Est. 1998 — 27 years of woodworking knowledge
another "whoops!"
adrien
>Turning the bottom of a piece in my Vicmarc bowl jaws. It started up way too fast. Sounded like an airplane. Instinctively, I spun the speed control to slow.
Wow! that chuck can unwind off the headstock real fast!
I double checked, thinking I'd turned it to run clockwise. No, just the rapid deceleration did the trick.
Re: another "whoops!"
David Eaves
>Yikes, did the piece survive the incident?
If the chuck came flying off too, glad it sounds like you managed to avoid it. I've only had a faceplate fly off once, and I haven't left it on the outboard side of the lathe when I wasn't using it since then. :o)
David
Re: another "whoops!"
John Lucas
>Adrien
I've had it happen twice. Fortunately the tool rest stopped it. I had a chuck lock up on the spindle one time so I tend to install the chuck with less power than is needed. After almost losing it twice I put a little more pressure on the chuck when installing it.
This never happened when I had DC or straight AC power. The electronic braking of the VFD is what causes it. On my older VFD I set the braking to a slower setting. I don't have that option on the Powermatic but it seems to slow very nicely.
Re: another "whoops!"
mpwall
>How big was the piece and which sized chuck were you using. My 3520 hasn't spun one off yet, but I only have 100's and don't chuck up really heavy pieces. Just wondering what to watch for.
Thanks,
MP Wall
2 forces at work, I think
Andy in Raleigh
>This has happened to me with a faceplate. I think there are two forces at work. The first is the centrifugal force. It's at its greates because it's on rough stock at full size; probably the most weight you will have at the outer edges is just after chucking up a rough piece. And since you didn't use a toll, it never had resistence which provides additional tightening against the threads. The second force is the "wobble" or side to side out-of-balance motion which works to loosen the threads also.
Re: another "whoops!"
adrien
>the bowl jaws were mounted on a VM120 chuck--pretty heavy item.
The bowl was small enough so that when I (stupidly) caught it, it managed to remove a fair portion of skin before it stopped spinning. Fortunately the tool rest prevented my grabbing the spinning bowl jaws disk.
The piece will be titled "kamikaze special". {:-)
Re: another "whoops!"
GeeSeaWhy
>At some point, Teknatool added a setscrew to the inserts for their chucks to prevent this. It screws into the relieved area near the headstock so if the chuck starts to unwind, the setscrew jams against the threads and stops it. Also prevents you from removing the chuck until you loosen the setscrew, but that's what safety features tend to do, isn't it?
Graeme
Re: another "whoops!"
Dinyar Chavda
>If you are concerned about this happening again (say wiht a big off-round piece), or when you are reverse turning, here is a tio from Herman De Vries:
...there's another way to keep the chuck from unscrewing when turning in reverse. I simply take a 3/8" threaded rod and run it all the way
through the hollow spindle and the chuck with a nut and washed on each end. Impossible to lose the chuck and your spindle threads are safe.
Herm
By the way, if you haven't visited his site, http://www.hdv.net/, you should do so--he has some great jigs, advice on sharpening and making tools, and his comments on how to use the Termite are what lead me to be able to control mine.
Dinyar