Chucks and chucking

[Lennart Delin]

There has been some discussions lately on chucking. This is a description of how I chuck the bowl while rough turning the green blank and then finish turn the dried blank. The perhaps unusual part is that I always turn the foot as tenon or mortice as part of the final bowl before turning the inside. I. e. I never reverse to turn off the tenon.

 

[hughie]

There has been some discussions lately on chucking. This is a description of how I chuck the bowl while rough turning the green blank and then finish turn the dried blank. The perhaps unusual part is that I always turn the foot as tenon or mortice as part of the final bowl before turning the inside. I. e. I never reverse to turn off the tenon.
View attachment 75285

same here

 

[William Rogers]

We all have preferences. I always remove the tendon from my turnings. I just think I think it looks better.

 

[Bill Alston]

We all have preferences. I always remove the tendon from my turnings. I just think I think it looks better.

One of the turners at my club used to enter a lot of competitions years ago. He said if you wanted to win, any indication of how the bowl was held for turning had to be removed. One of the most obvious and sure to be noticed is a mortise. You can remove the dovetail inside but it’s still obviously a mounting point. A winning bowl had to have an elegant foot that’s in proportion to the bowl.

 

[Lennart Delin]

We all have preferences. I always remove the tendon from my turnings. I just think I think it looks better.

I think the your view depends on that you see it as a tendon, whereas I see it as a foot that lets the bowl float. Without a foot I think bowls tend to look like a lump of dough. Actually I have never heard any comments on the foot from a non-turner.

When I think of it, I remeber reading when I started turning more than 60-years ago: "A bowl is not finished until you have turned a foot". That was before any woodturning chucks. The standard was to glue on a sacrificial piece that was fastened to the faceplate with screws. After parting off the bowl from the sacrificial piece you just had a flat bottom that needed to be turned into a foot.

 

[Lennart Delin]

One of the turners at my club used to enter a lot of competitions years ago. He said if you wanted to win, any indication of how the bowl was held for turning had to be removed. One of the most obvious and sure to be noticed is a mortise. You can remove the dovetail inside but it’s still obviously a mounting point. A winning bowl had to have an elegant foot that’s in proportion to the bowl.

That is the foot I try to make, but I make it so I can still use it for mounting, may be it is because I aim at gallerys and not turning contests.

 

[Aaron Harris]

Lennart-How deep is that recess on the left, 3 or 4 mm at most? I have done this on platters and some bowls. It certainly saves a step if you're only turning for customers who don't care and in fact like the defined foot and ring. Different strokes for different folks!

Lastly, how are you mounted when you are turning the outside? Lately I have been turning an inside tenon for this, though a screw chuck on wide jaws secured with TiteBond gives a rock-solid and confident hold (and the bond is not that hard to break when you take it off for reversing).

 

[William Rogers]

That is the foot I try to make, but I make it so I can still use it for mounting, may be it is because I aim at gallerys and not turning contests.
View attachment 75314

I didn’t say I did not elevate the bowl. I just don’t use the tendon, more on the line what @Bill Alston said. I don’t want to be constrained with the tendon size dictating the foot diameter. To be truthful I rarely see the tendon incorporated into the final bowl. for me, it doesn’t have anything to do with galleries or contest it just looks better to me.

 

[Lennart Delin]

Lennart-How deep is that recess on the left, 3 or 4 mm at most? I have done this on platters and some bowls. It certainly saves a step if you're only turning for customers who don't care and in fact like the defined foot and ring. Different strokes for different folks!

Lastly, how are you mounted when you are turning the outside? Lately I have been turning an inside tenon for this, though a screw chuck on wide jaws secured with TiteBond gives a rock-solid and confident hold (and the bond is not that hard to break when you take it off for reversing).

Yes probably 3-4 mm. If you look in the PDF I published, you will get a full explanation.

 

[Aaron Harris]

Yes probably 3-4 mm. If you look in the PDF I published, you will get a full explanation.

D'oh, I didn't even think to open that! (The term Dad-clicking was invented for me, I think). Thanks!

 

[Bill Alston]

I don’t want to be constrained with the tendon size dictating the foot diameter. To be truthful I rarely see the tendon incorporated into the final bowl. for me, it doesn’t have anything to do with galleries or contest it just looks better to me.

