Cole Jaw question

[John Solie]

Hi, I've got an old SuperNova chuck which has served me well for many years. Way back when I purchased it, I also got a set of cole jaws which I've used several times. I've run into several situations recently where the cole jaws will not grip the bowl, regardless of jaw or rubber stop position. I've done bowls where I built up the outside with tape, but it's always a wild ride cleaning up the bottom of the bowl.

Apart from setting these aside and getting a Longworth, I'm looking for some ideas on how to safely grip bowls that are small enough to fit, yet the stops on the jaw are either too far away from the rim of the bowl to grip, or cannot be opened up wide enough for the bowl to fit.

Thanks!

 

[hockenbery]

John,
A vacuum chuck is a solution. And as pointed out in another thread not all that expensive.

Another easy an reliable method of finishing the bottom is to use a jamb chuck.
A small block of wood is turned like a thick bowl with rounded rim.
A pad ( paper towel) is place over the rim of the jamb chuck.
the bowl is placed over the rim of the jamb chuck with the pad between the two.
The tailstock brought up to the hold the bowl in place while you turn away the waste wood and refine the foot.
I use the center point from when the bowl was between centers. Sometime a new center needs to be found.
Also a center with a small contact are is essential. ONEWAY center works great.

I do this on most of my bowls and hollow forms.

I use a small spindle gouge 1/2 or 3/8 for most of the refining cuts.
Be sure to keep the gouge on top of the tenon. If the gouge runs under the tenon it will break the tenon or the tool will catch on the bowl.

The reverse chucking can be a bit intimidating but if you have fundamental skill with the small tools it is easy an quick.

Al

 

[Joe Greiner]

The pitch of the Cole jaws button radii "should" be less than the travel of the chuck jaws, with some extra travel to compress the buttons. I don't understand why yours should be incompatible.

Have you "recently" been turning bowls with substantially vertical walls? But not previously when you've used the Cole jaws successfully? If so, I don't think the Longworth would help.

Before I made my Longworths, I used a method proposed by Betty Scarpino in Fine Woodworking:
Mount a plywood disk on a faceplate;
turn a groove to mate with the bowl rim;
place the bowl on the disk, with at least four strips of tape wrapped around the walls to the back of the disk.

This works with any wall profile, and when you've used up all the space for new grooves, make a new disk. I still use the tape on the Longworth for insurance, especially for vertical walls.

Like Al says, shave the tenon down gently.

Joe

 

[Odie]

The pitch of the Cole jaws button radii "should" be less than the travel of the chuck jaws, with some extra travel to compress the buttons. I don't understand why yours should be incompatible.

Have you "recently" been turning bowls with substantially vertical walls? But not previously when you've used the Cole jaws successfully? If so, I don't think the Longworth would help.

Before I made my Longworths, I used a method proposed by Betty Scarpino in Fine Woodworking:
Mount a plywood disk on a faceplate;
turn a groove to mate with the bowl rim;
place the bowl on the disk, with at least four strips of tape wrapped around the walls to the back of the disk.

This works with any wall profile, and when you've used up all the space for new grooves, make a new disk. I still use the tape on the Longworth for insurance, especially for vertical walls.

Like Al says, shave the tenon down gently.

Joe

Joe......I sold my Cole Jaws a few years back, so can't check.....but, I was thinking the same thing. I don't remember there being any size bowl that the jaw travel won't accommodate.....maybe there is, and I was lucky to not run into it.

With Betty's method, are we talking about a jam chuck? Just wondering if there is a link to her article......? Thanks.

ko

 

[Michelle Rich]

I too ran into this ONCE in 30+ yrs..I just taped the rubber and used it. (with the tailstock)

 

[Rick H]

Pins

I have run into the problem too. I cut some air hose 3/8" inside diameter the length of the pins. Then just push these over the pins which makes them larger. Seems to take up that no go space the normal jaws won't fit.

 

[Ron Solfest]

Are the rubber stops old and hard? I replaced mine a few years ago when they didn't seem to grip as well. Regardless, I've gotten in the habit of using the tailstock when finishing off the bottom of bowls with the cole jaws, and then running without the tailstock only for the last 1/2" nib and sanding. I adopted that habit after bouncing a couple of bowls on the floor, no mishaps since.

