How can I pick & choose a new Sherline 3-jaw self-centering chuck?

[cazclocker]

FWIW- Bison makes a new 3-jaw chuck to fit Sherline. At $350, it's not cheap, but it may be what you're looking for.

Lee, thank you for the heads-up re: Bison. I'm currently out of town visiting family so when I get home I'll investigate the Bison line. At one time, I went through their products, but I did not see anything suitable.

Doug,

What you describe doesn't sound like runout at all to me. It sounds like the axis of rotation of the headstock is not parallel to the travel of the cross slide. It that is the case, you will cut a tapered cylinder. Chuck up a piece of stock a few inches long and take a cut. Mike the diameter at the beginning and end of the cut. If it is not the same that clinches it. Even with the alignment key in place, it may be possible to adjust parallelism a few thou. Also make sure that that the alignment key is installed with the ground sides of the key against the sides of the slot.

You don't say how you measured the veering off. The way to do it is with an indicator in the tool post.

Further checks: Indicate the drill rod in a collet, a well-centered 4 jaw chuck, and the 3 jaw. Are the results similar? Rotate the spindle by hand. Does the rod wobble?

"Self centering chuck" is a very misleading term. None of them are. They are not intended to be a centering datum. They are intended to be a way to quickly and firmly hold a work piece. If your work piece requires two or more coaxial diameters, and you use a 3 jaw chuck, you must cut each diameter in the same setup, without loosening the chuck. If this can't be done, you must cut the first diameter, then center on it in a 4 jaw to cut the others. Or, hold the first cut diameter in a collet.

For more on headstock alignment Google "Rollie's Dad's Method".

Finally, here's a fixture I've added to my Sherline to make and hold a very accurate spindle alignment.

Best regards,

David Clark in Southern Maryland, USA

View attachment 62850

David, thank you for your input. Here's how I know something's wrong with my 3-jaw chuck: my 4-jaw independent chuck (also a Sherline) holds work concentric to the headstock with NO veering off to the side. That is to say, when I chuck up a piece of 3/16" hardened drill rod in my 4-jaw, I can adjust it until the drill rod reads zero deviance with my DTI, held in my sliderest (I use the sliderest instead of the toolpost) when measuring 1/16" from the chuck jaws. Then, sliding the DTI over 2", the readings consistently show .005" to .006" wobble, and the HIGH point is always the same place relative to the #1 & #3 jaw. The VERY SAME test with my 4-jaw independent chuck reveals the exact same deviance from concentricity adjacent to the jaws and 2" away from the jaws. Therefore, the problem lies with my 3-jaw chuck and not the headstock or my 4-jaw.......UNLESS I'M MISSING SOMETHING!! I'm a newbie at machining, but I'm making my deductions from what seems to be bulletproof logic...but then again, it might be that I know just enough to be dangerous!

 

[D.C.Clark]

David, thank you for your input. Here's how I know something's wrong with my 3-jaw chuck: my 4-jaw independent chuck (also a Sherline) holds work concentric to the headstock with NO veering off to the side. That is to say, when I chuck up a piece of 3/16" hardened drill rod in my 4-jaw, I can adjust it until the drill rod reads zero deviance with my DTI, held in my sliderest (I use the sliderest instead of the toolpost) when measuring 1/16" from the chuck jaws. Then, sliding the DTI over 2", the readings consistently show .005" to .006" wobble, and the HIGH point is always the same place relative to the #1 & #3 jaw. The VERY SAME test with my 4-jaw independent chuck reveals the exact same deviance from concentricity adjacent to the jaws and 2" away from the jaws. Therefore, the problem lies with my 3-jaw chuck and not the headstock or my 4-jaw.......UNLESS I'M MISSING SOMETHING!! I'm a newbie at machining, but I'm making my deductions from what seems to be bulletproof logic...but then again, it might be that I know just enough to be dangerous!

Doug,

I'm afraid I'm not following your logic. If "The VERY SAME test with my 4-jaw independent chuck reveals the exact same deviance" how do you conclude that the 3 jaw is the problem?

DC

 

[cazclocker]

FWIW- Bison makes a new 3-jaw chuck to fit Sherline. At $350, it's not cheap, but it may be what you're looking for.

Lee, I found what I suspect is the chuck you're referring to: here it is....http://brassandtool.com/Machine.html. You're right, it's more than triple the price of a Sherline 3-jaw chuck but I would guess it would perform quite a bit better. It's on my wish list. Thanks for the pointer.

 

[cazclocker]

Doug,

I'm afraid I'm not following your logic. If "The VERY SAME test with my 4-jaw independent chuck reveals the exact same deviance" how do you conclude that the 3 jaw is the problem?

DC

DC, the problem is in my poorly worded description of my test - sorry. I should post pictures, but I'm away from my shop just now visiting family. Let me try again.

I have a Sherline 4-jaw independent chuck, and also a Sherline 3-jaw chuck. To check the workholding abilities of each chuck, here's what I did. I mounted my dial test indicator in a specially-made fixture mounted in my compound sliderest. That way I can mount a piece of 3/16" hardened drill rod in whatever chuck I put into the headstock, and apply the indicating tip of my DTI to the drill rod less than 1/16" from the chuck jaws and rotate the headstock. After a few rotations I mark down what the deviance is (with the 4-jaw, I adjust the jaws for zero or as close as I can get). Once I write down the deviance that I just read with the DTI tip at the chuck jaws, then I use the sliderest to draw the DTI down the length of my drill rod and perform the same test again. So.......what I do is read the deviance (is that the right word?) near the jaws, and then again some distance AWAY from the jaws .... both readings from the same chuck.

