Appreciating the 4-jaw chuck

My TH42 came with an independent 4 jaw, so I'm pretty quick setting it up. IE: It's all I've ever known.

It's so versatile and offers so many set up options, I can't imagine using anything else.

I only do the occasional bit of work for myself though. If I was doing production type things, I might prefer a 3 jaw....
 
When I first learned to use a lathe, way back when, I learned on a 4 jaw indepentant. A three jaw was not available. Granted, what I learned wasn't really machining, just how to make a part or repair with a machine. I used my Pop's hand drill chucked up in a vise and had access to the 4 jaw machine "on occasion". Only when I transferred to a ship did I learn to use a 3 jaw. (1969)

I still prefer a 4 jaw unless I'm working with hex material. The 3 jaw does have runout, but it doesn't matter if I'm using "one shot" chucking. It only matters if concentricity matters, not often with me. The main chuck I use is a scroll chuck. It has a low runout so doesn't get swapped for an independant very often. The 4 jaw is just what I learned on, so is the fall back "everything" unless it matters chuck.
 
@Nogoingback with a magnetic mount set on the cross slide, how would a dedicated tool holder on the QCTP make it faster? I don't doubt you, but I don't have a picture of how it would be faster. I engage the magnet, loosen the knob, put the indicator in place just above the surface, tighten the knob, and then dial down the indicator until it indicates as I spin the chuck. I can indicate inside a hole for boring or to the outside of a piece for turning equally easily. What's the corresponding easier/faster way with a dedicated tool holder?[/QUOTE]

I use this indicator mounted in a tool holder on the QCTP. Works great for OD but obviously not for ID

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The Bison 4J combination is the same price as their 6J scroll. QMT sells them, along with Ajax Industries and a few others. The prices vary widely, you do not need the forged version (vs. semi-steel) unless running over 2000 RPM. If you consider that the chuck could pretty much replace the 3J scroll and the 4J independent with one chuck, the price is reasonable. You can also save a bit of money by purchasing a Gator back plate which is 1/2 the price of the Bison. If someone needs part numbers let me know.

I do a lot of repeat work as previously mentioned, in/out of the chuck, so for me the setup time to dial in the TIR would be much longer if using a standard 4J independent. On smaller work I use a Bison 5C Set-Tru which I use ~50% of the time, the combo 40%, my 3J scroll less than 10%. On some smaller parts they may be in/out of the chuck 8 or 9 times, and I will do runs of a dozen, so time does matter to me if it is adding another day or two to make the parts. The major downside of the combo chucks is weight which is around 85lbs with the back plate. I always use a way protector when installing/removing it.

I use twin keys for dialing in the 4J until close to zeroing the TIR, then a slight tweak with a single chuck key. On measuring the TIR I have a dial indicator that drops into the QCTP and is already setup for for height, I can easily switch out to a test indicator for ID. I switched the test indicator to a Compac 215GLA which measures 0.0001" the same as the Starrett which is a 25-511.
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SubtleHustle said:
I ordered a independent 4 jaw 6", and a 3 jaw scroll 6", at the same time, about 6 months ago...my first 4 jaw. The 3 jaw is still in the box, only opened to inspect it. I really dont see me ever using it now. I love my 4 jaw! And as mksj stated, their great for holding irregular work. I just used it today, for that purpose.
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Thanks for sharing. Glad I'm not the only one who feels this way. My lathe came with both 3 jaw scroll and independent 4 jaw, and I never touched the 3 jaw. I set the work up till the indicator stays motionless. It's fast once you have done it a couple hundred times.
 
@mksj Oh, twin keys. Now I see that in your picture in your earlier reply. Apparently I have another set of tools to make! I keep being glad I bought the dividing head with the mill. This is just one more reason. I've been religious about blocks of wood on the ways when changing chucks.

I got the 6-jaw used along with the lathe, and it's not a bison, so it wouldn't have been a 1:1 $ swap for me. I haven't weighed it but I'd guess 85 lbs is in the ball park.
 
"Block of wood on the ways when changing chucks" ...how is it possible that this is the first time I've read about this (and of course it didn't occur to me...)

Thanks!

Tim
 
I will soon be trading a 2" thick 10" 4 jaw on my lathe with a 3 1/4" thick 10" 4 jaw from my rotab. I will definitely be deploying a wooden sled on the lathe when I make the changeover.
 
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