This is exactly right for me. The mounting method should not dictate what the final bowl looks like. This is why I believe one of the demonstrators at my club suggested not to use a recess unless absolutely necessary.

The trick is of course how you remove the chucking point. After experimentation I settled on the Donut Chuck as being the safest and most secure way of doing this. As a live centre is not required there is no cutting or hand sanding of any small remaining wood. Each to their own though. Whatever works for the individual to achieve the result they’re after.

Another thought, turn over a ceramic bowl or plate and look at the foot. Ignoring the actual size of it, look how elegant they normally are. There’s no reason the foot of a wooden bowl can’t be as elegant as this even if you do alter the size to fit the piece. Just my view.

 

[Lennart Delin]

The mounting method should not dictate what the final bowl looks like.

I have different jaws and can choose the diameter after the foot I want. I experience no restriction in the foot design.

 

[Lennart Delin]

I posted a memo on chucks and how I use them to turn bowls. Judging from the comments I get, it seems to me that you did not even bother to open the memo, or was it the nowadays popular TLDR, too long didn´t read?

 

[Barry Larson]

I posted a memo on chucks and how I use them to turn bowls. Judging from the comments I get, it seems to me that you did not even bother to open the memo, or was it the nowadays popular TLDR, too long didn´t read?

Lennart:
Thank you for posting the article. I've saved it for future reference.

Cheers.

Barry W. Larson
Calgary, Alberta, Canada eh!

 

[Bill Alston]

I posted a memo on chucks and how I use them to turn bowls. Judging from the comments I get, it seems to me that you did not even bother to open the memo, or was it the nowadays popular TLDR, too long didn´t read?

I for one did look at it, but I never turn green wood so much of the content wasn’t of interest to me. I also only use wood turning chucks, not modified metal turning chucks. It’s a good skill if you can do it, but so far I’ve only needed standard wood turning chucks.

 

[Ed Sandle]

Just looks unfinished to me where a much more finished result could be done in almost the same amount of time. There is no way I would want a chuck tenon left on a finished bowl. You may have different sized chucks and jaws for a variety, but that doesn't change the fact of what a pleasing and well thought foot should look like. It's a pretty simple matter, even without a vacuum chuck to finish turn the foot area. Yes I did read your PDF, but for my goal in a turned piece I would do it differently.

 

[Lennart Delin]

I think you have a preconcieved idea of the tenon/foot. Don´t look at my foot as a tenon. Look at is as a foot that can be gripped in the chuck. In fact your examples could also probably be gripped directly in a chuck, possibly a very minor change could be desirable. Also I like a plain foot without any embellishments, such as your rings.

 

[Jon Rista]

I think you have a preconcieved idea of the tenon/foot. Don´t look at my foot as a tenon. Look at is as a foot that can be gripped in the chuck. In fact your examples could also probably be gripped directly in a chuck, possibly a very minor change could be desirable. Also I like a plain foot without any embellishments, such as your rings.

Doesn't gripping in a chuck leave marks? At the very least, even if you do not remove the tendon, you would at least want to clean it up, right?

 

[Lennart Delin]

Doesn't gripping in a chuck leave marks? At the very least, even if you do not remove the tendon, you would at least want to clean it up, right?

No, it does not have to leave marks if the radius of the jaws is the same as the foot. I clean up the foot when I turn it. Here two examples of feet that have not been touched after being used for turning the inside.

 

[hockenbery]

Doesn't gripping in a chuck leave marks? At the very least, even if you do not remove the tendon, you would at least want to clean it up, right?

Dove tails at the perfect circle diameter don’t leave marks.

I use that often for ornaments and other small turnings
I get a 50mm diameter then make a decorative groove with a pyramid tool 1mm deep
Well it’s close enough to the 48mm perfect circle on the vicmarc jaws


Here is an example of an ornament in progress. 50mm diameter frame works well with a glass 35mm cabochon..

 

[Webb Willmott]

Is there a chart for tenon size for chucking or is it trial/error to get it right? Or both?

 

[Darryl Fective]

Is there a chart for tenon size for chucking or is it trial/error to get it right? Or both?

Ideal tenon size is dictated by the size of your chuck jaws. Chuck jaw choice is roughly dictated by the size of your work. I have multiple chucks with different jaws. I don't really measure, it's more of a gut feel and quick eyeball of 1/4 to 1/3 of the diameter of the workpiece. I'll go smaller for shallower depth, and larger for hollowing or deeper bowls.

