Centering workpiece on 4 jaw chuck

[gadget_lover]

OK, we did the 3 jaw chucks. I just mounted my 4 jaw independant for the first time. I'm going to need to do some off center stuff, so it was time.

I centered a rod with relative ease. I used the dial indicator and simply tightened/loosened opposite jaws till it was within 2 thou. I was just playing, so I did not go for closer.

It worked fine. Then I offset the work piece to create a lobe on one side. I simply loosened one jaw and tightened the other. That worked well too. I practiced cutting (thunk, thunk, thunk) until I noticed that the edges of the cut were sloped in. It appears that at some point the work was knocked out of whack. It was no longer parallel with the chuck.

So what do you check when chucking round stock in a 4 jaw?

Thanks,

Daniel

 

[McGizmo]

Daniel,

I believe you can still have your piece off axis some even though it is concentric in the plane that was measured by the dial indicator. I would submit thatthe further from the chuck that you measure concentricity, the less the part can be off axis. The few times I have used the 4 jaw, whenever posible, I would use a center drill on the end of the part and then use a live center to keep the part on axis. I don't recall if you ever saw a little right angle head light I made but the head was made from round barstock with the LED chamber on axis. The threads for bezel and bore for LED and reflector were turned in a normal fashion. I then chucked the round bar perpindicular ina 4 jaw and did the bore for my E-can and single pointed the internal threads for the battery tube. I marked a spot on the side of the head where I wanted thebattery tube axis to be and used the point of a spring loaded tap follower (don't know what its real name is) that was chucked in the tail stock to "point" to the mark when I alligned the part in the 4 jaw.

I don't know about the others but when I am using a 4 jaw with a part that has a center of mass off axis, I use the slowest possible spindle speed because at least on my old Atlas, the out of balance weight of part and jaws like to induce some vibration to the bench. You also need to be a bit more wary of the chuck jaws with your hands and cutting tools!

 

[gadget_lover]

Thanks Don.

I'm looking to make a simple part, with a flat disk 1/2 inch across by 1/10 inch thick. It will have a post that's 1/4 inch across by 3/10 of an inch. The post is offset to one side of the disk. I plan to mill a depression into a piece of aluminum (a tailcap) that the 1/2 inch disk will fit into, and somehow make a matching 1/4 inch hole for the post.

I'm thinking that I can't do that with just a lathe. I'll probably have to machine the post and disc seperately and join them with a screw.

If it can be done, what order do I do the parts?

Thanks,

Daniel

 

[McGizmo]

Daniel,
You can probably turn the excentric post on the disk but depending how far off center it is, you may need to start with a good size larger piece of barstock. Off set it until you hav centered the posts axix with the spindle and then turn the post. Now center the barstock and turn some of it down until you get to 1/2" OD. Then part it from the barstock. I can think of a couple ways to align the two pieces you want to make but I really don't have the time to try to type them out nor am I sure I understand completely what you are up to! Good luck!

 

[gadget_lover]

Thanks Don. That was what I was thinking too.

I'm modifying ARC twisty tailcaps into 'Tactical Twisties". Most of the tailcaps have room for a 1/2 inch plunger centered in the middle of the cap. Others have a milling on the side that is too deep, leaving only a touch over 1/4 inch for the
plunger if it's centered. The 1/4 inch is too small for easy use, so I'm thinking that I can add a larger cap to it and offset it.

The plunger has to be pretty much centered to make sure it contacts the neg terminal of the CR123 battery correctly.

I'm probably making it harder than it should be. I'll keep looking for hints on the net.

This 4 jaw chuck is fun so far /ubbthreads/images/graemlins/smile.gif


Daniel