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Help Cant seem to keep pieces in the chuck

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Forum topic by SAJPV posted 10-07-2015 05:34 PM 651 views 0 times favorited 8 replies Add to Favorites Watch
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SAJPV

1 post in 426 days


10-07-2015 05:34 PM

I have been turning pens for a few years and have recently decided to try and a bowl. I have KNOT had much success. Is it common to have the piece fly across the shop? I am using an older Delta with a Barracuda 4 jaw chuck. Once it leaves the lathe I have trouble centering again and have to start over. I started with a 9 inch bowl and will probably end up with a shot glass by the time I am done. Any help or suggestions would be great! Thanks in advance


8 replies so far

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MrUnix

4224 posts in 1662 days


#1 posted 10-07-2015 05:43 PM

I’ve found that it’s much easier to just glue a wooden faceplate to the blank and then part it off when done. You can take it off the lathe multiple times and be sure it will go back on in the exact same place :)

And you can make dozens of those faceplates for zero cost – just scrap 2x material drilled and taped for the correct spindle size/thread.

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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Underdog

902 posts in 1499 days


#2 posted 10-07-2015 05:57 PM

At least a couple reasons why one could be losing pieces out of a chuck.

1) The tenon is too long and it’s bottoming out in the chuck instead of the shoulders bottoming on the face of the jaws.
2) The shoulders of the tenon are not perpendicular to the lathe axis, so they don’t contact the face of the jaws properly.

If you see space between the shoulders of your tenon, and your jaw faces, stop and correct the problem. Good contact with the jaw faces keeps the workpiece from starting to wobble out of the jaws. You can tighten the jaws all you want, but it won’t stop the thing from starting to move if you don’t get that solid contact.

Even with a good chuck with proper tenon implementation, you can still lose a piece if you have a bad enough catch. And for that you need better technique…

-- "woodworker with an asterisk"

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LeeMills

271 posts in 764 days


#3 posted 10-07-2015 07:16 PM

It could be lots of problems or combinations of problems.
You do not say if you are using a recess or tenon.
Possibilities may include…
Too long of a tenon as Underdog described. The tenon can also be too short.
Wrong profile on the tenon, some are straight and some are dovetail depending on your jaws.
Not having a true flat area for the top of the jaws to seat against.
Having the jaws extended way out where only the corners grip.

I’m not sure why you have to re-center it? Are you breaking the tenon off when it orbits?
Stuart Batty has three excellent video’s on mounting with a chuck. They are about 10-15 minutes each.
Just look for the three on chucks, jaws, recesses, tenons.
https://vimeo.com/woodturning/videos/sort:alphabetical/format:thumbnail

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

View AlanHollar's profile

AlanHollar

9 posts in 425 days


#4 posted 10-08-2015 03:10 PM

Once it pulls out of the jaws that can affect the concentricity(roundness) of the tenon. If the wood is wet or unseasoned, it can compress and shrink, so checking the tightness of the jaws periodically is wise.

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soob

223 posts in 672 days


#5 posted 10-08-2015 03:15 PM

In addition to what was said above, I would not recommend removing the bowl from the chuck jaws if you can help it. It’s hard to get it seated exactly the same way again even if you do everything right. It’s also hard to get the bowl to spin exactly the same as it did before it was put on the chuck (usually you start with a screw chuck), and the bowl tends to go out of round shortly after it’s hollowed from the heat causing rapid drying.

In both cases, instead of insisting on making it perfectly round and true, just roll with it.

I’ve found that the easiest way to turn a bowl for a beginner is to mount on a screw chuck, shape the outside to the final shape (prepared for a recess mount), sand and finish. Then mount it to the chuck using the recess and do the inside. The chuck will do minimal harm to the recess and no remounting is required.

6-9” is a good size to start turning with as the chuck mount (should) be strong enough to hold if you get catches while hollowing. Leave a substantial for strength if using a recess mount. Smaller bowls will break and big ones can be dangerous.

ETA: also to get the best hold, you should make the tenon or recess as close to the closed size of your chuck jaws as possible, if that wasn’t mentioned before.

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Underdog

902 posts in 1499 days


#6 posted 10-08-2015 04:34 PM

And for safety sake, don’t spin it as fast as you would a spindle. Slow it down… These things generate considerable force and can launch pieces that will fly clear across the shop and embed themselves into ceilings and walls. Not to mention your head.

-- "woodworker with an asterisk"

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hairy

2384 posts in 2995 days


#7 posted 10-08-2015 06:40 PM

You should use tailstock support as long as possible, and I agree with Underdog, you’re probably too fast.

-- stay thirsty my friends...

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lew

11339 posts in 3219 days


#8 posted 10-09-2015 02:30 PM

Something that helps me “re-center” a workpiece in the chuck. I filed an index mark on the #1 jaw of the chuck. It’s just a V-shaped small notch. When I mount the workpiece, the first time, I make a pencil/sharpie mark on the workpiece at the V-shaped index mark. Now I can always re-mount the turning at the same position

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

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