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hughie
24th March 2013, 03:42 PM
I have a couple of Nova screw chucks that have stood me in good stead over the years. Well, finally one of them gave way http://www.woodturnersunlimited.com/forum/images/smilies/icon_eek.gif at speed, shock horror. It was a small piece of Dead Finish around 5" dia, very hard and very solid and it caught me by surprise.

I had an old Holden ute axle from the 60's, so its become a new screw chuck much bigger with a thread of 20 mm dia or 3/4" and twice as long.I have no idea what the steel is, other than to say it turned slowly and proved to be very stiff steel. Some sort of high tensile steel with high anti-torsional twist capabilities

The chuck its sitting on is not the chuck normally I use with my screw chucks. Its an old SN2 5" dia with the large bowl jaws it gives you an idea of size.

Skew ChiDAMN!!
24th March 2013, 03:57 PM
Looks like it's lucky you didn't suffer peripheral damages from that 'un! Nice job on the new one, too.

Any plans for an upcoming WIP on "how to remove broken screw chucks from Dead Finish"? :innocent::D

chuck1
24th March 2013, 05:30 PM
only one suggestion also a deeper pitch thread on the screw! I use coach bolts on my face plates and replace them every 18 month's regardless of how much work they have done! and use the chainsaw file to open up the thread. but bigger is better!

hughie
24th March 2013, 08:03 PM
Looks like it's lucky you didn't suffer peripheral damages from that 'un! Nice job on the new one, too.

Any plans for an upcoming WIP on "how to remove broken screw chucks from Dead Finish"? :innocent::D


Skew probably after Easter :2tsup:

Pat
24th March 2013, 08:49 PM
Neil, I am with Chuck on this one, the threads look like they are for threaded metal parts, not aggressive enough for timber.

hughie
24th March 2013, 08:55 PM
Neil, I am with Chuck on this one, the threads look like they are for threaded metal parts, not aggressive enough for timber.


Yeah I copied the Teknatool supplied thread form here 2mm pitch 2mm deep.

Drillit
25th March 2013, 09:04 AM
Hughie,
For what it is worth. Snapped one about 6 months ago - and tried to use an easy out.
Couldnt budge it at all. Had to drill all around it and used the easy out hole with punch to move
it sideways (back and forth). Didnt do much damage, but reverted to the trusty faceplate & coach screws.
I guess the good thing is that you were not injured in the process only the pride, eh. :B Drillit.

hughie
25th March 2013, 10:48 AM
Hughie,
For what it is worth. Snapped one about 6 months ago - and tried to use an easy out.
Couldnt budge it at all. Had to drill all around it and used the easy out hole with punch to move
it sideways (back and forth). Didnt do much damage, but reverted to the trusty faceplate & coach screws.
I guess the good thing is that you were not injured in the process only the pride, eh. :B Drillit.


Bit of a cardio work out tho' :U

nz_carver
25th March 2013, 11:39 AM
Neil, I am with Chuck on this one, the threads look like they are for threaded metal parts, not aggressive enough for timber.
Pat post a pic of that monster you got.

artme
25th March 2013, 12:49 PM
Looks like I'd best be careful with any Dead Finish I might be
(un)lucky enough to acquire!!!

Pat
25th March 2013, 01:30 PM
Pat post a pic of that monster you got.


Huey, one of my screw chucks has 25mm screw. Drill a 25mm hole with a forstner bit and on very low speed, mount the bowl to the chuck.
With all you fabrication experience, you'd be able to knock one up in a few minutes.

The lump is shown with the Woodfast Screw chuck for comparison.

Paul39
25th March 2013, 01:33 PM
Hughie,

You might try one at 6 threads per inch / 4.5 metric pitch. Go in deep enough to leave just a bit of flat on top of the threads, then put the lathe in back gear and use a round file to get them deeper.

That should give you a nice course thread to bite the timber and deep enough to get a good grip.

What you have may work fine. Even if it strips out all that will happen is the blank will stop turning.

Tim the Timber Turner
25th March 2013, 05:28 PM
Good luck trying to screw that into hard wood like dry Red Gum.

To get a solid mounting you need to screw into a shoulder on the screw.

Cheers

Tim:)

hughie
26th March 2013, 11:35 AM
Huey, one of my screw chucks has 25mm screw. Drill a 25mm hole with a forstner bit and on very low speed, mount the bowl to the chuck.
With all you fabrication experience, you'd be able to knock one up in a few minutes.

Pat thats some screw chuck I have planned to make another around 25mm dia. Unfortunately my lath ain't so accurate as to make a screw on type. I will have to use one of my chucks to use it on the wood lathe.