Good luck,
Ron

 

[Joe Greiner]

Joe......I sold my Cole Jaws a few years back, so can't check.....but, I was thinking the same thing. I don't remember there being any size bowl that the jaw travel won't accommodate.....maybe there is, and I was lucky to not run into it.

With Betty's method, are we talking about a jam chuck? Just wondering if there is a link to her article......? Thanks.

ko

I don't have a citation for the original article. It appears in "Lathes and Turning Techniques - The Best of Fine Woodworking," ISBN 1-56158-021-X. It would have been before 1991.

However, I just found an index here: http://www.cs.rochester.edu/u/roche/rec.wood.misc/fww.index
which contains this:
78,89,SEP/OCT,61,TURNING BOTTOMS,SCARPINO, BETTY

I guess that means vol. 78, 1989, page 61

Joe

 

[Dennis J Gooding]

I used to have that problem with my Nova cole jaws. Like Nick, I pressed tubing of one kind or another over buttons to enlarge them when needed. I also remember making a set of larger buttons to substitute when needed. I gave the jaws away when I upgraded to my present lathe with an incompatible spindle size.

 

[Dennis J Gooding]

By the way, there definitely were "no fly" zones in the range of diameters that the Nova jaws could hold.

 

[John Solie]

A vacuum chuck is a solution. And as pointed out in another thread not all that expensive.

Another easy an reliable method of finishing the bottom is to use a jamb chuck.
A small block of wood is turned like a thick bowl with rounded rim.
A pad ( paper towel) is place over the rim of the jamb chuck.
the bowl is placed over the rim of the jamb chuck with the pad between the two.
The tailstock brought up to the hold the bowl in place while you turn away the waste wood and refine the foot.
I use the center point from when the bowl was between centers. Sometime a new center needs to be found.
Also a center with a small contact are is essential. ONEWAY center works great.

I do this on most of my bowls and hollow forms.

I use a small spindle gouge 1/2 or 3/8 for most of the refining cuts.
Be sure to keep the gouge on top of the tenon. If the gouge runs under the tenon it will break the tenon or the tool will catch on the bowl.

The reverse chucking can be a bit intimidating but if you have fundamental skill with the small tools it is easy an quick.

Al

Hi Al,

I hadn't thought of a vacuum system in a while. I'll have to see if it's even viable option for my lathe, which is an old Jet 1236. I do like my handwheel. 🙂 😎 I've used a jam chuck in the past, and have had better luck with these finicky Cole jaws.

The pitch of the Cole jaws button radii "should" be less than the travel of the chuck jaws, with some extra travel to compress the buttons. I don't understand why yours should be incompatible.

Have you "recently" been turning bowls with substantially vertical walls? But not previously when you've used the Cole jaws successfully? If so, I don't think the Longworth would help.

Before I made my Longworths, I used a method proposed by Betty Scarpino in Fine Woodworking:
Mount a plywood disk on a faceplate;
turn a groove to mate with the bowl rim;
place the bowl on the disk, with at least four strips of tape wrapped around the walls to the back of the disk.

This works with any wall profile, and when you've used up all the space for new grooves, make a new disk. I still use the tape on the Longworth for insurance, especially for vertical walls.

Like Al says, shave the tenon down gently.

Joe

Hi Joe,

I've turned with both vertical walls and a nice gentle slope and have gripped both on the cole jaw set. It seems that I've hit on just the right bowl diameter where the bumpers/grippers are either too close or too far, regardless of the jaw position of the cuck. One bowl had a diameter that was close enough, so I "thickened" the bowl with tape. With the diameter increased, I was able to grip the bowl sufficiently and was able to successfully (and slowly) remove the tenon. Though I was wishing that my lathe could go slower. Another bowl that had a nice shape to it defied the bumpers/grippers. It was a thin rimmed bowl, and the only way I could get any grip on it was to remove two of the Cole jaws, so there were only four bumpers/grippers holding it. That bowl popped out at the last due to insufficient grip and bounced on the floor, cracking. That bowl now serves as a reminder that things happen.

