of course reverse the jaws,but that is a bother,and the reversed jaws do not hold your metal very deeply in the chuck,so it's less secure.
 
G'Day,
As a general rule of thumb most lathe manufacturers seem to recommend a max 3 jaw chuck diameter of about 1/2 the swing of the lathe, another thing to consider is the load on the drive system and bearings. I did consider an 8" chuck for my 12 x 36, but settled for a 6 1/2" as the 6 1/2" weighs 9Kg compared to 18 Kg for the 8" (Bison).
Regards,
Martin
 
It's also nice at times to be able to get the saddle/cross slide real close or even under the chuck. No can do with something that large.

-Ron
 
Reversing the jaws is generally only for holding short pieces,not long pieces,as the work cannot go far enough into the jaws to be held securely. You don't want a longer piece to suddenly get cockeyed while being cut,and beat your lathe up.
 
There are two independent strokes of genius in this thread -and I thank you all dearly.

1) Next chuck I get will be too big -and I'll just have to get a bigger lathe to fit it.
2) For every chuck I have, I'll need another. I agree w/George... I don't like flipping jaws. So I'll just have to have chucks setup each way.


Thanks guys!
 
So Bigger isn't always better? Strantor be careful opening it up to big, might make a BIG Bang when you turn on the spindle. I was also thinking of those "poor spindle bearings" I know where you can sell or donate the chuck on the board (wink, wink).
Seriously, be careful opening the jaws to wide. Rich
 
Thus is invented the big bang theory of lathe destruction!! Yes,that heavy chuck is hard on the lathe's bearings,too.

HOW MUCH runout does that chuck have? Chuck up something accurately ground,like the shank of an end mill,and check the portion sticking out with a dial indicator. These China chucks are usually rated for .003" run out. If it's better,I might buy it. I gave away the original chuck on my 16" Grizzly lathe,and if I sell it,I don't want my 8" bison going with it. They now cost 2X as before. You can take off the back plate and keep it. Mine is a D-6 spindle. Wonder if shipping would kill the deal?

Remember,Enco is always giving free shipping nearly every month. That's when I buy heavy stuff from them,like bars of 1" brass.
 
By the looks of that chuck in your lathe you have answered your own question. #1 -- You cannot open it as far as the smaller chucks. #2 -- You have limited the movement of the apron. #3 -- as Rich said, be prepared to change bearings often because of it's weight and mass. #4 -- It's belt driven stock up on belts, you'll need them. The start-up strain will be horrendous. Below is a 6" four jar in my 9X20. As you can see it is pretty much maxed out. With an 8" this would be impossible. That's a 5 1/4" diameter piece of aluminum. I could go on but I think you get the point. ------ "Billy G"

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