You might try one at 6 threads per inch / 4.5 metric pitch. Go in deep enough to leave just a bit of flat on top of the threads, then put the lathe in back gear and use a round file to get them deeper.

Paul as mentioned to Pat I plan a larger one,. I was looking at 8tpi but I have to check what my old lathes specs are . I am considering this sort of thread form ___|\___ not quite so pronounced and coming to a point..



Tim the Timber Turner

Good luck trying to screw that into hard wood like dry Red Gum.
To get a solid mounting you need to screw into a shoulder on the screw.



Tim I'll be using the Teknatool system or idea where the job butts up against the chuck jaws. I also have a series of 3 mm stainless discs of various diameters that fit over the screw chuck to give a wider area of support.

Paul39
26th March 2013, 12:18 PM
Paul as mentioned to Pat I plan a larger one,. I was looking at 8tpi but I have to check what my old lathes specs are . I am considering this sort of thread form ___|\___ not quite so pronounced and coming to a point..

I think 8 tpi would be fine for the hard timber available there. Much of what I turn is spalted or soft so a deep and coarse thread works better.

I think the thread form you describe above is called a buttress and works very well in the one direction.

Mobyturns
27th March 2013, 08:59 AM
I have a couple of Nova screw chucks that have stood me in good stead over the years. Well, finally one of them gave way http://www.woodturnersunlimited.com/forum/images/smilies/icon_eek.gif at speed, shock horror. It was a small piece of Dead Finish around 5" dia, very hard and very solid and it caught me by surprise.
........

Hughie, have you considered the reason for the screw chuck failure?

Just an observation on my part, but it seems that the blank face that is mating to the screw chuck plane is the curved natural surface of the blank. Perhaps this is allowing the screw to flex in use as you make cuts and is slowly working and fatigueing the metal untill eventually it fails over time.

DaveTTC
27th March 2013, 06:47 PM
Nice bit of work Hughie

issatree
29th March 2013, 10:21 AM
Hi, Hughie,
I watched Vic Wood many years ago, prepare a blank for a bowl.
Found a centre point, then jammed it up against the opened jaws of his chuck, with the T/Stock.
I've done this on occasions, & it works really well.
It is a bit hard to get at the wood, as the T/Stock gets in the way a bit.
This is only a temporary measure, so as you can make a decent hole or spigot, to fit the chuck.
Don't forget to turn the speed down, or you will have another flying bowl.
Worth a try.

NeilS
29th March 2013, 10:24 AM
Just an observation on my part, but it seems that the blank face that is mating to the screw chuck plane is the curved natural surface of the blank. Perhaps this is allowing the screw to flex in use as you make cuts and is slowly working and fatiguing the metal until eventually it fails over time.


If you are turning inboard you can bring the tailstock up against the foot to counter that flex in the screw. (I see since posting that issatree has made a related point)

If you are turning outboard without tailstock support then a flat against which to seat the face of the screw chuck is necessary on the natural edge end.

As I do most of my turning outboard, I have to add the flat on NE pieces, but find holding the blank while creating the flat a bit of pain. I make the flat with either a chain saw (tidy up with a chisel if necessary) or with a large Forstner bit on the drill press.

Paul39
29th March 2013, 10:49 AM
Hi, Hughie,
I watched Vic Wood many years ago, prepare a blank for a bowl.
Found a centre point, then jammed it up against the opened jaws of his chuck, with the T/Stock.
I've done this on occasions, & it works really well.
It is a bit hard to get at the wood, as the T/Stock gets in the way a bit.
This is only a temporary measure, so as you can make a decent hole or spigot, to fit the chuck.
Don't forget to turn the speed down, or you will have another flying bowl.
Worth a try.

I do the above with almost all my bowl blanks. I also have a kluge that is a piece of hard oak with a spigot on the back to grab in the chuck and a piece of 80 grit sandpaper glued to the flat front.

I have another one for the 20 inch swing Woodfast. It is another piece of oak with a spigot to fit the #3 jaws on the big chuck with 3 sharpened masonry nails set into holes to stick into the blank on the front side.

I use a cup center with a point. I'll put the blank or hacked out log against the chuck or kluge and bring up the tailstock, turn 90 degrees and eyeball center, turn 90 degrees and eyeball again, moving if needed.

I then rough the outside, sometimes moving the center to get better looking figure where I want it, and make a spigot or recess.

I then grab the bottom with the chuck and finish the bowl.

If I have an odd shaped piece or out of balance one, I can mount it, give it a spin by hand, adjust for balance, turn the bottom flat and knock off some of the high spots on the side.

I then take the blank out and knock off the bit that was under the center and recenter and / or readjust for balance.