I'll have to see if I can find that article you mentioned. It sounds a lot like a rim gripping jam chuck.

I have run into the problem too. I cut some air hose 3/8" inside diameter the length of the pins. Then just push these over the pins which makes them larger. Seems to take up that no go space the normal jaws won't fit.

Thanks for the idea! I suspect that moving the pins down a position on the face of the cole jaws (towards center) and doing something like this ought to be viable.

Are the rubber stops old and hard? I replaced mine a few years ago when they didn't seem to grip as well. Regardless, I've gotten in the habit of using the tailstock when finishing off the bottom of bowls with the cole jaws, and then running without the tailstock only for the last 1/2" nib and sanding. I adopted that habit after bouncing a couple of bowls on the floor, no mishaps since.

Good luck,
Ron

No, I had to replace them a year ago or so. The old ones had turned rock hard. It seems that my diameter luck started about this time, too. Hmm... Agree with tailstock. Also watch out for the pins as they look like they're always hungry for fresh knuckle meat.

I used to have that problem with my Nova cole jaws. Like Nick, I pressed tubing of one kind or another over buttons to enlarge them when needed. I also remember making a set of larger buttons to substitute when needed. I gave the jaws away when I upgraded to my present lathe with an incompatible spindle size.

Thanks for the idea!

 

[Gerald Lawrence]

Agree on the cole jaws.....just not worth it. I have a Penn State with extended jaws and bowls will pop out ,but the toolrest will stop the bowl. Also the same with a longworth.
So the overall solution is bringup the tailstock. Like Al said small cuts . The last stubb can be carved or sanded.
If you really want to do it a safe way (no floor meets bowl) use a power carver and then sand. Then there are other alternatives like a doughnut chuck.

 

[Bill Boehme]

... With Betty's method, are we talking about a jam chuck? Just wondering if there is a link to her article......

It's a "herd" secret and if I tell you, that will cause you to become one of "us" ... you know, information sharing and all of that sort of stuff. But, I can't help myself, so here goes. It's actually very simple : just fasten a large flat disk of wood to a faceplate. Then using calipers, transfer the diameter of the rim of the bowl to the disk. Next, use a parting tool or other tool of choice to cut a mortise (AKA, rabbet or perhaps rebate if you are one of Her Majesty's subjects). The rabbet should match the thickness of the bowl's rim and be an eighth inch deep or so -- deep enough that the bowl won't easily jump off the lathe. Put the bowl in position and bring up the tailstock. Proceed to finish the bottom. You can use a spindle gouge to work the bottom down to a very tiny nub. Of course, the lathe speed needs to be dialed down to a minimum. And, tape is for sissies. Herd bulls don't need no stinkin' tape ... nor dust protection, etc.

Oh, ... By the way, welcome to the herd. Now that you have been assimilated into the collective, you will have to surrender any vestige of creative tendencies or urges that you may have experienced. 😛

Just kidding, of course. All herd creatures are allowed to not only retain all mental faculties, but grow them them through sharing of experiences.

 

[Richard Findley]

It's actually very simple : just fasten a large flat disk of wood to a faceplate. Then using calipers, transfer the diameter of the rim of the bowl to the disk. Next, use a parting tool or other tool of choice to cut a mortise (AKA, rabbet or perhaps rebate if you are one of Her Majesty's subjects). The rabbet should match the thickness of the bowl's rim and be an eighth inch deep or so -- deep enough that the bowl won't easily jump off the lathe. Put the bowl in position and bring up the tailstock. Proceed to finish the bottom. You can use a spindle gouge to work the bottom down to a very tiny nub. Of course, the lathe speed needs to be dialed down to a minimum. And, tape is for sissies. Herd bulls don't need no stinkin' tape ... nor dust protection, etc.

So I've been reading this thread with interest. The thought I keep coming back to is 'all this seems rather over complicated'. If Cole jaws won't hold a bowl without tailstock support, then why bother? Likewise with a jam chuck. I do use a piece of MDF on a faceplate and bring up my tailstock, but see no reason to cut a rebate in the board (no rabbits in my workshop). This method is so quick, simple and safe that I don't really see why anyone would go to all the effort and expense of more complicated systems.

