How wide can you open YOUR jaws?

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BuckeyeDennis
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How wide can you open YOUR jaws?

Post by BuckeyeDennis »

Your lathe-chuck jaws, that is. :D

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Thanks to the new WoodAnchor fixturing system, mine can now grip the outside of a 13” diameter bowl!

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And those jaw extensions can also grip severely out-of-round bowls, no problem.

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Note that I'm using a speed reducer with this setup. Nova specifies a max RPM of 600 RPM for the stock cole jaws, so either a speed reducer or a PowerPro headstock is required for use on a Shopsmith.

The bowl in the pics had been sitting around rough-turned for over a year. When you turn bowls from green wood, they warp as they dry, shrinking across the grain. This particular applewood bowl dried a full ½” out of round. The round tenon had 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.

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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. Mark V’s have a 15-1/2” swing over the way tubes, so 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 I 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 that applewood bowl.

Jaws with standard buffers.jpg
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The other problem I discovered is that Cole jaws are designed only 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 included standard buffers. So my new Cole jaws just got stuck 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.

These simple Cole-jaw extenders increase the bowl-size capacity, and they can be adjusted as necessary to securely grip out-of-round bowls. This makes it a piece of cake to re-turn a warped bowl. They’re also a lot less expensive than commercial jaws with a similar bowl-size capacity. I did purchase the NOVA 6030 Cole Jaw Buffer Accessory kit, which comes with eight of the multisided buffers shown in the photos. These grip much better than the standard cylindrical buffers that are included with the jaws. The heavy-duty clamping ability of the WoodAnchor™ fixturing slots and sliding nuts ensure that the buffers stay put wherever you lock them down, and that in turn enables you to crank down tightly with the chuck.

As this is only my third bowl, I’ll be very interested to see what the real turners out there think of this solution.
Last edited by BuckeyeDennis on Mon Mar 29, 2021 4:47 pm, edited 4 times in total.
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BuckeyeDennis
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Re: How wide can you open YOUR jaws?

Post by BuckeyeDennis »

These jaw extenders are so easy to make that they hardly need any instructions. I'll let the pictures do most of the talking. All the work was done on my Mark V, Shopsmith bandsaw, and Shopsmith stand-alone overarm pin router (using the undertable router).


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Cut a square piece of plywood to the desired extension-jaw diameter. This will be the diameter when the jaws are closed. Lay out centerlines, diagonals, and the OD.


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With the jaws fully closed, clamp the chuck and cole-jaw assembly to the workpiece, aligned as shown. Transfer the jaw-extender mounting holes to the workpiece using a transfer punch.


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Now finish the layout (which I should have done originally). The corners have to be notched out as shown, to leave clearance for the T-handle of the chuck wrench. The inner circle is the OD of the cole jaws.


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Route WoodAnchor fixturing slots along both centerlines.


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Trim off the waste at the bandsaw, cutting outside of the lines.


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Separate the jaw-extender segments along the diagonal layout lines. This quick-and-dirty WoodAnchor small-parts sled (constructed of scrap plywood) made that operation very easy.


Drilled & sanded HD.JPG
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Sand each jaw-extender segment to the layout lines (I used the Shopsmith disc sander for this), and drill the mounting holes.

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Countersink the holes for the 8 mm flat-head mounting screws, and they're ready to use!


If anyone would like to make a set of these, let me know. I'd be happy to make a dimensioned drawing of the part layout.
Last edited by BuckeyeDennis on Mon Mar 29, 2021 2:25 am, edited 2 times in total.
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JPG
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Re: How wide can you open YOUR jaws?

Post by JPG »

That is some very nice looking plywood!!!!!

I like that 'solution'.
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reible
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Re: How wide can you open YOUR jaws?

Post by reible »

That looks interesting. How are you getting the bowl centered since each grip has its own location?

It looks like you have the same cole jaws I do, The model number for these is 6020 and at least on the box it claims to hold bowls up to 10". Maybe that is with another chuck and not the G3? Anyway I have not tried it on something that large.

Nova also now has a 12" 6040 which should grip larger things. I haven't needed it but it might be another option and it allows you to mount other jaws on it, not sure how that works as I haven't really looked at it.

Ed
{Knight of the Shopsmith} [Hero's don't wear capes, they wear dog tags]
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BuckeyeDennis
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Re: How wide can you open YOUR jaws?

Post by BuckeyeDennis »

Ed, I can't find the 6020 model number on any of my Nova packaging or literature. But when I Google it, it takes me right to the Nova JSCOLE product page. Like yours, presumably, my box says "Holds bowls up to 10"/250mm diameter (customizable for larger sizes if needed)"

Here's the relevant section on workhholding capacity from the Nova Chuck Accessory Jaw Travel Table:

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Ignore the "All measurements in mm" stuff -- this their imperial/inch table. From this, I can only conclude that the 10" bowl capacity is if you chuck a bowl from the inside, in expansion mode.

