Chuck diameter question

[borjawil]

New to metal lathes. Reading around I've read that the diameter of the middle of the chuck (spindle) limits the diameter of a piece you can work on. However, that doesn't make sense since the chuck will hold much bigger a size. So I'm missing something here. Any one care to elaborate?

 

[T Bredehoft]

If you want to bore out the chamber in a rifle barrel, you have to put the barrel through the spindle. If you want to make a dozen 2" pieces from bar stock, the bar has to go through the spindle. If you don't want to do either of these, the diameter of the through hole doesn't matter, you can chuck as large a piece in the chuck as it will hold.

 

[mikey]

Not sure where you read that but it is wrong. Your chuck can extend its jaws only so far before they don't grab properly; typically this will be 2/3 of their travel. If you extend the jaws to this max and the jaws don't hit the ways then that's the max diameter you can turn in front of the cross slide. Then there is the diameter that will fit over the cross slide; that is the max your lathe can turn from end to end.

 

[Bob Korves]

The spindle is not the chuck. The spindle is what the chuck attaches to. Most lathes have a hole through the spindle. The size of that hole determines the size of stock you can put through the spindle, which is a very useful thing to do. I have put a 20 foot length of 1/4" bar through my spindle so I could make a 1/4" - 20 pitch LEFT HAND thread because I did not have a die for the job. It requires considerable thought and care to make sure the 1/4" rod does not whip around and hurt somebody (I contained it in a pipe that was securely anchored), but it works just fine if you do it correctly. I was threading a longer piece, several feet, but by having the stock through the spindle you can make one short piece after another, pulling the bar out of the chuck for the next part. Much scrap is avoided by this process, and much wasted time as well.

 

[borjawil]

Ah I see. Well lets say i need to make bushings or spacers from bar stock where the diameter exceeds what will fit in my spindle, however I only need the spacer to be 1" long. Can I put a 4" piece of bar stock in the chuck, center it, face it, etc. And turn it to my specs? Why or why not

 

[Bob Korves]

Sure you can, That is a primary use of the lathe. Welcome to Hobby Machinist!

 

[T Bredehoft]

Depending on the distance between the chuck and a live center in the tailstock, you can turn a piece that long. It can be as big around as twice the distance from the center of the chuck to the top of the saddle/crossfeed.

 

[borjawil]

Ok, so if I'm able to do what I want to, then whats with the site of the spindle and getting a piece through that diameter? I think I'm missing the point of that.

 

[francist]

Well for one, there are practical limitations to doing what you want to do. You can't just take a one inch bar of twelve inches long, say, and chuck it by one end and have it. It's going to go sideways on you and ruin your day. Anything more than about 3 diameters sticking out of the chuck and you want to start thinking about second means of support -- like a tailstock or steady rest. And if you want to bore or face on the end of your part, having the tailstock sticking in there is going to create a challenge. Hence the desire to pass the work through the chuck and spindle, so that you can stick out of the chuck a safe amount to do your work on the end, part your piece as desired, and then advance more work through the spindle and out of the chuck for the next piece.

-frank

 

[Bob Korves]

Ok, so if I'm able to do what I want to, then whats with the site of the spindle and getting a piece through that diameter? I think I'm missing the point of that.

Look at my post #4 again. Smaller work up to the size of the spindle bore can extend all the way through the spindle and beyond, the part made and cut off, quickly and without wasting stock, often all in one setup. Any time you have to remove a part you are working on and then remount it, you lose the accuracy of the single setup and introduce errors in the part. If you use a longer piece of material just to hold it in the chuck, the stub in the jaws becomes leftover scrap metal at worst, a remnant at best.