My set up:



That said, a vacuum system would be handy at times but my headstock is solid and I have a strange old English thread on my lathe so options are limited.

Cheers

Richard

 

[hockenbery]

Richard
that is one of the jam chuck methods.
Works great!

Al

 

[Bill Boehme]

Richard, our rabbits are too lazy to serve as workshop helpers -- their main function in life being food for other creatures. And, on this side of the pond, a rebate is nothing more than a sales gimmick. This leaves us no choice but to use a rabbet or, more correctly, a mortise since a rabbet is a notch cut along the edge of a board.

As Al says, this flat board with a circular groove is just a variation of a jam chuck (or "jamb" as they say in Florida). Dang this English language with its homonyms and other word traps.

I don't own Cole jaws, so I can't comment on how well they function, but in theory they should hold something without tailstock pressure as long as not too much force is applied with a turning tool. The tailstock provides the useful function of saving the user the agony of knowing how much is "too much".

 

[Richard Findley]

Richard, our rabbits are too lazy to serve as workshop helpers -- their main function in life being food for other creatures. And, on this side of the pond, a rebate is nothing more than a sales gimmick. This leaves us no choice but to use a rabbet or, more correctly, a mortise since a rabbet is a notch cut along the edge of a board.

As Al says, this flat board with a circular groove is just a variation of a jam chuck (or "jamb" as they say in Florida). Dang this English language with its homonyms and other word traps.

The differences in our use of the same language always makes me smile. I remember having fun with it when demonstrating in Phoenix last year, in particular my use of the word spanner drew some very blank looks!

To us a jamb is part of a door frame... we also spread jam on toast.... 😉

Richard

Ps, apologies for derailing the thread!

 

[John Solie]

Richard, no apologies needed. If anything all this herd talk and language particularities made me smile. 🙂

Thanks for the pic on the jam/jamb chuck. You discussion on the variations of jam, made me think of that scene from the movie Spaceballs where the radar gets jammed--with raspberry. 😱 😎

I'm a knuckle-dragging neanderthal (sort of) from way back, so the Queen's English ain't no problemo (how's that for butchery?). Rabbits got chased away years ago by the (late) shop hound. Rebates are things my wife fills out and puts in the mail in hopes that a manufacturer sends her back a few pence in the form of a check/cheque. Spanners are not a problem, but that could be the fault of Top Gear.

You guys have given me good food for thought. I really like Al's idea of a vacuum chuck as that seems to eliminate fit issues, plus could help hold things in place should ham-fistedness come into play whilst removing tenons. I might have found something that will work on my JWL-1236. If that pans out, the next step would be running it past the Finance Committee. I think a damaged bowl might help get the Safety Committee to override the Finance Committee. Hmm.... 😉

 

[James Seyfried]

I really like Al's idea of a vacuum chuck as that seems to eliminate fit issues, plus could help hold things in place should ham-fistedness come into play whilst removing tenons. I might have found something that will work on my JWL-1236. If that pans out, the next step would be running it past the Finance Committee. I think a damaged bowl might help get the Safety Committee to override the Finance Committee. Hmm.... 😉

I had a vacuum setup for a year or so but was in too big of a hurry to set it up, so I jam chucked or used a Longworth chuck. Then I attended a demo using one and saw how useful it was. I got it set up and am impressed with how much easier or convent it is than other methods. It works real well, but, it is still possible to be ham-fisted and toss a bowl. Now, I leave the tailstock until it gets in the way. 😱

 

[Andy Chen]

"Donut" Chuck

John,

Vacuum chucking is great when it works and I know many people swear by it. However, I personally had an instance where the vacuum pump overheated and shut off. (I bought a rebuilt system and as I found out after it failed, the wiring in the motor was totally screwed up, neither for 120 V nor 240 V.) You know when you use the vacuum chucking, the final step. All that work, s---!!! Also, if you think about it, the ball bearings in the vacuum chuck can potentially seize up, especially with all the wood dust in a woodturning environment. (I am a firm believer of the many Murphy's laws.) I hate to contemplate the consequences when that happens.