What I was trying to say is that I performed the same procedure described above on my 3-jaw chuck, and then again on my 4-jaw chuck. When I get my 4-jaw chuck jaws set to center the drill rod next to the jaws, my DTI might read 0.0005" right next to the jaws. But when I draw the DTI down to maybe 2" away from the jaws and rotate the headstock a few revolutions, I will consistently get 0.0005" to maybe 0.001". So my setup shows that the drill rod is being held straight.

But, when I perform the above procedure using my 3-jaw chuck, I may get 0.002" deviance near the jaws but 0.006" when the DTI tip is 2" away from the jaws. That tells me the 3-jaw chuck is NOT holding my drill rod straight.

Did I 'splain it better this time? Sometimes my brain trips over itself trying to 'splain stuff.

...Doug

 

[Tony Wells]

Your description is correct for "runout", in shop parlance. Sounds like sprung jaws to me. TIR (Total Indicator Reading, or Total Indicated Runout) should be close to the same at the chuck and away from it at a reasonable distance, even if the spindle is not aligned with the ways. That's a separate issue. If the spindle is bent, it would look like what you were seeing, but with any chuck or collet. Since you have narrowed it to the 3 jaw, there seems to be a problem with it. You may want to check it at different diameters however, to determine if the scroll is damaged. If it seems to read about the same error regardless of test pin diameter, it would be worth stoning the errant jaw before spending the money to replace it. Time is generally cheap for us.

 

[cazclocker]

Your description is correct for "runout", in shop parlance. Sounds like sprung jaws to me. TIR (Total Indicator Reading, or Total Indicated Runout) should be close to the same at the chuck and away from it at a reasonable distance, even if the spindle is not aligned with the ways. That's a separate issue. If the spindle is bent, it would look like what you were seeing, but with any chuck or collet. Since you have narrowed it to the 3 jaw, there seems to be a problem with it. You may want to check it at different diameters however, to determine if the scroll is damaged. If it seems to read about the same error regardless of test pin diameter, it would be worth stoning the errant jaw before spending the money to replace it. Time is generally cheap for us.

Thank you Tony. I can't imagine how I could have sprung the jaws, but it is, regardless. The runout is excessive for any chuck, Sherline or not. When I get back from our trip, I plan on stoning one or more of the jaws - but I have to admit the Bison chuck looks mighty tempting. Expensive, though...!!!

 

[D.C.Clark]

DC, the problem is in my poorly worded description of my test - sorry. I should post pictures, but I'm away from my shop just now visiting family. Let me try again.


Did I 'splain it better this time? Sometimes my brain trips over itself trying to 'splain stuff.

...Doug

Much better, thanks, I understand now.

I'm going to get back latter today with some ideas to check out. I will have to set up and photograph them.

But I'll cut to the bottom line now: I would contact Sherline and send the chuck to them for evaluation.

DC

 

[cazclocker]

Much better, thanks, I understand now.

I'm going to get back latter today with some ideas to check out. I will have to set up and photograph them.

But I'll cut to the bottom line now: I would contact Sherline and send the chuck to them for evaluation.

DC

Thanks, DC. I'm out of town just now, arriving home early next week. When we get home I plan to send the chuck to Sherline for evaluation, as you suggested. But there's a strong possibility I'll order a Bison chuck to replace it, and keep the Sherline for a backup (or maybe just a doorstop). Actually, the Sherline chucks are surprisingly nice for their price point. I have NO complaints about my 4-jaw independent!

 

[D.C.Clark]

I'm going to get back latter today with some ideas to check out. I will have to set up and photograph them.

DC

OK. The first thing to do is to disassemble and thoroughly clean the chuck.



What you describe is consistent with the spindle nose thread not perpendicular to the rear chuck plate. You can run it out, both sides, like this:



On a surface plate, check the parallelism of the sides:



And the jaw tracks:



My chuck indicated perpendicularity of around 0.0015" and parallelisms around 0.001". This is somewhat worse than I expected. But, as I stated earlier in the thread, I would never rely on a 3 Jaw chuck for centration -- only concentricity of consecutive cuts.

You will note that the back plate and jaw tracks of this chuck are fairly thin. It is made (I believe) of 12L14 steel, which is wonderful stuff to machine, but not wonderfully stiff. What Tony Wells means by "sprung jaws" (I surmise) is the plate being deformed by excessive tightening or loading -- say taking an aggressive cut very far from the chuck. Imagine chucking a foot long bar and yanking on it hard sideways. That might deform the chuck in a way that would produce what you are seeing. (I'm not suggesting you've done this, I mention it only to clarify the geometry).

I don't know whether this will shed any light, sorry I can't be more helpful.

David Clark in Southern Maryland, USA

 

[cazclocker]

David, that's a pretty lucid description of what I could check when I get home. It makes sense, too. We're heading for home tomorrow morning, hope to be home Monday. I plan to make those measurements once I get a chance, probably Wednesday. I'll post my findings here.
Thanks again...that was really excellent.
...Doug Haeussler