Trouble centering square stock in 4 jaw chuck

[SwampDonkey]

Im new to this and really need to get this done for a project. Any help would be much appreciated.
I just cant seem to center a piece of square stock in my lathe using any of the videos or written instructions ive seen. It just doesn't seem to work when I try it. Is there a decent diagram around that illustrates the steps to this?

Thanks in advance!

[Delw]

heres an easy way to get it close
scribe a line from one corner to the other and another line for one corner to the other.
stick the part in the 4jaw chuck, put a center drill in your tail stock, bring your tail stock close to part, then move jaws till the intersection of the 2 lines meet the tip of the center drill. ie "X" marks the spot


Delw

[txcncman]

First, make sure your chuck is running true. Indicate and adjust as needed. A lot depends on how "clean" your material is, meaning not damaged, etc. Depending on your application and material condition, you may be able to just indicate the corners. Ideally, for concentricity and follow up mill work, you want to indicate the flats. Set up your indicator on the cross slide so that it can be moved onto and off of the material using the Z axis handle with vertical aligned at spindle center line (Y axis zero). Place your material in the check jaws and snug down equally. Measuring jaw position with a scale or depth rod of a caliper works fine for this. You should be able to get to within 0.020 just with this method alone. Then rotate spindle and place flat vertical. Mark this as #1. Move indicator onto flat as near chuck jaw as is reasonable. Rock flat back and forth and find smallest indicator reading and move indicator bezel to "0". Move indicator off of material and rotate spindle 180 degrees to side #3. Move indicator back onto material and rock again to find smallest reading and note difference from "0". Adjust jaws for sides #1 and #3 to 1/2 the total, moving indicator on and off of material as needed to rotate by loosening #1 and tightening #3 or vice versa as needed. When you are comfortable that the material has been centered in the chuck along the X axis, snug and recheck a final time and repeat process on sides #2 and #4. After centering across jaws for #2 and #4, recheck #1 and #3. Readjust if needed. For final tightening, it is important to tighten each jaw very sightly and in order while watching indicator for addition deflection while rotating to each side around the material. by doing this, you should be able to get it very tight without losing your center during this process. If you have material that is sticking out of the chuck jaws more than 2 times the material size, you will probably want to check the end of the material on the flats for run out. Bump material with soft face or dead blow hammer to adjust. Recheck near chuck and retighten as needed. A well practiced and skilled machinist can usually do this process in about as much time as it takes to read this instructions. You milage may vary.

[SwampDonkey]

First, make sure your chuck is running true. Indicate and adjust as needed. A lot depends on how "clean" your material is, meaning not damaged, etc. Depending on your application and material condition, you may be able to just indicate the corners. Ideally, for concentricity and follow up mill work, you want to indicate the flats. Set up your indicator on the cross slide so that it can be moved onto and off of the material using the Z axis handle with vertical aligned at spindle center line (Y axis zero). Place your material in the check jaws and snug down equally. Measuring jaw position with a scale or depth rod of a caliper works fine for this. You should be able to get to within 0.020 just with this method alone. Then rotate spindle and place flat vertical. Mark this as #1. Move indicator onto flat as near chuck jaw as is reasonable. Rock flat back and forth and find smallest indicator reading and move indicator bezel to "0". Move indicator off of material and rotate spindle 180 degrees to side #3. Move indicator back onto material and rock again to find smallest reading and note difference from "0". Adjust jaws for sides #1 and #3 to 1/2 the total, moving indicator on and off of material as needed to rotate by loosening #1 and tightening #3 or vice versa as needed. When you are comfortable that the material has been centered in the chuck along the X axis, snug and recheck a final time and repeat process on sides #2 and #4. After centering across jaws for #2 and #4, recheck #1 and #3. Readjust if needed. For final tightening, it is important to tighten each jaw very sightly and in order while watching indicator for addition deflection while rotating to each side around the material. by doing this, you should be able to get it very tight without losing your center during this process. If you have material that is sticking out of the chuck jaws more than 2 times the material size, you will probably want to check the end of the material on the flats for run out. Bump material with soft face or dead blow hammer to adjust. Recheck near chuck and retighten as needed. A well practiced and skilled machinist can usually do this process in about as much time as it takes to read this instructions. You milage may vary.

Yes, it needs to be fairly precise since I'll be machining a slot through the round section and it needs to be dead center.
And here's what im not understanding: Indicating using the flats and rocking the work to find the lowest reading. It just didnt seem to have any place in the process. I just ended up repeating this procedure for 45 mins. Something is being left out, but I have no idea what to ask in order to uncover the mystery. This is kinda why im looking for instructions with illustrations or a diagram.
Thank you though

[Geof]

Truing square stock in a four jaw is difficult because you can't simply use the dial gauge to read directly on the material as it rotates.

Try this approach:

Eyeball it using the circles inscribed on the face of the chuck to get it as true as possible. I hope your chuck does have circles, most do, and all you do is adjust opposite pairs of jaws until they are both the same distance from a circle. Cinch up the jaws fairly tight but not gorilla strength tight.

This will get it within 1/32" or so, maybe better if you have good eyes.

Now mount your dial so it can read on the outer tips of a jaw with the chuck positioned so two jaws are vertical and two horizontal.

Use the cross slide t bring the dial in so that it deflects only about twenty (small) divisions when it contacts a jaw and adjust the bezel to 0. Make a note of the cross slide handwheel reading and back it off to move the dial clear of the jaw.

Rotate the chuck to the opposite jaw, i.e. 1/2 a rotation.

