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View Full Version : Perhaps a dumb question but I just wondered if?



Alistair Hosie
02-10-2017, 03:17 PM
When setting anything hold able in a chuck especially a four jaw chuck, (now for the dumb question bit:confused::confused::confused:) Would it be possible to first put it into a scroll chuck held into the tailstock. Then wind the tailstock forward with it's prize work-piece held firmly on centre. and when it comes within range of the four jaw chuck tighten the four jaw independent up to tighten firmly and then release and back of the scroll jaw on the tailstock well away and, Now for the proverbial slap in my *coupon* er face hypothetically of course, as I am too old to be bashed around. Obviously it would not hold extremely out of circular work pieces. :cool:Alistair

danlb
02-10-2017, 04:15 PM
It takes me less time to dial in a rod in a 4 jaw than it does to mount a second chuck in the tail stock. I'm talking less than a minute.

Dan

Magicniner
02-10-2017, 04:34 PM
More messing than it's worth I suspect

BCRider
02-10-2017, 04:53 PM
I understand the idea. But the others are right. It would take far more time to set it up to do this. And even then you would still need to use a gauge to center the piece in the four jaw to achieve a degree of centering that is better than our "wobbly" three jaw.

Sounds like a slight case of "four jawphobia" to me. Don't be afraid of it, just do it.

You can really help yourself out by setting up a dial gauge that lives in a dedicated tool holder that puts the plunger right at the spindle height. If you're using a QCTP dedicate a holder to the dial gauge. If not then set up a "tool" with a bracket off it that holds the gauge.

After that just use the lines on the face of the chuck along with the edges of the jaws to get a rough centering so it's within a total runout of up to as much as an 1/8". From there you run the gauge.

I've struggled a little over the years to find the center never really realizing that I was working to a number. When I read the still current thread on a "Two Turn Zero" (http://bbs.homeshopmachinist.net/threads/72783-Centering-stock-in-4-jaw) it was like the proverbial "EUREKA!" light went on over my head. As it happened I was using the four jaw for a project and got to try the TTZ method twice. It really makes zeroing the 4 jaw a simple procedure.

Having two chuck keys would also help but even with one it's a less than a minute to zero in quite nicely and more closely than you can get from a 3 jaw. Maybe not the first time but with even a little pratice you'll have it nailed down solid.

And finally consider this.... The idea of the four jaw is to allow us to center an item up to a better accuracy then we can obtain from a 3 jaw. So even if you manage to clamp the 4 jaw to your tail stock mounted item held in the 3 jaw the BEST you can hope for at centering is the same runout as the 3 jaw has. And the whole point is to do better than the 3 jaw allows. So it sort of defeats the point.

Alistair Hosie
02-10-2017, 05:04 PM
Yes I thought this would be too good to be true. The guys who taught me used to wind in using just two opposing jaws and the bring in the others to centralize it.
It, as you guys say, did not take them long. And again as you guys all point out practice makes for perfection. I just need to try mine a good few times. Just as I need to do with my mig welding anyway god bless you guys. Alistair

Errol Groff
02-10-2017, 05:55 PM
The technical high school I taught at the students cycled from shop to classroom. Every time they were in shop I required them demonstrate using a 4 jaw to true up a round stock and a square or rectangular piece. I thought it was a good skill for them to learn. Some picked it up easily and some not so much.

BCRider
02-10-2017, 06:43 PM
Here's a trick to try to aid in getting the first eyeball centering.

Set the chuck so the two are sitting horizontal. You can start with them well retracted but somewhere sort of close. Now hold the work against the horizontal jaw closest to you and while looking down along the vertical jaws screw that horizontal one in until your work piece looks like it is lined up. Now turn the chuck 90 degrees so the jaw you just set is downwards. Rest the part on the jaw.

Now you can bring the two horizontal jaws in until the first one just barely moves the work piece. Then bring the opposite one in so it lightly pinche the work. And finally bring the top one down so it lightly pinches too. It should take less time to do than to read and visualize this post.

I'll bet by that time the part is within at worst 50 or 60 thou. Then use that trick with the dial gauge to zero the part up. Then one more time around to snug the jaws, recheck and adjust the tightening tensions as needed. By that time you should be centered easily within a thou and ready to go.

Paul Alciatore
02-11-2017, 01:10 AM
OK, let me get this straight.

You are going to use a four jaw... because it allows the work to be centered more accurately. At least, I assume that is your intent.

So you are going to mount a three jaw on the tailstock. So the scroll errors of the three jaw come into play and perhaps more error from the mount and the tailstock.

Then you are going to grip the work in the three jaw to center it for the four jaw.

Then carefully tighten the four jaw on the work and release the three jaw.

And the work is going to be centered? Without any dialing in?

I think the work would have been better centered if you just used the three jaw chuck in the first place. That would avoid several forms of error from adding to it's error with your process.

How about another tip?

Every four jaw chuck I have ever seen has concentric circles on the face of the chuck. They are there for a purpose: they allow you to quickly get the work roughly centered. Then you dial it in. You are going to have to dial it in with your idea anyway if you want the better accuracy that a four jaw allows.

wdtom44
02-11-2017, 09:57 AM
Sometimes I do something similar if I know where the center of a hole will be, a center punch mark or spotting on the drill press. Then I use a dead center in the tailstock to hold the work while I just snug the chuck jaws. Then I put a maybe 8 in. long 5/16" steel rod with a point turned on one end in a drill chuck in the tailstock chuck. I use a chuck to keep the rod from turning. Then with the dial indicator mounted over the rod up near the work and the point of the rod in the spotted center I can finish centering it up. As close as it is at the start the rod will spring enough and being so close it only takes a little to get it right. This is accurate enough for most things I do and fast.

Mike Amick
02-11-2017, 12:27 PM
Then I use a dead center in the tailstock to hold the work while I just snug the chuck jaws. Then I put a maybe 8 in. long 5/16" steel rod with a point turned on one end in a drill chuck in the tailstock chuck. I use a chuck to keep the rod from turning. Then with the dial indicator mounted over the rod up near the work and the point of the rod in the spotted center I can finish centering it up. As close as it is at the start the rod will spring enough and being so close it only takes a little to get it right. This is accurate enough for most things I do and fast.

I like this, thanks.