Longworth Offset Experiment

[joe greiner]

I moved two of the buttons on my Longworth chuck to neighboring slot intersections. This had the effect of relocating the center of the workpiece offset from the lathe axis, for turning an added feature. If the added feature were simply a round pocket of an exact size, a Forstner bit would be more effective. But for anything else, it works great, subject to limited variability.

I think a similar modification could be made to Cole jaws.

And in either case, the modification can be un-done to restore normal function.

(One of the faceplate screws was mis-aligned amd didn't pierce the front face. The sloppy initial rim was a product of haste.)

[vk4]

looks interesting , I am just building my first of these chucks.
I did a trial 1 out of 7mm ply and I wobbled all over the place due to the ply .
I am building my second with 20mm MDF as the back and (mm ply for the front, this is sitting correctly and no wobbles.

I have 8 arcs not 6 but that is a minor difference.

going by what you have done here , by rotating the work piece you could do multiple off center turnings on the piece .

[joe greiner]

Multiple features: I considered that, but I'm giving a demo Tuesday evening, and didn't want to cloud the issue. I'll mention it though.

I think Cole jaws would provide more opportunity for varying the offset because of all the possible locations for the buttons. Unfortunately, I don't have Cole jaws (yet).

Cheers,
Joe

[Cliff Rogers]

Top idea. :2tsup:

[Sawdust Maker]

Hmm

I think you may have provided a solution for something I've been pondering for a little while.
Either that or at least another experimental option

Thanks

[wheelinround]

Joe interesting out come. Look forward to whats produced after demo.

Not sure why the face plate screws :? was this from a test run.

[hughie]

here you go Joe


http://www.woodworkforums.com/f8/cole-jaws-part-1-a-41166/

http://www.woodworkforums.com/f8/cole-jaws-part-2-a-41169/

[Sawdust Maker]

Was just out in the shed

and tried this as a looksee

186410

as you can see there is a gap at about 5 oclock and around 10 oclock
also a smaller gap at 4 and 11

[WOODbTURNER]

Enzo (Vermec) has a bowl jaw clamp to suit square/rectangular blanks for offset use on cole jaws.

[wheelinround]

A face plate with individual adjustment of slides would be excellent for this I recall one such device being show when I started the forum.

For the Cole and Longworth use of a Cam'd button would be best or and offset centre one.

[joe greiner]

Hi all,

Yes this was a test run - very quick and very dirty.

Gil Jones and I are giving the demo on offset turning in general. This will be just a "By the way." And thanks for the Cole jaws test, Nick. It will be better than my hand-drawn graphic. Two of the buttons on my Longworth are also unused.

On a recent project, I briefly entertained the notion of building Cole jaws, but elected to use one-off tooling instead. I'm persuaded otherwise now. My Grizzly clone of Vicmarc doesn't have the extra holes, hughie. I figure to connect directly to the sliding bars. Interesting use of the long "buttons." Something like that doesn't work very well on the Longworth, although I stacked two rubber corks for some touch-up sanding.

Cheers,
Joe

[wheelinround]

Joe there is another way

OTI :: Eccentric Chuck (http://www.ornamentalturners.org/forum/gallery2.php?g2_itemId=6259)

[Sawdust Maker]

Joe

You're welcome to use the photo if you wish:2tsup:

[wheelinround]

Joe if you used Cole jaws with slotted adjustment instead of holes it may be a better secure.

[Sawdust Maker]

Joe if you used Cole jaws with slotted adjustment instead of holes it may be a better secure.

Hmm
stop reading my mind
that's what I was thinking along with different grippy bits

but then you could do it with a sacrificial circular piece, maybe

[vk4]

started to build a longworth chuck for the lathe , built the main disc from 20mmMDF, It was flat when I started, after mounting on a piece of 70mm Blue Gum for the chuck mount , and truing up in the lathe , all looked good, .

