measuring chuck jaws

[allen thunem]

stupid question here.
how are chuck jaws measured??
from their full closed position i assume???

[Thom Sturgill]

AFAIK there is no standard. Some measure inside others outside. For instance Nova calls this:
75mm.jpg
a 75mm (3") Jaw, but the inside grip is the same as the 50mm (2") jaw set.
JS100N.jpg
This is a (100mm) 4" Jaw set shown expanded to about 5". Details in the 'manual' will give you min/max for both inside and outside.

[John Keeton]

For Nova chucks, I believe the sizing is generally based on the minimum expansion capacity - i.e., the smallest recess a set of 50mm (2") jaws will expand in to is 2". 75mm would be 3", and so on. But, I have no idea on chucks other than Nova.

[Robert Henrickson]

Oneway Stronghold (and other Oneway?) chucks simply are numbered -- e.g., the jaws that come with the Stronghold are #2. The bigger the number, the larger the jaw. You have to check for expansion/compression figures.

[Reed Gray]

Yea, measure depends on whether you are making a tenon or a recess. 2 different measurements.

robo hippy

[Michael Mills]

Can get confusing..
Nova has two basic, the bowl jaws sized by closed exterior, and the spigot jaws sized by minimum gripping interior. The spigot jaws are serrated and deep.
Then they have the Pin Jaws; pin not as in small but as in Pin Chuck. The same interior and exterior as the 25mm bowl but with a one inch long nose. Drill a one inch diameter hole 1+ inches deep, expand, and you have a pin chuck.
The real odd duck, the 75mm Long Nose, is measured neither interior nor exterior (about the same as the 50mm) but the jaws are 75mm tall.
Also sounds odd but the 70mm has about 5/8 larger spigot than the 75mm. I really like my 70mm.
In short, you need to refer to the chart. Not all jaws are on the chart.
https://www.teknatool.com/products/Chuck_Accessories/Jaw_Sets/downloads/Min-Max%20Ranges%20Jaw%20Table%20(mm)Sep06.pdf

[allen thunem]

IM SO CONFUSED

[Larry Whitlow]

Maybe this will help. The following is for a Oneway Talon #2 jaw set:

External or compression chucking (meaning the inside measurement of the jaws) is 1 5/8" to 2-7/8". Internal or expansion chucking (meaning the outside measurement of the jaws) is 2" to 3-1/2". So with the #2 jaws the smallest thing you can clamp down on is 1-5/8. The largest thing (mortise) you can expand the jaws into is 3-1/2". If this is still clear as mud, you might want to go to Oneway.com. They have a capacity chart with a diagram that will probably make this clear.

[ray hampton]

when talking about woodchucks[groundhog] how can the Minus Size be anything other than Zero inches ?

[Michael Mills]

Allen,
I think we need more info on what you want to accomplish.
What size swing is your lathe 12”? 16”? …
Do you already have a chuck, if so what brand & model? i.e. Oneway Talon, Nova G3
What do you want to turn? Pens, platters, hollow forms, little of everything....
As far as how the jaws are measured, on Nova’s it is by the full closed position. The caveat is that the measurement is based upon the use. So for bowl jaws they are measured on the outside, for spigot jaws they are measured on the inside.

Maybe looking at this will most of the jaws shown will help clear it up for the Nova jaw sets.

http://www.teknatool.com/products/Ch...ries/Index.htm
Other brands may/probably differ.

[Michael Stafford]

For Nova chucks, I believe the sizing is generally based on the minimum expansion capacity - i.e., the smallest recess a set of 50mm (2") jaws will expand in to is 2". 75mm would be 3", and so on. But, I have no idea on chucks other than Nova.

John is correct. I asked this very question of a Nova representative and John's explanation was the answer I received. 50mm jaws fully closed should fit in a hole slightly less than 2" in diameter; 75 mm jaws fully closed should fit in a hole slightly less than 3" in diameter.

I am not metrically inclined but a little over 25 mm (25.4 mm to be exact) equals an inch.

[James Combs]

Got three Nova chucks and have used them for 3 years, figured I new most everything about them but even I have learned a couple things about them from this post.

Love this place(forum).

[Peter Fabricius]

Hi Allen;
Thanks for the question.
I am hoping that you are looking for something like I have been seeking for a little while without results so far. I would be nice to have a measuring tool / stick that would indicate the best tenon and recess sizes for each Jaw size. This would allow us to easily plan the diameters of tenons and recesses.
I have referred to this as a sizing stick but I have not had any suggestions to date.
Perhaps someone on SMC will have an idea. If a piece of 1/4" ply could be cut to show the interior and exterior capacity of one set of jaws on one end of a sizing stick and then a second jaw size on the other end. We would therefore have one stick for two jaw sizes with both the interior and exterior chucking options easily available.
Not sure if the stick should show the actual min and max sizing for each jaw set or show the optimum actual size of the tenon and recess???
I hope someone might have some suggestions and maybe a diagram / picture of this set up.
Thanks, and I hope this fits with your question Allen.
Peter F.

[Michael Mills]

Hi Allen;
I would be nice to have a measuring tool / stick that would indicate the best tenon and recess sizes for each Jaw size. This would allow us to easily plan the diameters of tenons and recesses.

This is what I came up with a while back. Works like a pair of divders and I believe the trammel points were from Grizzly for about $6. I am now planning a new one once I get a very thin one foot metric ruler. The one shown is for 3 jaw sets with the lines showing the setting for tenons and recesses and the color represents one size of jaws.

Now I am up to seven sets of jaws. The new one will have the sizes on the back noted such as
50mm - 42/51. If it is a recess then it is set to 51, for a tenon you add whatever you think you need such as +5mm for dry or +10mm for wet rough.
Anyone know where to buy a thin metric ruler maybe 3/8 wide? A cheap metric tape measure may be my best bet.

[Jamie Donaldson]

Its very simple to make a "go-no go" gauge that quickly and accurately sizes the jaw opening range for specific chucks and matched jaw sets. I have several sets around the lathes for the chucks that I use, and they save a ton of time and frustration. They can be made from a variety of materials, and I mostly use laminated panel scraps from the old RV modifications made long ago.