First chuck backplate turning/setup

[GunsOfNavarone]

Mikey! Mikey! These things take time... Actually I got called in for dinner, now were lounging around. I'll for sure open those holes up/mount it and check run out tomorrow. I sure am hopefully its very good, though I couldn't tell ya how the originals are that the lathe came with...that's just a bit ironic..no?

 

[mikey]

Time, hell! You going to make us wait?

Glad you got it worked out. First times are tough but you got it now.

EDIT: Forgot to add that lounging around with your wife is the best thing to do. I am sorry to hear about her challenges and will keep her in my prayers.

 

[GunsOfNavarone]

@mikey thanks brother

 

[GunsOfNavarone]

Looks like just under .002? I’m not sure where/how I measured is copacetic? I’m a .02” tolerance kinda guy...so well under that!

 

[mikey]

Mike, measuring on the outside of a chuck gives you no useful information. What we want to know is how accurate the chuck is on the inside. You are dealing with a 3 jaw scroll chuck so to check how accurate it is you have to turn something in it and then check the run out on that thing. Here are a few things to ponder:

• A scroll chuck should be dead on accurate for first operation work. That is, if you take a work piece and turn it for the first time and then check the run out on that piece, it should be zero. Even if the surface of that work piece is not perfect, the resulting turned surface should be concentric with the spindle centerline as long as you do not remove it from the chuck. This is called a first operation ... the first time something is turned.
• If you wish to measure how accurate your chuck is, measure that piece you just turned in that first operation. Do not remove it or loosen the jaws once you turn it. Put a dial indicator in your tool post and bring it up close to the chuck. Get the tip of the DI on center and zero it. Mark the work with a Sharpie somewhere close to the tip of the DI, then manually make a single revolution of the chuck and realign the mark with the tip of the DI. The DI should return to zero. If so, make another revolution and watch for any movement of the needle. In a first op, there should be no significant movement; that is, it should read zero run out. If there is run out then you have a problem with the chuck jaws or some other part of the chuck. Keep in mind that you cannot evaluate a thing running under power like in your video, be it the chuck body, a spindle or a test bar in the chuck. You have to do it manually.
• Now, if you took a test bar or pin or polished rod and mounted it in your scroll chuck and did the same run out check we just did above, that chuck will run out. On a high end chuck, this might be somewhere in the 0.001-0.003" range, and this will be true for any size of rod you put in there. On a lower end chuck, run out may be much higher. Does this tell you anything useful? Yup, it does. Putting something that has been previously been turned into a scroll chuck will always run out to some degree. If you turn something in a first operation, take it out of the chuck and then reinsert it in the chuck that work piece will have some degree of run out. Once you remove something done in a first op, the only way to get it to run concentrically with the spindle centerline is to put it in a 4 jaw independent chuck and dial it in. So, for first op work, use the scroll chuck. For second op work, use the 4 jaw or a collet chuck.
• If you want to know how much run out your chuck really has, chuck up an accurate pin or end mill and measure it like we did in bullet 1. That will give you the run out for THAT pin. Now, if you take another pin of a different diameter and measure the run out on it, it will be different from the first pin. Same chuck, same DI, same everything, but the run out will change. The reason for this is because the jaws are clamping down in a different part of the scroll so run out varies with the diameter. This might not make sense but it is what it is. If you want to test it, chuck up some drills of varying diameters and test it yourself and you'll see.

The bottom line is that if your 3 jaw chuck is accurate enough to give you zero run out on a first op turning then that chuck is good to go. Use it for first operations only or when concentricity of the part is not important. Try not to use it for second op work; use a 4 jaw or collet for that.

Hope that helps.

 

[GunsOfNavarone]

Thanks again Mikey, I'll be honest..I was worried about getting that chuck dead on center on the back plate..being that isn't such a concern, I'll move on and check run out the way you have laid out. Got so many iron in the fire right now, but at least I know I'm good to go on this chuck, that will reduce the amount I'm switching back n forth. Thanks everyone else that chimed in as well! Cheers!