I have a shelf right over my head where I keep my chucks. Hanging below each chuck is a plywood guide with the tenon size and mortise size closest to round. (jaws nearly closed)

 

[Webb Willmott]

So jaws nearly closed as in about 1/8 of an inch? Reason for asking is I don’t quite have it right yet on getting the jaws to match the circumference on the work.

 

[Dave Landers]

So jaws nearly closed as in about 1/8 of an inch? Reason for asking is I don’t quite have it right yet on getting the jaws to match the circumference on the work.

Yeah, usually around 1/8" or so. They (usually) make a set of jaws by turning them as one piece, then slice them apart - so the "perfect circle diameter" is when that saw kerf is left as a gap.

I made a set of gauges for myself - they're just scrap 1/4" plywood cut in a U (so it goes around the live center) - they let me gauge the right tenon size. I made them by basically making a tenon in scrap wood, putting that on a chuck, removing it and checking it - then tweaking the tenon till I was happy with it. I then made my plywood gauge to match that tenon. Doing it this way, it not only matches the jaws, but matches whatever personal thought process I have when I'm making a tenon (should I measure the top or the bottom or what, etc). More detail and pics here

 

[Jon Rista]

No, it does not have to leave marks if the radius of the jaws is the same as the foot. I clean up the foot when I turn it. Here two examples of feet that have not been touched after being used for turning the inside.

View attachment 75485View attachment 75486

Hmm. I wonder if it has to do with jaw design. I try to make my tenons the same diameter as the jaws, when nearly-closed. However I think my jaws have a small ridge at the outer edge of the dovetail, and that always seems to leave a mark in my tenons. I'd love to be able to turn without leaving any marks, as that would allow me to use the tenon as the foot, and waste less wood. A lot of my blanks are only 2-3" thick, and you lose some of that height right off the bat when trueing up, then if you turn off the tenon, you lose more.

I just have never been able to get away without marks, though. At the very least, they leave a ring impression. I guess also, I tend to turn my tenons so they fit the dovetail, rather than just have a strait edge, which I always fear will fly out of the dovetail jaws. Perhaps that itself is the issue: dovetail jaws? I actually don't have any other kind of jaw. My chucks are Record Power/Nova, and I have either dovetail jaws or spigot jaws, both of which leave marks.

 

[Dave Landers]

Hmm. I wonder if it has to do with jaw design. I try to make my tenons the same diameter as the jaws, when nearly-closed. However I think my jaws have a small ridge at the outer edge of the dovetail, and that always seems to leave a mark in my tenons. I'd love to be able to turn without leaving any marks, as that would allow me to use the tenon as the foot, and waste less wood. A lot of my blanks are only 2-3" thick, and you lose some of that height right off the bat when trueing up, then if you turn off the tenon, you lose more.

I just have never been able to get away without marks, though. At the very least, they leave a ring impression. I guess also, I tend to turn my tenons so they fit the dovetail, rather than just have a strait edge, which I always fear will fly out of the dovetail jaws. Perhaps that itself is the issue: dovetail jaws? I actually don't have any other kind of jaw. My chucks are Record Power/Nova, and I have either dovetail jaws or spigot jaws, both of which leave marks.

I have Vicmarc chucks with dovetail jaws, and a Nova chuck with their "bird beak" (as I call them) jaws.
If I make the right size tenon for the dovetails, they don't leave a mark. The bowl of this goblet was held in that little bead detail with Vic dovetail jaws. The bowl is about 2-1/2" dia (IIRC). No touch up required.


I ue the Nova jaws when making my Shot Barrels). Jaws happen to fit just right around a groove. Most of the turning (including hollowing) is done with them chucked like this. (One jaw removed in the first pic - this from one of my demo handouts)

 

[Bill Alston]

Some manufacturers give an indication of when the Jaws form a perfect circle, like this example from Axminster Tools below.
I used to think that the Jaws were sawn apart but looking at an Axminster Video they were in fact cut apart with a small milling cutter.
The cutter looked to be somewhere between 4mm and 6mm diameter?

 

[hockenbery]

Is there a chart for tenon size for chucking or is it trial/error to get it right? Or both?

