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Chuck loosenes during slowdown on 33520B

TJ Hamilton

TJ Hamilton

Joined
Jul 27, 2007
Messages
61
Likes
2
Location
Douglasville, GA
Today while turning a 2-3 lb piece on the 3520B, reversed on Oneway Big Jaws mounted in a Stronghold, the whole contraption unwound, loosened, when I turned the lathe off to check the progress.

This is a new development.

I seem to remember a thread about this, either here or on SWC, but naturally don't remember the details. It was not important, THEN!

I thought the 3520B had a "built in breaking system" for lack of a better term that prevented the chuck from unwinding (loosening) when slowing down.

Any counsel from the group?

Thanks, Tom, in Douglasville, keeping the tool rest real close to the work.
 
Well the 3520 does have electronic breaking but but the force of a good size bowl stopping fairly quickly can still unscrew a chuck. I put the chuck on and then use the chuck key to give it a little extra tug to tighten the chuck.
I don't own a Oneway chuck but I thought they had a setscrew in the insert to prevent unwinding. the 3520B has a flat area beyond the screw threads on the spindle to accept that set screw.
 
The lathe is slowing too quickly. The inertia of the spinning mass is greater than the friction grip of the chuck/spindle threads given the speed at which the lathe is slowing the spindle. At least that's what I think is happening...

On my lathe (non-Powermatic) there's a simple switch to change the ramp-down speed. I don't know if your Powermatic has similar circuitry but here's some detailed explanation of Oneway's braking resistor:
http://www.oneway.ca/faq/breaking_resistor.htm

Does your spindle allow the Stronghold to secure itself with the two setscrews located on the spindle adapter?
 
I tap all my chucks and face plates and use a grub screw to secure them the allen key is on a magnet on the headstock if you get into the habit even on small work things stay put, I use a washer behind the chuck made out of milk bottel plastic the chuck winds up tight dosent move and I can undo it by hand
Ian
 
Thanks, men. All those suggestions are helpful. I'm off to dig the grub screws out of the tool chest and cut a plastic washer.

Best regards, Tom
 
In my opinion the plastic washer does nothing. I had problems with my chuck sticking early on so I bought some. It seemed to keep the chuck from sticking but that was on a smaller lathe and I wasn't turning large work. Then I learned about rubbing some air tool oil on the threads and mating surfaces. Put some on and the use a paper towel to remove all you can. The chuck no longer sticks and I haven't had it come loose (using the method I mentioned above) and I never use the plastic washer which just promotes some chatter on larger bowls. I guess it's due to flexing of the plastic.
 
john lucas said:
In my opinion the plastic washer does nothing.....
Click to expand...

I agree with all that you say about the plastic washer. The plastic washer reduces the holding friction that keeps the chuck from unwinding when stopping the lathe. Besides that, adding a plastic washer distorts the metal-to-metal registration that is essential for precision alignment of the chuck to the spindle. And, as John pointed out, the connection is no longer solid.

Regarding braking -- not that it matters a great deal, but the 3520 only has a pseudo braking system. It produces a similar behavior to braking by having a programmed ramp down from the operating speed and injects a voltage to the motor that opposes the rotation. There is no way for the inverter to know that the chuck is loose on the spindle since it is only controlling the spindle speed in an open-loop manner. The inverter also has a braking resistor. The resistor does not provide any additional braking. Its purpose is to absorb the excess energy during a ramp down that would otherwise be dissipated as heat in the motor windings.

Trivia question: Regarding grub screws. In the UK and Oz, they are called grub screws. In the US, everybody except woodturners calls them set screws. Any thoughts on why?

More trivia: In the UK, a headed screw with a shoulder is called a bolt while the the same headed screw that is threaded full length is called a set screw. They call screws without heads grub screws. This leaves woodturners in a quandary since there is a ripple effect from adopting the British terminology for a headless screw.
 
Ditto on plastic washers. I don't use them.

A quick way to clean the threads is with a #2 pencil.
Run the lathe in reverse at low speed and push the pencil into the thread closest to the headstock and let the rotating spindle feed it out.
Repeat a few times. This gets the crude out of the threads and leaves behind a bit of pencil lead (graphite) as a lubricant.

I always tighten a chuck or faceplate with a good push. Makes them easy to get off as well as stay put.
The grub screws - aka set screws 🙂 ,keep the chuck in place for sure.
Just remember to loosen them enough so the don't mar the threads when you remove the chuck.

