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3rd June 2020, 12:31 PM #1
How to chuck a tenon with these jaws
Here's what I'm sure is a rudimentary question for those who know...
I have the jaws as shown below. I understand that when expending they need a dovetailed recess, I'm a little perplexed at the design for holding a tenon.
20200603_103611.jpg
I've poured over online jaw profiles but have been unable to find anything resembling the inside profile.
1. Am I correct in assuming that I would create a normal tenon, then part an extra little section for the lip?
2. What is the purpose of this profile over a regular spigot jaw?
Oh, and congratulations to Nova and Vicmarc. They were the only source I could find which clearly showed a range of jaw profiles in one place with cutaway illustrations.
https://www.teknatool.com/wp-content...7-2018-web.pdf
https://vicmarc.com/images/Catalogue/Catalogue_2020.pdf
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3rd June 2020, 02:44 PM #2
I think they are expanding only Lance.
Those were the droids I was looking for.
https://autoblastgates.com.au
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3rd June 2020, 07:41 PM #3
Out of curiosity what brand are they?
Mobyturns
In An Instant Your Life CanChange Forever
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3rd June 2020, 08:18 PM #4
They look similar to these, I think you do a flat spigot and it bites in as you do it up
R8178 - 62321 Standard Jaws - 35mm | Hare & Forbes Machineryhouse
Rick
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3rd June 2020, 09:38 PM #5
No idea, this chuck and jaws came with my lathe. The chuck has no identifier on it that I saw when it was stripped for cleaning, and I was unable to remove the jaws due to the screws being jammed.
When I got it the whole outside of the jaws look to have been coated in varnish, and I guess some must have sealed the screws. Soaking in vinegar while deducting made no difference. The “inside” screws came out with little effort.
Rick, that profile (hawk beak) is slightly different to mine as it tapers to a point allowing it to dig in, while mine has a flat top.
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3rd June 2020, 09:48 PM #6
Lance I've never been a fan of the "hawks beak" jaw profile. My belief is that it encourages a shearing force in the grain right where you do not want it - at the smallest diameter of a tenon and in the very corner. So Nova / Teknatool jaws are not high on my preferred list.
I'm wondering if that jaw set have been modified for a specific purpose. It will be interesting to find out more bout them.Mobyturns
In An Instant Your Life CanChange Forever
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4th June 2020, 12:06 AM #7
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4th June 2020, 08:54 AM #8
Thank you for the links. Looking at the OP photo it seemed that there was an unusual amount of wear on the inside faces and the cross sectional surface with the coating gone. I admit to not having used Axminster chucks or seen the type C jaw profile before and being a "Queenslander" I support Colwin Way's buy local philosophy with Vicmarc and Vermec products.
Mobyturns
In An Instant Your Life CanChange Forever
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4th June 2020, 08:57 AM #9
Good find Rick!
My assumption then is ...
For bowls, mortise only. The internal jaws should only be used for spindle work where it expectantly can't sheer the long grain it holds.
Edit:
Gah! And then I looked at the different pictures at the link posted by Rick and saw this:
410163_inset1_xl.jpg
Perhaps I'll send them an email and ask.
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4th June 2020, 12:37 PM #10
Personally I'd have no problem with using those jaws on a bowl in tenon mode.
I would use the tip of a narrow parting tool to make a clearance cut when making the tenon, mainly because I often want 'minimal cleanup' of the foot and crushed fibres don't help with that. But also to ensure that the inner walls are making contact for their whole length, should that lip not 'bite in' deep enough.
As for shearing... if I'm concerned about bowl size, weak grain and/or leverage possibly causing the tenon to shear there, then I wouldn't be using that size jaw at all. That's when I'd go up a diameter size or three, until I'm using the right jaws for the job...
- Andy Mc
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4th June 2020, 01:03 PM #11
Good advice! Those of us with a bit of experience under our belts would do the same, however for many turners with limited means they have a "one chuck (& jaw set) fits all tasks" approach. In the club's I have visited I have seen so many turners using a tenon way to small for the loads imposed whilst turning a bowl / platter of that size. A reasonable catch will severely stress the tenon or shear it, all because that is the only jaw set they have.
Mobyturns
In An Instant Your Life CanChange Forever
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4th June 2020, 01:12 PM #12
These jaws are the Nova shape jaws, best way is to close the jaws , measure the internal diameter and add 6mm,
This will then give you the diameter of the straight tenon you need to make. The tenon has to be shorter than the depth of the jaw so the bowl will sit on top of the jaws.
Once you have created the tenon, lay your skew chisel on its side on your toolrest and make a small indent at the base of the bowl for the notch to locate in, If you dont do this there is a good chance the bowl can slide out of the jaws.Jim Carroll
One Good Turn Deserves Another. CWS, Vicmarc, Robert Sorby, Woodcut, Tormek, Woodfast
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4th June 2020, 01:20 PM #13
Agreed.
But this is all part of 'Jam chucks 101.'
Mount a scrap blank to a faceplate and turn a suitably sized mortise for mounting the bowl.
If someone can't bear the thought of not using a chuck, spindle turn the scrap with a tenon sized for the jaws and mortise sized for the blank. This has more leeway for off-centre errors to creep in though.
For many years I had quite the array of different sized and styled jam-chucks hanging on my wall... while I scrimped and saved for my first scroll chuck. Some of them still see use.
- Andy Mc
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4th June 2020, 08:29 PM #14
Jim's advice (No. 12) is spot on. I have and use those jaws constantly. I made a thin "parting tool" from a heavy machine hacksaw blade. It will cut a groove in a spigot that the step inside the jaws, fits neatly. Not sure that "shear" forces are a problem, there is most likely other issues at work there. They were used on red cedar with out any issues. I have also found that rechucking is more accurate than the "dovetail" jaws.
As has already been mentioned, a waste piece screwed to a face plate and turned to suit the foot of your bowl, and glued bowl blank is far better imho. Also, the chuck should not determine the size of the foot of your bowl, again, imho.
JimSometimes in the daily challenges that life gives us, we miss what is really important...
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4th June 2020, 09:08 PM #15
The shear forces come into play because most turners do not make the small step cut and simply use brute force. Most struggle to even match the taper of dovetail jaws.
Mobyturns
In An Instant Your Life CanChange Forever
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