There are two methods of I use choosing tenon size.
1. For tenon strength and to allow a warped tenon to be trued round - I use a tenon larger than perfect circle by at least 25%
When using the standard jaws for the Vicmarc I use a greenwood tenon of 2.5” or slightly larger. What I do in practice is make the tenon out 1” from my live center which is 5/8” diameter. I’m really good a cutting an inch by eye. I can always turn a 2” tenon in a warped tenon that started as a 2.5” tenon

2. For perfect circle you need to look at the spec for individual chucks. Vicmarc has a nice chart for their jaws
Here is the chart for Vicmarc chuck

Standard jaws have the 48mm perfect circle. add 37mm to get 85mm max grip. Subtract 3mm for min grip.
Tenons less than perfect circle don’t hold well in my opinion.

 

[Gerald Lawrence]

I use calipers to mark a perfect tenon . To set the calipers I have a strip of melamine tacked up with a begin hole and an end hole for a regular compression tenon and another hole at the expansion mode diameter. This allows for very quick setting of calipers and then the turning . I have marks for each set of jaws I use.

 

[Mark Jundanian]

A while back I contacted Nova CS, but the representative was not able to give me the perfect circle dimensions for their jaws. I haven't seen the numbers listed elsewhere, either. I will admit I haven't looked that hard, nor do I get too wound up about it. But if anyone has the numbers, I'd be interested.

For those of us who are over thinking, super perfectionists: With dovetail jaws, the diameters that matter are taken at the narrow part of the dovetail rather than the fat part. Whether making a tenon or recess, you are going to turn the max/min diameter first, then trim a little more to create the matching slope for the dovetail. Of course you can't easily measure the jaw diameter at the narrow end of the dovetail, so you'll have to use trigonometry to calculate...

Ahhk! My brain hurts.

 

[hockenbery]

A while back I contacted Nova CS, but the representative was not able to give me the perfect circle dimensions for their jaws.

Most ( probably all) jaws get real close to perfect circle when opened with a 3mm or 1/8” gap between the jaws.

Machining of most(maybe all) jaws is done by making the jaw profile in the round then cutting the jaws into 4 parts.
The kerf is the gap you want to duplicate to get to perfect circle alignment.

 

[Darryl Fective]

A while back I contacted Nova CS, but the representative was not able to give me the perfect circle dimensions for their jaws. I haven't seen the numbers listed elsewhere, either. I will admit I haven't looked that hard, nor do I get too wound up about it. But if anyone has the numbers, I'd be interested.

For those of us who are over thinking, super perfectionists: With dovetail jaws, the diameters that matter are taken at the narrow part of the dovetail rather than the fat part. Whether making a tenon or recess, you are going to turn the max/min diameter first, then trim a little more to create the matching slope for the dovetail. Of course you can't easily measure the jaw diameter at the narrow end of the dovetail, so you'll have to use trigonometry to calculate...

Ahhk! My brain hurts.

You may be overthinking it, I can't follow your thoughts. I just measure the face. (jaws or workpiece) That's what you can measure easily, and where you can make a mark to cut to. (on a tenon, it's the largest part; on a mortise/recess, the smallest diameter)

 

[hockenbery]

Of course you can't easily measure the jaw diameter at the narrow end of the dovetail, so you'll have to use trigonometry to calculate.

This would be getting into the weeds a bit. I spent a lot of years working as an applied mathematician - my job was getting the wrong answers fast. Accuracy is overrated for the most part.

For the trig:
I’ve used SCaT - Oscar Had A Heap Of Apples since the 7 th grade. So Tangent is Opposite over Adjacent
Dovetail angles on my Vicmarc are 10 degrees and on my stronghold 7 degrees.

The height of the tenon is the adjacent side the little bit going into the dovetail is the opposite side and what you are interested in.
The opposite side is equal to the tangent of the dovetail angle x the tenon height
Twice that opposite side is what you want to add to the diameter. It varies with the height of the tenon.
It’s always small and it would be rare for it to matter.

Here is a chart of what you add to the diameter by dovetail angle and tenon height.
For a 1/2” tall tenon you add .176 inches to the diameter to account for a 10 degree dovetail that’s about 11/64 of an inch.
using an 1/8” tall tenon with 7degree ONEWAY jaws you add .031 inched to the diameter of about 1/32 of an inch.

 

[Mark Jundanian]

You may be overthinking it,

This would be getting into the weeds a bit.

Actually, my friends, I was trying to be facetious. But Al, I did enjoy reading your math explanation.