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Thread: chuck use question
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13th January 2021, 04:07 PM #1New Member
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chuck use question
I have a SuperNova chuck and recently purchased a set of Nova 50mm jaws. I made a recessed dovetail on a bowl I was roughing out and realized that in order to get the body of the jaws to butt up against the bottom of the bowl, my recess would have to be almost a 1/2" deep. Am i missing something here. Can I make the recess a little more shallow and just rely on the front edge of the jaws butting up against the bottom of the recess for stability? Would really appreciate any help. Thanks.
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13th January 2021, 05:39 PM #2Senior Member
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G'day Dave, and welcome to the forum.
It sounds like you have the bottom of the bowl resting up against the base of the jaws (the section where the retaining screws are located). The maximum recess should be 6mm (or 1/4" in your language) and the bottom of the bowl should sit firmly against the top of the dovetailed section of the jaws. The instruction sheet for the Super Nova would be much clearer if there was a diagram next to the note which says "Warning: Make sure the jaws are seated properly in the recess and that the bowl is not incorrectly riding on the flat shoulder section of the jaws behind the dovetail". Hope this helps.
Cheers, Gary H
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13th January 2021, 11:26 PM #3SENIOR MEMBER
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Welcome from Arizona, Dave. This is a pretty good site to belong to. You will acquire a lot of knowledge from these fine folks.
As far as your question, you do not need to have a recess or tenon over 1/4" deep or long. If the jaws are tightened properly and your wood is solid, it will take the punishment you give it. I use tenons exclusively, and I don't think I've ever made one longer than 3/16".
What part of Montana are you from? ................ Jerry (in Tucson)USA
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14th January 2021, 06:15 PM #4GOLD MEMBER
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Welcome to the forum Dave.
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16th January 2021, 11:10 AM #5
Dittto to what Gary has said.
If you make your recess too deep the dovetail jaws will not reach the bottom of your recess, where they need to be for two reasons; to give you the best grip and, equally important, to reduce the chance of the foot splitting.
On green wood I rough turn with a tenon on the base and a recess on the inside bottom of the bowl.
Once seasoned, I remount the blank using the inside recess to re-turn the outside, adding a recess to the foot. Once the sanding and polish is added the outside of the bowl is done. Only the very largest bowls and platters would get a recess as deep as 1/4" and most only get a recess of about 1/8" or less deep. That is usually sufficient to hold a seasoned bowl for re-turning the inside.
When the inside is finished, the bowl is done.
And, welcome to the forum Dave.Stay sharp and stay safe!
Neil
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16th January 2021, 08:17 PM #6
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5th October 2022, 11:54 AM #7New Members
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Nova Powergrip jaws
Hey Guys,
Handy info for mounting bowls using a recess with thanks and now I hope for similar clear answers to my query of mounting bowls onto the Nova Powergrip jaws (code PJSN) attached to a SuperNova2 ProTek chuck.
For mounting onto a tenon/spigot (called contracting mode) these jaws have a dovetail section nominally 12.5mm deep and then below that is a series of annular rings resembling a male thread nominally 12mm deep, so my query is what is the use of this "ringed section" if the dovetail is adequate to firmly mount a bowl to? I also note that the nominal 50mm ProTek jaws (code JS50N) but stamped with 6087 numbering also have this "ringed section" when used in contraction mode onto a tenon/spigot.
Have searched for Nova info on line but with limited success so any help is much appreciated.
Cheers, Keith
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6th October 2022, 12:09 PM #8
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7th October 2022, 03:38 PM #9New Members
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Thanks Neil,
I agree with your comment as a Nova Accessory Jaws table states the PJSN Powergrip jaws in contraction mode are suitable for 200mm dia x 310mm long workpiece size, however as a test I attached a 250mm dia x 100mm deep (approx) bowl blank with a spigot turned to accept the Powergrip jaws (at near a circle for maximum grip) and proceeded to core the blank with a Woodcut Bowlsaver which went ok until the cutter started into the end grain of the blank and which resulted in numerous "catches" ( with a very light feed rate) which dislodged the jaws from the spigot to the extent that I gave up on coring and settled for hollowing out the blank.
So, the issue is ( I think) one of having the dovetail sized to accept the jaws for a near circle maximum grip size and then sizing the "ringed section" diameter so that when the jaws are tightened down BOTH the dovetail and the "ringed section" clamp onto the spigot with near equal force resulting in an extended length gripping of the spigot BUT this proves very difficult to achieve as the amount of "squish" of wood in the "ringed section" is subject to different types of wood strength, whether green or dry etc
Hope my ramblings make sense of the problem and again any comments will be appreciated.
Cheers, Keith
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7th October 2022, 08:08 PM #10
If I need the depth of grip provided by the Powergrip jaws I don't go down to 'near to circle' with the tenon/spigot size. I want those jaws to bite into the wood and the two outer edges on each jaw will do that when the they are griping with a diameter larger than 'near to circle'. The expectation is that you will be turning off the tenon at some stage, so any indents in the tenon from the jaws are temporary.
The 'near to circle' grip becomes important when you want to avoid indents on tenons or recesses that will remain on the finished piece.
In my experience, you shouldn't need the Powergrip jaws to hold a blank sufficiently secure for coring. Perhaps if the blanks are very deep, like 200mm or more, but I have never used mine for coring and I have cored some larger blanks...
I find that standard dovetail jaws are sufficient for any coring that I done. But, the dovetail should seat on both the face and shoulder of the jaws to provide max grip.
Your coring technique may be a factor if blanks are coming off the chuck and, if so, I expect that will improve with practice...Stay sharp and stay safe!
Neil
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9th October 2022, 03:47 PM #11GOLD MEMBER
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Dave
It is also important if you are using your chuck in contraction mode that the face of the jaws is hard up against the shoulder of the tennon .
Ted
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9th October 2022, 05:42 PM #12GOLD MEMBER
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Keith, while I don't have Nova chucks, I do have a Woodcut Bowl Saver and have used it a reasonable amount of times.
While having a near perfect circle for holding the blank to be cored is great if the wood is fairly dry, it isn't too great if the wood is wet (or green). My experience of my Bowl Saver is similar to yours when I finally cored some wet blanks for the first time.
What I assumed happened is that the wet wood compressed slightly from the coring and as I got to the business end, it pretty much did exactly as you mentioned. With my till then experience of the bowl saver being with reasonably dried timber, this hadn't happened before.
With wet wood I now make the tenon a bit oversize and as I core through the blank, I check and adjust as necessary during the coring operation. Within reason since adopting that practice, I have hardly had a blank depart from the lathe before it was meant to depart.
I also use a credit card diamond sharpener, with a pass or two after each coring, this also made a difference.
Another possible reason for things getting slightly iffy with my Woodcut Bowl Saver, is if for whatever reason the cutting face is not dead centre of the turning axis.
Mick.
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