Carefully bring the cross slide in to the same hand wheel reading as before watching the dial deflection. If it goes past the 0 this jaw is too far out and if it does not reach the 0 this jaw is too far in.

With the dial in place gently adjust this jaw in or out while watching the dial.

You want to move the dial half the distance between where it is and the 0. There is always a bit of spring in the chucks and if you are tightening the chuck in it will move but get tighter. If you are bringing it out the stock will move slightly but as the jaw gets looser it will stop springing and the dial will stop moving.

Either way you will have to move to the opposite jaw and move it also and move back and forth until both jaws show the same dial reading at the same cross slide position.

Repeat this on the other pair of jaws.

Now your stock is centered as good as the accuracy of the length of the jaws. This is probably pretty good and actually you can check how good it is by truing up a piece of round stock first and then checking how true the outer ends of the jaws are. If they do differ simply make a note of the difference and compensate when you are truing the square stock.

Finally adjust your dial against the stock and move the carriage along the bed. This will tell you if the stock is parallel to the centerline. If it needs truing up tap it with a hammer then go back and check the jaws again.

[SwampDonkey]

Truing square stock in a four jaw is difficult because you can't simply use the dial gauge to read directly on the material as it rotates.

Try this approach:

Eyeball it using the circles inscribed on the face of the chuck to get it as true as possible. I hope your chuck does have circles, most do, and all you do is adjust opposite pairs of jaws until they are both the same distance from a circle. Cinch up the jaws fairly tight but not gorilla strength tight.

This will get it within 1/32" or so, maybe better if you have good eyes.

Now mount your dial so it can read on the outer tips of a jaw with the chuck positioned so two jaws are vertical and two horizontal.

Use the cross slide t bring the dial in so that it deflects only about twenty (small) divisions when it contacts a jaw and adjust the bezel to 0. Make a note of the cross slide handwheel reading and back it off to move the dial clear of the jaw.

Rotate the chuck to the opposite jaw, i.e. 1/2 a rotation.

Carefully bring the cross slide in to the same hand wheel reading as before watching the dial deflection. If it goes past the 0 this jaw is too far out and if it does not reach the 0 this jaw is too far in.

With the dial in place gently adjust this jaw in or out while watching the dial.

You want to move the dial half the distance between where it is and the 0. There is always a bit of spring in the chucks and if you are tightening the chuck in it will move but get tighter. If you are bringing it out the stock will move slightly but as the jaw gets looser it will stop springing and the dial will stop moving.

Either way you will have to move to the opposite jaw and move it also and move back and forth until both jaws show the same dial reading at the same cross slide position.

Repeat this on the other pair of jaws.

Now your stock is centered as good as the accuracy of the length of the jaws. This is probably pretty good and actually you can check how good it is by truing up a piece of round stock first and then checking how true the outer ends of the jaws are. If they do differ simply make a note of the difference and compensate when you are truing the square stock.

Finally adjust your dial against the stock and move the carriage along the bed. This will tell you if the stock is parallel to the centerline. If it needs truing up tap it with a hammer then go back and check the jaws again.

Thank you Geof, that was very thorough. I feel confident enough to take another whack at it
This is my first "real" project and its an insanely tough one. Remember the scene in Terminator 2 where Arnold shucks the skin off his arm revealing the endoskeleton underneath? Im building that, the working arm and every one of its 112 pieces. Seems like a decent project that will expose me to lots of problems to learn solutions to.
How good are these self-centering 4 jaw chucks?

[Geof]

Self centering four jaws are good but I say do not get one. It does take a while to become proficient using an independent four jaw and sometimes you have to align things indirectly like I described. But with an independent jaw chuck you can also set the stock a known distance off center. Or you can grip an uneven piece of stock or a casting and get a particular point running true.

If you are doing production on square stock that has to run true then a self centering chuck is the way to go.

[txcncman]

Try this video. http://www.youtube.com/watch?v=2CJNEyy3QiY&feature=related]Centering Square Stuff in a Lathe - YouTube

Sign up for a machining technology class.

I don't know how else to help.

[SwampDonkey]

Yeah that video was one of the problems. It starts with him chucking up and "finding the low spot" with his indicator by rotating the piece back and forth. I found that I could rotate the peice MUCH more than he could (or did) and the low spot kept getting lower as it rotated away from the indicator.

Try this video.

Sign up for a machining technology class.

I don't know how else to help.

[txcncman]

That means you did not have your indicator on the center line of the spindle from what I can determine. The tip of your indicator should have been at the same height as a tool used for cutting would have been. No worries. I am sure you will figure it out soon enough.

[handlewanker]

Hi swampey, my 2 cents worth....I just place a flat piece of 1/2" thick X 3" wide hot rolled steel bar, that smooth shiny stuff, across the ways on the lathe bed and use a dial indicator in a scribing block to indicate ON TOP OF THE SQUARE STUFF....makes it easier to move the indicator off the job when rotating the chuck.

If'n you use the indicator in the scribing block (never a magnetic base) you'll be able to slide it back and forth and have more control over the adjusting screw to get the indicator to zero on one side before turning the chuck 180 deg to check the other side.

You'll have to rock the chuck slightly to get the indicator to read level across the square, but you only want to get zero zero on two opposite sides.

Don't grip the bar too tightly when adjusting the jaws or you'll have a job to move it the last few thou.

If'n you haven't got circles on your 4 jaw chuck, start by just measuring the back end of the jaw to the outside diam of the chuck body....gets you to within .010" of centre for initial rough set-up.
Ian.

[eaglezsoar]

See this PDF file:
http://www.littlemachineshop.com/Ref...4-JawChuck.pdf