3-Jaw

bonneblktrk

bonneblktrk

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I have a Logan 820 it came with a 4-jaw. And a 4-jaw with independent moveable jaws, which has been useful when switching from internal to external turning large diameters. Do I need a 3-jaw? Is it better for round stock.
Thanks
Tom
 
Need? No. Nice to have? Yes. Quicker to chuck stock in reasonably true? Yes. More expensive? Generally yes. If you do a lot of work, and chuck and indication time is dragging you down, and you don't need the part to run dead true, then a 3 jaw is an advantage. Or if you want to go to the trouble of boring soft jaws for the stock/part you are machining, then a 3 jaw wins again. But if you are only doing a part or two now and then, and don't mind indicating it in each time, or need to chuck irregularly shaped parts, the 4 jaw wins.
 
Thanks for quick response. I just recently discovered (new to me) that when I re-chuck a part it isn't running true anymore. Now I put an dial indicator on the apron and gently tap the part with brass hammer as I tighten jaws. Seems to be running truer.
 
Try putting a small piece of shim stock on the 1 jaw of the 3 jaw that is allowing the part to "stick out" further on 1 side. Find the high side,put in the piece of shim stock,and try the indicator again. Try different thicknesses of shim till you get the one that works best to make your stock run true.
 
Vince_O said:
Tony

In laymans terms what would be something irregular.

remember Im new to this.
Click to expand...


Vince,
"regular" shapes would be simple round or square pieces. "Irregular" is just about everything else. Alternator housing casting, electric motor end bell, rectangular stock, or simply material you want to put a hole in or work an OD feature that is off center intentionally, like a cam or crankshaft. Irregular might even branch out further to include some work that would be also done on a faceplate with clamps, such as the ends of a connecting rod for an engine of some sort.
 
I have a 3 jaw and a 4 jaw. The 4 jaw gets 98% of the work. Couple of reasons, 1) the 3 jaw is worn and needs refurbishment or binning. 2) 3 jaws wont repeat on a workpiece. If you need to remove something from the chuck and set it up again, only a collet, (or 4 jaw) will get you back exact again 3) I can get a round workpiece running within 1-2 thou in very short order in a 4 jaw. most 3 jaws wont get that out of the box. 4) A lot of my turning is square stock, or round stuff that needs to be centred spot on, (I really need to make ozzie46's collet holder)

Cheers Phil
 
A lathe is a very, very versatile machine. The more you use it, the more you will think of other ways to use it.
 
The 3-jaw chuck you cant live with out.
The 4- jaw is a must have item, and the most used type of chuck I own.

Ill only mount the 3-jaw chuck if I have a run of the same parts that dont need to be perfect, and the runout wont matter any.
 
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