Have fun,
Al
 
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Bill Boehme said:
I agree with all that you say about the plastic washer. The plastic washer reduces the holding friction that keeps the chuck from unwinding when stopping the lathe. Besides that, adding a plastic washer distorts the metal-to-metal registration that is essential for precision alignment of the chuck to the spindle. And, as John pointed out, the connection is no longer solid.
Click to expand...

I, also, agree Bill. From what little machine and physics knowledge I have about the mechanics of screw holding, I believe the flat mating surfaces between the shoulder of the spindle and the flat of the chuck adapter provide not only alignment but substantially more of the holding forces than the thread contact areas. Plastic washers between these surfaces will diminish the positive contact and holding ability - which is exactly what is seen through easier chuck removal.
 
TJ Hamilton said:
Today while turning a 2-3 lb piece on the 3520B, reversed on Oneway Big Jaws mounted in a Stronghold, the whole contraption unwound, loosened, when I turned the lathe off to check the progress.
Click to expand...

Just to add to your original message (^), I've had it happen to me as well. It was a confusing situation because it's so foreign to what I was expecting. "What in the world is going on?" 😕 And then it's startling because you don't quite know what to do. 😱

I suppose appropriate reactions would be to:
#1 - GET OUT OF THE WAY! (And hope for the best.) (This is my usual plan for any unexpected occurrences.)

#2 - Turn the lathe back on as quickly as possible. (And hope for the best.)

#3 - Jamb the tool that's still in your hands into the wood quickly so that the tool lodges against the rest and retightens or at least stops the unscrewing activity. (And hope for the best.)
 
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Well, it's always an educating process when one posts here. Up post was a link from Owen to the Oneway web site. Imagine that, go to the source. So I did and even clicked over to the INSTRUCTION MANUAL for the Stronghold.

To paraphrase: lock the spindle, unwind the chuck a half turn or so and spin it home by hand. No mention of using set screws to hold the chuck to the spindle shaft SHAZZAM, the chuck locked tight, did not loosen during slowdown the rest of the day.

So I put on a new big blank, 10-12 lbs, and the process worked. Snap the chuck home against the spindle with a little wrist snap and it is secure.

Who knew!

Tom, in Douglasville, hoping his "man-card" is not inactivated for actually reading an instruction manual.
 
TJ Just noticed your post saying Hoosier by birth. Me too. Tennessean by the grace of god.
The one time I had my chuck come loose I as using my Jumbo Jaws. That's a lot of mass trying to stop when you have a big bowl on them.
 
TJ Hamilton said:
..... Tom, in Douglasville, hoping his "man-card" is not inactivated for actually reading an instruction manual.
Click to expand...

I'm checking on the man rules. 😀
MAN RULES: §501, ¶c(3) Reading of Instruction Manuals
Reading instruction manuals is strictly prohibited. Looking at the pictures is OK. Fine for first offense: Mild slap on wrist. Repeat offense: Automatic deactiviation of Man Card. Appeals: Any lame excuse is acceptable.
​
You can claim that you thought that you were looking at the 2013 NASCAR schedule and get off scot-free. No charge for the legal services.


jschnell1203 said:
I had the same problem with my BIG RIM Longworth chuck and use the set screws. Just make sure you loosen them all up before removing the chucks. I chewed up my threads by the head stock a little.
Click to expand...

Most setscrews have a sharp edged cup on the bottom so that they can bite into whatever they are holding. That is great for things that are meant to be locked together either permanently or seldom moved. I discovered that there is another type of setscrew when I bought a couple Easy Wood Tools faceplates. Their setscrews have a smooth slightly-rounded button on the end. That is very nice because that type of setscrew does not damage the spindle.

The only time that I had something try to unwind was when I had a 60 pound hunk wood on a faceplate. This was pre-EWT so my solution was to let it freewheel to a stop.
 
Chucks and grub screws

I like a chuck that can be locked down by means of grub screws. Even though I normally spin-lock mine on when I turn, I discovered reverse turning became possible when I started using a chuck which had the grub screw facility on the collar.

Quite apart from the added safety aspect, that ability opened a new door for me - being able to hollow out a form over a period of an hour or two without back pain or a crick-in-the-neck. These days there is no more precarious balancing over the lathe bed as I get my face too close to the turning in order to see what is happening inside - now I just aim the light in the hole I have made and take a casual look.

Recommended for those who have never tried it before.
 
John:

Muncie growing up, Burris HS; Greencastle for college, DePauw University, 68.

Best regards, Tom
 
I believe most premium lathes made recently have hardened spindles. These are best for using set screws without any damage. You don't want to take the chance with any damage, because it could effect the alignment between spindle and mating threads of accessories.

