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Cole-jaw extenders #1: Fixturing an out-of-round bowl

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Blog entry by BuckeyeDennis posted 04-06-2021 08:42 PM 442 reads 0 times favorited 3 comments Add to Favorites Watch
no previous part Part 1 of Cole-jaw extenders series no next part

I’ve been an avid woodworking hobbyist for quite some time, but I’m still a novice when it comes to turning. On my third bowl I ran into a bit of a challenge, and came up with a workholding solution that I haven’t seen elsewhere. But I don’t know what I don’t know, so I’d appreciate any opinions and suggestions from you experienced woodturners.

This particular woodworking adventure started when the rough-turned applewood bowl in the pic below dried a full ½” out of round. The tenon that I had chucked onto for rough turning also turned into an oval, so I wasn’t going to get a secure grip on it with my standard chuck jaws. The only way I could think of to true up the tenon was to try turning the bowl between some sort of jam chuck and a live center. Which sounded like a fussy setup to me, and I wasn’t looking forward to it.

As my shop is rather small, I use my Shopsmith Mark V as a lathe, with a speed reducer to drop the speed range to about 100 – 770 RPM when turning bowls. My chuck is a Nova G3, which is Shopsmith’s standard chuck offering. Mark V’s have a 15-1/2” swing over the way tubes, so you can fit a good-sized bowl on them, but you have to take it slow and easy due to the light weight of the machine.

So on to Plan B. I added a set of Nova JSCOLE Cole jaws for my Nova G3 chuck to my wish list. Per Nova, these jaws are for lathes with a minimum 12” swing. I would have preferred larger jaws, but those are the biggest ones that Nova makes to fit a G3 chuck. And it sounded as if they’d be big enough for this 10-1/2” bowl.

My family bought the Cole jaws for me as a Christmas present in 2019. What didn’t know until I opened them was that these jaws have a max outside gripping diameter of only 9.29”, when mounted on a G3 chuck. I eventually found that info buried deep in the product manual, but it isn’t mentioned on the product pages at either Technatool or Amazon. So my new jaws weren’t big enough for the applewood bowl.

The other problem I discovered is that Cole jaws are designed to grip round things. Given that the threaded “buffer” mounting holes in the Cole jaws are spaced about 3/8” apart radially, they can’t be adjusted to properly fit an out-of-round bowl (unless perhaps you remove half of the buffers, and then orient the bowl just so). This is pretty obvious from the stock photo above, showing the factory buffers. So I stuck my new Cole jaws in a drawer to await a smaller bowl, and there they languished for the next year or so.

When I finally I pulled the Cole jaws back out of the drawer, I noticed a mention in the instruction manual of making your own wooden extenders (at your own risk, of course). And voila! I realized that my new WoodAnchor™ fixturing system could solve the problem quite nicely.

So I made up a set of simple jaw extender segments from ¾” Baltic birch plywood. The segments mount to the Cole jaws, and have fixturing slots milled right down their centerlines. They not only increase the bowl-size capacity, but they can be adjusted as necessary to securely grip out-of-round bowls. This makes it dead simple to re-turn a warped bowl. They’re also a lot less expensive than commercial jaws with a similar bowl-size capacity, and a whale of a lot less expensive than a whole new chuck that can accept those larger jaws.

(Full disclosure: As the founder of ToolQuest, I have a direct financial interest in the WoodAnchor system. But I’ve always enjoyed participating in woodworking forums as a hobbyist, and I’ll endeavor to keep my posts on LJ both interesting and non-commercial.)

And here’s that rough turned applewood bowl again, chucked up in the jaw extenders.

I did purchase the NOVA 6030 Cole Jaw Buffer Accessory kit, which comes with eight of the multisided buffers shown in the photos. With slightly canted sides that capture the rim of the bowl, these grip much better than the standard cylindrical buffers that are included with the jaws. I mounted them with WoodAnchor sliding nuts, which are each rated for 500 lb. of clamping force. So you can lock them down hard, and then crank down tightly with the chuck. That bowl is going nowhere.

I’ll be very interested to hear what you experienced turners out there think of this fixture. It solved my immediate problem, and now I’m wondering what other uses it might have. What about eccentric turning? I’d need a much heavier lathe to turn anything very far out of balance, but what do you guys with big lathes think of the idea?

-- Dennis 'We are all faced with a series of great opportunities, brilliantly disguised as impossible situations.' Charles Swindoll



3 comments so far

View pottz's profile (online now)

pottz

16141 posts in 2036 days


#1 posted 04-06-2021 09:50 PM

gotta follow this i have that same cole jaw set with the optional buffers myself,curious as to the opinions you get.

-- working with my hands is a joy,it gives me a sense of fulfillment,somthing so many seek and so few find.-SAM MALOOF.

View Redoak49's profile

Redoak49

5177 posts in 3041 days


#2 posted 04-07-2021 01:21 AM

Very nice and using a Shopsmith. I may have to try it hat on mine.

View BuckeyeDennis's profile

BuckeyeDennis

103 posts in 750 days


#3 posted 04-07-2021 02:13 AM

Thanks, guys. It dawned on me after I posted this first blog installment that I should be able try turning some decorative offset rings on the bottom of that very bowl when I finish-turn it. I’ll report on that in a future installment.

-- Dennis 'We are all faced with a series of great opportunities, brilliantly disguised as impossible situations.' Charles Swindoll

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