I then sealed the MDF with a water based floor finish, 2 hours later the MDF has deformed and has a 3mm woof on the face , which before sealing was true.:rolleyes::rolleyes:

NOT HAPPY JAN!!!:rolleyes::rolleyes:

Obviously the coating caused the MDF to warp., I suspected this could happen:rolleyes: , but hoped it would not:D.

I will now source some 12-15mm ply and start again.:2tsup:

Jeff

[cookie48]

OK I have read this, but I am wary about offset because the holding clams/plugs (what ever you call them) do not look safe enough to hold the work piece off centre for working. Am I being too cautious or silly thinking???
Cookie

[Sturdee]

I figure to connect directly to the sliding bars. Interesting use of the long "buttons."
Cheers,
Joe

Joe,

The bowl jaw clamps (http://vermec.tripod.com/PDFs/Vermec_Bowl_Jaw_Clamp_Set.pdf) from Vermec might be helpful for holding your work. Easy enough to make a few using a few bolts and some bits of timber.


Peter.

[Sawdust Maker]

OK I have read this, but I am wary about offset because the holding clams/plugs (what ever you call them) do not look safe enough to hold the work piece off centre for working. Am I being too cautious or silly thinking???
Cookie

Sorry

From my point of view this is conceptual

for myself I'd be using some other type of "button" I have a couple of ideas to try and see how they might work - something else for the future

[Paul39]

One could mount a piece of 25mm MDF to a face plate and using wood screws and buttons, bought or made, mount anywhere your heart desired.

Mark your second center point, run the tail center up to hold the turning against the MDF, and screw on buttons.

[Cliff Rogers]

One could mount a piece of 25mm MDF to a face plate and using wood screws and buttons, bought or made, mount anywhere your heart desired.

Mark your second center point, run the tail center up to hold the turning against the MDF, and screw on buttons.
Yup, that would work. :2tsup:

[joe greiner]

One could mount a piece of 25mm MDF to a face plate and using wood screws and buttons, bought or made, mount anywhere your heart desired.

Mark your second center point, run the tail center up to hold the turning against the MDF, and screw on buttons.

Or use plywood instead of MDF, and attach the workpiece directly to the plywood.

Re-set from last night's demo.:wink:

Cheers,
Joe

[Paul39]

Or use plywood instead of MDF, and attach the workpiece directly to the plywood.

Re-set from last night's demo.:wink:

Cheers,
Joe

Joe,

Perfect. Great minds run in the same ditch.

[Skew ChiDAMN!!]

I once saw a home-made adapter which will offset any faceplate/chuck by up to an inch or two.

Basically it was just two metal squares, about 3" to a side and maybe 1/2" thick. A threaded spindle for the chucks was welded to the centre face of one and it's female counterpart to the centre of t'other square. (I don't recall whether the one I saw threaded onto the spindle or was a tenon for mounting on a chuck. But minor detail. :shrug: )

The mating faces of the two squares were machined into a sliding dovetail, which was locked into the offset position via a grub-screw.

I remember thinking that it'd be safer to have made it a stopped dovetail, with a long adjuster bolt coming in from the stopped end. (Similar to a machinists vise for a drill-press.)

Never got around to making one myself... I'm a wood hack, not a machinist. :sigh:


started to build a longworth chuck for the lathe , built the main disc from 20mmMDF, It was flat when I started, after mounting on a piece of 70mm Blue Gum for the chuck mount , and truing up in the lathe , all looked good, .

I then sealed the MDF with a water based floor finish, 2 hours later the MDF has deformed and has a 3mm woof on the face , which before sealing was true.:rolleyes::rolleyes:

NOT HAPPY JAN!!!:rolleyes::rolleyes:

Obviously the coating caused the MDF to warp., I suspected this could happen:rolleyes: , but hoped it would not:D.

I will now source some 12-15mm ply and start again.:2tsup:

Jeff

:oo:

Good move. MDF really, really isn't good choice for a faceplate/cole jaw/longworth chuck.

Even if it hadn't warped on you, further down the track there'd be one day when, in use, it just lets go with a BANG. It has insufficient structural strength for spinning around at any speed.

