Need new chuck...am I going to go too big?

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62Scout

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I have an old HF 8.5x18 lathe that I picked up used a few years ago, came with a 4 inch 3 jaw chuck that has been nothing but problems for me. I didn't get the outside jaws for it which has been severely limiting for me as I frequently need to turn parts that are just a bit larger than the limit of the jaws, the outside part of the inside jaws are well worn (not sure what the technical terms are for this, lol...using the inside jaws to attempt to hold a tube on the ID..the "serrated" part of the jaws that would contact the ID are worn to the point of being completely rounded over, and doesn't grip much of anything), and the scroll seems to bind up with swarf virtually every time I move the jaws requiring me to frequently pull the chuck off to disassemble and clean it.

I have a current project in mind that will require me to turn a tube of roughly 5.850" OD, 5.730" ID, 3" long, and I'm considering using this an an excuse to buy a new 6 inch 4 jaw independent chuck, as I have seen many times when a 4 jaw would be very handy as well..so kill two birds with one stone?

I understand that I need to be aware of chuck to carriage clearance, and jaw to bed clearance, with the 6 inch being a tad too large to get the carriage completely under the chuck. There is also a concern of the lathe itself being up to the task of spinning the larger chuck and material...but I don't know how to know when it would be too much without buying things and trying it, which will require buying a non returnable adapter as well to fit it on the current non-removeable backplate (either it was machined as part of the spindle, or the threads have seized to the point that I fear I'll damage the spindle bearings attempting to get it off).

I also considered a smaller chuck with removeable jaws so that I could make a set of extended jaws just for this one project, but they don't seem to exist for chucks smaller than 5", and I'm not sure my machining skills are quite up to the task yet of doing that completely from scratch either.
 
My 6" 4 jaw is all my SB 9 wants.......
5" 3 jaw is good, just lacks outside jaws.......
 
I think you should consider it this way:

3-jaw is for speed and where you are always turning at lest 0.005" off the part.
4-jaw is for when you want concentricity
 
My 12'' swing lathe came with a 6'' 3jaw scroll chuck and an 8'' 4 jaw.
Having both is a necessity to me.
I bet that a 5'' 4 jaw would work fine on your lathe.
 
I have a lathe similar to yours. It's a Lathemaster 8x14. What came with it were a 4" 3jaw, a 5"4jaw, and a face plate. Depending on the project, I have used all three. You will find that a 5" 4jaw will work just fine and will be much more useful than you can imagine.
 
If you plan on buying one chuck, get a four jaw. They're more versatile and they can be dialed in very accurately.
Don't let concerns about centering stock each time deter you: when you do it regularly it takes very little time.
Just set up an indicator on a QC toolholder and you'll be GTG.
5" sounds like a good size for the chuck.
 
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There are several of us who have the old HF 9x20 and I have a 4” 3jw, 5” 3jw( that’s the chuck that’s in it all the time) and a 6” 4jw. The 6” I think it a little bit too big because of clearance. I often wish it was a 5.5” instead. YMMV.
 
AmericanMachinist said:
Why would the size of the chuck matter as long as it physically fits over the bed? Thanks
Click to expand...

Overhang is a factor on smaller machines. A large chuck that might extend 3 or 4 inches past the end of the spindle is a lot of leverage which can lead to chatter.
 
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