My most trusted reverse-chucking method is the donut chuck. I don't know who invented it but Kevin Neeley has a great set of instructions on how to construct one and how to use it on his website (http://www.turnedwood.com/tools&jigs.html#Reverse) among other fantastic tips Kevin shares generously for free. It can work with any brand chuck and Cole jaws. I have recently modified it a little by eliminating the board behind the Cole jaw and use the Cole jaw itself for securing the front board, for vessels with a diameter smaller than the Cole jaw. The system works for any vessel, open or hollow, as long as it is not cylindrical. It can work with vessels of practically any height by using couplings to adjust the length of the all-thread rods. Of course you want to observe common-sense precautions like the safe speed and staying clear of the nuts and bolts.

Good luck and have fun.

 

[John Solie]

Andy, thank you very much for that link. That site has a wealth of information.

 

[Bill Boehme]

Where did the vacuum go?

Vacuum pumps can indeed shut off. They have thermal overload circuit breakers and my pump did shut off once when it got too hot. Fortunately, I didn't have anything mounted at the time ... I was running the pump through the prescribed cool-down procedure after finishing a bowl. The cool-down procedure involves a certain amount of time running blocked port and then open port. I had a senior moment (or hour) and lost track of time while it was running blocked port and the pump got hotter than the radiant heater in my shop before it shut down. These Gast rotary vane pumps run hot anyway, but that was nothing compared to how hot it got and I was afraid that it was toast. Fortunately, it was cool enough to handle in a couple hours and ran just fine. The moral of that story is to not make reverse chucking a marathon event. Also, keep the tailstock in place until removing the little nub at the bottom.

Air can leak through wood. Until you get a vacuum chuck, you won't fully appreciate how much. This past week I've been turning a bunch of small ambrosia maple bowls to donate to our local Empty Bowls project. I had a batch of them ready to vacuum chuck and when I had the first one set up and ready to go, I noticed that the vacuum gauge was barely registering a reading. I have had experience with air bleeding through wood before, but nothing like that. I remembered reading on this forum where someone (I believe it was John Lucas) used tape on the outside of the bowl to reduce air leakage so I gave it a try. With each strip of painters masking tape that I applied, I could see the vacuum gauge reading increase and after taping most of the end grain, I was able to safely turn the tenon off and create a foot for the bowl. Another thing about ambrosia maple is the tiny borer holes -- they are only about 1/32" diameter, but that is sufficient to significantly reduce vacuum especially if your system is a diaphragm or piston system.

 

[John Solie]

Hi Bill, thanks for that info. I had been reading about vacuum loss on woods, and was wondering about methods to stem the tide, so to speak. I hadn't gotten around to tape yet, and was puzzling about plastic wrap.

Not to drift too far off my own thread, I can see the benefit of using a dedicated vacuum pump over a venturi-based vacuum generator. Aside from other uses (like stabilization and not being able to draw as deep a vacuum), is there a reason to totally eschew a venturi vacuum generator until the need arises for a better vacuum?

Thanks,

 

[Bill Boehme]

..... Aside from other uses (like stabilization and not being able to draw as deep a vacuum), is there a reason to totally eschew a venturi vacuum generator until the need arises for a better vacuum?

Thanks,

Besides the one thing that you mentioned, venturi systems don't like leaks. They are not so great when you need both strong vacuum and ability to handle leaks -- something has to give (literally) and it usually that vacuum level drops really fast with leakage. The other thing to consider is your compressor. If you have an industrial Ingersol-Rand then no worry. If you have a Sears dry lube flapper valve type, maybe time to be concerned. Most consumer grade compressors are designed for intermittent duty. A venturi will require frequent cycling on average compressors and constant running on low end compressors. Besides that, it is a real rip what they charge for a box that is not much more than some plumbing and a vacuum gauge (the link is to a Wikipedia article on the Venturi effect for anybody who cares to read it). It wouldn't cost much more to get a Harbor Freight vacuum pump. If you have a paint spray rig then you probably own a Venturi and didn't know it (doesn't apply to gravity feed or airless).