(I destroyed 3 of these MDF versions before I learned to wear brown pants while turning. :;)

Ply is far, far better... but have you looked at making a plexiglass version? No harder to work, looks mighty good and, apparently, just as strong as ply.

[wheelinround]

Joe see thread here (http://www.woodworkforums.com/f22/indexed-bowls-113827/) why not just make one of these (http://www.otga.org.au/Gallery_files/8th%20June%202010%20Update%20The%20OTGA%20Off%20Centre%20Bowl%20Chuck%20FULL.pdf)

[wheelinround]

I once saw a home-made adapter which will offset any faceplate/chuck by up to an inch or two.

Basically it was just two metal squares, about 3" to a side and maybe 1/2" thick. A threaded spindle for the chucks was welded to the centre face of one and it's female counterpart to the centre of t'other square. (I don't recall whether the one I saw threaded onto the spindle or was a tenon for mounting on a chuck. But minor detail. :shrug: )

The mating faces of the two squares were machined into a sliding dovetail, which was locked into the offset position via a grub-screw.

I remember thinking that it'd be safer to have made it a stopped dovetail, with a long adjuster bolt coming in from the stopped end. (Similar to a machinists vise for a drill-press.)




Never got around to making one myself... I'm a wood hack, not a machinist. :sigh:



:oo:

Good move. MDF really, really isn't good choice for a faceplate/cole jaw/longworth chuck.

Even if it hadn't warped on you, further down the track there'd be one day when, in use, it just lets go with a BANG. It has insufficient structural strength for spinning around at any speed.

(I destroyed 3 of these MDF versions before I learned to wear brown pants while turning. :;)

Ply is far, far better... but have you looked at making a plexiglass version? No harder to work, looks mighty good and, apparently, just as strong as ply.


Plexy become brittle with age and like MDF shatters

[joe greiner]

Joe see thread here (http://www.woodworkforums.com/f22/indexed-bowls-113827/) why not just make one of these (http://www.otga.org.au/Gallery_files/8th%20June%202010%20Update%20The%20OTGA%20Off%20Centre%20Bowl%20Chuck%20FULL.pdf)
One of the problems with off-center work is the need for counterweights. And as the article says, counterweight requirements change as material is removed. Before settling on laminated veneer for the lattice circle, I tried thicker timber - hopeless without counterweights.

Tuesday's demo was intended to include turning a 3-center roller (Reuleaux triangle - Google is your friend). In rehearsal I used lead wing nuts of my own manufacture, but wasn't satisfied. In the end, I simply described them and suggested use of bookends with dead centers, connecting boards, and router table for gentler production; similar to this: http://www.woodworkforums.com/f8/cart-before-horse-57412/

Cheers,
Joe

[wheelinround]

One of the problems with off-center work is the need for counterweights. And as the article says, counterweight requirements change as material is removed. Before settling on laminated veneer for the lattice circle, I tried thicker timber - hopeless without counterweights.

Tuesday's demo was intended to include turning a 3-center roller (Reuleaux triangle - Google is your friend). In rehearsal I used lead wing nuts of my own manufacture, but wasn't satisfied. In the end, I simply described them and suggested use of bookends with dead centers, connecting boards, and router table for gentler production; similar to this: http://www.woodworkforums.com/f8/cart-before-horse-57412/

Cheers,
Joe


Joe sounds interesting did you use an eccentric chuck ?

Hope this works

http://upload.wikimedia.org/wikipedia/commons/2/20/Rouleaux_triangle_Animation.gif

[joe greiner]

No. Spur drive and live center; triangle layout. Also used small fillets instead of sharp corners in an oversize blank. At the end hubs I drilled three transverse holes for all-thread securing the lead wing nuts on the lighter side. The small fillets were turned all at once without eccentricity and without counterweights; essentially just chopped off. The major disappointment was that the blank was too short for close cutting. Even in a longer blank for closer cutting, the end hubs would be wasted; not so with the bookends and router table.

There were, of course, some sphincter exercises too.:oo:

Cheers,
Joe

[wheelinround]

:2tsup:

TMI Joe :U