Turning threads off rod fine but now rod advances out of chuck.

[Ulma Doctor]

I see the predicament, if you were to use steel instead of aluminum, it may offer more resistance to slippage. Adding some rosin may add to the grip

 

[helmbelly]

You may be taking to deep a cut and/or too high a feed and the insert gets caught on the thread and unwinds the bolt. Also the type of carbide cutter and profile. I use CCMT inserts and haven't had any issue with the bolt/rod turning. Ideally you would want something like a 5C collet. Make sure it is free of any oil or lubricant as this can significantly decrease the holding power. I routinely either turn down SS bolts and/or thread cut down bolts w/o any issues. The other approach would be to use a through the spindle stop system.

I'm using brazed carbide bit- in the photo. Got a micro grain carbide coming in tomorrow Mcmaster describes them as specific to SS. Interested - I don't work with carbide or SS much, mostly alum and HSS.

 

[helmbelly]

You may be taking to deep a cut and/or too high a feed and the insert gets caught on the thread and unwinds the bolt. Also the type of carbide cutter and profile. I use CCMT inserts and haven't had any issue with the bolt/rod turning. Ideally you would want something like a 5C collet. Make sure it is free of any oil or lubricant as this can significantly decrease the holding power. I routinely either turn down SS bolts and/or thread cut down bolts w/o any issues. The other approach would be to use a through the spindle stop system.

I have 5c collets but not sure what that gains me- I mostly use them on the mill.

 

[helmbelly]

I should have mentioned- after I turned the hex round I noticed some out of cencentric wobble. I didn't notice it before I had the problem just when I started trying to figure out what happened. Maybe I didn't have it chucked true when I turned it down so when I flipped it end for end I had an oval coupling -biting into threads when the orbit got close and wrenching it out. hmmm

 

[helmbelly]

I see the predicament, if you were to use steel instead of aluminum, it may offer more resistance to slippage. Adding some rosin may add to the grip

True, but I like using a softer metal than the thread, brass or alum, to baby them - they are going to be used in a product. And I'm not an engineer but maybe a softer metal grabs better bc it conforms more? Not sure

 

[Ulma Doctor]

I was wondering if having to over tighten the chuck was deforming the aluminum for subsequent chuckings , maybe I’m overthinking this

 

[helmbelly]

I was wondering if having to over tighten the chuck was deforming the aluminum for subsequent chuckings , maybe I’m overthinking this

it was never tightened w/o the stud loaded so nowhere to really deform to you know? couple dings maybe. I didn't reef on it.

 

[markba633csi]

Better yet, make a fixture out of hex stock- threaded and slit so it clamps the bolt tight

 

[WobblyHand]

Why slit the hex stock at all? Can't you just jam a nut against the threaded hex stock and chuck the hex stock? The nut would go below the jaws of the chuck. Aren't you just trying to immobilize the stud from turning? A steel nut against an aluminum stud shouldn't mark anything.

What is the advantage of the original method? Better concentricity?

 

[helmbelly]

Better yet, make a fixture out of hex stock- threaded and slit so it clamps the bolt tight

That's what I did. Worked fine. Then I rounded off the back and it all went to south.