How to chuck a tenon with these jaws

[LanceC]

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.

474760

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/uploads/2017/12/Chuck_Catalog_2017-2018-web.pdf
https://vicmarc.com/images/Catalogue/Catalogue_2020.pdf

[NCArcher]

I think they are expanding only Lance.

[Mobyturns]

Out of curiosity what brand are they?

[warrick]

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 (https://www.machineryhouse.com.au/r8178)

Rick

[LanceC]

Out of curiosity what brand are they?

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.

[Mobyturns]

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.

[warrick]

Here you go

Axminster SK80 Dovetail Jaws Type C - Jaws for Axminster 100mm Chucks - Chuck Jaws - Woodturning Chucks - Lathe Accessories - Machinery Accessories - Accessories | Axminster Tools & Machinery (https://www.axminstertools.com/80mm-c-jaws-410163)
Woodturning Chuck Jaws - The Knowledge Blog (https://knowledge.axminstertools.com/woodturning-chuck-jaws/)

Rick

[Mobyturns]

Here you go

Axminster SK80 Dovetail Jaws Type C - Jaws for Axminster 100mm Chucks - Chuck Jaws - Woodturning Chucks - Lathe Accessories - Machinery Accessories - Accessories | Axminster Tools & Machinery (https://www.axminstertools.com/80mm-c-jaws-410163)
Woodturning Chuck Jaws - The Knowledge Blog (https://knowledge.axminstertools.com/woodturning-chuck-jaws/)

Rick

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.

[LanceC]

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:

474861
Perhaps I'll send them an email and ask.

[Skew ChiDAMN!!]

Personally I'd have no problem with using those jaws on a bowl in tenon mode. :shrug:

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... ;)

[Mobyturns]

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... ;)

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.

[Jim Carroll]

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.

[Skew ChiDAMN!!]

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.

Agreed.

But this is all part of 'Jam chucks 101.' :D

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. :)

[powderpost]

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.

Jim

[Mobyturns]

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.

[tonzeyd]

Probably bit late, but i'm a new turner and have only been using the above style chuck in tenon mode. As others have pointed out its important to match the taper of the dovetail jaws.

The other things i've noticed when using mine is to re tighten the jaws after you've roughed the bowl out especially if your blank was square or particularly off kilter. The vibrations when truing up the blanks seems to loosen the chuck enough that by the time you're almost done the slightest bump sends your nicely turned bowl flying. Tightening it up after rounding the blank has eliminated this from happening.

Plus I've found that you need to take much more off the blank that you realise the wood just below the bark is still soft and spongy. Turning a tenon using this layer is just playing with fire, a couple of extra mm off and its plenty strong even with a tenon thats only a few mm thick.

You can also use those jaws to clamp down on square blanks that fit inside the jaws, it'll squash the corners abit so you'll need to plan your blank accordingly and accept that you'll be losing about 5-10mm of your blank when you part off at the chuck end.

To answer your questions:
1) Yes, just try and match the taper of the jaws as close as possible
2) no difference, spigots are used for small blanks, while the pictured is used for bowls or larger blanks. Both essentially hold wood.

[LanceC]

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.

Are you talking about a jam chuck? Also, can you expand on the glued bowl blank?

I have spent a fair portion of this evening researching online trying to understand what has been discussed.

So thank-you all for your input, this has been a steep, but fascinating learning curve.

[powderpost]

Are you talking about a jam chuck? Also, can you expand on the glued bowl blank?

Lance, Both jam chucks and glue chucks start by screwing a waste block, at least 19mm thick, to a face plate. For a jam chuck a recess is cut into the waste block. That recess needs to be a "jam" fit for a spigot or bowl to fit and have enough friction to hold the bowl firmly enough without glue, so that the bowl can be worked on. This method is often used to finish off the bottom of the bowl.

A glue chuck can be used after the back of the bowl has been turned and the foot size determined as before. The waste block fitted to the face plate is now turned to match the foot on the bottom of the bowl so that the they are exactly the same shape and size, so that the bowl can be centred. Imagine two saucers glued back to back. The idea is now to turn out the inside of the bowl.

As I mentioned in the previous post, this method allows you to determine the size and shape of the foot of the bowl and not be dictated to by a chuck. The down side is that you have to wait for glue to dry properly, or the outcome can be more that unsatisfactory. Don't ask!!! :C

Hope this is clear enough to get the picture.


Jim

[LanceC]

Excellent description Jim. Thanks for taking the time to explain it.

[Mobyturns]

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, these are not quite the same as the standard Nova style jaws which have a Triangular lip inside the jaws. The Axminster type C have a square shouldered lip. I use the same technique as you mention for the Nova style jaws. I've never liked the cylindrical inside profile and the high reliance on the "beak."

One thing that I commend though is the very well put together Teknatool jaw manual, probably the best and most descriptive in the industry. Well worth the read & turners should pay close attention to Teknatool's recommended max blank size and max recommended speeds for each jaw design.


https://www.teknatool.com/wp-content/uploads/2018/04/Accessory-Jaw-Manual_June08.pdf

[Dalboy]

Not sure of the brand that you have normally the Axminster sets have a 6 digit number on them. With this design internal jaws, the tenon needed to hold a piece is a straight tenon compared to the dovetailed used with many other chuck jaw designs. I have a number of their jaws, as I am in England they are very common here.

The Axminster C jaws have a tenon size around the 57mm (2.24") mark The same principle applies to the rest of the tenon as you would use in a dovetailed set