My older Woodfast lathe does not have a hardened spindle, and if I wish to use a set screw, I'll use a little piece of brass rod to place in the hole between the set screw and my spindle. Since the brass is softer than my spindle, there will be no damage. I'll only use the set screw for really heavy turnings......where the added weight will be an increased risk of unscrewing during a shut-down.

After having a couple of turnings unscrew on a shut-down, I now do as a few others have suggested. When mounting the faceplate, or chuck, I give it a little spin just before it seats. This will lock the two pieces together, and will prevent unscrewing during a shut-down on all but the most extreme cases.

I used one of the commercially made plastic washers between chuck and spindle for a time, but decided I'd rather have to two parts "lock" together, than to have a more easy task of manually breaking the friction fit.

ooc
 
I use the oneway chucks and other oneway items on my 3520B. On the chuck when I think there may be a problem I use the Brass Tipped Hex Socket Set Screw they are bit more expensive than the regular set screw, but I think they are worth it. I use the same size set screw on most of the stuff I make for the lathe so I don't need a lot of allen wrenches. I had to repair a really nice FL Rosewood platter that "unwound" I was not happy. I use the set screw especially when finishing with the jumbo jaws.
 
Ian's "man rules"

Ian-what a hoot!!!!!! I scanned quickly and will study further. If you don't mind I am going to copy and send to some male friends!!!!!
 
Now I know that there are two distinct social strata in Oz -- chaps and blokes. Apparently is is preferable to be a bloke than a chap, but more clarification seems necessary. I am wondering if a similar code of chap behavior exists.

I have been using an online Oz to US dictionary to translate the document. I figured out that Oz "shed" = US "man cave". At first, I thought they were into polygamy before finding out that Oz "mates" = US "buds". I'm still working on translating a few other terms. Apparently, "bum" is something you sit on as opposed to a bud who is down on his luck.
 
Bill Boehme said:
Now I know that there are two distinct social strata in Oz -- chaps and blokes. Apparently is is preferable to be a bloke than a chap, but more clarification seems necessary. I am wondering if a similar code of chap behavior exists.

I have been using an online Oz to US dictionary to translate the document. I figured out that Oz "shed" = US "man cave". At first, I thought they were into polygamy before finding out that Oz "mates" = US "buds". I'm still working on translating a few other terms. Apparently, "bum" is something you sit on as opposed to a bud who is down on his luck.
Click to expand...

chaps is a name for a heavy -duty apron that are wore by horse riders and by hunters for protecting against briars and thorns but are a old English word for other people
 
I think that you need to start a thread on Sherlock Holmes and the good Doctor Watson, it been many moons since I watch this team but I think that they call people " old chap " every fore night, finding the meaning of fore night took me a forenight
 
The only time I have had bowls and chucks come loose on the lathe is when hand sanding in reverse. If when you hit the off button, if it unwinds, there could be a couple of problems. I have never used set screws, and don't even have them on my chucks. I do turn at high speeds. My lathes with braking features have been a PM 3520A and my Robust. Never spent any time on a Oneway.

Being loose to start with would not be one of them. All of the resistance when cutting would serve to tighten the chuck, not loosen it.

Braking too fast might be part of the problem. All of the phase converters can be programmed in all sorts of ways, including ramp up and ramp down speeds/times.

It could be possible that the chuck is not seated properly, or all the way down to the spindle shaft hub, or flat spot, and is seated only on the threads. Is it only one chuck that this happens with, or all of them?

I used plastic washers for years. I started after getting a chuck stuck once or thrice on the lathe. It did seem to prevent that from happening any more. There was no increase in run out that I could see. The plastic used was about 1/16 inch thick, and one of the very hard ones, but not sure of which type. I would think that if you used milk carton, it would be an inconsistent thickness material, and there could be some wobble factor, but because it is so thin, the pressure would squish things out more evenly. The washers I used have since gotten lost, and one got eaten during another turning situation on one of my lathes. My chucks don't seem to get stuck any more. I don't know if the plastic helps keep your chucks from getting stuck any more or not. I do like the idea of chasing the threads with a pencil (that should go to the AAW mag for turning tips, forward to Betty!).

If a bowl is coming off as you slow down, as long as it isn't winged or natural edge, your left hand applied gently to the outside of the bowl will slow it down so the spindle can catch up. NOTE: Master Class Skill/Professional driver on closed course, do not attempt!!!!!

robo hippy
 
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