Per this Nova 6040 product page, those larger 6040 accessory jaws are compatible only with the Nova SuperNova and Titan 2 chucks. Assuming that's correct, these are not an option for all of us that bought the G3 chuck for our Shopsmith's. And now I'm wondering what the claimed 12" capacity really means.

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But one thing is clear about the 6040 jaws ... they can accept the Nova 6039 extension jaws. If, that is, your lathe has a 16" minimum swing capacity. Which rules out our Mark V's.

But even if they did fit our Mark V's, the 6040 jaws cost $100 from Amazon, and the 6039 extension jaws cost another $40 from Amazon. Which makes the WoodAnchor extension jaws look pretty attractive, IMHO. :)

Regarding centering a workpiece in the WoodAnchor extension jaws, for the photos I simply used a small combination square to roughly equalize the distance from the extension-jaw OD to the "buffers", on opposing pairs. But what I plan to do in the future is to mark concentric rings on the jaw extensions. I'll temporarily stick a scale on the tool rest, and use a carpenter's pencil to mark the rings every 1/4", while the jaws are closed and spinning. Afterward, I'll be able to quickly center a bowl, with reasonable accuracy, by simply aligning it with those concentric rings.
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Re: How wide can you open YOUR jaws?

Post by RFGuy »

Yeah that is Baltic Birch plywood. I love that stuff and that is all I buy anymore for sheet goods. It is expensive but well worth it IMHO. I think I have those same jaws but haven't used them yet (only tried dry bowl turning so far). Didn't know they had this limitation for out of round bowls so I appreciate you pointing this out and the WoodAnchor system looks like a great solution. Yeah, I was thinking you could just use a compass to mark concentric rings on the plywood before the plywood is cut into 4 pieces. Using a pen or fine Sharpie should be good enough for most of us but if someone has a CNC or laser engraver even better. Perhaps a business opportunity for you Dennis to produce these and sell these on your website? Just keep in mind that there will always be some error in concentricity between the chuck used to turn the inside of the bowl and the outside of the bowl. I found this out the hard way when I did my first salt/pepper mills. IF you intend to turn thin sidewalls on the bowl you may have to re-turn the outside when it is chucked with the base of the bowl.
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reible
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Re: How wide can you open YOUR jaws?

Post by reible »

Had to get my G3 and cole jaws out to see what I could see. In terms of approximate dimensions the fully open jaws turn out to be 10-11/16" (more then likely metric measurements but who cares for this). The last hole center is about 3/16" in so the circle would be the outside dimension minus 3/8" or about 10-5/16" then with the grips on you can subtract another 3/4" for best guess as 9-9/16" largest grip. This is larger then the table shows but still way less then 10". I don't see any mention of doing inside grips so where the "10"" comes from is anyone's guess.

The jaws have the part number on them:
colej.jpg
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I think the 6040 jaws could physically fit the G3 but the tool to tighten the jaws would hit them. The super nova2 which it will work on has the other style tightening system. It is 8mm hex so you can use any style tool you want to tighten, shown on the right here:
hexit.jpg
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But it could be that they feel the G3 is to light duty???

And the table they provide doesn't say how large this would go so you still might not get the required size..... so your option seems more reasonable both in cost and size.

Fear factor is of course higher with all that open area between spinning along. How fast are you turning it? I now the cole jaws are good to just 600 rpm so standard shopsmith is to fast to use them. Speed reducer or PP required.

Ed
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BuckeyeDennis
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Re: How wide can you open YOUR jaws?

Post by BuckeyeDennis »

Thanks Ed. Now that I know where to look, I can see that same part number on my Cole jaws, even in the "transfer punch" photo above.

I bet you're exactly right about the T-handled chuck wrench being the limiting factor for the Cole jaw OD on a G3 chuck. On mine, the T-bar clears the jaws by a only very small distance when they're fully open.

I also wondered if the physical robustness of the chuck might be the issue for the larger Cole jaws. But after thinking about it, I don't think that's the case. For starters, the cole jaws are positively featherweight in comparison with a large un-hollowed bowl blank. Plus, Nova explicitly suggests that you can make custom wooden jaw extenders for larger bowls.

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I do use the Cole jaws with a speed reducer on my 520, as you can see in the second pic in the first post. Thanks for pointing that out -- I had intended to be explicit about it in my original post, but then I forgot about it. I'm going to edit it in right now, as a safety warning.

As for danger from the discontinuous jaw-extender segments, I don't find them any scarier than a lot of rough bowl blanks. But it probably wouldn't hurt to put more radius on their corners, just in case you brush up against them. The bigger safety issue to me is how the "buffers" stick out past the bowl rim. Anything more than a light kiss with lathe chisel could cause the "mother of all catches"!
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